Classifications

• • 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
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D1/00—Investigation of foundation soil in situ
  • E02D1/02—Investigation of foundation soil in situ before construction work
  • E02D1/022—Investigation of foundation soil in situ before construction work by investigating mechanical properties of the soil
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/24—Earth materials

Definitions

• the present invention relates to the field of geotechnics and geology. It relates to a process for measuring the elastoplastic properties of a soil using a static penetrometer. It also relates to a static penetrometer for the implementation of said method.
• the first approach it is necessary to be able to ensure a continuous qualitative chain comprising at least: core sampling, packaging, transport, sample preparation and testing. To this, it should be noted that each sample measures only a few cm3 and that the representativeness of the analysis therefore requires a large number of samples and measurements.
• the major drawbacks of this first approach are the cost, the reliability of the test and the time taken to obtain a result.
• the second approach using a pressuremeter the in situ expansion tests consist in dilating in the soil, in a previously made borehole, a probe with deformable walls and in determining the relationship between the pressure applied to the soil and the displacement of the wall of the probe.
• the pressuremeter approach nevertheless suffers from several shortcomings, in particular the impact of the quality of the drilling on the representativeness of the test, because the soil is precisely measured at the level of the walls of the drilling.
• Another drawback lies in the complexity of the material used and the frequent bursting of the probe as soon as the test pressure and the volume of the probe increase.
• the challenge is therefore to propose a method for measuring the elastoplastic properties of a soil, allowing relatively direct measurements, avoiding empirical correlations, and relatively simple, in particular avoiding the complexity of implementing laboratory or pressuremeter tests. . OBJECT OF THE INVENTION
• An object of the present invention is to propose a solution overcoming the drawbacks of the state of the art, in particular a method for in situ measurement of the elastoplastic properties of a soil using a static penetrometer.
• the present invention relates to a method for measuring the elastoplastic properties of a soil, using a static penetrometer provided with a hollow tube surrounding a central rod capable of sliding inside the hollow tube and terminated at a first end by a measuring tip.
• the process includes the following steps:
• the method comprises a step c ') for measuring a first intermediate displacement, associated with the insertion of the measuring tip into the ground, at the end of an intermediate duration less than the determined duration;
• step d) includes the reiteration of step c ') in parallel with the reiteration of steps b) and c);
• the present invention also relates to a static penetrometer for implementing the method described above, comprising:
• At least one central rod terminated at a first end by a measuring tip, said measuring tip being intended to sink into the ground;
• a jack comprising an external body integral with the hollow tube and a movable body, said movable body being configured to apply a force to a second end of the rod, leading to a depression of the measuring tip in the ground, and to measure a displacement associated with this depression, said second end being intended to remain above the ground,
• An electronic controller to slave the cylinder, so as to apply a given force, for a fixed period, and to record the movement of the moving body as a function of time during the fixed period.
• the jack is an electric jack.
• FIG. 1 shows a method according to the invention
• FIG. 2 shows a curve plotting the final displacement of the measuring tip as a function of the applied force, established according to a process in accordance with the invention, for extracting elastoplastic properties from the soil;
• FIG. 3 shows a curve plotting the final displacement of the measuring tip as a function of the applied force and a curve plotting an intermediate displacement as a function of the force applied, the curves being established according to a method according to the invention, for extracting elastoplastic properties of the soil;
• Figure 4 shows a static penetrometer for the implementation of a method according to the invention.
• the invention relates to a method for measuring the elastoplastic properties of a soil, using a static penetrometer 100.
• a penetrometer conventionally comprises rods connected end to end to form a string of rods at the end of which is fixed a measuring point, intended to sink into the ground to depths of up to several tens of meters.
• the drill string In static mode, the drill string is pushed by cylinders, causing the progressive insertion of the measuring tip; this latter measure in particular the peak resistance, representative of the breaking stress Qc of the soil.
• the measurements are recorded continuously or discontinuously at a regular step.
• the penetrometer 100 used in the context of the invention is provided with a hollow tube 2 surrounding a central rod 1; said central rod 1 is capable of sliding inside the hollow tube 2 and is terminated at a first end by a point of sour 11 intended to be driven into the ground.
• a well-known “Gouda” type tip may be used, having a surface at its plane section of 10 cm 2 .
• the measurement method according to the invention firstly comprises a step a) consisting in driving the torque formed by the hollow tube 2 and the central rod 1 into the ground to bring the measuring tip 11 at a desired depth P for measuring the elastoplastic properties of the soil. Arriving at said depth P, the measuring tip 11 is erased, that is to say placed in abutment against the hollow tube 2.
• the measurement method then comprises a step b) during which a first constant force Fi is applied to a second end of the rod 1, for a determined period t. Recall that the second end of the rod 1 is out of the ground.
• the constant force Fi applied is transmitted by the rod 1 to the measuring tip 11, which will more or less sink into the ground, depending on the mechanical characteristics thereof.
• the first applied force Fi may be between 100N and 500N; considering a 10 cm2 section of the measuring tip 11, this corresponds to an applied stress between 1 and 5 bars.
• a first final displacement D is measured, associated with the insertion of the measuring tip 11 into the ground, at the end of the determined duration t.
• the term “final” is used to describe a displacement corresponding to the displacement recorded at the end of the determined duration t.
• Step d) of the method according to the invention consists in repeating steps b) and c), with increasing applied forces, to form a curve representing the final displacement as a function of the force applied.
• a second constant force F 2 greater than Fi, is applied to the second end of the rod 1, for the determined duration t.
• a measurement is made of the second final displacement D
• a third constant force F 3 greater than F 2 , is then applied, still for the determined duration t, then a measurement of the third final displacement Df is carried out at the end of said duration t, and so on.
• the increment between two successive applied forces is between 100 and 500N.
• the sequence of applying a force and measuring the final displacement is repeated n times (application of yet another force F n constant, greater than F ni , and measurement of yet another final displacement D) until reaching the stress at break in soil Qc.
• the stress at rupture of the ground will correspond to a force F n generating a maximum final displacement D due to a significant depression of the measuring tip 11.
• the maximum displacement representative of the rupture of the ground is defined at approximately 5 cm (output amplitude of the tip 11 relative to its position erased against the hollow tube 2).
• a curve C t can be drawn representing the final displacement as a function of the force applied (FIG. 2).
• the curve C t is formed of a first domain E corresponding to elastic deformations of the soil. It is formed, after an inflection point I, of a second domain PI corresponding to plastic deformations of the soil, until reaching the breaking point (Qc).
• step e) comprises the extraction of the modulus of deformation M of the soil from the slope of the curve C t final displacement / force, in the first domain E of elastic deformation situated before a point of inflection I.
• the deformation modulus M in MPa / m, is calculated from the expression: with p the slope of the first
• the method according to the invention also makes it possible to determine the creep stress (Qf), the elastic limit of the soil. Indeed, starting from the curve C t final displacement / force, the force F f corresponding to the inflection point I, translates said creep stress Qf.
• the creep stress is expressed:
• the method according to the invention gives a value of the permissible stress Qa based on the management of the permissible settlement with respect to the structure, which makes it much more relevant.
• the method comprises a step c ') during which the intermediate displacements are measured as a function of time, said intermediate displacements being associated with the gradual sinking of the measuring tip 11 during the determined duration t .
• the difference AD between the intermediate displacement Dé measured at the end of tl (for example 15 seconds) and the final displacement D measured at the end of the determined duration (eg 60s) is representative of the liquefaction potential of the soil.
• a deviation AD greater than 20% could reflect a potentially liquefiable soil.
• the applicant has developed a method for the pre-identification of liquefiable soils (cf. H. Hosseini-Sadrabadi et al, “Identification of liquefiable soils by static penetrometer: principle and numerical modeling ", National Geotechnical and Engineering Geology Days, Nancy 2016) based on static penetration tests with double measurement: a resistance measurement of n2cm / s
• the method according to the invention by giving access to the deviation D ⁇ , could reinforce the representativeness of the deviation AQ C vis-à-vis the pore pressures and the liquefaction potential of the soil considered.
• step a) of the method the couple hollow tube 2 / central rod 1 of the static penetrometer 100 may be driven into the ground according to a conventional static mode, allowing a measurement of the breaking stress. from the ground as a function of the depth, up to the desired depth P for the elastoplastic measurement.
• the couple hollow tube 2 / central rod 1 can be introduced into a hole previously drilled in the ground up to the depth P desired for the elastoplastic measurement.
• the soil to be analyzed, under the tip was not modified by the step of bringing the tube / rod couple, which ensures good representativeness of the measurements.
• the measurement method according to the invention uses a static penetrometer 100, provides an in situ measurement means for directly reconstructing the action / reaction relationship of a foundation / soil assembly by giving access to the effective behavior under soil load: lift, settlements, creep over time.
• the measurement process is not conditioned in its result by the quality of the execution of the drilling, nor by the heterogeneity of the soil, nor even by the sensitivity or the complexity of the measurement equipment used. .
• the present invention also relates to a static penetrometer 100 for measuring the elastoplastic properties of a soil.
• the penetrometer 100 (FIG. 4) comprises at least one central rod 1 terminated at one end by a measuring tip 11. It also comprises at least one hollow tube 2 surrounding the central rod 1. The respective diameters of the hollow tube 2 and of the central rod 1 are adapted so that the latter can slide freely inside the hollow tube 2.
• the couple formed by the central rod 1 and the hollow tube 2 is intended to sink into the ground, the tip 11 at the head.
• additional rods 1 and tubes 2 can be connected end at the end, to form a train of rod / tube pairs, which can be driven into the ground over several tens of meters. It being understood that a second end of the rod 1 and of the hollow tube (or second end of the drill string and of the train of hollow tubes) is intended to remain above ground, on the surface.
• the penetrometer 100 further comprises a jack 6 comprising an external body 61 integral with the hollow tube 2 and a movable body 62 capable of coming into contact with the central rod 1.
• the movable body 62 is capable of achieving a maximum displacement of approximately 7 cm between a retracted position (movable body 62 retracted and measuring tip 11 abutting against the hollow tube 2) and a deployed position (movable body 62 extended to the maximum , peak output 11 maximum).
• the movable body 62 is configured to apply a force to a second end 12 of the central rod 1, which will lead to a more or less significant depression of the measuring tip 11, depending on the characteristics of the soil. The displacement of the movable body 62, associated with this depression is measured.
• the power of the actuator motor is preferably chosen so that the movable body 62 is capable of applying forces typically between 100N and 20kN.
• the jack 6 is an electric jack.
• the penetrometer 100 also includes an electronic controller 7 for controlling the actuator 6, so as to apply a given force, for a determined duration t, and to record the movement of the mobile body 62 as a function of time, and this for the determined duration t .
• the penetrometer according to the present invention offers a practical and industrial solution allowing the efficient and economical implementation of the aforementioned method for measuring the elasto-plastic properties of a soil.
• the penetrometer 100 according to the invention advantageously comprises support means integral with the hollow tube 2 by means of a clamping jaw 3.
• the support means allow a depression in static mode in the ground of the couple formed by the hollow tube 2 and the central rod 1 up to the given depth (s) to be investigated.
• the support means may in particular consist of a hydraulic cylinder.
• the mobile part of the hydraulic cylinder fixed to the hollow tube 2 applies to it the pressing force necessary for the continuous sinking of the tube / rod couple.
• the fixed part of the hydraulic cylinder must be secured to a reaction block.
• the support means may include a self-propelled hydraulic group, for actuating the hydraulic cylinder.
• the support means are held by a chassis.
• the chassis is provided with at least one mechanical connection element intended to be connected to the reaction mass.
• This mechanical connection element may for example consist of a hydraulic or mechanical clamp, or even a vice of the same type.
• the fact that the chassis is equipped with such a mechanical connection element makes it connectable to any kind of reaction mass.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Analytical Chemistry (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• General Health & Medical Sciences (AREA)
• Biochemistry (AREA)
• Paleontology (AREA)
• Mining & Mineral Resources (AREA)
• Soil Sciences (AREA)
• Civil Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Structural Engineering (AREA)
• Environmental & Geological Engineering (AREA)
• Geology (AREA)
• Remote Sensing (AREA)
• Food Science & Technology (AREA)
• Medicinal Chemistry (AREA)
• Investigation Of Foundation Soil And Reinforcement Of Foundation Soil By Compacting Or Drainage (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=65861383

Family Applications (1)

Country Status (3)

Families Citing this family (1)

Family Cites Families (4)

• 2018
  • 2018-10-31 FR FR1860074A patent/FR3087800B1/fr active Active
• 2019
  • 2019-10-23 WO PCT/FR2019/052526 patent/WO2020089547A1/fr unknown
  • 2019-10-23 EP EP19813097.3A patent/EP3874251A1/de active Pending

Also Published As

Similar Documents

Legal Events