WO2016051345A1 - Device and method for determining unconfined compressive strength in disc-shaped samples of rock or other materials subjected to diametral loading - Google Patents

Device and method for determining unconfined compressive strength in disc-shaped samples of rock or other materials subjected to diametral loading Download PDF

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Publication number
WO2016051345A1
WO2016051345A1 PCT/IB2015/057463 IB2015057463W WO2016051345A1 WO 2016051345 A1 WO2016051345 A1 WO 2016051345A1 IB 2015057463 W IB2015057463 W IB 2015057463W WO 2016051345 A1 WO2016051345 A1 WO 2016051345A1
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disc
samples
compression
loading
compressive strength
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PCT/IB2015/057463
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Spanish (es)
French (fr)
Inventor
Adolfo Camilo TORRES PRADA
Fabian Augusto LAMUS BÁEZ
Juan Sebastian VESGA MEDINA
Sebastian BAHAMÓN BLANCO
Jenny Magaly PIRA RUIZ
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Universidad De La Salle
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Publication of WO2016051345A1 publication Critical patent/WO2016051345A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/02—Details
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces

Definitions

  • the object of the present invention is a device and a methodology to obtain the unconfined compression resistance in disc-shaped samples of specimens of samples of rocks or other materials, ensuring the obtaining of this mechanical parameters by means of a diametral type load, and whose specimen geometry has a similarity to that used in ASTM D3967.
  • the method of the present invention ensures a complete compression failure of the sample.
  • the present invention has its application within the field of geotechnical exploration and more specifically in the analysis of samples of rocky materials for its geomechanical characterization, in addition its application can be extended to the field of resistance of materials.
  • Geotechnical explorations make it necessary to recover specimens using different drilling instruments. These recovered specimens are subjected to different laboratory tests in order to find the mechanical properties of the material and which will be an integral part of the development of a civil work. All of these tests are parameterized by the ASTM-American Society for Testing and Materials- (Committee C-18) and for tests mainly on rock materials by the ISRM-International Society for Rock Mechanics, which provide some basic parameters for the execution of laboratory procedures for Sample handling.
  • the size of the recovered specimen is smaller than required, consequently the low RQD values in certain areas due to the given geological conditions, provides an insufficient recovery for a complete characterization. of the massif studied.
  • the need to adapt new test procedures for the research context is an indispensable task and thus be able to use specimens with less strict diameter / length ranges, and thus achieve a characterization of the massif from the obtaining of its mechanical properties.
  • Unconfined compression resistance a mechanical parameter that is obtained from the application of compression loads to a specimen with specific geometry specifications, this is subject to a net compression stress field and an environment without confinement, until it reaches its point of failure or rupture, at which time it is said that its maximum compressive strength was obtained.
  • Tensile strength mechanical parameter that is obtained from the submission of the specimen to a system of charges that try to separate its structure, these charges are applied in opposite directions, until the sample is broken, materials such as rocks and Simple concretes have a relatively low tensile strength.
  • Indirect tensile strength a mechanical parameter for determining tensile strength, by applying compression loads concentrated on a disk-shaped specimen, in which the stress-generated stress field exceeds compressions; therefore the sample will fail through an induced voltage but not direct.
  • the unconfined compression test in unaltered rock cores is understood as the determination of the uniaxial compression resistance of rock specimens of a regular geometry, provides the classification of strength and characterization of the rock samples, specifies the procedures for the Determination of deformations and axial stresses, deformations and lateral stresses, their characteristic curves, modulus of elasticity, and Poisson constant.
  • the specimens should not be smaller than the NX drill diameters, with an effective sample diameter of 54mm, with a Length / Diameter ratio between 2.0 and 3.0 (Numeral 3. ISRM Doc. 1978).
  • ASTM allows the use of specimens of an approximate diameter of 47mm, that is to say a drill bit diameter NQ series and a Length / Diameter ratio between 2.0 and 2.5 (Section 8.1 and 8.2. ASTM D7012-10).
  • the specimens must be properly calibrated and prepared cylinders according to ASTM D4543-08.
  • ASTM D4543-08 the specimens must be properly calibrated and prepared cylinders according to ASTM D4543-08.
  • it must be a test with constant load application with a duration of 5 to 10 min (Numeral 3. ISRM Doc. 1978) or a duration of 2 to 15 min (Numeral 10.4.1 .1, ASTM D7012-10), This application control by constant load must be performed in a rat between 0.5 to 1.0 MPa / s.
  • the tensile strength is obtained by the direct uniaxial tension test, but this test has operating difficulties due to its applicability and generated cost, so the determination of the tensile strength in the specimen is more practical if Performed by the indirect or Brazilian tensile test, mainly for operation and cost issues.
  • This It is one of the simplest tests in rock mechanics and in which large stress fields are generated in the specimen that induce the failure of the sample by stress.
  • the loading machine must meet the requirements of ASTM E-4, the contact blocks between specimen and load cell must ensure a failure angle between 10 ° and 15 ° and the arc contact length must not be shorter at the value of D / 6, where D is the diameter of the sample. (Numeral 5.2.2, ASTM D3967-08) or an angle of failure that does not exceed 10 ° (Numeral 1. Part 2. ISRM Doc. 1978).
  • the test specimen must have a minimum diameter corresponding to an NX series drill bit, with an effective sample of 54mm (Numeral 3. Part 2. ISRM Doc. 1978) and with a thickness / diameter ratio between 0.2 and 0.75 (Numeral 7.1, ASTM D3967-08).
  • the load application control is carried out with a range of 200 N / s (Numeral 3 (e). Part 2. ISRM Doc. 1978) or with an effort control between 0.05 and 0.35 MPa / s with a test duration between 1 and 10 min (Numeral 8.3, ASTM D3967-08). This test does not allow to ensure a tensile failure of the material, so inconsistencies are obtained with respect to the true tensile strength values.
  • document CA2250090 provides a rock compression test method, the method develops the value of compression as a function of porosity and specific lithology.
  • the document proposes a systemic method to perform the same standard compression tests on standard cylindrical samples, intended for periodic review of well drilling plans. (Selection of drill bits for different sections of the well, weight and speed of the rotation of the hole, etc.)
  • CA23221 18 a technique is presented to directly determine the resistance to the understanding of a rock formation sample by means of an indentation technique, with which the mechanical properties of rock fragments can be determined.
  • the proposed method measures the force and displacement that occur when testing a rock sample, the relationship between the two force-displacement registers can provide estimates of the value of the compressive strength of the material.
  • the invention consists of an indenter test equipment but with systematized readings of force and displacement, where the readings correspond to specific tests on the surfaces of the samples.
  • Document CA2591058 teaches a method to estimate the compressive strength of the rock confined to the working depth where it must be drilled by a drill and a drilling fluid, but it requires initially knowing the parameter of the unconfined resistance of the Rock, and then theoretically it provides a solution based on the change in pore volume due to the charges applied by the drilling fluid.
  • the CN1619285 patent refers to a multifunctional portable testing instrument for rock mechanics.
  • the instrument includes top panel, bottom panel, front panel, rear panel, vertical columns, drawbar, vertical jack, horizontal jack, vertical piston end plate connector, horizontal jack terminal plate, positioning component, box upper cut and lower cut box, etc.
  • Said invention also provides the connection method
  • the equipment of this invention is quite complex and is designed to work primarily on prismatic type samples (Cubes).
  • the method of the CN1018191 1 1 patent refers to a method for finding the tensile modulus of a fragile material, characterized in that it comprises the following steps of: arranging a test sample in the Brazilian test, applying a load in a manner symmetrically on the line of the test sample in the radial direction of the test sample, measure the total displacement of the center of the test sample in the direction of the diameter in which the direction of the total displacement is vertical to the direction of the load of the application of the test sample, calculate to obtain the tensile modulus of the material.
  • This document theoretically addresses a solution to estimate a property different from compressive strength.
  • document EP0206737 refers to a new improvement of abrasive tool with novelty in the type, distribution and geometry of the elements in the drill, whose main object is the variation for a new drill bit
  • Document EP1836509 generally deals with the drilling of drills in underground formations, and more particularly, to methods to predict and optimize the speed at which the holes are drilled, as well as the proper selection of drill bits and performance evaluation. This is a theoretical proposal that also requires the data of sludge pressures and other drilling data during the drilling progress.
  • the invention of EP2310844 is directed to the use of systems and methods that determine geological properties using acoustic analysis.
  • the acoustic signals are collected during the processing of the geological medium, as in rock samples, for the determination of geological properties according to the methods established in the invention.
  • the proposal is mainly theoretical based on non-destructive methods that the data needs during the progress of the survey.
  • Patent US4981037 presents a method for the calculation of total overload stresses, vertical effective stress, pore pressure and horizontal effective stress by means of registration data during drilling.
  • the invention can be practiced in real time by the use of measurement techniques during drilling or after drilling by using the recorded data or measurement data by openhole drilling. This document also corresponds to a theoretical proposal that needs the registration of the data during the drilling of the well.
  • Document US5345819 proposes a method and equipment to determine the degradation of rock resistance at the bottom of the drilling due to the application of the drilling fluid pressure, the effects of the fluid is estimated by recording wave velocity of ultrasound in the samples. This is a theoretical proposal based on non-destructive methods that needs the data during the progress of the survey.
  • the method and apparatus of US5442950 are used to determine the compressibility of the pore volume, the porosity to the stress and the change of the relative porosity of rock samples from a rocky deposit.
  • the invention applies a new model for determining the compressibility of pore volume as a function of pressure. This model simplifies the determination of the compressibility of the pore volume of a sample, since the measurement of the pore volume in only two different pressure states is required.
  • WO9408127 proposes an improved technique to more accurately determine the pore pressure of sedimentary rock drilled by a borehole from the surface. Overload is measured directly at one or more locations in the borehole, and a record of the overload formation is generated using the measured overload pressures and conventional geophysical data.
  • WO0125597 teaches a method for the selection of drilling parameters for drilling a well through rock formations in the subsoil. The method includes the determination of a compressive strength of the samples of the rock formations to be drilled from measurements made of the displacements and load in the samples. Displacement and load measurements are made by a penetrator. The drilling parameters are selected from the values of the determined compressive strength.
  • the invention consists of an indenter test equipment but with systematized readings of force and displacement, where the readings correspond to specific tests on the surfaces of the samples.
  • WO0240824 a device and method for the sampling of core samples from underground formations is presented. Specifically, the invention relates to a "sponge" type witness, and the method of use thereof, for obtaining a rock core sample and which ensures the structural and chemical integrity of the core sample for later analysis.
  • WO2009002872 refers to a complex method, system and equipment for estimating geomechanical parameters of rock samples based on the analysis of acoustic signals in different states of the waves generated by the equipment.
  • this is a theoretical proposal based on non-destructive methods.
  • the rock sample recovery process can be complicated due to the geological conditions of certain areas. This has the effect that the samples obtained do not comply with the provisions of the ASTM and ISRM standards with respect to the minimum diameter / length ratios. For this reason a large number of samples are discarded and in many cases, the characteristics of the rock cannot be determined properly.
  • Field explorations, carried out along an infrastructure or research project require in-depth physical inspection of the land. Specifically for rock explorations, the use of drill bits and robust drilling equipment sometimes makes the maneuvering of nuclei different, the operator's experience also has an important impact on the specimens obtained being suitable for the minimum laboratory tests. .
  • the loading machine is required to conform to the requirements of the ASTM E-4 standard; the contact blocks between specimen and load cell must ensure a failure angle between 10 ° and 15 ° and the contact length of the load arc must not be less than the value of D / 6, where D is the diameter of the sample (Numeral 5.2.2, ASTM D3967-08) or a failure angle must be ensured that does not exceed 10 ° (Numeral 1. Part 2. ISRM Doc. 1978).
  • the state of efforts experienced by specimens under the characteristics of a Brazilian trial has been studied theoretically by various researchers for a long time, in order to be able to relate the load produced by the disk failure with the true tensile strength of the material .
  • the present invention considers the component ⁇ ( ⁇ ) ⁇ 3) of the load and is not considered the friction component ⁇ ( ⁇ ) (5), and in the analysis of results this simplification is considered, therefore , according to the conditions mentioned above, the equations to determine the field of stress of the disk due to the action of the sinusoidal and radial external load or pressure p, are related to the stress values: the magnitude of the radial stress component or m the magnitude of the normal stress component Ow and the magnitude of the shear force component 7> ⁇ , for any point inside the disc.
  • the great advantage of the solution in two zones lies in the fact that the intense stress gradients that appear near the loaded ends when a radial distributed load is considered, are eliminated, getting closer to the natural behaviors during the experimental tests .
  • the internal stresses of a disk of approximate diameter of 47.60 mm were sought, which in practice would correspond to specimens of rock recovered with a drill bit type NQ.
  • NQ drill bit type
  • the calculations of the magnitudes of the stress field in its three components or m OQQ and ⁇ were made for any point inside the disk.
  • the geometry of the disk characterized by its radius R ⁇ 8) which corresponds to a sample recovered with a drill bit NQ
  • the magnitude of the applied stress is around 50 MPa, a value that corresponds to the allowable compressive stresses of a medium strength rock.
  • the distribution of the load on the perimeter of the sample has been set as variable, in terms of the internal angle ⁇ 0 (9) measured from the center of the disk and sweeping the boundaries of the loaded area.
  • Five variation values of u> or so have been established: concentrated load, 7.5 °, 15 °, 30 ° and 45 °.
  • the geometry of the stress field to be calculated was also established, by means of a mesh in polar coordinates that define the points where the three components of the stress or m OQQ and ⁇ are calculated.
  • the present invention allows an optimization in the use of the recovered specimen, ensuring the obtaining of mechanical parameters by means of a total unconfined compression of the sample, when it is subjected to a diametral type load, whose geometry of the specimen has a similarity with that used in ASTM D3967.
  • the correlation with results obtained from classic unconfined compressions allows to give evidence of this, the use of analytical proposals, modeling using MEF (Finite Element Method) and a robust and extensive series of physical laboratory tests, gave the necessary results to ensure a complete Sample compression failure.
  • a model of confinement jaws and a method to characterize material specimens were developed through the application of unconfined compression in disc-shaped samples and subjected to diametrically distributed loads.
  • the characterization method comprises the following stages:
  • the developed jaws comprise the following characteristics:
  • the area that makes contact with the disk has a curved contour that follows the circular profile of the disk.
  • the angle of curvature is between 60 and 75 °.
  • the edges of the curved contour have a rounded or chamfer finish.
  • FIG. 1 Analytical scheme of a disc subjected to diametral loading
  • FIG. 2 General scheme of the unconfined compression test of rock cores for the determination of the modulus of elasticity according to the standards
  • FIG. 3 Proposed scheme to determine unconfined compression resistance in samples of rocks or other materials, disk-shaped and subjected to diametral loading
  • FIG. 4 Description of the variables within the geometric model of a disk subjected to diametral loading and the jaw of confinement.
  • FIG. 5 Front view of the jaw developed in the present invention.
  • FIG. 6 Isometric view of the jaw developed in the present invention.
  • FIG. 7 Bottom isometric view of the jaw developed in the present invention.
  • the compressive strength of rock is used in many design formulas and is sometimes used as an index property to select the appropriate excavation technique.
  • the deformation and resistance properties of rock cores measured in the laboratory generally do not accurately reflect the properties in situ, since the latter is strongly influenced by diaclases, faults, heterogeneity, fault planes and others. Therefore, laboratory values of intact samples should be used with proper judgment in engineering applications.
  • the object of the present invention presents an option to apply in those samples of rock cores that do not comply with the length-diameter (L / D) ratio as specified in the standards such as ASTM D 4543.
  • L / D length-diameter
  • the compression test system (10) comprises a cylinder compression system (1 1), by adjusting a load frame (12).
  • the system has a reading system by means of a deformimeter (13) that can be of traditional or digital needle, placed in a fixed area (14) of the assembly.
  • the deformimeter (13) allows to read the displacement of the frame during the axial compression test, this displacement reading is related to the constant of the load ring and in this way the load applied on the sample can be determined and taking into account the area loaded the effort applied is determined.
  • the sample of material (15) is supported by means of an upper support (16) and a lower one (17) which are connected to the cylinders (1 1) of the compression system.
  • the material sample (15) has a cylindrical shape of radius r (D / 2) and length L, where the ratio (L / D) must have a value between 2 and 3.
  • the sample is subjected to axial understanding , and the maximum applied load, the cracking load, the effort, the duration of the test, the type of fracture and the load application rate are recorded.
  • the execution of the unconfined compression test with diametral loading application shown in figure 3 involves the analysis and elaboration of a set (18) determined for the control of deformations of the load frame and the jaws of confinement, for this the use of the cylinder compression system (1 1) similar to that used in the axial load test is used. It also comprises a reading system using a deformimeter (13) to read the displacement of the frame during the diametral compression test.
  • the disc type mortar sample (19) is located between a pair of confinement jaws (20) which have a design that adapts to the circular profile of the disc type sample (19).
  • the adapted form of the jaws of confinement (20) allows to distribute the force applied in the body of the sample of material with disk form (19).
  • the sample is subjected to stresses similar to those it receives with the standard axial load test, however the test method proposed in the present invention does not require samples of great length L, but it allows to use samples where the ratio (L / D) can have low values, including values less than 1.
  • the main contribution of the new geomechanical characterization test is the possibility of having a large amount of resistance data even with low percentages of recovery of samples and with less strict diameter / length ratios, to avoid the loss of specimens by not complying with regulations, thus allowing to have an important statistical representation and to characterize the rock massif in a more adequate way.
  • the confinement jaw configurations are obtained from analytical studies for a disc subjected to diametral loading. From this and according to the properties of the materials used, the main characteristics of the jaw geometry are shown in Figure 4. The work was carried out using the concept of symmetry both on the x-axis, and on the y-axis. ; leaving the origin as a fixed support node and the xy axis with a skate support system.
  • the figure shows a section of the test disk (19) of radius r, which is under compression of the confinement jaw (20). To obtain a compression failure in the test specimen (19) the tip of the jaw fin must cover the edge of the specimen up to a loading angle ⁇ (22).
  • a loading angle is 75 °, it provides the best compression stress behavior within the specimen.
  • the other configuration parameter is the effective height of the part h (23). This parameter is presented as an option for the reduction of the stress concentration at the contact points of the load arc. The results showed a notable decrease in the concentration of the piece when it had an effective height (23) of 5mm.
  • the angle of the ⁇ (24) fin was determined as tangential to the contact with the specimen (45 ° by machining requirements), which showed a marked reduction of the stresses within the specimen.
  • Figure 5 shows a front view of the confinement jaw (20).
  • the confinement jaw comprises a configuration consisting mainly of three bodies: the fin jaw (25), a support block (26) and a clamping flange (27), where the three bodies are aligned on a common axis (not shown in the figure).
  • the flange (27) is arranged to engage the compression jaws of the compression system.
  • the shape of the flange is hollow cylindrical, but it can take any other geometry according to the compression jaws.
  • the flange (27) is solidly connected to the support block (26), and preferably the three pieces: the support (26), the flange (27) and the jaw of fins (25), are configured from a single solid piece of high strength material such as steel.
  • the support block (26) consists of a solid piece that serves as a base for the jaw of fins (25). These pieces must be constructed in such a way that they support the load that is transferred to the sample, through a compression machine or universal machine, additionally to achieve a defined geometry it becomes necessary: to use an industrial machining technique that allows to obtain shapes defined from steel blocks.
  • the fins of the fin jaw (25) form an angle (24) with the support block, this An angle should preferably be tangential to the test specimen to ensure uniform compression, however for machining reasons, it was found that the optimum angle should be around 45 °.
  • the fin jaw (25) has a curved surface of radius r, corresponding to the radius of the test disk.
  • the curved jaw surface covers a surface of the test disk corresponding to the distance swept by the loading angle (22) (Fig. 4).
  • the jaw fins have a bevel (28) at their tips, which is molded with the piece in order to avoid deformations in the same jaw.
  • at the bottom base of the fins (25) in contact with the support block (26) there is a rounded finish (29) that guarantees the adequate mechanical work of the steel at that point so that it does not suffer excessive compressions that may destroy the piece
  • Figure 6 shows a top isometric view of the jaw (20).
  • the support piece (26) comprises an area greater than the fin jaw (25) in order to give the piece greater stability.
  • Figure 7 shows a bottom view of the compression jaw (20). It can be seen that the flange (27) is located on the same axis of the fin jaw (25), which allows the force of the cylinder compression system to be directly transferred to the test piece.

Abstract

The present invention consists of a model for confinement clamps and a method for characterising material specimens by determining compressive strength, with the application of unconfined compression on disc-shaped samples subjected to diametrally distributed loads. According to the invention, the disc-shaped samples are samples of intact rock that have a length-to-diameter ratio (L/D) below that established by Standard ASTM D4543. The clamps developed are characterised, inter alia, in that: the area in contact with the disc has a curved edge that follows the circular profile of the disc; the clamps have a pair of fins at the ends of the arc, such that the force exerted by the press is regularly distributed across the whole area of the clamp that is in contact with the disc. The fins have a rounded or bevelled end to prevent deformations in the clamp. The base of the clamp also comprises curved edges that ensure appropriate mechanical working of the material so that the clamp does not experience excessive compression that could destroy the part.

Description

DISPOSITIVO Y MÉTODO PARA DETERMINAR LA RESISTENCIA A LA COMPRESIÓN INCONFINADA EN MUESTRAS DE ROCAS U OTROS MATERIALES EN FORMA DE DISCO Y SOMETIDAS A CARGA DIAMETRAL  DEVICE AND METHOD FOR DETERMINING THE RESISTANCE TO INCONFINED COMPRESSION IN SAMPLES OF ROCKS OR OTHER MATERIALS IN THE FORM OF A DISC AND SUBJECTED TO DIAMETRAL LOAD
Objetivo de la invención Object of the invention
El objeto de la presente invención es un dispositivo y una metodología para obtener la resistencia a la compresión inconfinada en muestras en forma de disco de especímenes de muestras de rocas u otros materiales, asegurando la obtención de éste parámetros mecánico mediante una carga de tipo diametral, y cuya geometría del espécimen tiene una similitud con la utilizada en la norma ASTM D3967. El método de la presente invención, permite asegurar una completa falla a compresión de la muestra. The object of the present invention is a device and a methodology to obtain the unconfined compression resistance in disc-shaped samples of specimens of samples of rocks or other materials, ensuring the obtaining of this mechanical parameters by means of a diametral type load, and whose specimen geometry has a similarity to that used in ASTM D3967. The method of the present invention, ensures a complete compression failure of the sample.
Campo de la invención Field of the Invention
La presente invención tiene su aplicación dentro del campo de la exploración geotécnica y más específicamente en el análisis de muestras de materiales rocosos para su caracterización geomecánica, además se puede ampliar su aplicación al campo de resistencia de materiales. The present invention has its application within the field of geotechnical exploration and more specifically in the analysis of samples of rocky materials for its geomechanical characterization, in addition its application can be extended to the field of resistance of materials.
Antecedentes de la invención Las exploraciones geotécnicas hacen necesaria la recuperación de especímenes mediante diferentes instrumentos de perforación. Estos especímenes recuperados son sometidos a distintos ensayos de laboratorio con el ánimo de encontrar las propiedades mecánicas del material y que hará parte integral del desarrollo de una obra civil. Todos estos ensayos están parametrizados por la ASTM-American Society forTesting and Materials- (Comité C-18) y para los ensayos principalmente en materiales rocosos por la ISRM-International Societyfor Rock Mechanics, quienes proporcionan algunos parámetros básicos de ejecución de procedimientos en laboratorio para el manejo de las muestras. Sin embargo, en muchos casos los parámetros geométricos mínimos requeridos en las actuales normas no son posibles de cumplir debido a: las condiciones particulares de cada trabajo de perforación; la utilización de menores diámetros de broca que los sugeridos en las normas, las estructuras y edad geológica de algunas formaciones, las condiciones de ambiente e intemperismo (ambientes propios de las zonas tropicales) y en muchos casos los muy bajos valores de RQD (índice de calidad de la roca. Rock Quality Designation). BACKGROUND OF THE INVENTION Geotechnical explorations make it necessary to recover specimens using different drilling instruments. These recovered specimens are subjected to different laboratory tests in order to find the mechanical properties of the material and which will be an integral part of the development of a civil work. All of these tests are parameterized by the ASTM-American Society for Testing and Materials- (Committee C-18) and for tests mainly on rock materials by the ISRM-International Society for Rock Mechanics, which provide some basic parameters for the execution of laboratory procedures for Sample handling. However, in many cases the minimum geometric parameters required in the current standards are not possible due to: the conditions particular of each drilling job; the use of smaller drill diameters than those suggested in the norms, structures and geological age of some formations, the environment and weather conditions (environments typical of tropical areas) and in many cases the very low RQD values (index of Rock quality. Rock Quality Designation).
El ensayo estándar para determinar la compresión inconfinada de núcleos de roca es sugerido por la ASTM D7012 y la ISRM 1978 (Blue Book), dentro de las cuales los núcleos de roca deben cumplir con una relación estricta la cual especifica que la altura del cilindro debe ser entre 2 a 2.5 veces el diámetro de la base del espécimen, entre tanto en el caso de las recomendaciones de la ISRM se establece una altura que debe ser entre 2.5 a 3 veces el diámetro del espécimen, debido a las condiciones anteriormente descritas el cumplimiento de estas exigencias geométricas para los especímenes son por lo general muy difíciles de cumplir. The standard test to determine unconfined compression of rock cores is suggested by ASTM D7012 and ISRM 1978 (Blue Book), within which rock cores must meet a strict relationship which specifies that the height of the cylinder must be between 2 to 2.5 times the diameter of the base of the specimen, meanwhile in the case of the recommendations of the ISRM a height is established that must be between 2.5 to 3 times the diameter of the specimen, due to the conditions described above compliance of these geometric requirements for specimens are usually very difficult to meet.
Así por ejemplo, en regiones geológicamente jóvenes o con alto grado de fracturamiento, el tamaño del espécimen recuperado es menor al requerido, de manera consecuente los bajos valores de RQD en ciertas zonas por las condiciones geológicas dadas, proporciona una recuperación insuficiente para una caracterización completa del macizo estudiado. De esta manera la necesidad de adaptación de nuevos procedimientos de ensayo para el contexto de investigación, es una tarea indispensable y así poder utilizar especímenes con rangos menos estrictos de diámetro/longitud, y así lograr una caracterización del macizo a partir de la obtención de sus propiedades mecánicas. Thus, for example, in geologically young regions or with a high degree of fracturing, the size of the recovered specimen is smaller than required, consequently the low RQD values in certain areas due to the given geological conditions, provides an insufficient recovery for a complete characterization. of the massif studied. In this way the need to adapt new test procedures for the research context is an indispensable task and thus be able to use specimens with less strict diameter / length ranges, and thus achieve a characterization of the massif from the obtaining of its mechanical properties.
Algunos de los problemas encontrados radican en que el proceso de recuperación resulta ser complicado, en la mayoría de los casos tanto para las técnicas de la perforación condicionadas al operador como por el estado y tipo de maquinaria de perforación, y también debido a las condiciones particulares geológicas de ciertas zonas. Esto repercute en que las muestras que se obtienen no cumplen con lo estipulados en las normas ASTM e ISRM, con respecto a las relaciones diámetro/longitud, de esta manera después de la gran inversión de recursos durante los trabajos de perforación, una gran cantidad de muestras son desechadas por no cumplir con dichos requerimientos. Para especificar mejor la presente invención, se presentan a continuación la definición de algunos conceptos relacionados: Some of the problems encountered lie in the fact that the recovery process turns out to be complicated, in most cases both for drilling techniques conditional on the operator and for the state and type of drilling machinery, and also due to the particular conditions Geological of certain areas. This has the effect that the samples obtained do not comply with the stipulations of the ASTM and ISRM standards, with respect to the relationships diameter / length, in this way after the large investment of resources during drilling, a large number of samples are discarded because they do not meet these requirements. To better specify the present invention, the definition of some related concepts is presented below:
Resistencia a la compresión inconfinada, parámetro mecánico que se obtiene de la aplicación de cargas de compresión a un espécimen con especificaciones de geometría determinadas, este se encuentra sometido a un campo de esfuerzos neto de compresión y un ambiente sin confinamiento, hasta que llegue a su punto de falla o ruptura, momento en el cual se dice que se obtuvo su máxima resistencia a la compresión. Resistencia a la tensión, parámetro mecánico que se obtiene del sometimiento del espécimen a un sistema de cargas que tratan de separar su estructura, estas cargas se aplican en sentidos contrarios, hasta que se produce la ruptura de la muestra, materiales como las rocas y los concretos simples tienen una resistencia relativamente baja a la tensión. Unconfined compression resistance, a mechanical parameter that is obtained from the application of compression loads to a specimen with specific geometry specifications, this is subject to a net compression stress field and an environment without confinement, until it reaches its point of failure or rupture, at which time it is said that its maximum compressive strength was obtained. Tensile strength, mechanical parameter that is obtained from the submission of the specimen to a system of charges that try to separate its structure, these charges are applied in opposite directions, until the sample is broken, materials such as rocks and Simple concretes have a relatively low tensile strength.
Resistencia a la tracción indirecta, parámetro mecánico para determinar la resistencia a la tensión, mediante la aplicación de cargas de compresión concentradas en un espécimen en forma de disco, en el cual el campo de esfuerzos generado a tensión supera las compresiones; por tanto la muestra fallará a través de una tensión inducida más no directa. Indirect tensile strength, a mechanical parameter for determining tensile strength, by applying compression loads concentrated on a disk-shaped specimen, in which the stress-generated stress field exceeds compressions; therefore the sample will fail through an induced voltage but not direct.
La anisotropía, muchos tipos de rocas tienen diferentes características en direcciones variadas, la foliación, la estructura, la conformación, son parte fundamental de las propiedades anisotrópicasde las rocas. Por tanto todos los ensayos destinados a la determinación de los módulos, constantes y resistencias consideran las desviaciones estadísticas que se pueden generar por la presencia de anisotropía en los especímenes. Para la determinación de la resistencia de los especímenes de roca, se utilizan los ensayos especificados anteriormente. La compresión inconfinada de núcleos de roca para la determinación del módulo de elasticidad (ASTM D7012-10 e ISRM Doc. 1978) y la resistencia a la tensión indirecta o ensayo brasilero (ASTM D3967-08 e ISRM Doc. 1978). Anisotropy, many types of rocks have different characteristics in varied directions, foliation, structure, conformation, are a fundamental part of the anisotropic properties of rocks. Therefore all the tests destined to the determination of the modules, constants and resistances consider the statistical deviations that can be generated by the presence of anisotropy in the specimens. For the determination of the strength of rock specimens, the tests specified above are used. Unconfined compression of rock cores for the determination of the modulus of elasticity (ASTM D7012-10 and ISRM Doc. 1978) and resistance to indirect stress or Brazilian test (ASTM D3967-08 and ISRM Doc. 1978).
El ensayo de compresión inconfinada en núcleos inalterados de roca, se entiende como la determinación de la resistencia a la compresión uniaxial de especímenes de roca de una geometría regular, proporciona la clasificación de resistencia y caracterización de las muestras de roca, especifica los procedimientos para la determinación deformaciones y esfuerzos axiales, deformaciones y esfuerzos laterales, sus curvas características, módulo de elasticidad, y constante de Poisson. Los especímenes no deben ser menores que los diámetros de broca NX, con un diámetro efectivo de muestra de 54mm, con una relación de Longitud/Diámetro entre 2.0 y 3.0 (Numeral 3. ISRM Doc. 1978). The unconfined compression test in unaltered rock cores, is understood as the determination of the uniaxial compression resistance of rock specimens of a regular geometry, provides the classification of strength and characterization of the rock samples, specifies the procedures for the Determination of deformations and axial stresses, deformations and lateral stresses, their characteristic curves, modulus of elasticity, and Poisson constant. The specimens should not be smaller than the NX drill diameters, with an effective sample diameter of 54mm, with a Length / Diameter ratio between 2.0 and 3.0 (Numeral 3. ISRM Doc. 1978).
Mientras que la ASTM permite la utilización de especímenes de un diámetro aproximado de 47mm, es decir un diámetro de broca serie NQ y una relación Longitud/Diámetro entre 2.0 y 2.5 (Numeral 8.1 y 8.2. ASTM D7012-10). Por su parte los especímenes deben ser cilindros debidamente calibrados y preparados según la ASTM D4543-08. Finalmente debe ser un ensayo con aplicación de carga constante con una duración de 5 a 10 min (Numeral 3. ISRM Doc. 1978) o de una duración de 2 a 15 min (Numeral 10.4.1 .1 , ASTM D7012-10), este control de aplicación por carga constante se debe realizar en una rata entre 0.5 a 1 .0 MPa/s. While the ASTM allows the use of specimens of an approximate diameter of 47mm, that is to say a drill bit diameter NQ series and a Length / Diameter ratio between 2.0 and 2.5 (Section 8.1 and 8.2. ASTM D7012-10). For their part, the specimens must be properly calibrated and prepared cylinders according to ASTM D4543-08. Finally, it must be a test with constant load application with a duration of 5 to 10 min (Numeral 3. ISRM Doc. 1978) or a duration of 2 to 15 min (Numeral 10.4.1 .1, ASTM D7012-10), This application control by constant load must be performed in a rat between 0.5 to 1.0 MPa / s.
Por definición la resistencia a la tensión es obtenida por el ensayo de tensión uniaxial directa, pero este ensayo tiene dificultades de operación por su aplicabilidad y costo generado, de esta manera la determinación de la resistencia a la tensión en el espécimen es más practico si se realiza por el ensayo de tracción indirecta o brasilero, principalmente por temas de operación y costo. Este es uno de los ensayos más simples en la mecánica de rocas y en el cual se generan en el espécimen grandes campos de esfuerzos que inducen la falla de la muestra por tensión. La fractura diametral que se produce en el espécimen producido por la carga constante aplicada en un rango determinado, permite la aparición de la falla y los esfuerzos esperados. La máquina de carga debe ajustarse a los requerimientos de la ASTM E-4, los bloques de contacto entre espécimen y celda de carga deben asegurar un ángulo de falla entre los 10° y 15° y la longitud de contacto del arco no debe ser inferior al valor de D/6, siendo D el diámetro de la muestra. (Numeral 5.2.2, ASTM D3967-08) o un ángulo de falla que no supere los 10° (Numeral 1 . Parte 2. ISRM Doc. 1978). By definition the tensile strength is obtained by the direct uniaxial tension test, but this test has operating difficulties due to its applicability and generated cost, so the determination of the tensile strength in the specimen is more practical if Performed by the indirect or Brazilian tensile test, mainly for operation and cost issues. This It is one of the simplest tests in rock mechanics and in which large stress fields are generated in the specimen that induce the failure of the sample by stress. The diametral fracture that occurs in the specimen produced by the constant load applied in a given range, allows the appearance of the failure and the expected efforts. The loading machine must meet the requirements of ASTM E-4, the contact blocks between specimen and load cell must ensure a failure angle between 10 ° and 15 ° and the arc contact length must not be shorter at the value of D / 6, where D is the diameter of the sample. (Numeral 5.2.2, ASTM D3967-08) or an angle of failure that does not exceed 10 ° (Numeral 1. Part 2. ISRM Doc. 1978).
El espécimen de ensayo debe tener un diámetro mínimo correspondiente a una broca de perforación de serie NX, con una muestra efectiva de 54mm (Numeral 3. Parte 2. ISRM Doc. 1978) y con una relación espesor/diámetro entre 0.2 y 0.75 (Numeral 7.1 , ASTM D3967-08). El control de aplicación de carga se realiza con un rango de 200 N/s (Numeral 3(e). Parte 2. ISRM Doc. 1978) o con un control por esfuerzos entre 0.05 y 0.35 MPa/s con una duración de ensayo entre 1 y 10 min (Numeral 8.3, ASTM D3967-08). Este ensayo no permite asegurar una falla por tracción del material por lo cual se obtienen inconsistencias con respecto a los verdaderos valores de resistencia a la tensión. The test specimen must have a minimum diameter corresponding to an NX series drill bit, with an effective sample of 54mm (Numeral 3. Part 2. ISRM Doc. 1978) and with a thickness / diameter ratio between 0.2 and 0.75 (Numeral 7.1, ASTM D3967-08). The load application control is carried out with a range of 200 N / s (Numeral 3 (e). Part 2. ISRM Doc. 1978) or with an effort control between 0.05 and 0.35 MPa / s with a test duration between 1 and 10 min (Numeral 8.3, ASTM D3967-08). This test does not allow to ensure a tensile failure of the material, so inconsistencies are obtained with respect to the true tensile strength values.
En el estado de la técnica se han propuesto diversos métodos y equipos para obtener las características mecánicas de materiales rocosos. Así por ejemplo el documento CA2250090 proporciona un método de ensayo de compresión de la roca, el método desarrolla el valor de la compresión en función de la porosidad y de la litología específica. El documento plantea un método sistémico para realizar los mismos ensayos estándar de compresión sobre muestras cilindricas estándar, destinado para la revisión periódica de los planes deperforación de pozos. (Selección de brocas para diferentes secciones del pozo, peso y velocidad de la rotación del barreno, etc.) En la patente CA23221 18 se presenta una técnica para determinar de forma directa la resistencia a la comprensión de una muestra de formación rocosa por medio de una técnica de indentación, con la cual se pueden determinar las propiedades mecánicas de fragmentos de roca. El método propuesto mide la fuerza y desplazamiento que se producen al ensayar una muestra de roca, la relación entre los dos registros fuerza-desplazamiento puede proporcionar estimativos del valor de la resistencia a la compresión del material. La invención consiste en un equipo de ensayos indentador pero con lecturas sistematizadas de la fuerza y el desplazamiento, donde las lecturas corresponden a pruebas puntuales sobre las superficies de las muestras. Various methods and equipment have been proposed in the state of the art to obtain the mechanical characteristics of rock materials. Thus, for example, document CA2250090 provides a rock compression test method, the method develops the value of compression as a function of porosity and specific lithology. The document proposes a systemic method to perform the same standard compression tests on standard cylindrical samples, intended for periodic review of well drilling plans. (Selection of drill bits for different sections of the well, weight and speed of the rotation of the hole, etc.) In CA23221 18 a technique is presented to directly determine the resistance to the understanding of a rock formation sample by means of an indentation technique, with which the mechanical properties of rock fragments can be determined. The proposed method measures the force and displacement that occur when testing a rock sample, the relationship between the two force-displacement registers can provide estimates of the value of the compressive strength of the material. The invention consists of an indenter test equipment but with systematized readings of force and displacement, where the readings correspond to specific tests on the surfaces of the samples.
El documento CA2591058 enseña un método para estimar la resistencia a la compresión confinada de la roca a la profundidad de trabajo donde debe ser perforada por una broca y un fluido de perforación, pero requiere conocer inicialmente el parámetro de la resistencia inconfinada de la Roca, y después teóricamente proporciona una solución basados en el cambio en el volumen de poros debidos a las cargas aplicadas por el fluido en la perforación. Document CA2591058 teaches a method to estimate the compressive strength of the rock confined to the working depth where it must be drilled by a drill and a drilling fluid, but it requires initially knowing the parameter of the unconfined resistance of the Rock, and then theoretically it provides a solution based on the change in pore volume due to the charges applied by the drilling fluid.
En la patente CA26531 15 se muestra un método para la determinación de propiedades de las rocas y, más particularmente, a un método que utiliza un modelo matemático de una broca para determinar las propiedades de las rocas. Entre ellas la resistencia inconfinada y confinada de la roca y su porosidad. Esta es una propuesta teórica que necesita el registro de los datos de fuerzas, presiones, revoluciones, etc., durante la perforación del sondeo A method for the determination of rock properties and, more particularly, a method that uses a mathematical model of a drill to determine the properties of rocks is shown in patent CA26531 15. Among them the unconfined and confined resistance of the rock and its porosity. This is a theoretical proposal that requires the registration of the data of forces, pressures, revolutions, etc., during the drilling of the survey.
La patente CN1619285 se refiere a un instrumento portátil multifuncional de pruebas para mecánica de rocas. El instrumento Incluye panel superior, panel inferior, panel frontal, panel trasero, columnas verticales, barra de tiro, toma vertical, gato horizontal, vertical conector de la placa de extremo del pistón, placa terminal del gato horizontal, componente de posicionamiento, caja de corte superior y la caja de corte inferior, etc. Dicho invención también proporciona el método de conexión. El equipo de esta invención es bastante complejo y está diseñado para trabajar principalmente sobre muestras tipo prismático(Cubos). The CN1619285 patent refers to a multifunctional portable testing instrument for rock mechanics. The instrument includes top panel, bottom panel, front panel, rear panel, vertical columns, drawbar, vertical jack, horizontal jack, vertical piston end plate connector, horizontal jack terminal plate, positioning component, box upper cut and lower cut box, etc. Said invention also provides the connection method The equipment of this invention is quite complex and is designed to work primarily on prismatic type samples (Cubes).
El método de la patente CN1018191 1 1 hace referencia a un método para encontrar el módulo de tracción de un material frágil , que se caracteriza por que comprende las siguientes etapas de: disponer una muestra de ensayo en la prueba brasilera, aplicar una carga de forma simétricamente sobre la línea de la muestra de ensayo en la dirección radial de la muestra de ensayo, medir el desplazamiento total del centro de la muestra de ensayo en la dirección del diámetro en el que la dirección del desplazamiento total es vertical a la dirección de la carga de la aplicación de la muestra de ensayo, calcular para obtener el módulo de tracción del material. Este documento atiende teóricamente una solución para estimar una propiedad diferente a la resistencia a la compresión. La invención del documento EP0206737 se refiere a una nueva mejora de herramienta abrasiva con novedad en el tipo, distribución y geometría de los elementos en la broca, cuyo objeto principal es la variación para una nueva de broca de perforación El documento EP1836509 trata en general a la perforación de taladros en formaciones subterráneas, y más particularmente, a métodos para predecir y optimizar la velocidad a la que se perforan los orificios así como la selección adecuada de las brocas taladradoras y de evaluación del rendimiento. Esta es una propuesta teórica que también necesita el dato de las presiones de los lodos y otros datos de la perforación durante el avance del sondeo The method of the CN1018191 1 1 patent refers to a method for finding the tensile modulus of a fragile material, characterized in that it comprises the following steps of: arranging a test sample in the Brazilian test, applying a load in a manner symmetrically on the line of the test sample in the radial direction of the test sample, measure the total displacement of the center of the test sample in the direction of the diameter in which the direction of the total displacement is vertical to the direction of the load of the application of the test sample, calculate to obtain the tensile modulus of the material. This document theoretically addresses a solution to estimate a property different from compressive strength. The invention of document EP0206737 refers to a new improvement of abrasive tool with novelty in the type, distribution and geometry of the elements in the drill, whose main object is the variation for a new drill bit Document EP1836509 generally deals with the drilling of drills in underground formations, and more particularly, to methods to predict and optimize the speed at which the holes are drilled, as well as the proper selection of drill bits and performance evaluation. This is a theoretical proposal that also requires the data of sludge pressures and other drilling data during the drilling progress.
La invención del documento EP2310844 está dirigida al uso de sistemas y métodos que determinan las propiedades geológicas utilizando análisis acústico. Las señales acústicas se recogen durante el procesamiento del medio geológicos, como en muestras de roca, para la determinación de propiedades geológicas de acuerdo con los métodos establecidos en la invención. La propuesta es principalmente teórica basada en métodos no destructivos que necesita los datos durante el avance del sondeo. The invention of EP2310844 is directed to the use of systems and methods that determine geological properties using acoustic analysis. The acoustic signals are collected during the processing of the geological medium, as in rock samples, for the determination of geological properties according to the methods established in the invention. The proposal is mainly theoretical based on non-destructive methods that the data needs during the progress of the survey.
La patente US4981037 presenta un método para el cálculo de los esfuerzos totales de sobrecarga, el esfuerzo efectivo vertical, la presión de poros y el esfuerzo efectivo horizontal por medio de los datos del registro durante la perforación. La invención se puede practicar en tiempo real mediante el uso de técnicas de medición durante la perforación o después de la perforación mediante el uso de los datos grabados o datos de mediciones por sondeo en pozo abierto. Este documento también corresponde a una propuesta teórica que necesita el registro de los datos durante la perforación del pozo. Patent US4981037 presents a method for the calculation of total overload stresses, vertical effective stress, pore pressure and horizontal effective stress by means of registration data during drilling. The invention can be practiced in real time by the use of measurement techniques during drilling or after drilling by using the recorded data or measurement data by openhole drilling. This document also corresponds to a theoretical proposal that needs the registration of the data during the drilling of the well.
El documento US5345819propone un método y un equipo para determinar la degradación de la resistencia de la roca en el fondo de la perforación debido a la aplicación de la presión del fluido de perforación, los efectos del fluido se estima mediante el registro de velocidad de ondas de ultrasonido en las muestras. Esta es una propuesta teórica basada en métodos no destructivos que necesita los datos durante el avance del sondeo. El método y aparato del documento US5442950 se utilizan para determinar la compresibilidad del volumen de poros, la porosidad al esfuerzo y el cambio de la porosidad relativa de muestras de roca de un depósito rocoso. La invención aplica un nuevo modelo para determinar la compresibilidad del volumen de poro como una función de la presión. Este modelo simplifica la determinación de la compresibilidad del volumen de poros de una muestra, ya que se requiere la medición del volumen de poros en sólo dos estados de presión diferentes. Sin embargo esta sigue siendo una propuesta teórica basada en métodos no destructivos que necesita los datos durante el avance del sondeo. El documento WO9408127 propone una técnica mejorada para determina con más precisión la presión de poro de roca sedimentaria perforada por un pozo de sondeo desde la superficie. La sobrecarga se mide directamente en uno o más lugares en el pozo del sondeo, y un registro de la formación de sobrecarga se genera utilizando las presiones de sobrecargas medidas y datos geofísicos convencionales. Así mismo, el documento WO0125597 enseña un método para la selección de los parámetros de perforación para la perforación de un pozo a través de formaciones rocosas en el subsuelo. El método incluye la determinación de una resistencia a la compresión de las muestras de las formaciones rocosas que han de ser perforadas a partir de mediciones realizadas de los desplazamientos y carga en las muestras. Las mediciones de desplazamiento y carga se hacen por un penetrador. Los parámetros de perforación se seleccionan a partir de los valores de la resistencia a la compresión determinada. La invención consiste en un equipo de ensayos indentador pero con lecturas sistematizadas de la fuerza y el desplazamiento, donde las lecturas corresponden a pruebas puntuales sobre las superficies de las muestras. Document US5345819 proposes a method and equipment to determine the degradation of rock resistance at the bottom of the drilling due to the application of the drilling fluid pressure, the effects of the fluid is estimated by recording wave velocity of ultrasound in the samples. This is a theoretical proposal based on non-destructive methods that needs the data during the progress of the survey. The method and apparatus of US5442950 are used to determine the compressibility of the pore volume, the porosity to the stress and the change of the relative porosity of rock samples from a rocky deposit. The invention applies a new model for determining the compressibility of pore volume as a function of pressure. This model simplifies the determination of the compressibility of the pore volume of a sample, since the measurement of the pore volume in only two different pressure states is required. However, this is still a theoretical proposal based on non-destructive methods that needs the data during the progress of the survey. WO9408127 proposes an improved technique to more accurately determine the pore pressure of sedimentary rock drilled by a borehole from the surface. Overload is measured directly at one or more locations in the borehole, and a record of the overload formation is generated using the measured overload pressures and conventional geophysical data. Also, WO0125597 teaches a method for the selection of drilling parameters for drilling a well through rock formations in the subsoil. The method includes the determination of a compressive strength of the samples of the rock formations to be drilled from measurements made of the displacements and load in the samples. Displacement and load measurements are made by a penetrator. The drilling parameters are selected from the values of the determined compressive strength. The invention consists of an indenter test equipment but with systematized readings of force and displacement, where the readings correspond to specific tests on the surfaces of the samples.
En el documento WO0240824 se presenta un equipo y método para la toma de muestras de núcleo de formaciones subterráneas. Específicamente, la invención se refiere a un sacatestigo tipo "esponja", y el método de uso de la misma, para la obtención de una muestra de núcleo de roca y el cual asegura la integridad estructural y química de la muestra de núcleo para su posterior análisis. In WO0240824 a device and method for the sampling of core samples from underground formations is presented. Specifically, the invention relates to a "sponge" type witness, and the method of use thereof, for obtaining a rock core sample and which ensures the structural and chemical integrity of the core sample for later analysis.
El documento WO2009002872 se refiere a un método, sistema y equipo complejo para estimar parámetros geomecánicos de las muestras de roca basados en el análisis de señales acústicas en diferentes estados de las ondas que genera el equipo. Sin embargo esta es una propuesta teórica basada en métodos no destructivos WO2009002872 refers to a complex method, system and equipment for estimating geomechanical parameters of rock samples based on the analysis of acoustic signals in different states of the waves generated by the equipment. However, this is a theoretical proposal based on non-destructive methods.
Como se puede ver, ninguno de los documentos presenta una metodología para determinar la resistencia a la compresión inconfinada en muestras de rocas, sino que se presentan equipos muy complejos en su montaje, y que requieren un elevado grado de instrumentación y de registro de los datos instrumentales. De esta manera, se ve la necesidad de adaptación de nuevos procedimientos de ensayo para utilizar muestras con una menor relación diámetro/longitud, y así lograr una caracterización del macizo a partir de la obtención de sus propiedades mecánicas. As you can see, none of the documents presents a methodology to determine the resistance to unconfined compression in rock samples, but very complex equipment is presented in its assembly, and that require a high degree of instrumentation and data recording Instrumental From In this way, the need to adapt new test procedures to use samples with a smaller diameter / length ratio is seen, and thus achieve a characterization of the massif from obtaining its mechanical properties.
Descripción de la invención Description of the invention
El proceso de recuperación de muestras de roca puede ser complicado debido a las condiciones geológicas de ciertas zonas. Esto repercute en que las muestras que se obtienen no cumplen con lo estipulados en las normas ASTM e ISRM con respecto a las relaciones diámetro/longitud mínimas. Por esta razón una gran cantidad de muestras son desechadas y en muchos casos, las características de la roca no pueden ser determinadas apropiadamente. Las exploraciones de campo, realizadas a lo largo de un proyecto de infraestructura o investigación requiere la inspección física en profundidad del terreno. Específicamente para exploraciones en roca la utilización de brocas y equipos robustos de perforación hacen en ocasiones dispendiosas las maniobras de obtención de núcleos, también la experiencia del operador incide de manera importante en que los especímenes obtenidos sean adecuados para la realización de las mínimas pruebas en laboratorio. The rock sample recovery process can be complicated due to the geological conditions of certain areas. This has the effect that the samples obtained do not comply with the provisions of the ASTM and ISRM standards with respect to the minimum diameter / length ratios. For this reason a large number of samples are discarded and in many cases, the characteristics of the rock cannot be determined properly. Field explorations, carried out along an infrastructure or research project require in-depth physical inspection of the land. Specifically for rock explorations, the use of drill bits and robust drilling equipment sometimes makes the maneuvering of nuclei different, the operator's experience also has an important impact on the specimens obtained being suitable for the minimum laboratory tests. .
Basado en los métodos de la exploración geotécnica de roca, los bajos valores de RQD y las directrices proporcionadas por la ASTM e ISRM para ensayos de laboratorio en estos materiales, se desarrolló un Nuevo modelo de mordazas de confinamiento y un nuevo ensayo de compresión inconfinada en muestras de rocas en forma de disco y sometidas a cargas distribuidas diametralmente, con el fin de caracterizar de una mejor manera los especímenes de roca (de materiales), aprovechar de forma eficiente las muestras teniendo bajos valores de diámetro/longitud y garantizando que la falla se produzca mediante la compresión del material. El estado de esfuerzos internos en un disco sometido a cargas diametrales presenta una distribución muy compleja que varía notablemente en función del tipo de carga aplicada. Los análisis teóricos de la distribución de los esfuerzos en este problema han tenido diversas propuestas de soluciones a partir de la mecánica de materiales. Based on the methods of geotechnical rock exploration, low RQD values and guidelines provided by ASTM and ISRM for laboratory tests on these materials, a new model of confinement jaws and a new unconfined compression test were developed in samples of disc-shaped rocks and subjected to diametrically distributed loads, in order to better characterize rock specimens (of materials), efficiently take advantage of samples having low diameter / length values and ensuring that the fault It is produced by compressing the material. The state of internal stresses in a disc subjected to diametral loads has a very complex distribution that varies significantly depending on the type of load applied. Theoretical analyzes of the distribution of efforts in this problem have had various proposals for solutions based on the mechanics of materials.
Las soluciones hasta ahora consideradas son propuestas netamente teóricas, pues se parte del supuesto de una solución en un estado plano de esfuerzos, es decir completamente bidimensional. La practicidad depoder conocer el estado de esfuerzos dentro del disco sometido a carga, radica entre muchos otros casos en llegar a determinar parámetros de resistencia del material. Bajo esta premisa, se han desarrollado múltiples ensayos de caracterización de materiales para diversos sectores como la industria de la construcción y en el caso particular de la mecánica de rocas para desarrollar pruebas rápidas, sencillas de realizar y de bajo costo que permitan conocer la resistencia de la roca intacta. The solutions considered so far are purely theoretical proposals, since it is based on the assumption of a solution in a flat state of efforts, that is to say completely two-dimensional. The practicality of being able to know the state of stress within the disc under load, lies among many other cases in determining resistance parameters of the material. Under this premise, multiple material characterization tests have been developed for various sectors such as the construction industry and in the particular case of rock mechanics to develop rapid, simple to perform and low-cost tests that allow to know the resistance of The rock intact.
Uno de los ensayos más aplicados en este aspecto es el denominado ensayo de tracción indirecta o brasilero desarrollado a mediados del siglo XX. Por definición la resistencia a la tracción es obtenida por el ensayo de tracción uniaxial directa, pero este ensayo tiene determinado grado de dificultad en su aplicación, de esta manera la determinación de la tracción indirecta es más práctico en temas de operación y de costo, es uno de los ensayos más simples en la mecánica de rocas, la fractura diametral que se produce en el espécimen es producida por la carga aplicada en un rango determinado(ISRM, 2010). One of the most applied tests in this aspect is the so-called indirect or Brazilian tensile test developed in the mid-twentieth century. By definition the tensile strength is obtained by the direct uniaxial tensile test, but this test has a certain degree of difficulty in its application, in this way the determination of indirect traction is more practical in terms of operation and cost, it is One of the simplest tests in rock mechanics, the diametral fracture that occurs in the specimen is produced by the load applied in a given range (ISRM, 2010).
A manera de resumen se puede establecer que para el ensayo brasilero se requiere que la máquina de carga se ajuste a los requerimientos de la norma ASTM E-4; los bloques de contacto entre espécimen y celda de carga deben asegurar un ángulo de falla entre los 10° y 15° y la longitud de contacto del arco de carga no debe ser inferior al valor de D/6, siendo D el diámetro de la muestra(Numeral 5.2.2, ASTM D3967-08) ó se debe asegurar un ángulo de falla que no supere los 10° (Numeral 1 . Parte 2. ISRM Doc. 1978). El estado de esfuerzos que experimentan los especímenes bajo las características de un ensayo brasilero ha sido estudiado de manera teóricapor diversos investigadores por largo tiempo, con el fin de poder relacionar la carga que produce la falla del disco con la verdadera resistencia del material a la tracción. En el trabajo de Ye J.H. et al. (2012) se presenta la solución analítica para los estados de esfuerzos y deformaciones dentro del espécimen de disco en un ensayo brasileño con el supuesto de aplicación de cargas concentradas. La solución se trabaja en coordenadas cartesianas y los resultados teóricos en este estudio son comparados con dos series de pruebas experimentales; dentro de las conclusiones de ese estudio se plantea que en algunos casos existen grandes discrepancias entre los cálculos teóricos de deformaciones dentro del espécimen y los registrados en las pruebas experimentales, y se establecen algunos límitesrespecto a en cuáles condiciones existe correspondencia con las pruebas experimentales. As a summary, it can be established that for the Brazilian test, the loading machine is required to conform to the requirements of the ASTM E-4 standard; the contact blocks between specimen and load cell must ensure a failure angle between 10 ° and 15 ° and the contact length of the load arc must not be less than the value of D / 6, where D is the diameter of the sample (Numeral 5.2.2, ASTM D3967-08) or a failure angle must be ensured that does not exceed 10 ° (Numeral 1. Part 2. ISRM Doc. 1978). The state of efforts experienced by specimens under the characteristics of a Brazilian trial has been studied theoretically by various researchers for a long time, in order to be able to relate the load produced by the disk failure with the true tensile strength of the material . In the work of Ye JH et al. (2012) the analytical solution for stress and strain states within the disk specimen is presented in a Brazilian test with the assumption of application of concentrated loads. The solution is worked on Cartesian coordinates and the theoretical results in this study are compared with two series of experimental tests; Within the conclusions of this study, it is suggested that in some cases there are large discrepancies between the theoretical calculations of deformations within the specimen and those recorded in the experimental tests, and some limits are established regarding the conditions under which correspondence exists with the experimental tests.
La usual idealización de que la fuerza de compresión aplicada durante el ensayo brasilero trabaja como una carga concentrada, ha sido cuestionada desde hace tiempo, y se sabe por la práctica ingenieril y experimental que durante el ensayo brasilero, en realidad la carga se aplica en un área de contacto. Por lo anterior se han desarrollado intensos trabajos teóricos y experimentales que permiten avanzar en determinar el estado interno de esfuerzos del disco durante la prueba, bajo la hipótesis de diferentes tipos de distribución de la carga. Dentro de las conclusiones se expone que los resultados entre la solución teórica y las pruebas experimentales desarrolladas son, en general, satisfactorios en casi todo el espacio del disco, a excepción de los puntos muy cercanos a la zona cargada, adicionalmente establecen que en la práctica la inevitable inclinación de los ejes de carga respecto a los planos del contorno del espécimen introducen discrepancias adicionales en la veracidad de los planos de esfuerzos y deformaciones asumidas en el análisis teórico. La solución teórica del problema planteada por MarkidesCh.F., et al. (2010), fue la de dividir o condicionar el análisis del estado de esfuerzos dentro del disco en dos zonas, tal como se muestra en la figura 1 : la zona (1 ) para puntos del disco dentro o por debajo del área cargada, y la zona (2) para puntos del disco por fuera del área de carga; para cada una de las dos zonas las ecuaciones para determinar los esfuerzos dentro del disco son condicionadas mediante una serie de argumentos matemáticos. The usual idealization that the compression force applied during the Brazilian test works as a concentrated load has long been questioned, and it is known from the engineering and experimental practice that during the Brazilian test, the load is actually applied in a Contact area. Therefore, intense theoretical and experimental works have been developed that allow progress in determining the internal stress state of the disk during the test, under the hypothesis of different types of load distribution. Within the conclusions it is stated that the results between the theoretical solution and the experimental tests developed are, in general, satisfactory in almost all the disk space, except for the points very close to the loaded area, additionally establish that in practice The inevitable inclination of the axes of load with respect to the planes of the contour of the specimen introduce additional discrepancies in the veracity of the planes of stresses and deformations assumed in the theoretical analysis. The theoretical solution of the problem posed by MarkidesCh.F., Et al. (2010), was to divide or condition the analysis of the state of stress within the disk into two zones, as shown in Figure 1: the zone (1) for points of the disk within or below the loaded area, and the zone (2) for disc points outside the loading area; For each of the two zones, the equations to determine the stresses within the disk are conditioned by a series of mathematical arguments.
Entre los nuevos conceptos se destaca el cambio en la distribución de la carga aplicada, ρ(θ) (3), que varía de magnitud desde un máximo en el punto central en la posición del eje (4) vertical de disco y decrece de forma sinusoidal y radial hasta cero en los extremos del área de carga, también se introduce una respectiva fuerza de fricción Τ(θ) (5) no uniforme que actúa en el área de carga. La solución propuesta en forma de una serie robusta de ecuaciones parte de los siguientes supuestos: a) El problema es completamente simétrico, por tanto el análisis se realiza para el primer cuarto de circunferencia. Among the new concepts, the change in the distribution of the applied load, ρ (θ) (3), which varies in magnitude from a maximum at the central point in the position of the vertical disk axis (4) and decreases in shape, stands out Sinusoidal and radial to zero at the ends of the load area, a respective non-uniform friction force Τ (θ) (5) is also introduced that acts in the load area. The solution proposed in the form of a robust series of equations is based on the following assumptions: a) The problem is completely symmetrical, so the analysis is performed for the first quarter of the circle.
b) Se realiza la diferenciación de las dos zonas de análisis, éstas son determinantes para la selección correcta de los parámetros de condición de las ecuaciones. b) Differentiation of the two analysis zones is performed, these are determinants for the correct selection of the condition parameters of the equations.
c) Para la determinación de los esfuerzos se toma un valor de radio r(6) y un ángulo de dirección Θ (7). Por lo tanto el resultado quedará en términos de coordenadas polares. c) For the determination of the stresses, a radius value r (6) and a steering angle Θ (7) are taken. Therefore the result will be in terms of polar coordinates.
Dentro de las principales conclusiones de la solución planteada (Marquides Ch.F., 2012), se destaca que el estado de esfuerzos en la parte central del disco se comporta de manera similar al estado de esfuerzos para un disco sometido a una carga distribuida radial pero en el contorno y puntos próximos al área de carga cambian drásticamente. El hecho de introducir la fuerza de fricción introduce cambios importantes en el estado de esfuerzos en las proximidades de la zona de aplicación de la carga, sin embargo hacia el interior del disco su incidencia se hace despreciable. Among the main conclusions of the proposed solution (Marquides Ch.F., 2012), it is emphasized that the state of efforts in the central part of the disk behaves similarly to the state of efforts for a disk subjected to a radial distributed load but in the contour and points close to the cargo area change dramatically. The fact of introducing the friction force introduces important changes in the state of stress in the vicinity of the area of application of the load, however towards the inside of the disk its incidence becomes negligible.
Además se resalta que en el cálculo general la introducción de la fricción amplifica notablemente el estado de esfuerzos cerca de los arcos cargados, lo cual debe ser tema de mayor investigación, ya que en pruebas experimentales se ha observado que este incremento no se produce en la realidad debido a la micro fracturación periférica del disco en los arcos cargados. Por lo anterior, la presente invención considera el componente ρ(θ){3) de la carga y no se considera el componente de fricción Τ(θ) (5), y en los análisis de resultados se considera esta simplificación, por lo tanto, de acuerdo a las condiciones mencionadas anteriormente, las ecuaciones para determinar el campo de esfuerzosdel disco debido a la acción de la carga o presión externa sinusoidal y radial p, se relaciona con los valores de esfuerzo: lamagnitud del componente de esfuerzo radial om la magnitud del componente de esfuerzo normal Ow y la magnitud del componente de esfuerzo cortante 7>©, para cualquier punto al interior del disco. La gran ventaja de la solución en dos zonas, radica en el hecho de que los intensos gradientes de esfuerzos que aparecen cerca de los extremos cargados cuando se considera una carga distribuida radial, son eliminados, aproximándose mucho más a los comportamientos naturales durante las pruebas experimentales. En la presente invención se buscaron los esfuerzos internos de un disco de diámetro aproximado a 47,60 mm, que en la práctica correspondería a especímenes de roca recuperados con una broca de perforación tipo NQ. Para esto se realizaron los cálculos de las magnitudes del campo de esfuerzos en sus tres componentes om OQQ y τ para cualquier punto en el interior del disco. Como constantes se han establecido: la geometría del disco caracterizado por su radio R{8), que corresponde a una muestra recuperada con una broca de perforación NQ, la magnitud del esfuerzo aplicado es de alrededor de 50 MPa, valor que corresponde a los esfuerzos admisibles a compresión de una roca de resistencia media. In addition, it is highlighted that in the general calculation the introduction of friction significantly amplifies the state of stress near the loaded arches, which should be the subject of further investigation, since in experimental tests it has been observed that this increase does not occur in the reality due to peripheral micro fracture of the disc in the loaded arches. Therefore, the present invention considers the component ρ (θ) {3) of the load and is not considered the friction component Τ (θ) (5), and in the analysis of results this simplification is considered, therefore , according to the conditions mentioned above, the equations to determine the field of stress of the disk due to the action of the sinusoidal and radial external load or pressure p, are related to the stress values: the magnitude of the radial stress component or m the magnitude of the normal stress component Ow and the magnitude of the shear force component 7> ©, for any point inside the disc. The great advantage of the solution in two zones, lies in the fact that the intense stress gradients that appear near the loaded ends when a radial distributed load is considered, are eliminated, getting closer to the natural behaviors during the experimental tests . In the present invention, the internal stresses of a disk of approximate diameter of 47.60 mm were sought, which in practice would correspond to specimens of rock recovered with a drill bit type NQ. For this, the calculations of the magnitudes of the stress field in its three components or m OQQ and τ were made for any point inside the disk. As constants have been established: the geometry of the disk characterized by its radius R {8), which corresponds to a sample recovered with a drill bit NQ, the magnitude of the applied stress is around 50 MPa, a value that corresponds to the allowable compressive stresses of a medium strength rock.
Entre tanto se ha fijado como variable la distribución de la carga en el perímetro de la muestra, en términos del ángulo interno ω0(9) medido desde el centro del disco y que barre los límites del área cargada. Se han establecido cinco valores de variación de u>o así: carga concentrada, 7,5°, 15°, 30° y 45°. Se estableció además la geometría del campo de esfuerzos a calcular, por medio de un mallado en coordenadas polares que definen los puntos en donde se calculan las tres componentes del esfuerzo om OQQ y τ . In the meantime, the distribution of the load on the perimeter of the sample has been set as variable, in terms of the internal angle ω 0 (9) measured from the center of the disk and sweeping the boundaries of the loaded area. Five variation values of u> or so have been established: concentrated load, 7.5 °, 15 °, 30 ° and 45 °. The geometry of the stress field to be calculated was also established, by means of a mesh in polar coordinates that define the points where the three components of the stress or m OQQ and τ are calculated.
En términos generales, los resultados muestran un comportamiento del estado de esfuerzo en correspondencia con la discusión previa de la introducción, en particular se destaca que en los puntos próximos al centro del disco /«O y en los puntos del perímetro cercanos al arco de carga, es decir con una condición de u>o≠0, se tienen esfuerzos a„ y Ow extremadamente magnificados, entre tanto el comportamiento del esfuerzo cortante es confiable para todo el disco, por ejemplo para ω0 = 45Q existen esfuerzos máximos calculados de o„ = 1563.03 Mpa y de Ow = -1582.01 localizados en el centro del disco, también existen esfuerzos de tracción cercanos a los máximos valores calculados de 1500 Mpa, tanto para a„ como para el componente Ow en los puntos donde termina el arco de carga en el disco. Estos picos extremos son resultado propio de las condiciones algebraicas de la solución en las fronteras del espacio de cálculo. Para un adecuado análisis de los resultados se debe, por lo tanto, depurar inicialmente los datos considerando los puntos particulares descritos anteriormente donde se excede el valor normal de la magnitud del esfuerzo, que en teoría deben ser de magnitud similar al esfuerzo máximo aplicado. Para tal fin, la representación de la distribución de esfuerzos puede realizarse a partir de líneas de un mismo nivel de esfuerzo. Una vez obtenidos los estados depurados de esfuerzos, se puedenobservar las variaciones por cada componente de esfuerzosen relación con un aumento del arco cargado ω0 (9). En términos generales con respecto a los componentes de esfuerzo orr y Oee se aprecia que la variación del estado de esfuerzos para el componente o„ dentro de la zona central del disco aumenta en aproximadamente 10 veces pero se mantiene en condiciones de tracción, entre tanto la variación del estado de esfuerzos para el componente OQQ aumenta pero en menor proporcionan aproximadamente solo dos veces, manteniéndose el estado a compresión para esta componente. In general terms, the results show a behavior of the state of effort in correspondence with the previous discussion of the introduction, in particular it is noted that at the points near the center of the disk / «O and at the perimeter points near the load arc , that is to say with a condition of u> or ≠ 0, efforts are made to „and Ow extremely magnified, meanwhile the shear stress behavior is reliable for the entire disk, for example for ω 0 = 45 Q there are calculated maximum stresses of or „= 1563.03 Mpa and of Ow = -1582.01 located in the center of the disc, there are also tensile stresses close to the maximum calculated values of 1500 Mpa, both for a„ and for the Ow component at the points where the arc of load on disk These extreme peaks are the result of the algebraic conditions of the solution at the boundaries of the calculation space. For an adequate analysis of the results, it is therefore necessary to initially purify the data considering the particular points described above where the normal value of the magnitude of the effort is exceeded, which in theory should be of similar magnitude to the maximum effort applied. For this purpose, the representation of the distribution of efforts can be made from lines of the same level of effort. Once the states cleared of stress have been obtained, the variations for each stress component can be observed in relation to an increase in the loaded arc ω 0 (9). In terms general with respect to the stress components or rr and Oee it is appreciated that the variation of the stress state for the component or „within the central area of the disk increases by approximately 10 times but remains in tensile conditions, meanwhile the variation of the stress state for the OQQ component increases but to a lesser extent they provide approximately only twice, maintaining the compression state for this component.
Con relación al esfuerzo cortante se puede observar una variación de la distribución pero que en general se mantiene en magnitudes muy pequeñas, y a lo largo del eje vertical del disco son cercanas a cero. In relation to the shear stress, a variation of the distribution can be observed, but in general it is maintained in very small quantities, and along the vertical axis of the disk they are close to zero.
Del análisis anterior se destacan condiciones de tracciónque se presentan en el componente radial del esfuerzo, entre tanto, que en el componente normal prevalece la condición a compresión del material y que el componente del esfuerzo cortante es variable pero de valores bajos de magnitud. En este orden de ideas, bajo las condiciones establecidas en el presente estudio la mejor condición de esfuerzos a compresión prevalece en el material del disco cuando se tiene una carga aplicada p(3) en un arco (9) de valor ωο= 30Q. La propuesta analítica para la solución del problema de determinar el estado de esfuerzos internos en un disco sometido a una carga diametral, presenta un adecuado resultado de la magnitud y distribución de los esfuerzos en el interior del disco, sin embargo se hace necesaria una depuración de datos puntuales en determinadas zonas donde hay una magnificación del valor del esfuerzo, principalmente en el centro del disco y en puntos cercanos al perímetro que se encuentran en carga, especialmente en los puntos extremos del arco de carga. From the previous analysis, tensile conditions stand out, which are presented in the radial stress component, meanwhile, that in the normal component the compression condition of the material prevails and that the shear stress component is variable but of low magnitude values. In this order of ideas, under the conditions established in the present study the best condition of compressive stresses prevails in the disc material when there is an applied load p (3) in an arc (9) of value ωο = 30 Q. The analytical proposal for the solution of the problem of determining the state of internal stresses in a disk subjected to a diametral load, presents an adequate result of the magnitude and distribution of the stresses inside the disk, however a purification of punctual data in certain areas where there is a magnification of the value of the effort, mainly in the center of the disc and in points near the perimeter that are in load, especially in the extreme points of the load arc.
Existe una clara incidencia en el estado tensión al dentro del disco por la variación de la longitud de los arcos de contacto de la carga aplicada; con respecto a este punto se determinó que en el rango de variación de 7,5° <u>o< 45° la variación del estado de esfuerzos para el componente o„ dentro de la zona central del disco aumenta en aproximadamente 10 veces pero se mantiene en condiciones de tracción, entre tanto se aprecia que la variación del estado de esfuerzos para el componente OQQ aumenta pero en menor proporción, en aproximadamente solo dos veces, manteniéndose el estado a compresión. En el análisis de la variación del esfuerzo radial se determinó que la menor relación de esfuerzos de tracción- compresión se alcanza para ωα= 30Q, con un valor de o o 5 0.6. Entre tanto en el análisis realizado para la variación del esfuerzo normal se hizo evidente que para un valor de ωο= 30Q se tiene el mayor grado de compresión en el disco. Existe un punto geométrico particular cercano al valor de r ~ 0.6R en donde se presentan las mayores variaciones en el estado de los esfuerzos. There is a clear incidence in the state of tension within the disk due to the variation in the length of the contact arcs of the applied load; with respect to this point it was determined that in the variation range of 7.5 ° <u> or <45 ° the variation of the stress state for the component or „within the central area of the disk increases by approximately 10 times but it keeps in conditions of traction, meanwhile it is appreciated that the variation of the stress state for the OQQ component increases but in a smaller proportion, in approximately only twice, maintaining the state under compression. In the analysis of the radial stress variation it was determined that the lowest tensile-compression stress ratio is reached for alcanzaα = 30 Q , with a value of 0 0.6. Meanwhile, in the analysis carried out for the variation of the normal effort, it became clear that for a value of ωο = 30 Q there is a greater degree of compression in the disc. There is a particular geometric point close to the value of r ~ 0.6R where the greatest variations in the stress state are presented.
Del análisis de resultados realizado se puede concluir que en el componente radial del esfuerzo se presentan esfuerzos de tracción y que, por lo contrario, en el componente normal no existen esfuerzos de tracción en el material del disco y que el componente del esfuerzo cortante es variable pero de valores bajos de magnitud. From the analysis of the results carried out, it can be concluded that in the radial component of the stress there are tensile stresses and that, on the contrary, in the normal component there are no tensile stresses in the disc material and that the component of the shear stress is variable but of low magnitude values.
Se pretende la optimización y la utilización de especímenes con relaciones diámetro/longitud menos estrictos, para evitar la pérdida de muestras por no cumplir la normatividad y así lograr un notable mejoramiento en el número de datos para la estadística y a su vez en la caracterización del material extraído. The optimization and use of specimens with less strict diameter / length ratios is intended, in order to avoid the loss of samples for not complying with the regulations and thus achieve a notable improvement in the number of data for statistics and in turn in the characterization of the material extracted.
De acuerdo a las desviaciones estándar presentadas en las pruebas físicas experimentales realizadas se establece que mediante la aplicación de cargas diametrales en muestras con forma de disco, utilizando las mordazas diseñadas y el protocolo establecido para el ensayo, se obtiene la resistencia a la compresión del material, optimizando procesos como: reducción en el tiempo de corte y preparación de muestras, así como la obtención de más muestras de un mismo espécimen debido a la relación diámetro/altura necesarias en el nuevo ensayo. De esta manera la presente invención permite realizar una optimización en el uso del espécimen recuperado, asegurando la obtención de parámetros mecánicos mediante una compresión inconfinada total de la muestra, cuando esta se encuentra sometida a una carga de tipo diametral, cuya geometría del espécimen tiene una similitud con la utilizada en la norma ASTM D3967. La correlación con resultados obtenidos de compresiones inconfinadas clásicas permiten dar evidencia de ello, la utilización de propuestas analíticas, modelaciones mediante MEF (Método de elementos finitos) y una robusta y extensa serie de ensayos físicos de laboratorio, dieron los resultados necesarios para asegurar una completa falla a compresión de la muestra. According to the standard deviations presented in the experimental physical tests performed, it is established that through the application of diametric loads in disc-shaped samples, using the jaws designed and the protocol established for the test, the compressive strength of the material is obtained , optimizing processes such as: reduction in the time of cutting and preparation of samples, as well as obtaining more samples of the same specimen due to the diameter / height ratio needed in the new test. In this way the present invention allows an optimization in the use of the recovered specimen, ensuring the obtaining of mechanical parameters by means of a total unconfined compression of the sample, when it is subjected to a diametral type load, whose geometry of the specimen has a similarity with that used in ASTM D3967. The correlation with results obtained from classic unconfined compressions allows to give evidence of this, the use of analytical proposals, modeling using MEF (Finite Element Method) and a robust and extensive series of physical laboratory tests, gave the necessary results to ensure a complete Sample compression failure.
Para lograr los objetivos propuestos anteriormente, se desarrolló un modelo de mordazas de confinamiento y un método para caracterizar los especímenes de materiales por medio de la aplicación de compresión inconfinada en muestras con forma de disco y sometidas a cargas distribuidas diametralmente. El método de caracterización comprende las siguientes etapas: In order to achieve the objectives set out above, a model of confinement jaws and a method to characterize material specimens were developed through the application of unconfined compression in disc-shaped samples and subjected to diametrically distributed loads. The characterization method comprises the following stages:
• Preparar muestras de material en forma de disco. Se debe garantizar una superficie fina sobre la superficie perimetral del disco, y se debe engrasar la región de contacto con las mordazas de confinamiento. • Prepare samples of disc-shaped material. A thin surface must be guaranteed on the perimeter surface of the disk, and the contact region with the confinement jaws must be greased.
• Colocar el marco de compresión sobre los platos del dispositivo de carga. Las mordazas de confinamiento deben estar engrasadas y quedar alineadas axialmente para evitar la deformación de sus aletas durante el contacto con el disco del núcleo de roca • Place the compression frame on the plates of the loading device. The confinement jaws must be greased and aligned axially to avoid deformation of their fins during contact with the disc of the rock core
• Generar compresión inconfinada en las muestras por medio de la aplicación carga diametral distribuida utilizando las mordazas diseñadas. La carga se aplica de forma continua e incremental con una tasa la cual debe producir una deformación constante durante toda la prueba. La tasa de carga o se aplicará hasta que el valor del esfuerzo haya decaído al 20% de su máxima resistencia • Registradas las lecturas de deformación observadas y hacer los cálculos de esfuerzo a partir de las lecturas registradas. • Generate unconfined compression in the samples by means of the distributed diametral loading application using the designed jaws. The load is applied continuously and incrementally with a rate which must produce a constant deformation throughout the test. The load rate or will be applied until the value of the effort has fallen to 20% of its maximum resistance • Recorded the deformation readings observed and make the stress calculations from the recorded readings.
Para realizar el ensayo de manera correcta, se debe desarrollar un modelo de mordaza que permita aplicar la fuerza de compresión sobre la muestra de una manera uniforme. Por tal motivo, las mordazas desarrolladas comprenden las siguientes características: To perform the test correctly, a jaw model must be developed that allows the compression force to be applied to the sample evenly. For this reason, the developed jaws comprise the following characteristics:
• El área que hace contacto con el disco, tiene un contorno curvo que sigue el perfil circular del disco. • The area that makes contact with the disk has a curved contour that follows the circular profile of the disk.
• Presenta un par de aletas en los extremos del arco, de manera que la fuerza que ejerce la prensa se distribuye de forma regular sobre toda el área de contacto de la mordaza con el disco. • It has a pair of fins at the ends of the arch, so that the force exerted by the press is distributed regularly over the entire area of contact of the jaw with the disc.
• El ángulo de curvatura se encuentra entre 60 y 75°. • The angle of curvature is between 60 and 75 °.
• Los bordes del contorno curvo presentan una terminación redondeada o en chaflán. • The edges of the curved contour have a rounded or chamfer finish.
Para completar la descripción y con objeto de ayudar a una mejor comprensión de las características del invento, se adjunta a la presente memoria descriptiva una serie de figuras ilustrativas donde se podrá comprender más fácilmente las innovaciones y ventajas del método desarrollado. To complete the description and in order to help a better understanding of the features of the invention, a series of illustrative figures are attached to the present specification where the innovations and advantages of the developed method can be more easily understood.
Breve descripción de los dibujos Brief description of the drawings
Los aspectos relevantes y las ventajas de la presente invención serán mejor entendidos con relación a las siguientes figuras, en las cuales: The relevant aspects and advantages of the present invention will be better understood in relation to the following figures, in which:
FIG. 1 Esquema analítico de un disco sometido a carga diametral FIG. 2 Esquema general del ensayo de compresión inconfinada de núcleos de roca para la determinación del módulo de elasticidad según las normasFIG. 1 Analytical scheme of a disc subjected to diametral loading FIG. 2 General scheme of the unconfined compression test of rock cores for the determination of the modulus of elasticity according to the standards
ASTM D7012-10 e ISRM Doc. 1978. ASTM D7012-10 and ISRM Doc. 1978.
FIG. 3 Esquema propuesto para determinar la resistencia a la compresión inconfinada en muestras de rocas u otros materiales, en forma de disco y sometidas a carga diametral FIG. 3 Proposed scheme to determine unconfined compression resistance in samples of rocks or other materials, disk-shaped and subjected to diametral loading
FIG. 4 Descripción de las variables dentro del modelo geométrico de un disco sometido a carga diametral y la mordaza de confinamiento. FIG. 4 Description of the variables within the geometric model of a disk subjected to diametral loading and the jaw of confinement.
FIG. 5 Vista frontal de la mordaza desarrollada en la presente invención. FIG. 5 Front view of the jaw developed in the present invention.
FIG. 6 Vista isométrica de la mordaza desarrollada en la presente invención. FIG. 7 Vista isométrica inferior de la mordaza desarrollada en la presente invención. FIG. 6 Isometric view of the jaw developed in the present invention. FIG. 7 Bottom isometric view of the jaw developed in the present invention.
Descripción Detallada de las Modalidades Preferidas. Detailed Description of the Preferred Modalities.
La resistencia a compresión de la roca se utiliza en muchas fórmulas de diseño y se utiliza a veces como una propiedad índice para seleccionar la técnica de excavación apropiada. Las propiedades de deformación y resistencia de núcleos de rocas medidos en el laboratorio por lo general no reflejan con precisión las propiedades in situ, ya que este último está fuertemente influenciado por las diaclasas, fallas, heterogeneidad, planos de falla y otros. Por lo tanto, los valores de laboratorio de las muestras intactas se deben emplear con un juicio adecuado en aplicaciones de ingeniería. El objeto de la presente invención, presenta una opción para aplicar en aquellas muestras de núcleos de roca que no cumplan con la relación longitud-diámetro (L/D) tal como se especifica en las normas tal como la ASTM D 4543. En la figura 2, se muestra el esquema convencional para realizar el ensayo de compresión inconfinada con aplicación de carga axial. El sistema para la prueba de compresión (10), comprende un sistema de compresión de cilindros (1 1 ), mediante el ajuste de un marco de carga (12). Para el control de deformaciones del marco de carga,el sistema dispone de un sistema de lectura mediante un deformimetro (13) que puede ser de aguja tradicional o digital, colocado en una zona fija (14) del montaje. El deformimetro (13) permite leer el desplazamiento del marco durante el ensayo de compresión axial, esta lectura de desplazamiento se relaciona con la constante del anillo de carga y de esta manera se puede determinar la carga aplicada sobre la muestra y teniendo en cuenta el área cargada se determina el esfuerzo aplicado. The compressive strength of rock is used in many design formulas and is sometimes used as an index property to select the appropriate excavation technique. The deformation and resistance properties of rock cores measured in the laboratory generally do not accurately reflect the properties in situ, since the latter is strongly influenced by diaclases, faults, heterogeneity, fault planes and others. Therefore, laboratory values of intact samples should be used with proper judgment in engineering applications. The object of the present invention presents an option to apply in those samples of rock cores that do not comply with the length-diameter (L / D) ratio as specified in the standards such as ASTM D 4543. In the figure 2, the conventional scheme for performing the unconfined compression test with axial load application is shown. The compression test system (10) comprises a cylinder compression system (1 1), by adjusting a load frame (12). For the control of deformations of the load frame, the system has a reading system by means of a deformimeter (13) that can be of traditional or digital needle, placed in a fixed area (14) of the assembly. The deformimeter (13) allows to read the displacement of the frame during the axial compression test, this displacement reading is related to the constant of the load ring and in this way the load applied on the sample can be determined and taking into account the area loaded the effort applied is determined.
Para la realización del ensayo, la muestra de material (15) se sostiene por medio de un soporte superior (16) y uno inferior (17) los cuales están unidos con los cilindros (1 1 ) del sistema de compresión. La muestra de material (15) tiene forma cilindrica de radio r (D/2) y longitud L, donde la relación (L/D) debe tener un valor entre 2 y 3. Durante el ensayo, se somete la muestra a comprensión axial, y se registra la carga máxima aplicada, la carga de agrietamiento, el esfuerzo, la duración del ensayo, el tipo de fractura y la tasa de aplicación de carga. For the performance of the test, the sample of material (15) is supported by means of an upper support (16) and a lower one (17) which are connected to the cylinders (1 1) of the compression system. The material sample (15) has a cylindrical shape of radius r (D / 2) and length L, where the ratio (L / D) must have a value between 2 and 3. During the test, the sample is subjected to axial understanding , and the maximum applied load, the cracking load, the effort, the duration of the test, the type of fracture and the load application rate are recorded.
La ejecución del ensayo de compresión inconfinada con aplicación de carga diametral que se muestra en la figura 3, involucra el análisis y la elaboración de un montaje (18) determinado para el control de deformaciones del marco de carga y las mordazas de confinamiento, para ello se recurre a la utilización del sistema de compresión de cilindros (1 1 ) similar al utilizado en la prueba de carga axial. Igualmente comprende un sistema de lectura mediante un deformimetro (13) para leer el desplazamiento del marco durante el ensayo de compresión diametral. La muestra de mortero tipo disco (19) se ubica entre un par de mordazas de confinamiento (20) las cuales presentan un diseño que se adapta al perfil circular de la muestra tipo disco (19). The execution of the unconfined compression test with diametral loading application shown in figure 3, involves the analysis and elaboration of a set (18) determined for the control of deformations of the load frame and the jaws of confinement, for this the use of the cylinder compression system (1 1) similar to that used in the axial load test is used. It also comprises a reading system using a deformimeter (13) to read the displacement of the frame during the diametral compression test. The disc type mortar sample (19) is located between a pair of confinement jaws (20) which have a design that adapts to the circular profile of the disc type sample (19).
Para tener un completo control del ensayo, se debe seguir la deformación de las aletas de la mordaza de confinamiento (20). Para ello se coloca una galga extensiométrica (21 ) la cual permite obtener lecturas de la deformación de la aleta mediante el voltaje medido en un puente de Wheatstone. Los valores de desplazamiento no deben superar el valor de 0.7% para evitar una deformación permanente en la mordaza, y así determinar su óptimo comportamiento durante el ensayo. In order to have complete control of the test, the deformation of the jaws of the confinement jaw (20) must be followed. For this, an extensiometric gauge (21) is placed, which allows to obtain readings of the deformation of the fin by means of the voltage measured on a Wheatstone bridge. Displacement values must not exceed 0.7% to avoid deformation. permanent in the jaw, and thus determine its optimal behavior during the test.
La forma adaptada de las mordazas de confinamiento (20) permite distribuir la fuerza aplicada en el cuerpo de la muestra de material con forma de disco (19). De esta manera y a diferencia del ensayo de esfuerzo de tracción indirecta (ensayo brasileño), la muestra se somete a esfuerzos similares a los que recibe con la prueba estándar de carga axial, sin embargo el método de ensayo propuesto en la presente invención no requiere muestras de gran longitud L, sino que permite utilizar muestras donde la relación (L/D) puede tener valores bajos, inclusive valores menores a 1 . De esta manera, el principal aporte del nuevo ensayo de caracterización geomecánica es la posibilidad de contar con una gran cantidad de datos de resistencia aún con bajos porcentajes de recuperación de muestras y con relaciones diámetro/longitud menos estrictos, para evitar la pérdida de especímenes por no cumplir la normatividad, permitiendo así tener una representación estadística importante y caracterizar de una forma más adecuada el macizo rocoso. The adapted form of the jaws of confinement (20) allows to distribute the force applied in the body of the sample of material with disk form (19). In this way and unlike the indirect tensile stress test (Brazilian test), the sample is subjected to stresses similar to those it receives with the standard axial load test, however the test method proposed in the present invention does not require samples of great length L, but it allows to use samples where the ratio (L / D) can have low values, including values less than 1. In this way, the main contribution of the new geomechanical characterization test is the possibility of having a large amount of resistance data even with low percentages of recovery of samples and with less strict diameter / length ratios, to avoid the loss of specimens by not complying with regulations, thus allowing to have an important statistical representation and to characterize the rock massif in a more adequate way.
Las configuraciones de la mordaza de confinamiento se obtienen de los estudios analíticos para un disco sometido a carga diametral. A partir de ello y de acuerdo a las propiedades de los materiales utilizados las principales características de la geometría de la mordaza se muestran en la figura 4. El trabajo se realizó mediante el concepto de simetría tanto sobre el eje x, como sobre el eje y; dejando el origen como un nodo de apoyo fijo y el eje x-y con un sistema de apoyos en patín. En la figura se aprecia una sección del disco de prueba (19) de radio r, el cual se encuentra bajo compresión de la mordaza de confinamiento (20). Para obtener una falla de compresión en el espécimen de prueba (19) la punta de la aleta de la mordaza debe cubrir el borde del espécimen hasta un ángulo de carga ω (22). De acuerdo a las pruebas se establece que un ángulo de carga es de 75°, proporciona el mejor comportamiento de esfuerzos a compresión dentro del espécimen. El otro parámetro de configuración es la altura efectiva de la pieza h (23). Este parámetro se presenta como una opción para la disminución de la concentración de esfuerzos en los puntos de contacto del arco de carga. Los resultados mostraron una notable disminución en la concentración la pieza cuando se tenía una altura efectiva (23) de 5mm. Con estos dos parámetros se determinó el ángulo de la aleta α (24) lo más tangencial al contacto con el espécimen (45° por requerimientos de mecanizado), lo cual mostró una reducción notable de los esfuerzos dentro del espécimen. Con la configuración anterior, se obtiene una compresión en la muestra, que puede llevar a una fractura de la muestra. Los esfuerzos a tensión se hacen más evidentes hacia el centro de la circunferencia, mientras que la compresión se presenta en los extremos. The confinement jaw configurations are obtained from analytical studies for a disc subjected to diametral loading. From this and according to the properties of the materials used, the main characteristics of the jaw geometry are shown in Figure 4. The work was carried out using the concept of symmetry both on the x-axis, and on the y-axis. ; leaving the origin as a fixed support node and the xy axis with a skate support system. The figure shows a section of the test disk (19) of radius r, which is under compression of the confinement jaw (20). To obtain a compression failure in the test specimen (19) the tip of the jaw fin must cover the edge of the specimen up to a loading angle ω (22). According to the tests it is established that a loading angle is 75 °, it provides the best compression stress behavior within the specimen. The other configuration parameter is the effective height of the part h (23). This parameter is presented as an option for the reduction of the stress concentration at the contact points of the load arc. The results showed a notable decrease in the concentration of the piece when it had an effective height (23) of 5mm. With these two parameters, the angle of the α (24) fin was determined as tangential to the contact with the specimen (45 ° by machining requirements), which showed a marked reduction of the stresses within the specimen. With the above configuration, compression is obtained in the sample, which can lead to a fracture of the sample. Tension stresses become more evident towards the center of the circumference, while compression occurs at the ends.
La figura 5 muestra una vista frontal de la mordaza de confinamiento (20). Para asegurar la distribución y valores de esfuerzo dentro del espécimen la mordaza de confinamiento comprende una configuración conformada principalmente por tres cuerpos: la mordaza de aletas (25), un bloque de soporte (26) y un reborde de sujeción (27), donde los tres cuerpos están alineados sobre un eje común (no mostrado en la figura). El reborde (27) se dispone para acoplarse a las mordazas de confinamiento del sistema de compresión. En este caso la forma del reborde es cilindrica hueca, pero puede tomar cualquier otra geometría acorde a las mordazas de compresión. El reborde (27) se encuentra unido sólidamente al bloque de soporte (26), y preferiblemente las tres piezas: el soporte (26), el reborde (27) y la mordaza de aletas (25), se configuran a partir de una única pieza sólida de material de alta resistencia tal como el acero. Figure 5 shows a front view of the confinement jaw (20). To ensure the distribution and stress values within the specimen the confinement jaw comprises a configuration consisting mainly of three bodies: the fin jaw (25), a support block (26) and a clamping flange (27), where the three bodies are aligned on a common axis (not shown in the figure). The flange (27) is arranged to engage the compression jaws of the compression system. In this case the shape of the flange is hollow cylindrical, but it can take any other geometry according to the compression jaws. The flange (27) is solidly connected to the support block (26), and preferably the three pieces: the support (26), the flange (27) and the jaw of fins (25), are configured from a single solid piece of high strength material such as steel.
El bloque de soporte (26) consiste en una pieza maciza que sirve como base para la mordaza de aletas (25). Estas piezas deben ser construidas de tal manera que soporten la carga que se transfiere a la muestra, a través de una máquina de compresión o máquina universal, adicionalmente para lograr una geometría definida se hace necesario: utilizar una técnica de mecanizado industrial que permita obtener formas definidas a partir de bloques de acero. Las aletas de la mordaza de aletas (25) forman un ángulo (24) con el bloque de soporte, este ángulo debe ser preferiblemente tangencial al espécimen de prueba para asegurar una compresión uniforme, sin embargo por razones de mecanizado, se encontró que el ángulo óptimo debe ser de alrededor de 45°. La mordaza de aletas (25) presenta una superficie curva de radio r, correspondiente al radio del disco de prueba. La superficie curva de la mordaza cubre una superficie del disco de prueba correspondiente a la distancia barrida por el ángulo de carga (22) (Fig. 4). Las aletas de la mordaza presentan un bisel (28) en sus puntas, el cual se moldea con la pieza con el fin de evitar deformaciones en la misma mordaza. Además, en la base inferior de las aletas (25) en el contacto con el bloque de soporte (26) se presenta un acabado redondeado (29) que garantiza el adecuado trabajo mecánico del acero en ese punto para que no sufra excesivas compresiones que puedan destruir la pieza La figura 6 muestra una vista isométrica superior de la mordaza (20). Como se puede ver la pieza de soporte (26) comprende un área mayor a la mordaza de aletas (25) con el fin de dar mayor estabilidad a la pieza. La figura 7 muestra una vista inferior de la mordaza de compresión (20). Se puede ver que el reborde (27) se ubica sobre el mismo eje de la mordaza de aletas (25), lo cual permite transferir directamente la fuerza del sistema de compresión de cilindros, a la pieza de prueba. The support block (26) consists of a solid piece that serves as a base for the jaw of fins (25). These pieces must be constructed in such a way that they support the load that is transferred to the sample, through a compression machine or universal machine, additionally to achieve a defined geometry it becomes necessary: to use an industrial machining technique that allows to obtain shapes defined from steel blocks. The fins of the fin jaw (25) form an angle (24) with the support block, this An angle should preferably be tangential to the test specimen to ensure uniform compression, however for machining reasons, it was found that the optimum angle should be around 45 °. The fin jaw (25) has a curved surface of radius r, corresponding to the radius of the test disk. The curved jaw surface covers a surface of the test disk corresponding to the distance swept by the loading angle (22) (Fig. 4). The jaw fins have a bevel (28) at their tips, which is molded with the piece in order to avoid deformations in the same jaw. In addition, at the bottom base of the fins (25) in contact with the support block (26) there is a rounded finish (29) that guarantees the adequate mechanical work of the steel at that point so that it does not suffer excessive compressions that may destroy the piece Figure 6 shows a top isometric view of the jaw (20). As can be seen, the support piece (26) comprises an area greater than the fin jaw (25) in order to give the piece greater stability. Figure 7 shows a bottom view of the compression jaw (20). It can be seen that the flange (27) is located on the same axis of the fin jaw (25), which allows the force of the cylinder compression system to be directly transferred to the test piece.
Se considera no necesario hacer más extensa esta descripción para que un experto en la materia comprenda el alcance y las ventajas de la invención. Los materiales, formas, tamaño y disposición de los elementos serán susceptibles de variación siempre y cuando ello no suponga alteración en la forma esencial del invento. Todos los términos técnicos y científicos aquí empleados tienen el mismo significado tal como comúnmente los entienden aquellos expertos en la técnica. Todas las publicaciones, solicitudes de patente y patentes y otras referencias mencionadas, quedan incorporadas por referencia en su totalidad. It is considered not necessary to make this description more extensive for a person skilled in the art to understand the scope and advantages of the invention. The materials, shapes, size and arrangement of the elements will be subject to variation as long as this does not involve alteration in the essential form of the invention. All the technical and scientific terms used here have the same meaning as those of ordinary skill in the art understand them. All publications, patent and patent applications and other references mentioned, are incorporated by reference in their entirety.

Claims

Reivindicaciones Claims
1 . Un dispositivo para determinar la resistencia a la compresión inconfinada en muestras de rocas u otros materiales en forma de disco y sometidas a carga diametral, conformado por un sistema de compresión de cilindros (1 1 ), un marco de carga (12), un deformimetro (13) colocado en una zona fija (14) del montaje y una muestra de material en forma de disco (19) sujeta por medio de soportes unidos con los cilindros (1 1 ) del sistema de compresión. Dispositivo caracterizado porque: la muestra en forma de disco (19) se ubica entre un par de mordazas de confinamiento (20) las cuales presentan un contorno o arco curvo que sigue el perfil circular del disco. Y comprende un par de aletas en los extremos del arco cuyos bordes presentan una terminación redondeada o en bisel (28) y donde cada punta de las aletas se extiende por el borde del espécimen (19) hasta un ángulo de carga (22), la base entre las aletas (25) y el bloque de soporte (26) también tiene un acabado redondeado (29). La configuración de la mordaza de compresión (20) también comprende una altura efectiva de la pieza h (23), un ángulo de la aleta (24) para reducir los esfuerzos dentro del espécimen o muestra tipo disco (19) y una galga extensiométrica (21 ) la cual permite obtener lecturas de la deformación de la aleta mediante el voltaje medido en un puente de Wheatstone. one . A device for determining uncontrolled compressive strength in samples of rocks or other disc-shaped materials and subjected to diametral loading, consisting of a cylinder compression system (1 1), a loading frame (12), a deformimeter (13) placed in a fixed area (14) of the assembly and a sample of disc-shaped material (19) held by means of supports connected with the cylinders (1 1) of the compression system. Device characterized in that: the disk-shaped sample (19) is located between a pair of confinement jaws (20) which have a curved contour or arc that follows the circular profile of the disk. And it comprises a pair of fins at the ends of the arch whose edges have a rounded or bevelled termination (28) and where each tip of the fins extends along the edge of the specimen (19) to a loading angle (22), the Base between the fins (25) and the support block (26) also has a rounded finish (29). The configuration of the compression jaw (20) also comprises an effective height of the piece h (23), an angle of the fin (24) to reduce the stresses within the specimen or disc type sample (19) and a strain gauge ( 21) which allows to obtain readings of the deformation of the fin by means of the voltage measured on a Wheatstone bridge.
2. Un dispositivo para determinar la resistencia a la compresión inconfinada en muestras de rocas u otros materiales en forma de disco y sometidas a carga diametral de acuerdo a la reivindicación 1 donde la mordaza de confinamiento (20) está conformada por tres cuerpos: la mordaza de aletas (25), un bloque de soporte (26) y un reborde de sujeción (27), donde los tres cuerpos están alineados sobre un eje común y se configuran a partir de una única pieza sólida de material de alta resistencia. 2. A device for determining uncontrolled compressive strength in samples of rocks or other disc-shaped materials and subjected to diametral loading according to claim 1 wherein the confinement jaw (20) is formed by three bodies: the jaw of fins (25), a support block (26) and a clamping flange (27), where the three bodies are aligned on a common axis and are configured from a single solid piece of high strength material.
3. Un dispositivo para determinar la resistencia a la compresión inconfinada en muestras de rocas u otros material en forma de disco y sometida a carga diametral según la reivindicación 1 donde el ángulo de carga (22) se encuentra entre 60 y 75°, preferiblemente 75° que proporciona el mejor comportamiento de esfuerzos a compresión dentro del espécimen 3. A device for determining uncontrolled compressive strength in samples of rocks or other disc-shaped material and subjected to diametral loading according to claim 1 wherein the loading angle (22) is between 60 and 75 °, preferably 75 ° that provides the best compression stress behavior within the specimen
4. Un dispositivo para determinar la resistencia a la compresión inconfinada en muestras de rocas u otros materiales en forma de disco y sometidas a carga diametral de acuerdo a la reivindicación 1 donde las aletas de la mordaza de aletas (25) forman un ángulo (24) con el bloque de soporte, el cual debe ser preferiblemente tangencial al espécimen de prueba (19) para asegurar una compresión uniforme. 4. A device for determining uncontrolled compressive strength in samples of rocks or other disc-shaped materials and subjected to diametral loading according to claim 1 wherein the fins of the fin jaw (25) form an angle (24 ) with the support block, which should preferably be tangential to the test specimen (19) to ensure uniform compression.
5. Un dispositivo para determinar la resistencia a la compresión inconfinada en muestras de rocas u otros materiales en forma de disco y sometidas a carga diametral de acuerdo a la reivindicación 1 donde el sistema de lectura puede ser de aguja tradicional o digital. 5. A device for determining uncontrolled compressive strength in samples of rocks or other disc-shaped materials and subjected to diametral loading according to claim 1 wherein the reading system can be traditional or digital needle.
6. Un dispositivo para determinar la resistencia a la compresión inconfinada en muestras de rocas u otros materiales en forma de disco y sometidas a carga diametral de acuerdo a la reivindicación 1 donde la forma del reborde de sujeción (27) se configura acorde a la geometría de los cilindros de compresión preferiblemente de forma cilindrica hueca. 6. A device for determining uncontrolled compressive strength in samples of rocks or other disc-shaped materials and subjected to diametral loading according to claim 1 wherein the shape of the clamping flange (27) is configured according to the geometry of compression cylinders preferably hollow cylindrical.
7. Un método para determinar la resistencia a la compresión inconfinada en muestras de rocas u otros materiales en forma de disco y sometidas a carga diametral, por medio de la aplicación de fuerza a través de un par de mordazas de confinamiento, el cual se caracteriza porque comprende las siguientes etapas: 7. A method for determining uncontrolled compressive strength in samples of rocks or other disc-shaped materials and subjected to diametral loading, by applying force to through a pair of confinement jaws, which is characterized in that it comprises the following stages:
• Preparar muestras de material en forma de disco.  • Prepare samples of disc-shaped material.
• Alisar la superficie perimetral del disco.  • Smooth the perimeter surface of the disk.
· Engrasar la región de contacto con las mordazas de confinamiento.· Grease the contact region with the jaws of confinement.
• Colocar un marco de compresión sobre los soportes de un dispositivo de carga. • Place a compression frame on the supports of a loading device.
• Alinear las mordazas de confinamiento axialmente para evitar la deformación de sus aletas.  • Align the axial jaws to avoid deformation of their fins.
· Generar compresión inconfinada en las muestras por medio de la aplicación carga diametral distribuida utilizando las mordazas diseñadas. · Generate unconfined compression in the samples by means of the distributed diametral loading application using the designed jaws.
• Aplicar la carga de forma continua con una tasa la cual debe producir una deformación constante durante toda la prueba.  • Apply the load continuously with a rate which should produce a constant deformation throughout the test.
· Registrar las lecturas de deformación observadas y hacer los cálculos de esfuerzo a partir de las lecturas registradas. · Record the observed strain readings and make the stress calculations from the recorded readings.
8. Un método para determinar la resistencia a la compresión inconfinada en muestras de rocas u otros materiales en forma de disco y sometidas a carga diametral según la reivindicación 7 donde la tasa de carga se aplica hasta que el valor del esfuerzo haya decaído al 20% de su máxima resistencia 8. A method for determining uncontrolled compressive strength in samples of rocks or other disc-shaped materials and subjected to diametral loading according to claim 7 wherein the loading rate is applied until the stress value has decayed to 20% of its maximum resistance
9. Un método para determinar la resistencia a la compresión inconfinada en muestras de rocas u otros materiales en forma de disco y sometidas a carga diametral según la reivindicación 7 donde las mordazas desarrolladas comprenden un área que hace contacto con el disco, la cual tiene un contorno curvo que sigue el perfil circular del disco con un Angulo de carga que se encuentra entre 60 y 75°. Un par de aletas en los extremos del arco, yuna terminación redondeada o biselen los bordes del contorno curvo y en la base. 9. A method for determining uncontrolled compressive strength in samples of rocks or other disc-shaped materials and subjected to diametral loading according to claim 7 wherein the developed jaws comprise an area that makes contact with the disc, which has a curved contour that follows the circular profile of the disc with a loading angle that is between 60 and 75 °. A pair of fins at the ends of the arch, and a rounded end or bevel the edges of the curved contour and at the base.
PCT/IB2015/057463 2014-09-30 2015-09-30 Device and method for determining unconfined compressive strength in disc-shaped samples of rock or other materials subjected to diametral loading WO2016051345A1 (en)

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CN112033810A (en) * 2020-01-20 2020-12-04 廊坊市阳光建设工程质量检测有限公司 Device and method for detecting compressive strength of concrete by cambered surface opposite compression method

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