RU2453840C2 - METHOD OF DETERMINING PLASTIC LIMIT (Wp) OF CLAY SOIL BY COMPACTION AND DEVICE TO THIS END - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: proposed device comprises manual press with specimen arranged thereon and prepared by filling metal pattern with cylindrical opening with premade clay paste, and stiff top and bottom dies. Said pattern is made up of thin-wall cylinder with larger-diameter bottom. Said dies represent shot cups with perforated bottoms. Bottom die bottom has ring-shaped ledge. Pattern is furnished with smaller inner diameter ring passed there through to rest upon said die bottom ring-shaped ledge to rotate thereabout in cycles to align calibrated 3.2 mm-dia hole made in ring wall with similar hole made in pattern wall for periodical formation of bundle of clay paste to be controlled. Manual press is made up nut and screw, nut representing central threaded opening in crossbar. Elongated screw is furnished with lever on upper end and centering skid on lower end aligned with recess formed on top die bottom inner surface.

EFFECT: reduced labour input, faster determination of elastic limit, reliable and stable data.

3 cl, 10 dwg

Description

The invention relates to a technique for determining, by a laboratory method, soil moisture at the rolling boundary (W _P ), and using the known initial moisture content W,%, as well as moisture at the yield point (W _L ), a moisture range can be obtained in which clay soil will remain plastic.

The lower ductility limit W _P is a critical indicator. It is used to calculate the plasticity number I _P = W _L -W _P , the consistency index (or yield strength) I _L = (WW _P ) / I _P , when classifying clay soils, as well as to indirectly evaluate their mineral composition, dispersion and range physico-chemical properties, which leads to the widespread use of this indicator in engineering and geological research.

According to SNiP 11-15-74, the following types of consistency of clay soils are distinguished, depending on I _L :

Clays and loams:

Solid I _L <0 Semi-solid I _L = 0 ÷ 0.25 Refractory I _L = 0.25 ÷ 0.5 Soft plastic I _L = 0.5 ÷ 0.75 Fluid plastic I _L = 0.75 ÷ 1.0 Flowing I _L => 1

Known methods for determining the boundary of rolling W _P (ductility) in the domestic standard - GOST 5180-84 [1], as well as in the US standard - Test Method D4318-95a [2]. According to these standards, the value of W _P corresponds to the moisture of the soil paste being rolled into a tourniquet until they lose their ductility, when the tourniquet, drying out during rolling, begins to crumble. After this, pieces of soil that have lost plasticity are collected to the desired amount, weighed, dried, weighed again, and W _{P is} calculated from the difference in weighings.

For a comparative analysis of the existence of significant operations, their sequence and equipment used in obtaining W _P in [1] and PL in [2], which is one and the same, we will present their enumeration in tabular form:

GOST 5180-84 [1] (Russia) Test Method D 4318-95a [2] (USA) one. The rolling (plasticity) boundary is defined as the moisture content of the paste prepared from the test soil sample at which the paste rolled into a bundle with a diameter of 3 mm begins to disintegrate into pieces 3-10 mm long. - "- 2. The preparation of the soil for the test is carried out according to a known method (claims 4.2.1-4.2.5 [1]) or a part of the soil (40-50 g) prepared to determine the yield strength W _{L is used} . To determine the boundary of rolling use a soil paste prepared for testing for yield strength after drying the soil to the limit when it can be rolled without sticking to the fingers. 3. Prepared for testing, the soil paste is thoroughly mixed, then a small piece weighing 1.5-2 g is taken and rolled out with a palm on a glass or plastic plate to form a bundle with a diameter of 3 mm. From a mass of soil paste of 20 g a portion of soil 1.5-2 g is selected, a sample is formed into an oval shape and rolled with the pressure necessary to roll to a diameter of 3.2 mm over the entire length using a rod with a diameter of 3.2 mm for visual comparison . four. If at this thickness the tourniquet retains coherence and ductility, it is collected into a lump and rolled again until a tourniquet with a diameter of 3.2 mm is formed. - "- 5. When rolling, lightly press the tourniquet, while the length of the tourniquet should not exceed the width of the palm. - "- 6. Rolling continues until the tourniquet begins to disintegrate along transverse cracks into pieces 3-10 mm long. - "- 7. Pieces of a disintegrating tow are collected in pre-dried, weighed and numbered cups with tight-fitting lids. - "- 8. When the mass of soil in the cups reaches 15 g, determine the humidity according to a known method (paragraphs 2.3-2.4). The mass of soil in the cups should reach at least 6 g. 9. The value of the characteristic W _P according to the test results is calculated as the arithmetic average of the results of parallel determinations of humidity at the boundary of rolling (at least two) from the same soil sample. - "-

From a comparative analysis of the above operations and their sequence in the known methods [1] and [2], we conclude that they are essentially identical and differ only in the primary sources underlying these standards [1] and [2], and some refinement obtained in different empirical data laboratories.

The main disadvantage of the known methods is the considerable complexity of the process of repeatedly rolling the harnesses of the test soil manually, as well as the low reliability of the results due to the inability to accurately control the measurement of the diameter of the rolled harnesses, which can lead, as a result, to an incorrect determination of the type of consistency of clay soils depending on calculated by known W, W _L and W _P plasticity index I _P and a consistency index I _L.

The prototype of the invention essentially solved the problem and the number of common essential features in part of the method is a method for determining the boundaries of rolling (plasticity) by pressing [3]. The essence of the method lies in the fact that the rolling border is defined as the moisture content of the sample taken from a previously prepared portion of the soil paste with the loss of plasticity and cohesion, which is established by pressing it in contact with cellulose (filter paper) under a constant pressure of 2 MPa (20 kg / cm ²⁾ to complete fluid loss ground, wherein the extracted from the sample under a press break when it is bent, and then determined by weighing its moisture before and after drying to constant weight, and the difference quiet weightings calculated soil moisture at the interface rolling (W _P).

In this method, first, a 2 mm thick template in the form of a plate having a hole with a diameter of 5 cm is placed on a cotton cloth and this hole is filled with a portion of previously prepared paste (40-45 g), the excess paste is cut with a knife flush with the upper surface of the template, the template is removed, and the obtained sample is covered on top with the same cotton cloth, after which 20 sheets of filter paper are placed on the bottom and top of the sample prepared for the test, and then the sample prepared for the test is placed between metal and with wooden plates, a sample is placed on the lower table, for example, a hydraulic press, the upper press stop is brought to the sample and a pressure of 2 MPa (20 kg / cm ² ) is created on the sample for 10 minutes, after which the pressure is removed, the pressure is removed the sample and, removing the filter paper and cotton fabric, bend the sample in half, and the rolling border is considered to be reached if a crack forms on the bend of the sample. If there is no crack, the determination is repeated on a new portion of the paste, increasing the pressing time by 10 minutes compared to the duration of the previous test, and repeated tests are performed until the boundary of rolling the soil is reached. Upon reaching the rolling limit, the moisture content of the sample is immediately determined by a known method, and the lower plasticity limit (W _P ) is determined using at least two moisture determinations carried out on two samples from the same portion of the paste, and their arithmetic average value is taken into account.

The disadvantage of the prototype in terms of the method lies in the need to conduct tests on an unknown number of samples using the approximation method (trial and error method) to achieve the rolling border at the same pressure of 2 MPa and with the same time intervals of 10 min for all types of soils (consistency). Under the accepted restrictions on pressure parameters and time intervals, there is a high probability of “slipping” the moment of moisture determination and obtaining an erroneous consistency, determined according to SNiP 11-15-74.

The problem to be solved by the invention in terms of the method is to reduce the complexity and reduce the time for determining the lower plasticity limit (W _P ) of clay soils by the pressing method, which consists in laying layers of filter material, placing the sample between rigid dies, and using the press, sets the specified axial pressure on the sample , the test is carried out until the border of rolling the soil, which is determined visually, and determine the lower limit of plasticity (W _P ) according to the invention in a template made in the form e cylinder having an increased outer diameter on its lower part, set the lower stamp in the form of a short glass having a protrusion in the form of a ring on its lower outer part and a perforated bottom on its upper part with a layer of sealing filter material on the upper surface of the bottom, the template is loaded from above pre-prepared for testing with soil paste and place the top stamp in the cylinder in the form of a short glass with a perforated bottom down with a layer of sealing filter material, and then and the upper part of the template set the ground ring all the way into the ledge of the lower cylindrical part of the larger diameter of the template having a calibrated hole on the cylindrical surface with the possibility of its free rotation around the axis and alignment with the same calibrated hole with a diameter of 3.2 mm formed on the cylindrical surface template, after which the template with stamps and a soil sample is installed in the base, having a base plate, motionlessly connected to the work table, with two or more vertical uprights having a larger diameter at their lower end than at the upper, as well as thread sections at the upper end with a larger diameter and at the upper end with a smaller diameter for fastening by means of nuts on the support flange and the upper crosshead, while the template is first placed to the stop of the outer protrusion of the lower stamp in the socket of the support flange, and then pressed using the upper beam, which is fixed to the uprights, moreover, the manual press is made in the form of a screw-nut pair, the nut of which is the central threaded hole stie formed in the yoke, and the screw having an elongated shape and an arm at the top end is passed through the thread traverses the way into the slot formed in the bottom of a upper die, after which the screw creates a vertical pressure σ ₁ for the soil sample, and after a certain period time, the ring is rotated around the axis until the calibrated holes in the ring and in the template are aligned and due to the created lateral pressures σ _{2-3, the} soil harness is squeezed through these holes to visually monitor the appearance of cracks on the tourniquet, while of each control, during which no cracks form on the tourniquet, the holes are closed by turning the ring and increase the pressure σ ₁ on the soil sample, reducing the time interval between visual inspection until cracking occurs and the tourniquet breaks into separate parts under its own weight, and W _{P is} determined from known technique. After cracks appear on the tourniquet, the calibrated holes on the ring and the template are closed by turning the ring, the lower stamp is removed, the template with soil is installed again and the elongated screw is moved, the soil sample with the upper stamp is moved into the cavity of the base, which has a through slot to extract the sample, which is weighed, then dried and again weighed, and W _{P is} calculated.

A prototype of a device that implements the proposed method for determining the lower plasticity limit (W _P ) of clay soils, essentially the task being solved, is equipment for determining the moisture “maximum molecular moisture capacity” W _MMB using the method of moisture-intensive media [4]. The device includes a manual hydraulic or mechanical press equipped with a device for measuring and maintaining constant pressure with a sample of the studied portion of pre-prepared soil paste placed between its lower table and upper clamp, which has a cylindrical shape with gaskets made of filter material laid below and above the sample, as well as rigid gaskets that perform the function of dies, and the dimensions and shape of the sample are preformed by filling with a soil paste bristle pattern formed as a plate having a cylindrical hole, removable prior to placing the sample between the gaskets.

A disadvantage of the known device is that it does not allow for one cycle of its use to determine the consistency of the soil sample corresponding to the humidity for measuring W _P , and the resulting sample, which reaches brittleness when bent, allows the possibility of uncontrolled low humidity, which reduces the likelihood obtaining reliable values of I _P and I _L.

The object of the invention to be solved in terms of the device is, as in the method it implements, to reduce the complexity and reduce the time for determining the lower limit of rolling (plasticity) W _{P of} clay soils, as well as to increase the stability and reliability of the results obtained.

The solution to this problem lies in the fact that the device for implementing the method for determining the lower plasticity limit (W _P ) of clay soils, including a hand press with a placed sample formed by filling a metal template with a cylindrical hole with pre-prepared soil paste and rigid upper and lower dies moreover, between the sample and the stamps laid gaskets of filter material, according to the invention, a template for the formation of the shape and size of the sample of soil paste made in the form of a thin-walled cylinder of a given size, having an increased outer diameter in the lower part, and the rigid upper and lower dies are made in the form of short glasses with perforated bottoms freely placed in the cavity of the template under the sample upside down and above the sample downward bottom, while the lower stamp has a protrusion in the form of a ring on the lower cylindrical part, and the template is additionally equipped with a ring freely passed through its smaller outer diameter, abutting against a ledge of the lower cylindrical part the diameter of the template, with the possibility of its free periodic rotation to align the calibrated hole, the diameter of which is 3.2 mm, made in the wall of the ring, with the same hole formed in the wall of the template, for the periodic formation of a tourniquet of soil paste for its control during periodic pressurization σ ₁ and forcing out water, due to the occurrence of lateral pressure σ _2-3, wherein the pattern is fixed by clamping between the support flange coupled to the two or more vertical uprights, for replicated on a base plate fixedly connected to the working table, and having threaded portions on the upper end of the lower part of the struts having a larger diameter, as well as between the upper traverse fixed with a thread formed on the upper ends of the struts using union nuts, the hand press is made in the form of a screw-nut pair, the nut of which is formed as a central threaded hole in the traverse, and the screw has an elongated shape and is equipped with a lever at its upper end, and at the lower end - a centralizer, combined with a recess m formed in the center of the upper surface of the bottom of the upper stamp.

The advantage of the invention in terms of the method and device over the known prototypes is as follows:

- obtaining a tourniquet with its visual control of the desired consistency to determine W _P using the method of the proposed device that provides high performance while eliminating a number of manual intermediate operations associated with the repeated testing of new portions of soil to achieve its desired moisture content;

- the proposed method allows you to stop the soil compaction process in a timely manner without overexposure to ten minute intervals and excessive loss of moisture, since an experienced laboratory technician, when rolling out the next tourniquet in his fingers, accurately determines the approach of the onset of brittleness of the sample, and therefore the entire sample, and proceed with collecting the necessary the number of fragile tows for weighing, increasing the pressure with the press as the tows are displaced;

- one laboratory assistant can serve several devices with different soils simultaneously, bypassing these devices one by one, taking a sample and increasing the pressure. At the same time, productivity is significantly increased, the time for determining W _{P is} reduced, while the reliability of the obtained determinations is increased due to the stability of the parameters of the obtained samples;

- the method and the device also provide the ability to weigh the entire volume of soil immediately after reaching the rolling border on only one received harness having cracks, after removing the sample from the template.

Indicated in the invention are distinctive, essential for solving the problem, signs, in combination with known signs, expand the scope of the method and device and ensure their industrial applicability.

The invention is illustrated by a drawing in a schematic form, which shows a General view of a device that implements the method in the process of obtaining a bundle.

In the drawing, on a fixed table 1, a base is fixed, including a lower plate 2, on which at least two vertical posts 3 and 4 are mounted, having threads 5 and 6 at the upper end for connection to the upper crosshead 6 using nuts 7. The lower part of the racks has an enlarged diameter 8 with a thread portion 10 for fastening the support flange 11 with nuts 12 for abutment in the ring 11 of the template 13, made in the form of a cylinder having in the lower part an enlarged outer diameter 14 with a step 15 for abutting the ring 17 in it, freely fitted on a smaller Shab diameter bosom 13 with the possibility of rotation around the axis to combine formed in the cylindrical walls of the ring 17 and the template 13 calibrated holes 18 and 19 to expel from the sample 20, placed in the template 13, the sample of the tow 21 of the soil paste. Sample 20 is placed in the template 13 between the lower stamp 22 and the upper stamp 23, made in the form of short glasses with perforated bottoms 24 and 25, with the bottoms turned to the sample, with gaskets made of filter material 26 laid between the stamps and the sample. The manual press is made in the form a screw-nut pair, the nut of which is a threaded hole 27, formed in the center of the crosshead 6, and the screw 28 is made of an elongated shape with a centering stop in the socket 29, formed in the center of the bottom 25 in the upper die 23, and equipped on the upper end are movable m lever 30, freely passed through the hole in the head 31 of the screw. The lower stamp has a protrusion 32 in the form of a ring on the lower outer part for abutment against the support flange 11.

The described device operates as follows.

In the template 13, the lower stamp 22 is installed with the filter seal 26 with the bottom 24 facing up, the cavity of the template is filled with a prepared sample of soil paste 20, and the filter pad 26 is placed on top of the sample and the upper stamp 23 with the bottom 25 facing down. After that, using a screw 28 with a lever 30, the soil sample 20 together with the dies 23 and 24 are moved to the lower position and the sample is removed between the uprights 8 in the base 2, the dies 23 and 24 are removed, the sample is ground and weighed, and then after drying the sample to a constant the weights weigh it again and calculate W _P.

According to another embodiment, the desired number of fragments of tows with cracks is collected and weighed according to a known method and W _{P is} calculated.

An example implementation of the method and device

The soil was taken from the core of a well made from a drilling vessel in the Caspian Sea. The soil sample is a hard clay with ductility indices W _P = 31.5%, W _L = 57.4%. The sample was tested according to the claimed method and device. The results on the graph in the coordinates of humidity W,% and time t, min. The lowest humidity limit W _{P was} reached at the 20th minute.

According to the GOST 5180-84 method, the lower humidity limit was reached at 35 minutes (manual rolling method) and at 30 minutes (pressing method).

The authors made and tested samples of the device that implements the proposed method, and tested them. Positive results - significantly reduces the complexity of the tests and the timing of their implementation. The results obtained comply with all the requirements of GOST 5180-84 and show stable results. The present invention has significant novelty in comparison with prototypes and meets the criterion of industrial applicability. The authors and the applicant believe that the invention may be protected by the RF Patent.

If necessary, the authors and the applicant can submit additional materials confirming the operability of the proposed device and the method implemented with its help, in addition to those attached to this application.

Information sources

1. Determination of the rolling boundary. Section 5. Soils. Laboratory methods for determining physical characteristics. GOST 5180-84.

2. Determination of the lower limit of ductility. Test Method for yield strength, yield strength and soil plasticity index. D 4318-95a (USA, translation in the Russian version).

3. Determination of the rolling boundary (ductility) by pressing. Appendix 12. Soils. Laboratory methods for determining physical characteristics. GOST 5180-84 (prototype in terms of the method).

4. Equipment for determining the moisture content of the "maximum molecular moisture capacity" by the method of moisture-intensive media (W _MMB ). Laboratory work in soil science. Edited by V.T. Trofimov, V.A. Korolev. - M .: Higher school, 2008. S.266-269 (prototype in terms of the device).

Claims (3)

1. The method of determining the lower limit of plasticity (W _P ) of clay soils by pressing, which consists in laying layers of filter material, placing the sample between the hard dies, using the press to create the specified axial pressure on the sample, the test is carried out until the boundary of rolling the soil, which is determined visually, and the lower limit of ductility (W _P ) is determined, characterized in that in the template made in the form of a cylinder having an increased outer diameter on its lower part, the lower a stamp in the form of a short glass having a protrusion in the form of a ring on its lower outer part and a perforated bottom on its upper part with a layer of sealing filter material on the upper surface of the bottom; from above, load a template with soil paste previously prepared for testing and place the upper stamp in the cylinder in the form of a short glass with a perforated bottom down with a layer of sealing filter material, after which a ground ring is installed on the upper part of the template until it stops in the ledge of the lower cylinder part of the larger diameter of the template, having a calibrated hole on the cylindrical surface with the possibility of its free rotation around the axis and alignment with the same calibrated hole with a diameter of 3.2 mm formed on the cylindrical surface of the template, after which the template with stamps and a soil sample are installed in the base, having a base plate fixedly connected to the working table, with two or more vertical posts fixed to the plate having a larger diameter at their lower end than at the upper, and pieces of thread at the upper end with a larger diameter and at the upper end with a smaller diameter for fastening by means of the nuts of the support flange, as well as the upper crosshead, while the template is first placed until the stop of the outer protrusion of the lower stamp in the socket of the support flange, and then pressed using the upper crosshead which is fixed to the uprights, and the hand press is made in the form of a screw-nut pair, the nut of which is the central threaded hole formed in the traverse, and I miss the screw with an elongated shape and a lever at the upper end through the thread traverses the way into the slot formed in the bottom of a upper die, after which the screw creates a vertical pressure σ ₁ on a soil sample and after a certain period of time rotated a ring around the axis to align the calibrated holes in the ring and in the pattern and thus creates lateral σ _2-3 squeeze pressure through these openings harness soil for visual inspection of the appearance of cracks on the tow, wherein after each monitoring, during which the cracks on the wiring is not formed, the holes overlap the rotation ring and increase the pressure on the sample ₁ σ soil, reducing the time interval between the appearance of visual control to spalling cracks and decay on the harness parts under their own weight, and W _P is determined in a known manner. 2. The method according to claim 1, characterized in that after cracks appear on the tourniquet, the calibrated holes on the ring and the template are closed by turning the ring, the lower stamp is removed, the template with soil is again installed and the soil sample with the upper stamp is moved to the base cavity by rotation of the elongated screw, having a through slot for extracting a sample that is weighed, then dried, and again weighed, and W _{P is} calculated. 3. A device for determining the lower limit of plasticity (W _P ) of clay soils, including a hand press with a placed sample formed by filling a previously prepared soil paste of a metal template with a cylindrical hole, and rigid upper and lower dies, with gaskets between the sample and dies of filter material, characterized in that the template for the formation of the shape and dimensions of the soil paste sample is made in the form of a thin-walled cylinder of predetermined dimensions and in the lower part there is an increased outer diameter, and the rigid upper and lower dies are made in the form of short glasses with perforated bottoms freely placed in the cavity of the template under the sample up bottom and above the sample down bottom, while the lower stamp has a ring protrusion on the lower cylindrical part , and the template is additionally equipped with a ring freely passed through its smaller outer diameter, abutting against a ledge of the lower cylindrical part of the larger diameter of the template, with the possibility of its free periodic rotation to combine a calibrated hole with a diameter of 3.2 mm, made in the wall of the ring with the same hole formed in the wall of the template, for the periodic formation of a tourniquet of soil paste for its control in the process of periodically increasing pressure σ ₁ and squeezing water due to lateral pressure σ _2-3 , and the template is fixed by pressing between the support flange connected to two or more vertical racks mounted on a base plate fixedly connected to the desktop, and having threads with thread on the upper end of the lower part of the uprights having a larger diameter, as well as between the upper traverse secured with a thread formed on the upper ends of the uprights using union nuts, wherein the hand press is made in the form of a screw-nut pair, the nut of which is formed in the form of a central threaded hole in the traverse, and the screw has an elongated shape and is equipped with a lever at its upper end, and at the lower end - a centralizer, combined with a recess formed in the center of the upper surface of the bottom of the upper stamp.

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