Tensile strength test device for over-consolidated clay and implementation method

Abstract

The invention discloses a tensile strength test device for over-consolidated clay and an implementation method, and relates to the technical field of geotechnical test equipment, the tensile strength test device comprises a test box, and the top surface of the test box is a transparent panel; a stress loading assembly is arranged in the test box, the stress loading assembly comprises two curved plates which are symmetrically arranged, and the two ends of the two curved plates are fixedly connected through two parallel fixing plates to define a soil sample loading chamber; the invention provides the device with pressure loading and tensile loading functions, and before a tensile test is carried out, the soil sample can have different consolidation pressures by carrying out load applying operation on the soil sample, so that the tensile strength test of clay with different consolidation histories can be realized. According to the invention, the stretching section adopts a mode of combining a rigid component and an elastic component, so that uniform stretching of a soil sample is realized, and the problem of concentrated tensile deformation before tensile failure is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical testing equipment, and in particular to a tensile strength testing device and an implementation method for overconsolidated clay. Background Art

[0002] ‌‌ As an engineering material, the tensile strength of clay is an important indicator for evaluating its performance. Although the tensile strength of clay is relatively low, in many engineering applications, such as foundation engineering and earth-rock dam construction, the tensile properties of clay need to be fully considered to ensure the stability and safety of the project. When the tensile strength of clay is insufficient, the soil is prone to cracking under the action of tension, and even causes the collapse of the overall structure. This is more common in engineering problems such as earth-rock dams, embankments and slopes, and may cause serious safety accidents. Due to the cracks that are easy to appear in the soil after being tensile, the strength of the soil layer is reduced. At the same time, the tension cracks can also provide channels for rainwater infiltration. The engineering problems caused by this are endless, and there is an urgent need to study the tensile strength of soil in engineering. In-depth discussion of the tensile strength characteristics of soil not only helps to improve the strength theory of soil, but also has important significance for solving practical engineering problems.

[0003] Since the tensile strength value of soil is small and difficult to measure, there is no unified instrument and test specification for measuring the tensile strength of soil at this stage, and homemade instruments are mostly used for testing. Patent 202310045762.2 discloses an integrated device for uniaxial tension and sample preparation of clay soil and its use method, which solves the problem of difficult sample preparation of clay soil. Patent 202211183917.0 has developed a horizontal uniaxial tension test device for a mixture of variable-size gravel and clay. However, the current soil tensile strength test device rarely considers the influence of the consolidation process of clay soil on the tensile strength. In fact, the mechanical properties of clay soil are closely related to the consolidation history. For example, as the initial consolidation pressure of clay increases, the shear strength also increases to a certain extent. It can be seen that the strength parameters of clay depend on the consolidation history of the soil. In actual engineering, such as earth-rock dams, artificial slopes and roadbed filling, the soil is often in an over-consolidated state. It is necessary to reflect the influence of the initial consolidation process on the tensile strength of clay in the tensile strength test device. In addition, in the test of soil tensile strength, the position of the soil sample chamber is often fixed during the stretching process, which may cause the soil sample to be stretched unevenly, thus affecting the test results of tensile strength. In addition, the stretching of the soil sample is affected by the aspect ratio of the sample, but existing equipment rarely considers the influence of the shape of the soil sample on its tensile strength. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a tensile strength test device and an implementation method for overconsolidated clay.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is: Provided is a tensile strength test device for overconsolidated clay, comprising a test box, the top surface of which is a transparent panel; a stress loading assembly is arranged inside the test box, the stress loading assembly comprises two symmetrically arranged curved plates, the two ends of the two curved plates are fixedly connected by two parallel fixed plates to enclose a soil sample loading chamber; a pressure plate is arranged on one side of the two fixed plates close to the center of the soil sample loading chamber, the pressure plate is connected to the fixed plate by a first hydraulic rod, and under the action of the first hydraulic rod, the pressure plate moves perpendicular to the length direction of the fixed plate; A second hydraulic rod is disposed at both ends of the curved plate, the second hydraulic rod is disposed perpendicular to the fixed plate, one end of the second hydraulic rod is fixedly connected to the curved plate, and the other end of the second hydraulic rod is fixedly connected to the inner side of the test box; The middle of the curved plate is a stretching section, which is made of elastic rubber. Under the action of the first hydraulic rod, the stretching section can stretch and shrink in a direction perpendicular to the fixed plate. It also includes a measuring assembly, which includes a pressure sensor arranged at the first hydraulic rod, a tension sensor arranged at the second hydraulic rod, a displacement sensor arranged on the pressure plate, and a camera located above the test box, the camera facing the soil sample loading chamber.

[0006] Furthermore, the gap between the stretching sections of the two curved plates is smaller than the length of the fixed plate, arc sections are provided at both ends of the stretching sections, and the curved plates are divided into stretching sections, arc sections and straight sections.

[0007] Furthermore, the stretching section is obtained by alternately connecting a plurality of rigid connection units and elastic connection units made of rubber material in sequence, and dovetail grooves for the elastic connection units are arranged on both sides of the rigid connection units, and dovetail tenons for matching with the dovetail grooves are arranged on both sides of the elastic connection units.

[0008] Furthermore, a plurality of limit blocks are arranged outside the stretching section of the soil sample loading chamber, the number of the limit blocks is consistent with the elastic connection unit, one end of the limit block abuts against the elastic connection unit, and the other end of the limit block abuts against the side wall of the test box.

[0009] Furthermore, a positioning groove is arranged on the inner side wall of the test box, and a positioning block which is matched and connected with the positioning groove is arranged on the limiting block.

[0010] Furthermore, a quick positioning assembly is provided on one side of the soil sample loading chamber, and the quick positioning assembly includes a positioning plate, which is located on the side of the adjacent fixed plate away from the center of the soil sample loading chamber; and the positioning plate is parallel to the adjacent fixed plate; the positioning plate is connected to the curved plate through a second hydraulic rod; the positioning plate and the test box are connected through a telescopic rod, and the telescopic rod is perpendicular to the fixed plate.

[0011] Furthermore, positioning blocks which are matched and connected with the positioning grooves are arranged at both ends of the positioning plate.

[0012] The present invention also provides a soil sample tensile strength test method using the above-mentioned overconsolidated clay tensile strength test device, comprising the following specific steps: A1: According to the soil sample design parameters, determine the number of elastic connection units and assemble the tensile section to obtain the soil sample loading chamber; A2: Lock the first hydraulic rod. In the initial state, all the second hydraulic rods are in the extended state, and the tensile load at the second hydraulic rod is 0; make all the second hydraulic rods shrink synchronously, collect the displacement data of each pressure plate through the displacement sensor, collect the tensile load of the second hydraulic rod through the tensile sensor, and calculate the elastic coefficient of the curved plate: ;in, is the tensile load of the second hydraulic rod; and are the displacement distances of the two pressure plates respectively; the second hydraulic rod is restored; A3: Fill the soil layer in the soil sample loading chamber and obtain the initial porosity ratio The top surface of the soil sample is in contact with the transparent panel; A4: Synchronously contract all the second hydraulic rods step by step, measure and record the displacement of the pressure plate and the tensile load of the second hydraulic rod during the tension application process through the measuring assembly, and calculate the stress of the tensile section soil sample under any level of tension during the loading process and deformation ; ; ; in, For the The tensile load of the second hydraulic rod under the first-stage tension; and They are The displacement distance of the two lower pressure plates; is the soil sample thickness, is the width of the soil sample in the tensile section; is the length of the initial soil sample in the tensile section; A5: Collect the tensile crack area of ​​soil samples through cameras ; Tensile crack length and the average width of tensile cracks ; ; ; ; in, and They are respectively the tensile section of soil sample Crack pixel area and crack pixel length under level tension; are image transformation parameters, and , is the actual surface area of ​​the tensile soil sample before tensile loading, is the pixel area of ​​the tensile section soil sample before tensile loading; A6: Drawing Tensile crack area , tensile crack length and the average width of tensile cracks The relationship curve of the development process of the crack is obtained, and the tensile stress and strain of the soil sample when the crack initially appears and the tensile stress and strain of the soil sample when the crack penetrates are recorded according to the image information taken by the camera. The peak point of the tensile stress of the soil sample and the peak point of the tensile stress are determined according to the relationship curve. That is the tensile strength of the soil sample, completing the tensile test.

[0013] The present invention also provides a soil sample consolidation test method using the above-mentioned tensile strength test device for overconsolidated clay, comprising the following specific steps: B1: According to the soil sample design parameters, determine the number of elastic connection units and assemble the tensile section to obtain the soil sample loading chamber; B2: Lock the first hydraulic rod. In the initial state, all the second hydraulic rods are in the extended state, and the tensile load at the second hydraulic rod is 0; make all the second hydraulic rods contract synchronously, collect the displacement data of each pressure plate through the displacement sensor, collect the load of the second hydraulic rod through the tension sensor, and calculate the elastic coefficient of the curved plate: ;in, is the tensile load of the second hydraulic rod; and are the displacement distances of the two pressure plates respectively; the second hydraulic rod is restored; B3: Unlock the first hydraulic rod and lock the second hydraulic rod. In the initial state, all the first hydraulic rods are in a contracted state. Fill the soil layer in the soil sample loading chamber and obtain an initial porosity ratio of The soil sample is placed in contact with the transparent panel; the pressure sensor is reset to zero; B4: Set the maximum compressive stress value , gradually extend the first hydraulic rod, and the increment of compressive stress at each stage is 50 kPa, and the maximum pressure load applied to the first hydraulic rod is calculated. And each level of incremental load ; ; ; in, is the soil sample thickness, is the width of the soil sample in the tensile section; Under each level of pressure load, continue until the displacement is stable, record the displacement of the pressure plate under each level of pressure load, and calculate the compressive stress of the soil sample under any level of pressure , compressive strain and porosity ratio ; ; ; ; in, is the pressure load of a single first hydraulic rod under the j-th level pressure load; is the cross-sectional area of ​​the soil sample of the straight segment under the j-th level pressure load; is the volume of the straight segment soil sample under the j-th level pressure load; is the volume of the arc-shaped soil sample under the j-th level pressure load; is the volume of the tensile section of the soil sample under the jth level of pressure load; after reaching the designed maximum pressure load, the first hydraulic rod stops extending; and are the displacement distances of the two pressure plates under the j-th level of pressure load; B5: Draw the logarithm of the compressive stress-porosity ratio curve of the soil sample during the loading process. The sudden turning point in the logarithm of the compressive stress-porosity ratio curve is the initial consolidation pressure of the soil sample. At the same time, the consolidation pressure of the soil sample at the maximum pressure load is obtained to complete the consolidation test method.

[0014] The present invention also provides a soil sample stress test method of a tensile strength test device for overconsolidated clay, wherein the soil sample is consolidated to a designed porosity ratio using the consolidation test method to obtain a consolidated soil sample; and then the tensile strength test method is used to perform a tensile strength test on the consolidated soil sample.

[0015] The beneficial effects of the present invention are: 1. The present invention provides a device with pressure loading and tensile loading functions. Before conducting a tensile test, by applying load and unloading the soil sample, the soil sample can have different initial consolidation pressures, thereby being able to test the tensile strength of clay with different consolidation histories.

[0016] 2. The present invention realizes uniform stretching of soil samples by combining rigid components and elastic components in the stretching section, avoiding the problem of concentrated tensile deformation before tensile failure. The additional calculation parameters brought by the elastic components can be determined by elastic coefficient calibration experiments, thereby improving the accuracy of measurement.

[0017] 3. The present invention adopts a combined special-shaped plate component, and the initial installation length of the soil sample loading chamber is variable, so that the tensile test of soil samples with different aspect ratios can be realized, and the tensile strength experiment of the soil sample to test the influence of the soil sample shape on the tensile strength is realized.

[0018] 4. The present invention uses image recognition technology to observe the generation and development process of tiny tensile cracks in soil samples during tensile loading, providing conditions for analyzing the influence of different consolidation stresses, different aspect ratios of soil samples and different tensile deformation loading rates on the development law of tensile cracks in tensile section soil samples, including the evolution of actual area, actual length and average width.

[0019] 5. The present invention adopts a method of directly preparing samples in the soil sample loading chamber, which avoids disturbance of sample preparation, ensures the quality of test sample preparation, and improves the accuracy of test measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a three-dimensional schematic diagram of the tensile strength test device for overconsolidated clay; Figure 2 This is a schematic diagram of the internal structure of the tensile strength test device for overconsolidated clay; Figure 3 It is a three-dimensional structural schematic diagram of the soil sample loading chamber; Figure 4 This is a schematic diagram of the stretching section assembly; Figure 5 Schematic diagram of the relationship curve between tensile stress and tensile strain of the soil sample in Example 2; Figure 6 Schematic diagram of the logarithm of the compressive stress-void ratio curve of the soil sample during the loading process in Example 3; Among them, 1. test box; 2. transparent panel; 3. curved plate; 4. fixed plate; 5. pressure plate; 6. first hydraulic rod; 7. second hydraulic rod; 8. stretching section; 9. camera; 10. arc section; 11. straight section; 12. rigid connection unit; 13. elastic connection unit; 14. dovetail groove; 15. dovetail tenon; 16. limit block; 17. positioning groove; 18. positioning block; 19. positioning plate; 20. telescopic rod; 21. slide groove. DETAILED DESCRIPTION

[0021] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0022] Example 1 like Figure 1-4 As shown, a tensile strength test device for overconsolidated clay comprises a test box 1, the top surface of the test box 1 is a transparent panel 2; a stress loading assembly is arranged inside the test box 1, and the stress loading assembly comprises two symmetrically arranged curved plates 3, and the two ends of the two curved plates 3 are fixedly connected by two parallel fixed plates 4 to form a soil sample loading chamber; a pressure plate 5 is arranged on one side of the two fixed plates 4 close to the center of the soil sample loading chamber, and the pressure plate 5 is connected to the fixed plate 4 by a first hydraulic rod 6, and under the action of the first hydraulic rod 6, the pressure plate 5 moves perpendicular to the length direction of the fixed plate 4; A second hydraulic rod 7 is disposed at both ends of the curved plate 3. The second hydraulic rod 7 is disposed perpendicular to the fixed plate 4. One end of the second hydraulic rod 7 is fixedly connected to the curved plate 3, and the other end of the second hydraulic rod 7 is fixedly connected to the inner side of the test box 1. The middle of the curved plate 3 is a stretching section 8, which is made of elastic rubber. Under the action of the first hydraulic rod 6, the stretching section 8 can stretch and shrink in a direction perpendicular to the fixed plate 4; It also includes a measuring assembly, which includes a pressure sensor arranged at the first hydraulic rod 6, a tension sensor arranged at the second hydraulic rod 7, a displacement sensor arranged on the pressure plate 5, and a camera 9 located above the test box 1, and the camera 9 is facing the soil sample loading chamber.

[0023] The gap between the stretching sections 8 of the two curved plates 3 is smaller than the length of the fixed plate 4, and arc sections 10 are provided at both ends of the stretching section 8. The curved plate 3 is divided into the stretching section 8, the arc section 10 and the straight section 11. In a specific implementation, the arc section 10 is an S-shape composed of two arcs, and the arc section 10 and the straight section 11 are integrally formed, and the central angles of the two arcs are both 45°.

[0024] The stretching section 8 is obtained by alternately connecting a plurality of rigid connection units 12 and elastic connection units 13 made of rubber material. The rigid connection units 12 are provided with dovetail grooves 14 for the elastic connection units 13 on both sides, and the elastic connection units 13 are provided with dovetail tenons 15 for matching with the dovetail grooves on both sides.

[0025] A plurality of limit blocks 16 are arranged outside the stretching section 8 of the soil sample loading chamber. The number of the limit blocks 16 is consistent with the elastic connection unit 13 . One end of the limit block 16 abuts against the elastic connection unit 13 , and the other end of the limit block 16 abuts against the side wall of the test box 1 .

[0026] A positioning groove 17 is provided on the inner wall of the test box 1 , and a positioning block 18 which is matched and connected with the positioning groove 17 is provided on the limiting block 16 .

[0027] A quick positioning assembly is also provided on one side of the soil sample loading chamber, and the quick positioning assembly includes a positioning plate 19, which is located on the side of the adjacent fixed plate 4 away from the center of the soil sample loading chamber; and the positioning plate 19 is parallel to the adjacent fixed plate 4; the positioning plate 19 is connected to the curved plate 3 through the second hydraulic rod 7; the positioning plate 19 is connected to the test box 1 through a telescopic rod 20, and the telescopic rod 20 is perpendicular to the fixed plate 4. In specific implementation, balance limit blocks 16 are also provided at both ends of the positioning plate 19, and two symmetrically arranged slide grooves 21 are provided on the bottom plate of the test box 1, and the slide grooves 21 are parallel to the telescopic rod 20, and the balance limit blocks 16 slide in cooperation with the slide grooves 21; The two ends of the positioning plate 19 are provided with positioning blocks 18 that cooperate with the positioning grooves 17. In specific implementation, the positioning blocks 18 can be compressed spring beads, or the front and rear side plates of the test box 1 can be detachably arranged to facilitate the positioning blocks 18 to cooperate with the positioning grooves 17.

[0028] Example 2 A soil sample tensile test method using the tensile strength test device for overconsolidated clay of Example 1 comprises the following specific steps: A1: According to the soil sample design parameters, the number of elastic connection units 13 is determined. In this embodiment, the number of elastic connection units 13 is 6, the number of rigid connection units 12 is 5, and the tensile section 8 is assembled to obtain the soil sample loading chamber; A2: Lock the first hydraulic rod 6. In the initial state, all the second hydraulic rods 7 are in the extended state, and the tensile load at the second hydraulic rod 7 is 0; make all the second hydraulic rods 7 contract synchronously, collect the displacement data of each pressure plate 5 through the displacement sensor, collect the tensile load of the second hydraulic rod 7 through the tensile sensor, and calculate the elastic coefficient of the curved plate 3: ;in, is the tensile load of the second hydraulic rod 7; and are the displacement distances of the two pressure plates 5 respectively; the second hydraulic rod 7 is restored; A3: Fill the soil layer in the soil sample loading chamber and obtain the initial porosity ratio The top surface of the soil sample is in contact with the transparent panel 2; before filling the soil sample, the dry soil is mixed with water according to the designed moisture content and placed in a sealed bag for 24 hours. During the specific implementation, the soil layers are filled in 5 layers according to the design in the soil sample loading chamber, and the soil samples of specified weight are taken each time to fill to the designed height.

[0029] A4: Synchronously contract all the second hydraulic rods 7 step by step, measure and record the displacement of the pressure plate 5 and the tensile load of the second hydraulic rod 7 during the tensile force application process through the measuring assembly, and calculate the stress of the tensile section soil sample under any level of tensile force during the loading process and deformation ; ; ; in, For the The tensile load of the second hydraulic rod 7 under the first level of tension; and They are The displacement distance of the lower two pressure plates 5; is the soil sample thickness, is the width of soil sample in stretching section 8; is the length of the initial soil sample in the stretching section 8; A5: The tensile crack area of ​​the soil sample is collected by camera 9 ; Tensile crack length and the average width of tensile cracks ; ; ; ; in, and They are respectively the 8th and 8th tensile sections of the soil sample Crack pixel area and crack pixel length under level tension; are image transformation parameters, and , is the actual surface area of ​​the tensile section 8 soil sample before tensile loading, is the pixel area of ​​the soil sample in the tensile section 8 before tensile loading; A6: Drawing Tensile crack area , tensile crack length and the average width of tensile cracks The relationship curve of the development process of the crack is obtained, and the tensile stress and strain of the soil sample when the crack initially appears and the tensile stress and strain of the soil sample when the crack penetrates are recorded according to the image information taken by the camera. Figure 5 The tensile stress and strain relationship curve shown in the figure can be used to determine the peak point of the tensile stress of the soil sample. That is the tensile strength of the soil sample, completing the tensile test. is the tensile stress when the soil sample initially cracks, is the tensile stress when the soil crack penetrates, During specific implementation, different numbers of elastic components can be set, and the tensile strength of soil samples of different shapes can be obtained by respectively testing using the tensile method.

[0030] Example 3 A soil sample consolidation test method using the tensile strength test device for overconsolidated clay of Example 1 comprises the following specific steps: B1: According to the soil sample design parameters, the number of elastic connection units 13 is determined. In this embodiment, the number of elastic connection units 13 is 6, the number of rigid connection units 12 is 5, and the tensile section 8 is assembled to obtain the soil sample loading chamber; B2: Lock the first hydraulic rod 6. In the initial state, all the second hydraulic rods 7 are in the extended state, and the tension load at the second hydraulic rod 7 is 0; make all the second hydraulic rods 7 contract synchronously, collect the displacement data of each pressure plate 5 through the displacement sensor, collect the load of the second hydraulic rod 7 through the tension sensor, and calculate the elastic coefficient of the curved plate 3: ;in, is the tensile load of the second hydraulic rod 7; and are the displacement distances of the two pressure plates 5 respectively; the second hydraulic rod 7 is restored; B3: Unlock the first hydraulic rod 6 and lock the second hydraulic rod 7. In the initial state, all the first hydraulic rods 6 are in a contracted state. Fill the soil layer in the soil sample loading chamber and obtain an initial porosity ratio of The soil sample is placed in contact with the transparent panel 2; the pressure sensor is reset to zero; B4: Set the maximum compressive stress value , gradually extend the first hydraulic rod 6, and the increment of compressive stress loaded at each stage is 50 kPa, and the maximum pressure load applied to the first hydraulic rod 6 is calculated. And each level of incremental load ; ; ; in, is the soil sample thickness, is the width of soil sample in stretching section 8; Under each level of pressure load, continue until the displacement is stable, record the displacement of the pressure plate 5 under each level of pressure load, and calculate the compressive stress of the soil sample under any level of pressure , compressive strain and porosity ratio ; ; ; ; in, is the pressure load of the single first hydraulic rod 6 under the j-th level pressure load; is the cross-sectional area of ​​the soil sample of the straight segment 11 under the j-th level pressure load; is the volume of the soil sample of straight segment 11 under the j-th level pressure load; is the volume of the arc segment 10 soil sample under the j-th level pressure load; is the volume of the soil sample in the tensile section 8 under the j-th level of pressure load; after reaching the designed maximum pressure load, the first hydraulic rod 6 stops extending; and are the displacement distances of the two pressure plates 5 under the j-th level pressure load; B5: Draw the logarithm of the compressive stress-void ratio curve of the soil sample during the loading process, such as Figure 6 As shown in the figure, the sudden turning point in the curve is the initial consolidation pressure of the soil sample. , and the consolidation pressure of the soil sample at the maximum pressure load is obtained , completing the consolidation test method. The stress mutation turning point means that the soil sample begins to enter the plastic deformation stage. At this time, even if the pressure disappears, the clay cannot return to its initial state and will produce permanent deformation.

[0031] During specific implementation, a tensile test is performed on the consolidated soil sample, and a tensile test comparison of soil samples under different consolidation pressures may also be set.

Claims

1. A tensile strength test device for overconsolidated clay, characterized in that: The test box comprises a test box, the top surface of which is a transparent panel; a stress loading assembly is arranged inside the test box, and the stress loading assembly comprises two symmetrically arranged curved plates, the two ends of which are fixedly connected by two parallel fixed plates to enclose a soil sample loading chamber; a pressure plate is arranged on one side of the two fixed plates close to the center of the soil sample loading chamber, the pressure plate is connected to the fixed plate by a first hydraulic rod, and under the action of the first hydraulic rod, the pressure plate moves perpendicular to the length direction of the fixed plate; A second hydraulic rod is disposed at both ends of the curved plate, the second hydraulic rod is disposed perpendicular to the fixed plate, one end of the second hydraulic rod is fixedly connected to the curved plate, and the other end of the second hydraulic rod is fixedly connected to the inner side of the test box; The middle of the curved plate is a stretching section, which is made of elastic rubber. Under the action of the first hydraulic rod, the stretching section can stretch and shrink in a direction perpendicular to the fixed plate; It also includes a measuring assembly, which includes a pressure sensor arranged at the first hydraulic rod, a tension sensor arranged at the second hydraulic rod, a displacement sensor arranged on the pressure plate, and a camera located above the test box, the camera facing the soil sample loading chamber.

2. The tensile strength test device for overconsolidated clay according to claim 1, characterized in that: The gap between the stretching sections of the two curved plates is smaller than the length of the fixed plate, arc sections are arranged at both ends of the stretching section, and the curved plate is divided into a stretching section, an arc section and a straight section.

3. The tensile strength test device for overconsolidated clay according to claim 2, characterized in that: The stretching section is obtained by alternately connecting a plurality of rigid connection units and elastic connection units made of rubber material in sequence. The rigid connection units are provided with dovetail grooves for the elastic connection units on both sides, and the elastic connection units are provided with dovetail tenons for matching with the dovetail grooves on both sides.

4. The tensile strength test device for overconsolidated clay according to claim 3, characterized in that: A plurality of limit blocks are arranged outside the stretching section of the soil sample loading chamber, the number of the limit blocks is consistent with the elastic connection unit, one end of the limit block abuts against the elastic connection unit, and the other end of the limit block abuts against the side wall of the test box.

5. The tensile strength test device for overconsolidated clay according to claim 4, characterized in that: The inner wall of the test box is provided with a positioning groove, and the limiting block is provided with a positioning block which is matched and connected with the positioning groove.

6. The tensile strength test device for overconsolidated clay according to claim 5, characterized in that: A quick positioning assembly is also provided on one side of the soil sample loading chamber, and the quick positioning assembly includes a positioning plate, and the positioning plate is located on a side of the adjacent fixed plate away from the center of the soil sample loading chamber; and the positioning plate is parallel to the adjacent fixed plate; the positioning plate is connected to the curved plate through a second hydraulic rod; the positioning plate and the test box are connected through a telescopic rod, and the telescopic rod is perpendicular to the fixed plate.

7. The tensile strength test device for overconsolidated clay according to claim 6, characterized in that: Both ends of the positioning plate are provided with positioning blocks which are matched and connected with the positioning grooves.

8. A soil sample tensile test method using the tensile strength test device for overconsolidated clay according to claim 7, characterized in that: The specific steps include: A1: According to the soil sample design parameters, determine the number of elastic connection units and assemble the tensile section to obtain the soil sample loading chamber; A2: Lock the first hydraulic rod. In the initial state, all the second hydraulic rods are in the extended state, and the tensile load at the second hydraulic rod is 0; make all the second hydraulic rods shrink synchronously, collect the displacement data of each pressure plate through the displacement sensor, collect the tensile load of the second hydraulic rod through the tensile sensor, and calculate the elastic coefficient of the curved plate: ;in, is the tensile load of the second hydraulic rod; and are the displacement distances of the two pressure plates respectively; the second hydraulic rod is restored; A3: Fill the soil layer in the soil sample loading chamber and obtain the initial porosity ratio The top surface of the soil sample is in contact with the transparent panel; A4: Synchronously contract all the second hydraulic rods step by step, measure and record the displacement of the pressure plate and the tensile load of the second hydraulic rod during the tension application process through the measuring assembly, and calculate the stress of the tensile section soil sample under any level of tension during the loading process and deformation ; ； ； in, For the The tensile load of the second hydraulic rod under the first-stage tension; and They are The displacement distance of the two lower pressure plates; is the soil sample thickness, is the width of the soil sample in the tensile section; is the length of the initial soil sample in the tensile section; A5: Collect the tensile crack area of ​​soil samples through cameras ; Tensile crack length and the average width of tensile cracks ; ； ； ； in, and They are respectively the tensile section of soil sample Crack pixel area and crack pixel length under level tension; are image transformation parameters, and , is the actual surface area of ​​the tensile soil sample before tensile loading, is the pixel area of ​​the tensile section soil sample before tensile loading; A6: Drawing Tensile crack area , tensile crack length and the average width of tensile cracks The relationship curve of the development process of the crack is obtained, and the tensile stress and strain of the soil sample when the crack initially appears and the tensile stress and strain of the soil sample when the crack penetrates are recorded according to the image information taken by the camera. The peak point of the tensile stress and the peak point of the tensile stress are determined according to the relationship curve. That is the tensile strength of the soil sample, completing the tensile test.

9. A soil sample consolidation test method using the tensile strength test device for overconsolidated clay according to claim 7, characterized in that: The specific steps include: B1: According to the soil sample design parameters, determine the number of elastic connection units and assemble the tensile section to obtain the soil sample loading chamber; B2: Lock the first hydraulic rod. In the initial state, all the second hydraulic rods are in the extended state, and the tensile load at the second hydraulic rod is 0; make all the second hydraulic rods contract synchronously, collect the displacement data of each pressure plate through the displacement sensor, collect the load of the second hydraulic rod through the tension sensor, and calculate the elastic coefficient of the curved plate: ;in, is the tensile load of the second hydraulic rod; and are the displacement distances of the two pressure plates respectively; the second hydraulic rod is restored; B3: Unlock the first hydraulic rod and lock the second hydraulic rod. In the initial state, all the first hydraulic rods are in a contracted state. Fill the soil layer in the soil sample loading chamber and obtain an initial porosity ratio of The soil sample is placed in contact with the transparent panel; the pressure sensor is reset to zero; B4: Set the maximum compressive stress value , gradually extend the first hydraulic rod, and the increment of compressive stress at each stage is 50 kPa, and the maximum pressure load applied to the first hydraulic rod is calculated. And each level of incremental load ; ； ； in, is the soil sample thickness, is the width of the soil sample in the tensile section; Under each level of pressure load, continue until the displacement is stable, record the displacement of the pressure plate under each level of pressure load, and calculate the compressive stress of the soil sample under any level of pressure , compressive strain and porosity ratio ; ； ； ； in, is the pressure load of a single first hydraulic rod under the j-th level pressure load; is the cross-sectional area of ​​the soil sample of the straight segment under the j-th level pressure load; is the volume of the straight segment soil sample under the j-th level pressure load; is the volume of the arc-shaped soil sample under the j-th level pressure load; is the volume of the tensile section of the soil sample under the jth level of pressure load; after reaching the designed maximum pressure load, the first hydraulic rod stops extending; and are the displacement distances of the two pressure plates under the j-th level of pressure load; B5: Draw the logarithm of the compressive stress-porosity ratio curve of the soil sample during the loading process. The sudden turning point in the logarithm of the compressive stress-porosity ratio curve is the initial consolidation pressure of the soil sample. At the same time, the consolidation pressure of the soil sample at the maximum pressure load is obtained to complete the consolidation test method.

10. A soil sample stress test method for a tensile strength test device for overconsolidated clay, characterized in that: The soil sample is consolidated to the designed porosity ratio by the consolidation test method described in claim 9 to obtain a consolidated soil sample; and the consolidated soil sample is then subjected to a tensile strength test by the tensile test method described in claim 8.

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