Geotechnical test device for simulating slope soil stress and deformation process

Abstract

The utility model discloses a soil test device for simulating a slope soil stress deformation process. The soil test device comprises a bottom motor, a reaction frame, a cylindrical metal hoop sleeve, a metal ring support, a bidirectional motor, an inhaul cable, a vertical force transmission column, a lifting rod, a test sensor, a multifunctional data acquisition instrument and a data processing system, the bidirectional motor is fixed on the cross rod, and the vertical force transmission column transmits counter force on the cross rod to the core sample to realize uniaxial compression; the two ends of the inhaul cable are connected with the pulley and the metal ring support on the transverse rod respectively, the pulley is in transmission connection with the two-way motor, and the metal hoop sleeve and the metal ring support are driven by the two-way motor to move upwards synchronously. The metal ring support is a metal ring of which the outer diameter is the same as the outer diameter of the metal hoop sleeve and the inner diameter is the same as the diameter of the core sample, and is used for driving the annular soil body and forming a cylindrical shearing surface between the core sample and the annular soil body; the metal hoop sleeve applies limited lateral confinement to the core sample by using an annular soil body in the metal hoop sleeve; and the sensors synchronously test the change process of the pressure, suction and moisture content of the inner side of the soil sample.

Description

Technical Field

[0001] This utility model belongs to the field of geotechnical testing in slope engineering, specifically relating to a geotechnical testing device for simulating the stress and deformation process of slope soil. Background Technology

[0002] As is well known, in the last century, geotechnical testing devices such as direct shear apparatus and triaxial apparatus were invented. In the experiment, the stress and deformation process of foundation soil was simulated in three stages, namely (1) first, the soil sample was saturated to meet the requirements of soil saturation under the groundwater level, (2) then consolidation pressure was applied to meet the consolidation history of foundation soil under self-weight stress during the deposition process, and (3) the actual drainage or non-drainage conditions of foundation soil were simulated by using the triaxial apparatus drainage valve (whether it is closed or not) or controlling the shear rate of the direct shear apparatus. It can be seen that people have conducted sufficient, reasonable and feasible research and application on geotechnical testing devices and methods for simulating the stress process of saturated foundation soil.

[0003] However, when using traditional testing instruments to conduct geotechnical tests to simulate the stress and deformation process of slope soil, many problems are encountered. For example, (1) Generally, the stress and deformation process of slope soil and the slope instability mechanism are as follows: (a) Under the action of landslide thrust, the deteriorated soil strip (deformable body) on the surface of the slope first undergoes compression deformation along the slope direction. (b) When the compression deformation along the slope direction reaches a certain level, the bottom surface of the soil strip begins to generate shear slip to form a slip zone (or shear layer), thereby initiating the instability process of the slope along the slip surface. (c) This stress and deformation development process of the soil strip along the slope direction of "compression-shear-instability" is something that the direct shear test cannot simulate, because the direct shear test artificially simulates the vertical compression direction and the horizontal shear direction of the soil, which are two different stress directions. This is a two-dimensional action. However, the soil strips used for slopes need to simulate the compression along the slope and the shear along the slip surface (these are two similar directions). In addition to bearing the landslide thrust and the soil strip's own weight stress, the soil on both sides orthogonal to the slope will also exert lateral confinement and friction on the soil strip. This is a three-dimensional action. (2) Using a direct shear apparatus for geotechnical testing, a thin 2cm high sample is placed in a rigid shear box. The soil is constrained by the rigid box and can only undergo shear slip along the plane between the upper and lower boxes (slip surface), rather than shear failure along the weakest surface caused by deterioration. (3) Slope soil is generally a deformable body rather than a rigid body. Therefore, the shear deformation characteristics and shear strength of the soil measured in this way are very unreliable. (4) Using a thin sample in a ring cutter to conduct deterioration tests on slope soil (wet-dry cycle, freeze-thaw cycle, vibration damage, etc.) can only reflect the deterioration of the soil on the slope surface and cannot take into account the scale effect of the sample. (5) Although triaxial tests can simulate the compression deformation and shear failure process caused by bias pressure of soil (close to the "compression-shear" stress and deformation development process along the slope), the samples are generally required to be saturated. However, if the test results of saturated soil are used to calculate and analyze the stability of the slope, it will cause a lot of waste. Most of the geotechnical tests for slope engineering are still based on saturated soil, which is inconsistent with the fact that the slope soil in the field is mostly unsaturated. (6) Slope soil is generally unsaturated, so its test involves not only stress conditions but also the application and control of suction. Since the suction of the triaxial test of unsaturated soil is difficult to control accurately and the test is time-consuming, the efficiency of the triaxial test of unsaturated soil is low.

[0004] As the above analysis shows, the application of traditional testing instruments in geotechnical testing to simulate the stress and deformation processes of unsaturated slope soil is still far from "sufficient, reasonable, and feasible." Therefore, in order to achieve the goal of using geotechnical tests to simulate the stress and deformation development process of slope soil strips (deformable bodies), especially deteriorated slope soil, along the slope direction, there is an urgent need to develop a new type of simple and practical geotechnical testing simulation device that can reflect the true stress and deformation processes of slope soil strips as deformable bodies. Summary of the Invention

[0005] This invention aims to address the shortcomings of existing technologies by providing a geotechnical testing device for simulating the stress and deformation process of slope soil. It enables the use of geotechnical tests to simulate the stress and deformation development process of soil strips (deformable bodies) on slopes, especially deteriorated slope soil, in the "compression-shear-instability" direction, thereby more realistically reflecting the evolution of slope stability.

[0006] This invention is supported by the ongoing National Natural Science Foundation of China projects (U2340227, U22A20602).

[0007] This invention proposes an improved test device for simulating the "compression-shear-instability" stress and deformation process of slope soil, which is used to conduct tests simulating the "compression-shear-instability" stress and deformation process of slope soil.

[0008] Generally, the stress and deformation of slope soil are not completely confined by lateral compression, therefore confined compression curves cannot be used for analysis. The softening or brittle failure caused by completely unconfined compression in traditional uniaxial compression tests does not conform to the stress and deformation characteristics of slope soil in the field, and the test curve after the peak of the traditional unconfined compression curve is inaccurate and lacks practical value. However, traditional unconfined compression tests can be further improved to approximate the stress and deformation process of slope soil in the field:

[0009] (1) The conventional unconfined compression small-diameter specimen is improved into a large specimen, that is, a ring soil is made by surrounding the conventional unconfined compression relatively small-diameter specimen (referred to as core sample) with a large-diameter metal hoop to achieve a certain lateral confinement effect (lateral pressure can be measured by earth pressure cell). (2) Under the limited lateral confinement effect of the ring soil, the core sample is subjected to compression test and the compression curve is measured to approximate the real "compression" stress state of the slope soil strip under the thrust of landslide. (3) Then, through the metal ring support at the bottom of the large-diameter metal hoop, a shear load in the same direction as the vertical load of the compression test is applied to the ring soil. A cylindrical shear surface is formed between the core sample and the ring soil to realize the simulation of the "shear" stress and deformation development process of the slope soil strip after "compression" in the slope direction. This improves the defects of the traditional direct shear test. (4) In the process of simulating the stress and deformation development of the slope soil strip along the slope direction of "compression-shear-instability" by using the improved geotechnical test of "first performing uniaxial compression and then cylindrical shearing", the change process of hydraulic characteristic parameters such as suction and water content of soil sample can be tested. The "suction is difficult to control" method of controlling the suction value of the sample in the traditional test is transformed into dynamic "suction observation" in the sample, which improves the problem of difficulty in accurately controlling the suction of soil sample, such as the triaxial tester for unsaturated soil.

[0010] Based on the above innovative ideas and methods, this utility model provides a geotechnical testing device for simulating the stress and deformation process of slope soil. The structure includes a bottom motor drive device, a reaction frame, a metal hoop for preparing a large specimen based on the core sample, a metal ring support located at the bottom of the large specimen during sample preparation, a bidirectional motor, a cable (or chain), a vertical force transmission column, a lifting rod, a testing sensor, a multifunctional data acquisition instrument, and a data processing system. The reaction frame consists of several vertical rods and several horizontal rods connected to the vertical rods. The bidirectional motor is fixed on the horizontal rods of the reaction frame. The vertical force transmission column is located between the specimen and the horizontal rods and is coaxial with the specimen, used to transmit the reaction force on the horizontal rods of the reaction frame to the specimen. The lifting rod is connected to the motor drive device, and the lifting rod and the vertical force transmission column are on the same vertical line, used to apply pressure to the core sample placed between them under the drive of the motor drive device.

[0011] The metal hoop is a cylindrical hoop used to create annular soil around a small-diameter core sample subjected to conventional unconfined compression, thus improving the core sample into a large-diameter specimen and providing some lateral confinement for the compressed core sample. The metal ring support is a metal ring with the same outer diameter as the metal hoop, serving as a substrate for the metal hoop and used to drive the annular soil around the core sample. The metal ring support and the metal hoop can be integrated or separate. There are two cables (or chains), each end of which is connected to a pulley mounted on the reaction frame crossbar and the annular metal ring support, respectively. The pulleys are connected to a motor drive, enabling the metal hoop and the annular metal ring support to move upward under the drive of a bidirectional motor. A shearing process is carried out by applying a staggered shear force to the core sample and the annular soil mass, performing a direct shearing process on a cylindrical shear plane. A vertical pressure sensor is installed between the vertical force transmission column and the reaction frame crossbar. Lateral earth pressure sensors, suction sensors, and moisture content sensors are installed on the inner wall of the metal hoop and within the annular soil mass. A tension sensor is installed on the cable to simultaneously test the changes in internal pressure, suction, and moisture content of the soil sample during sample compression and direct shearing. A pad is installed between the lifting rod and the force transmission column to ensure close contact between the force transmission column and the top surface of the sample. Each sensor is connected to a multi-functional data acquisition instrument via a data cable, and the data acquisition instrument is connected to a data processing system.

[0012] Furthermore, the outer diameter of the vertical force transmission column and the outer diameter of the pad are both equal to the diameter of the core sample.

[0013] Furthermore, the earth pressure cell for testing lateral earth pressure is attached to the inner wall of the metal hoop and is horizontally buried in the annular soil body. The suction sensor and the moisture content sensor can be buried horizontally or vertically in the annular soil body.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. The geotechnical testing device of this utility model can realize the simulation of the entire process of slope stress and deformation and even instability and initiation of sliding using geotechnical tests: (1) Under the action of the landslide thrust along the slope, the soil strip unit of the slope first undergoes compressive deformation along the slope due to the deterioration effect. When the compressive deformation reaches a certain value, a shear layer is formed at the bottom of the soil strip, and the bottom surface of the unit begins to produce shear slip, thereby initiating the instability and initiation of sliding of the slope. (2) Since the unit of the slope is identified as a deformable body rather than a rigid body in the traditional analysis method, the adjacent units on the slope maintain the continuity between them through changes in geometric shape after being subjected to stress and deformation. (3) The unit of the slope is subjected to the landslide thrust along the slope direction and is subjected to lateral confinement in another horizontal orthogonal direction.

[0016] 2. The geotechnical testing device of this utility model has excellent technical and economic advantages: (1) Using large-diameter and high-height specimens instead of small and thin specimens can better reflect the scale effect of slope soil degradation tests (wet-dry cycle, freeze-thaw cycle, vibration damage, etc.). (2) During the test, hydraulic characteristic parameters such as suction and water content of soil samples can be tested, changing the "difficulty in controlling suction" of conventional test methods to the real-time "suction observation" of the current method, and improving the problem of difficulty in accurately controlling soil sample suction, such as the triaxial apparatus for unsaturated soil. (3) Based on the traditional unconfined compression test device, a new type of indoor test device for testing the stress and deformation process of slope soil strip unit is obtained without significantly increasing the manufacturing cost. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the test apparatus in an embodiment of this utility model.

[0018] Figure 2 This is a schematic diagram of the installation of the core sample, annular soil, metal hoop and its bottom annular metal ring support, internal sensor and other components in the embodiment of this utility model: (a) side view of the uniaxial compression stage, (b) side view of the cylindrical shearing stage, (c) top view.

[0019] Figure 3 This is a schematic diagram of the stress and deformation of the slope soil strip described in the embodiment of this utility model: The method of this utility model assumes that (a1) the soil strip is first compressed along the slope, (a2) and then the soil strip slides rigidly along the bottom surface of the soil strip, (b) the traditional method assumes that the rigid sliding of the soil strip is directly generated.

[0020] Figure 4The following are the geotechnical test curves in the embodiments of this utility model: (a) the compressive stress-compressive strain curve of the "first uniaxial compression" stage and the curve of the conventional unconfined compression test in the embodiment of this utility model; (b) the shear stress-shear displacement curve of the "then cylindrical shear" stage in the embodiment of this utility model (the lateral pressure measured by the new test, i.e., the normal stress during shearing, is 242 kPa, and shearing begins when the compressive strain reaches 15%) and the curve of the conventional horizontal direct shear test of the ring sample (the normal stress during shearing applied artificially is 250 kPa); (c) the response curves of the matrix suction and volumetric water content measured by the "sensor" when simulating the first compression of the soil strip along the slope in the embodiment of this utility model.

[0021] Figure 5 This is the geotechnical test curve in the embodiment of this utility model ( Figure 4 The fitting curves are as follows: (a) The compressive stress-compressive strain curve of the "first uniaxial compression" stage in the experiment of this utility model embodiment is fitted to a straight line, and (b) The shear stress-shear displacement curve of the "then cylindrical shear" stage in the experiment of this utility model embodiment is fitted to a hyperbola.

[0022] In the diagram, 1-1 is a core sample (simulating a slope unit or soil strip subjected to landslide thrust and partial lateral confinement pressure), 1-2 is annular soil sample (simulating the shear layer of the slope sliding surface), 2-1 is a metal hoop (simulating the slope rock mass sliding bed), 2-2 is a metal ring support (simulating the application of landslide thrust and the resulting shear force at the bottom of the soil strip), 3 is a cylindrical shear surface between the core sample and the annular sample (simulating the sliding surface), 4 is a suction sensor, 5 is a lateral earth pressure sensor (measuring the lateral normal stress on the core sample under partial lateral confinement), 6 is a moisture content sensor, 7 is a magnetic fixing bracket, 8 is a displacement sensor, 9 is a vertical pressure sensor, 10 is a vertical force transmission column, 11 is a pad, 12 is a lifting rod, 13 is a cable (or chain), 14 is a tension sensor, 15 is a bidirectional motor, 16 is a crossbar, 17 is a reaction frame support, 18 is a bottom motor drive device, 19 is a multi-functional data acquisition instrument, and 20 is a data processing system. Detailed Implementation

[0023] The present invention will be further illustrated below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above-described invention, and these improvements and adjustments still fall within the scope of protection of the invention.

[0024] Example

[0025] (1) Geotechnical testing apparatus for simulating the stress and deformation process of slope soil:

[0026] The test apparatus includes a bottom motor drive unit, a reaction frame, a metal hoop for making large specimens, an annular metal ring support, a bidirectional motor, a cable (or chain), a vertical force transmission column, a lifting rod, a test sensor, a multi-functional data acquisition instrument, and a data processing system. The reaction frame consists of several vertical rods and several horizontal rods connected to the vertical rods. The bidirectional motor is fixed on the horizontal rods of the reaction frame. The vertical force transmission column is located between the specimen and the horizontal rods and is on the same central axis as the specimen, used to transmit the reaction force on the horizontal rods of the reaction frame to the specimen. The lifting rod is connected to the motor drive unit, and the lifting rod and the vertical force transmission column are on the same vertical line, used to apply pressure to the specimen placed between them under the drive of the motor drive unit.

[0027] The metal hoop is a cylindrical hoop used to create annular soil around a small-diameter core sample subjected to conventional unconfined compression, thus improving the core sample into a large-diameter specimen and achieving a certain degree of lateral confinement for the compressed core sample. The metal ring support is a metal ring with the same outer diameter as the metal hoop and the same inner diameter as the core sample, serving as a substrate for the metal hoop and driving the annular soil around the core sample. The metal ring support and the metal hoop can be integrated or separate. There are two cables (or chains), each end of which is connected to a pulley mounted on the reaction frame crossbar and the annular metal ring support, respectively. The pulleys are connected to a motor drive, enabling the metal hoop and the annular metal ring support to move upward under the drive of a bidirectional motor. A vertical force transmission column is installed between the vertical force transmission column and the crossbar. A pressure sensor is used to simultaneously test the changes in internal pressure, suction, and moisture content of the soil sample during sample compression and direct shearing. Lateral earth pressure sensors, suction sensors, and moisture content sensors are installed on the inner wall of the metal hoop and the annular soil body. The earth pressure cell for testing lateral earth pressure is horizontally embedded in the annular soil body, attached to the inner wall of the metal hoop. The suction and moisture content sensors can be embedded horizontally or vertically within the annular soil body. A tension sensor is installed on the cable. A pad is placed between the lifting rod and the force transmission column to ensure close contact between the force transmission column and the top surface of the sample. The outer diameters of the vertical force transmission column and the pad are equal to the outer diameter of the core sample. Each sensor is connected to a multi-functional data acquisition instrument via a data cable, and the data acquisition instrument is connected to a data processing system.

[0028] (2) Determine the stress range

[0029] The new geotechnical test uses large specimens to simulate the stress and deformation of soil strips. First, the landslide thrust line method (or transfer coefficient method) in the specification is used to calculate the residual landslide thrust of each unit (or soil strip) of the slope. Then, the weight of each unit and the surface force on the landslide thrust surface are estimated using the geometric information and physical and mechanical properties of each unit. This determines the stress range of the large specimen for the new indoor test to be carried out below.

[0030] (3) Preparation of test samples

[0031] The specimen is a large cylindrical specimen, or large specimen, prepared based on a small-diameter cylindrical core sample (the diameter of which is similar to that of a specimen in a conventional test, but the height can be increased). The large specimen is obtained by adding a ring of soil around the core sample to increase its diameter. First, a core sample (A) for a conventional unconfined compression test is prepared. Then, using the same preparation method, a large-diameter specimen (B) is prepared within a metal sleeve. A series of specimens are subjected to simulated deterioration processes such as alternating wet and dry conditions (A1 or B1), freeze-thaw cycles (A2 or B2), or vibration damage (A3 or B3). Alternatively, based on specimens (A) and specimens (A1, A2, A3), a large-diameter specimen (B) required for a novel indoor test is prepared. The specific method is as follows:

[0032] First, prepare a core sample (A) for a standard unconfined compression test. Then, based on the diameter of the metal hoop, compact soil of the same type as sample A onto the inner wall of the metal hoop to create an annular soil mass (C) approximately 2 cm thick. Embed a soil pressure cell, suction, and moisture content sensor within the annular soil mass, and extend the corresponding cables from the top side. Use the metal hoop with the annular soil mass on its inner wall to confine either sample (A) or samples (A1, A2, A3) required for the compression test, creating a large sample (B) for the laboratory test. Support sample B with an annular metal ring, tightly adhering to the annular soil mass on the inner wall of the metal hoop and the bottom of the hoop. The inner diameter of the annular metal ring should be the same as the diameter of sample (A) or sample (A1, A2, A3).

[0033] (4) Start of the experiment

[0034] First, start the motor drive at the bottom of the test device to conduct a "partially confined" vertical uniaxial compression test. During vertical compression, the metal sleeve transmits the confining effect to the specimen (A) or specimens (A1, A2, A3) through a ring of soil (C) about 2 cm thick. This simulates the mechanism of the slope unit undergoing compression deformation under the action of landslide thrust. The stress-strain curve obtained from the compression test will be different from the stress-strain curve obtained from the traditional unconfined compression test of specimen (A) or specimens (A1, A2, A3).

[0035] (5) When the vertical compression deformation of specimen (A) or specimen (A1, A2, A3) reaches a certain value, the vertical compressive stress and its corresponding lateral pressure (close to the normal stress or normal stress commonly used in conventional direct shear tests) are measured. This lateral pressure is used as the normal stress (or normal stress) of specimen (core sample) A. A cylindrical direct shear test of specimen (B) is carried out. A bidirectional motor is controlled to pull the metal hoop and the annular metal ring support at the bottom of the inner wall of the annular soil (C) through pulleys and cables. This causes the metal hoop and the annular soil on the inner wall to generate direct shear force and deformation between specimen (A) or specimen (A1, A2, A3). Then, a cylindrical shear process is carried out between the previously compressed specimen (A) or specimen (A1, A2, A3) and the annular soil (C). This simulates the process of the slope unit being compressed and deformed to a certain value under the action of landslide thrust, and then the shear slip begins to occur at the bottom of the unit. In addition to the compression test stage mentioned above, the shear test stage can also be used to simultaneously and continuously test the time-varying process of hydraulic characteristic parameters such as suction and water content of the soil sample.

Claims

1. A soil testing device for simulating stress and deformation processes in sloping soil, characterized by, The structure includes a bottom motor drive unit, a reaction frame, a metal hoop, a metal ring support, a bidirectional motor, a cable, a vertical force transmission column, a lifting rod, a test sensor, a multi-functional data acquisition instrument, and a data processing system. The reaction frame is a frame structure formed by connecting several vertical and horizontal bars. The bidirectional motor is fixed on the horizontal bar of the reaction frame. The vertical force transmission column is located between the sample and the horizontal bar and is on the same central axis as the sample. It is used to transmit the reaction force on the horizontal bar of the reaction frame to the sample. The lifting rod is connected to the motor drive unit, and the lifting rod, the vertical force transmission column, and the sample are on the same vertical line. It is used to apply pressure to the sample placed between them under the drive of the motor drive unit. The metal hoop is cylindrical and used to create a ring-shaped soil mass outside a conventional small-diameter core sample subjected to unconfined compression, thus improving the core sample into a large-diameter specimen and achieving a certain degree of lateral confinement for the compressed core sample. The metal ring support is a metal ring with the same outer diameter as the metal hoop and the same inner diameter as the core sample, serving as a substrate for the metal hoop and used to drive the ring-shaped soil mass. The metal ring support and the metal hoop can be integrated or separate. There are two cables, with each end connected to a pulley mounted on the reaction frame crossbar and the metal ring support, respectively. The pulleys are connected to a bidirectional motor drive, enabling the metal hoop and metal ring support to move upward under the drive of the bidirectional motor, thus confining the core sample and... A staggered shear force is applied to the annular soil mass to achieve a direct shearing process on a cylindrical shear plane. A vertical pressure sensor is installed between the vertical force transmission column and the crossbar of the reaction frame. Lateral soil pressure sensors, suction sensors, and moisture content sensors are installed on the inner wall of the metal hoop and within the annular soil mass to simultaneously test the changes in internal pressure, suction, and moisture content of the soil sample during sample compression and direct shearing. A tension sensor is installed on the cable. A pad is installed between the lifting rod and the force transmission column to ensure close contact between the force transmission column and the top surface of the sample. Each sensor is connected to a multi-functional data acquisition instrument via a data cable, and the data acquisition instrument is connected to a data processing system.

2. The apparatus of claim 1, wherein The outer diameter of the vertical force transmission column and the outer diameter of the pad are both equal to the diameter of the core sample.

3. The apparatus of claim 1, wherein The earth pressure cell for testing lateral earth pressure is horizontally embedded in the annular soil body along the inner wall of the metal hoop. The suction sensor and moisture content sensor are horizontally or vertically embedded in the annular soil body.

4. The apparatus of claim 1, wherein The cable is a steel wire or a metal chain.

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