Tensile Strength Test Device and Implementation Method for Overconsolidated Clay

Abstract

The present invention discloses a tensile strength test device and implementation method for overconsolidated clay, which relates to the technical field of geotechnical test equipment and includes a test box, the top surface of the test box being a transparent panel; a stress loading component is arranged inside the test box, and the stress loading component includes two symmetrically arranged curved plates, and the two ends of the two curved plates are fixedly connected and surrounded by two parallel fixing plates to form a soil sample loading chamber; the present invention provides a device with pressure loading and tensile loading functions. Before conducting a tensile test, by performing an operation of applying a load on the soil sample, the soil sample can have different consolidation pressures, so that the tensile strength of clays with different consolidation histories can be tested. By adopting a combination of rigid components and elastic components for the tensile section, the present invention realizes uniform stretching of the soil sample and avoids the problem of concentrated tensile deformation before tensile failure.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical test equipment, and specifically relates to a tensile strength test device and implementation method for overconsolidated clay. Background Art

[0002] As an engineering material, the tensile strength of clay is an important index for evaluating its performance. Although the tensile strength of clay is relatively low, in many engineering applications, such as foundation engineering, earth-rock dam construction, etc., it is necessary to fully consider the tensile properties of clay to ensure the stability and safety of the project. When the tensile strength of clay is insufficient, the soil mass is prone to cracking under tensile force, and even lead to the collapse of the overall structure. This is relatively common in engineering problems such as earth-rock dams, levees, and slopes, and may cause serious safety accidents. Due to the cracks that easily appear in the soil mass after being subjected to tension, the strength of the soil layer is reduced, and at the same time, the tensile cracks can provide channels for rainwater infiltration. As a result, 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 exploration of the tensile strength characteristics of soil mass not only helps to improve the strength theory of soil mass, but also has important significance for solving practical engineering problems.

[0003] Since the tensile strength value of the soil mass is small and difficult to measure, there is no unified instrument and test specification for measuring the tensile strength of the soil mass at the present stage, and currently, self-made instruments are mostly used for testing. Patent 202310045762.2 discloses a uniaxial tension and sample preparation integrated device for cohesive soil and its use method, which solves the problem of difficult sample preparation for cohesive soil. Patent 202211183917.0 developed a horizontal uniaxial tension test device for a mixture of variable-size gravel and clay. However, the current soil tensile strength test devices rarely consider the influence of the consolidation process of cohesive soil on the tensile strength. In fact, the mechanical properties of cohesive soil are closely related to the consolidation history. For example, as the pre-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 mass. In practical engineering, such as earth-rock dams, artificial slopes, and subgrade filling, the soil mass is often in an overconsolidated state. It is necessary to reflect the influence of the pre-consolidation process on the tensile strength of clay in the tensile strength test device. In addition, during the test of the tensile strength of the soil mass, since the stretching position of the soil sample chamber is often fixed during the stretching process, this may lead to uneven stretching of the soil sample, thereby affecting the test results of the tensile strength. In addition, the stretching of the soil sample is affected by the aspect ratio of the sample, but the existing equipment rarely considers the influence of the soil sample shape on its tensile strength. Summary of the Invention

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

[0005] To achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0006] Provide a tensile strength test device for overconsolidated clay, which includes a test box, and the top surface of the test box is a transparent panel; a stress loading component is arranged inside the test box, and the stress loading component includes 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; on one side of the two fixed plates close to the center of the soil sample loading chamber, a pressure plate is arranged, and the pressure plate is connected to the fixed plate through a first hydraulic rod. Under the action of the first hydraulic rod, the pressure plate moves perpendicular to the length direction of the fixed plate;

[0007] At both ends of the curved plate, a second hydraulic rod is arranged. The second hydraulic rod is 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;

[0008] The middle of the curved plate is a stretching section, and the stretching section is made of elastic rubber material. Under the action of the first hydraulic rod, the stretching section can extend and contract in a direction perpendicular to the fixed plate;

[0009] It also includes a measurement component, and the measurement component 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 is directly opposite to the soil sample loading chamber.

[0010] Further, the gap between the stretching sections of the two curved plates is smaller than the length of the fixed plate. Arc-shaped sections are arranged at both ends of the stretching section, and the curved plate is divided into a stretching section, an arc-shaped section, and a straight section.

[0011] Further, the stretching section is obtained by alternately connecting a plurality of rigid connection units and elastic connection units made of rubber material in sequence. Dovetail grooves for the elastic connection units are arranged on both sides of the rigid connection units, and dovetail tenons matched with the dovetail grooves are arranged on both sides of the elastic connection units.

[0012] Further, a plurality of limiting blocks are arranged on the outer side of the stretching section of the soil sample loading chamber. The number of limiting blocks is the same as that of the elastic connection units. One end of the limiting block abuts against the elastic connection unit, and the other end of the limiting block abuts against the side wall of the test box.

[0013] Further, positioning grooves are arranged on the inner side wall of the test box, and positioning blocks matched with the positioning grooves are arranged on the limiting blocks.

[0014] Further, a quick positioning component is also provided on one side of the soil sample loading chamber. The quick positioning component includes a positioning plate, which is located on the side of the adjacent fixing plate away from the center of the soil sample loading chamber; and the positioning plate is parallel to the adjacent fixing plate; the positioning plate is connected to the curved plate through a second hydraulic rod; the positioning plate is connected to the test box through a telescopic rod, and the telescopic rod is perpendicular to the fixing plate.

[0015] Further, positioning blocks are provided at both ends of the positioning plate for mating connection with the positioning grooves.

[0016] The present invention also provides a soil sample tensile test method using the above-mentioned tensile strength test device for overconsolidated clay, including the following specific steps:

[0017] 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;

[0018] 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; let all the second hydraulic rods contract 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: ; where is the tensile load of the second hydraulic rod; and are the displacement distances of the two pressure plates respectively; restore the second hydraulic rod;

[0019] A3: Fill the soil layer in the soil sample loading chamber to obtain a soil sample with an initial void ratio of ; the top surface of the soil sample is in contact with the transparent panel;

[0020] A4: Gradually and synchronously contract all the second hydraulic rods, measure and record the displacement of the pressure plate and the tensile load of the second hydraulic rod during the tensile force application process through the measuring component, and calculate the stress and the deformation of the soil sample in the tensile section at any level of tensile force during the loading process;

[0021] ;

[0022] ;

[0023] where is the tensile load of the second hydraulic rod at the th level of tensile force; and are respectively the displacement distances of the two pressure plates; is the thickness of the soil sample, is the width of the soil sample in the tensile section; is the length of the initial soil sample in the stretching section;

[0024] A5: Collect the tensile crack area of the soil sample through a camera ; Tensile crack length and average tensile crack width ;

[0025] ;

[0026] ;

[0027] ;

[0028] Among them, and are respectively the crack pixel area and crack pixel length of the soil sample in the stretching section under the -th level of tensile force; is the image conversion parameter, and , is the actual surface area of the soil sample in the stretching section before tensile force loading, is the pixel area of the soil sample in the stretching section before tensile force loading;

[0029] A6: Plot the relationship curves of with the tensile crack area , the tensile crack length and the average tensile crack width . Record the tensile stress and tensile strain of the soil sample when the crack initially appears and the tensile stress and tensile strain of the soil sample when the crack penetrates according to the image information captured by the camera. Determine the peak point of the tensile stress of the soil sample based on the relationship curves. The peak value of the tensile stress is the tensile strength of the soil sample, and the tensile test is completed.

[0030] The present invention also provides a soil sample consolidation test method using the above-mentioned tensile strength test device for overconsolidated clay, including the following specific steps:

[0031] B1: Determine the number of elastic connection units according to the soil sample design parameters, and assemble the stretching section to obtain a soil sample loading chamber;

[0032] 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; Synchronously contract all the second hydraulic rods, collect the displacement data of each pressure plate through a displacement sensor, collect the load of the second hydraulic rod through a tensile sensor, and calculate the elastic coefficient of the curved plate: ; Among them, is the tensile load of the second hydraulic rod; and They are the displacement distances of the two pressure plates respectively; Restore the second hydraulic rod;

[0033] B3: Unlock the first hydraulic rod and lock the second hydraulic rod. All the first hydraulic rods are in the retracted state under the initial condition; Fill the soil layer in the soil sample loading chamber to obtain a soil sample with an initial void ratio of such that the top surface of the soil sample contacts the transparent panel; Zero the pressure sensor;

[0034] B4: Set the maximum compressive stress value , Gradually extend the first hydraulic rod, and the increment of the compressive stress for each level of loading is 50 kPa, Calculate the maximum pressure load applied to the first hydraulic rod and the incremental load for each level;

[0035] ;

[0036] ;

[0037] Among them, is the thickness of the soil sample, is the width of the soil sample in the tensile section;

[0038] 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 at any level of pressure, the compressive strain and the void ratio ;

[0039] ;

[0040] ;

[0041] ;

[0042] Among them, is the pressure load of a single first hydraulic rod under the j-th level of pressure load; is the cross-sectional area of the soil sample in the straight section under the j-th level of pressure load; is the volume of the soil sample in the straight section under the j-th level of pressure load; is the volume of the soil sample in the arc section under the j-th level of pressure load; is the volume of the soil sample in the tensile section under the j-th 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 respectively;

[0043] B5: Plot the logarithmic compressive stress - void ratio curve during the loading process of the soil sample. The abrupt turning point in the logarithmic compressive stress - void ratio curve is the initial consolidation pressure of the soil sample. At the same time, obtain the consolidation pressure at the maximum pressure load of the soil sample to complete the consolidation test method.

[0044] The present invention also provides a soil sample stress test method for the tensile strength test device of overconsolidated clay. The soil sample is consolidated to the designed void ratio by using the above - mentioned consolidation test method to obtain a consolidated soil sample; then the tensile strength test is carried out on the consolidated soil sample by using the above - mentioned tensile test method.

[0045] The beneficial effects of the present invention are as follows:

[0046] 1. The present invention provides a device with pressure loading and tensile loading functions. Before conducting the tensile test, by applying load and unloading operations on the soil sample, the soil sample can have different pre - consolidation pressures, so that the tensile strength of clays with different consolidation histories can be tested.

[0047] 2. By adopting a combination of a rigid member and an elastic member in the tensile section, the present invention realizes the uniform stretching of the soil sample, avoiding the problem of concentrated tensile deformation before tensile failure. And the additional calculation parameters brought by the elastic member can be determined by the elastic coefficient calibration experiment, improving the measurement accuracy.

[0048] 3. The present invention adopts a combined special - shaped plate member with a variable initial installation length of the soil sample loading chamber. Therefore, the tensile test of soil samples with different length - width 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 achieved.

[0049] 4. Through the image recognition technology, the present invention can observe the generation and development process of micro - tensile cracks in the soil sample during the tensile loading process, providing conditions for studying the influence of different consolidation stresses, different soil sample length - width ratios, and different tensile deformation loading rates on the development law of tensile cracks in the tensile section of the soil sample, including the evolution of the actual area, actual length, and average width, etc.

[0050] 5. The present invention adopts the method of directly preparing the sample in the soil sample loading chamber, avoiding the disturbance of sample preparation, ensuring the quality of test sample preparation, and improving the accuracy of test measurement. Description of the Drawings

[0051] Figure 1 It is a three - dimensional schematic diagram of the tensile strength test device for overconsolidated clay;

[0052] Figure 2 It is a schematic diagram of the internal structure of the tensile strength test device for overconsolidated clay;

[0053] Figure 3Schematic three-dimensional structure diagram of the soil sample loading chamber;

[0054] Figure 4 Schematic assembly diagram of the tensile section;

[0055] Figure 5 Schematic diagram of the relationship curve between the tensile stress and tensile strain of the soil sample in Example 2;

[0056] Figure 6 Schematic diagram of the logarithm-void ratio curve of the compressive stress during the loading process of the soil sample in Example 3;

[0057] Wherein, 1. test box; 2. transparent panel; 3. curved plate; 4. fixed plate; 5. pressure plate; 6. first hydraulic rod; 7. second hydraulic rod; 8. tensile 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. sliding groove. Detailed implementation manners

[0058] The following describes the detailed implementation manners of the present invention to facilitate those skilled in the art of the present technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the detailed implementation manners. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

[0059] Example 1

[0060] As Figure 1-4 shown, a tensile strength test device for overconsolidated clay includes a test box 1, and 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 includes two symmetrically arranged curved plates 3. The two ends of the two curved plates 3 are fixedly connected by two parallel fixed plates 4 to enclose a soil sample loading chamber; on one side of the two fixed plates 4 close to the center of the soil sample loading chamber, a pressure plate 5 is arranged, and the pressure plate 5 is connected to the fixed plate 4 through a first hydraulic rod 6. Under the action of the first hydraulic rod 6, the pressure plate 5 moves perpendicular to the length direction of the fixed plate 4;

[0061] Both ends of the curved plate 3 are provided with second hydraulic rods 7, the second hydraulic rods 7 are arranged 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;

[0062] 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 extend and contract in a direction perpendicular to the fixed plate 4;

[0063] It also includes a measurement component. The measurement component 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 pressing plate 5, and a camera 9 located above the test box 1. The camera 9 is directly opposite to the soil sample loading chamber.

[0064] The gap between the stretching sections 8 of the two curved plates 3 is smaller than the length of the fixed plate 4. Arc-shaped sections 10 are arranged at both ends of the stretching section 8. The curved plate 3 is divided into a stretching section 8, an arc-shaped section 10, and a straight section 11. Specifically, in implementation, the arc-shaped section 10 is an S shape composed of two arcs, and the arc-shaped section 10 and the straight section 11 are integrally formed. The central angles of both arcs are 45°.

[0065] The stretching section 8 is obtained by alternately connecting a number of rigid connection units 12 and elastic connection units 13 made of rubber material in sequence. Dovetail grooves 14 for the elastic connection units 13 are arranged on both sides of the rigid connection unit 12, and dovetail tenons 15 matching the dovetail grooves are arranged on both sides of the elastic connection unit 13.

[0066] A number of limiting blocks 16 are arranged on the outer side of the stretching section 8 of the soil sample loading chamber. The number of the limiting blocks 16 is the same as that of the elastic connection units 13. One end of the limiting block 16 abuts against the elastic connection unit 13, and the other end of the limiting block 16 abuts against the side wall of the test box 1.

[0067] Positioning grooves 17 are arranged on the inner side wall of the test box 1, and positioning blocks 18 matching the positioning grooves 17 are arranged on the limiting blocks 16.

[0068] A quick positioning component is also arranged on one side of the soil sample loading chamber. The quick positioning component includes a positioning plate 19, and the positioning plate 19 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. Specifically, in implementation, balance limiting blocks 16 are also arranged at both ends of the positioning plate 19. Two symmetrically arranged sliding grooves 21 are arranged on the bottom plate of the test box 1, and the sliding grooves 21 are parallel to the telescopic rod 20. The balance limiting blocks 16 are in sliding fit with the sliding grooves 21;

[0069] Positioning blocks 18 matching the positioning grooves 17 are arranged at both ends of the positioning plate 19. Specifically, in implementation, the positioning blocks 18 can adopt compression spring beads, or the front and rear side plates of the test box 1 can be detachably arranged to facilitate the connection of the positioning blocks 18 with the positioning grooves 17.

[0070] Example 2

[0071] A method for tensile test of soil samples using the tensile strength test device of overconsolidated clay in Example 1 includes the following specific steps:

[0072] A1: Determine the number of elastic connection units 13 according to the design parameters of the soil sample. In this example, the number of elastic connection units 13 is 6, and the number of rigid connection units 12 is 5. Assemble the tensile section 8 to obtain the soil sample loading chamber;

[0073] 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. Synchronously contract all the second hydraulic rods 7. 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: ; where, is the tensile load of the second hydraulic rod 7; and are the displacement distances of the two pressure plates 5 respectively; Restore the second hydraulic rod 7;

[0074] A3: Fill the soil layer in the soil sample loading chamber to obtain a soil sample with an initial void ratio of ; The top surface of the soil sample is in contact with the transparent panel 2. Before filling the soil sample, mix the dry soil and water according to the designed water content and place them in a sealed bag for 24 hours. Specifically, when implementing, fill the soil layer in the soil sample loading chamber in 5 layers according to the design, and each time take a specified weight of soil sample and fill it to the designed height.

[0075] A4: Gradually and synchronously contract all the second hydraulic rods 7. Measure and record the displacement of the pressure plate 5 and the tensile load of the second hydraulic rod 7 during the process of applying the tensile force through the measuring component, and calculate the stress and the deformation of the soil sample in the tensile section under any level of tensile force during the loading process;

[0076] ;

[0077] ;

[0078] Where, is the tensile load of the second hydraulic rod 7 at the th level of tensile force; and are respectively the displacement distances of the two pressure plates 5 under; is the thickness of the soil sample, is the width of the soil sample in the tensile section 8; is the length of the initial soil sample in the tensile section 8;

[0079] A5: Collect the tensile crack area of the soil sample through the camera 9 ; the tensile crack length and the average width of the tensile crack ;

[0080] ;

[0081] ;

[0082] ;

[0083] Among them, and are respectively the crack pixel area and the crack pixel length of the soil sample in the tensile section 8 under the th level of tensile force; is the image conversion parameter, and , is the actual surface area of the soil sample in the tensile section 8 before the tensile force is applied, is the pixel area of the soil sample in the tensile section 8 before the tensile force is applied;

[0084] A6: Plot the relationship curves of with the tensile crack area , the tensile crack length and the average width of the tensile crack , and record the tensile stress and tensile strain of the soil sample when the crack initially appears and the tensile stress and tensile strain of the soil sample when the crack penetrates according to the image information captured by the camera, and obtain the tensile stress and tensile strain relationship curve as shown in Figure 5 . Determine the peak point of the tensile stress of the soil sample according to the tensile stress and tensile strain relationship curve, and the peak value of the tensile stress is the tensile strength of the soil sample, and the tensile test is completed. is the tensile stress when the crack initially appears in the soil sample, is the tensile stress when the crack penetrates in the soil sample,

[0085] Specifically, when implementing, different numbers of elastic components can be set, and the tensile strength under different shaped soil samples can be obtained separately by using the tensile method.

[0086] Example 3

[0087] A soil sample consolidation test method using the tensile strength test device for overconsolidated clay in Example 1 includes the following specific steps:

[0088] B1: According to the soil sample design parameters, determine the number of elastic connection units 13. In this example, the number of elastic connection units 13 is 6, and the number of rigid connection units 12 is 5. Assemble the tensile section 8 to obtain the soil sample loading chamber;

[0089] B2: 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. Synchronously contract all the second hydraulic rods 7, collect the displacement data of each pressure plate 5 through the displacement sensor, collect the load of the second hydraulic rod 7 through the tensile sensor, and calculate the elastic coefficient of the curved plate 3: ; where is the tensile load of the second hydraulic rod 7; and are the displacement distances of the two pressure plates 5 respectively; Restore the second hydraulic rod 7;

[0090] 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 the contracted state; Fill the soil layer in the soil sample loading chamber to obtain a soil sample with an initial void ratio of , and the top surface of the soil sample is in contact with the transparent panel 2; Zero the pressure sensor;

[0091] B4: Set the maximum compressive stress value , gradually extend the first hydraulic rod 6, and the compressive stress increment for each level of loading is 50 kPa, and calculate the maximum pressure load applied on the first hydraulic rod 6 and the incremental load for each level;

[0092] ;

[0093] ;

[0094] where is the thickness of the soil sample, is the width of the soil sample in the tensile section 8;

[0095] At each level of pressure load, after continuing until the displacement is stable, record the displacement of the pressure plate 5 under each level of pressure load, and calculate the compressive stress , the compressive strain and the void ratio ;

[0096] ;

[0097] ;

[0098] ;

[0099] where is the pressure load of a single first hydraulic rod 6 under the j-th level of pressure load; is the cross-sectional area of the soil sample in the straight section 11 under the j-th level of pressure load; is the volume of the soil sample in the straight segment 11 under the j-th level of pressure load; is the volume of the soil sample in the arc segment 10 under the j-th level of pressure load; is the volume of the soil sample in the tensile segment 8 under the j-th level of pressure load; after reaching the designed maximum pressure load, the first hydraulic rod 6 stops elongating; and are the displacement distances of the two pressure plates 5 under the j-th level of pressure load respectively;

[0100] B5: Plot the logarithmic - void ratio curve of the compressive stress during the loading process of the soil sample, as Figure 6 shown. The sudden turning point in the curve is the initial consolidation pressure of the soil sample , and at the same time, obtain the consolidation pressure of the soil sample at the maximum pressure load . Complete the consolidation test method. The stress sudden 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.

[0101] During specific implementation, conduct a tensile test on the consolidated soil sample, and it is also possible to set up a comparison of the tensile experiments of soil samples under different consolidation pressures.

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; 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; 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.

2. The tensile strength test device for overconsolidated clay according to claim 1, 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.

3. The tensile strength test device for overconsolidated clay according to claim 2, 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.

4. The tensile strength test device for overconsolidated clay according to claim 3, 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.

5. The tensile strength test device for overconsolidated clay according to claim 4, characterized in that: Both ends of the positioning plate are provided with positioning blocks which are matched and connected with the positioning grooves.

6. A soil sample tensile test method using the tensile strength test device for overconsolidated clay according to claim 5, 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 contract 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 lower two 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.

7. A soil sample consolidation test method using the tensile strength test device for overconsolidated clay according to claim 5, 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.

8. 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 7 to obtain a consolidated soil sample; and then the consolidated soil sample is subjected to a tensile strength test by the tensile test method described in claim 6.

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