Unsaturated soil tensile strength test device and test method

Abstract

The present application relates to the technical field of soil tensile strength testing, and discloses an unsaturated soil tensile strength test device and test method. The unsaturated soil tensile strength test device includes a closed chamber, a soil fixing mechanism, a loading mechanism, a stretching mechanism and an adjusting mechanism; the soil fixing mechanism is arranged in the closed chamber, can accommodate the soil to be tested and access an external water source, and is provided with a clay plate spaced between the soil to be tested and the external water source; the loading mechanism is configured to apply a vertical load to the soil to be tested; the stretching mechanism is configured to apply tension to the soil to be tested in the horizontal direction; the adjusting mechanism is configured to adjust the pore water pressure and pore air pressure of the soil to be tested so that the soil to be tested has a target matrix suction and adjust the magnitude and rate of change of the tension applied by the stretching mechanism to the soil to be tested. The embodiment of the present application can improve the test accuracy of the soil tensile strength test.

Description

Technical Field

[0001] The present application relates to the technical field of soil tensile strength testing, and in particular to an unsaturated soil tensile strength testing device and a testing method. Background Art

[0002] In related technologies, the test of soil tensile strength can be divided into indirect tensile test and direct tensile test. Direct tensile test mainly includes uniaxial tensile test and triaxial tensile test. Due to the uncertainty of material fracture surface in indirect tensile test, harsh test conditions and low test success rate of triaxial tensile test, uniaxial tensile test is generally used to test soil tensile strength.

[0003] However, the existing uniaxial tensile test relies on the soil-water characteristic curve obtained from the soil-water characteristic test to prepare soil samples with different water contents in order to consider the changes in soil matrix suction. It is unable to consider the influence of the suction changes of the soil under the actual dry-wet path on the corresponding soil properties. Compacting soil samples at different water contents usually produces different microstructures, which affects the accuracy of the test results. Summary of the invention

[0004] The purpose of this application is to provide an unsaturated soil tensile strength test device and test method, aiming to improve the test accuracy of soil tensile strength test.

[0005] The present application provides an unsaturated soil tensile strength test device, comprising:

[0006] Closed chamber;

[0007] A soil fixing mechanism is arranged in the closed chamber, can accommodate the soil to be tested and is connected to an external water source, and is provided with a clay plate spaced between the soil to be tested and the external water source;

[0008] A loading mechanism, configured to apply a vertical load to the soil to be tested;

[0009] a stretching mechanism connected to the soil fixing mechanism and configured to be stretched and matched with the soil fixing mechanism to apply a tensile force to the soil to be tested in a horizontal direction; and

[0010] The regulating mechanism connects the closed chamber, the soil fixing mechanism and the stretching mechanism, and is configured to regulate the pore water pressure and pore air pressure of the soil to be tested so that the soil to be tested has a target matrix suction, and is configured to regulate the magnitude and change rate of the tension applied by the stretching mechanism to the soil to be tested.

[0011] In some embodiments, the soil fixing mechanism comprises:

[0012] A fixing seat, fixedly disposed in the closed chamber, and embedded with the clay plate;

[0013] A sliding seat, which can reciprocate in the horizontal direction in the closed chamber and embed the clay plate;

[0014] A first clamp, fixed to the fixing seat;

[0015] a second fixture, fixed to the sliding seat, connected to the first fixture when the fixed seat and the sliding seat are in contact, and forming a fixture cavity when connected to the first fixture; and

[0016] A water outlet trough is provided on the fixed seat and the sliding seat, and can discharge water to a side of the clay plate away from the clamp cavity.

[0017] In some embodiments, the unsaturated soil tensile strength testing device further includes a sample preparation mechanism;

[0018] The sample preparation mechanism comprises:

[0019] A sample preparation mold having a sample pressing cavity adapted to the fixture cavity; and

[0020] The sample preparation piston is matched with the sample pressing cavity and can be embedded in the sample pressing cavity to statically press the soil in the sample pressing cavity for sampling. A limiting part for limiting the embedding depth is provided.

[0021] In some embodiments, the loading mechanism comprises:

[0022] A loading arm is disposed at the bottom of the closed chamber and is connected to a weight plate;

[0023] A pressure arm partially penetrates into the sealed chamber, one end of which is provided with a pressure transmission component, and one end outside the sealed chamber is provided with a vertical displacement sensor for detecting the vertical displacement distance of the pressure arm; and

[0024] A connecting frame connects the loading arm and the pressure arm, so that the loading arm drives the pressure arm to apply a vertical load to the soil to be tested through the pressure transmission assembly.

[0025] In some embodiments, the stretching mechanism comprises:

[0026] a stretching arm connected to the soil fixing mechanism and provided with a tension sensor for detecting the horizontal tension applied by the stretching arm to the soil to be tested and a horizontal displacement sensor for detecting the horizontal displacement distance of the stretching arm; and

[0027] The stretching driver cooperates with the stretching arm in transmission, so that the stretching arm applies a horizontal pulling force to the soil to be tested in the soil fixing mechanism when the stretching arm cooperates in transmission.

[0028] In some embodiments, the adjustment mechanism comprises:

[0029] an air pressure controller connected to an air pressure regulating valve and configured to set the internal air pressure of the closed chamber through the air pressure regulating valve to adjust the pore air pressure of the soil to be tested;

[0030] a water pressure controller connected to a water pressure regulating valve and configured to set the water pressure of the external water source through the water pressure regulating valve to adjust the pore water pressure of the soil body to be tested; and

[0031] A flushing pipe is connected to the soil fixing mechanism and the external water source, and can introduce the external water source into the soil fixing mechanism under the pressure of external force or suck out the external water source in the soil fixing mechanism when the external force disappears.

[0032] In some embodiments, the unsaturated soil tensile strength testing device further includes a control mechanism;

[0033] The control mechanism is configured to control the regulating mechanism to regulate the pore water pressure and pore air pressure of the soil to be tested and to regulate the magnitude and change rate of the tension applied by the stretching mechanism, and to collect the magnitude and change rate of the target matrix suction, the load and the tension.

[0034] The embodiment of the present application further provides a method for testing the tensile strength of unsaturated soil, using the above-mentioned unsaturated soil tensile strength testing device, and the method for testing the tensile strength of unsaturated soil includes:

[0035] After the clay plate is saturated, the soil to be tested is fixed to the soil fixing mechanism, and the regulating mechanism is controlled to adjust the pore water pressure and pore air pressure of the soil to be tested so that the soil to be tested has the target matrix suction;

[0036] Controlling the load mechanism to apply a load to the soil to be tested to a target load amount;

[0037] After the load is applied to the soil body to be tested, the adjusting mechanism is controlled to adjust the magnitude and the rate of change of the tensile force applied by the stretching mechanism to the soil body to be tested, so as to perform a tensile strength test on the soil body to be tested.

[0038] The embodiment of the present application further provides a method for testing the tensile strength of unsaturated soil, using the above-mentioned unsaturated soil tensile strength testing device, and the unsaturated soil tensile strength testing method includes:

[0039] After the clay plate is saturated, the soil to be tested is fixed to the soil fixing mechanism, so that the soil to be tested cannot be deformed in the horizontal direction;

[0040] Controlling the regulating mechanism to regulate the pore water pressure and pore air pressure of the soil body to be tested so that the soil body to be tested has the target matrix suction;

[0041] After the target matrix suction is obtained, the load mechanism is controlled to apply loads step by step to the soil body to be tested, so as to perform a compression test on the soil body to be tested.

[0042] The embodiment of the present application further provides a method for testing the tensile strength of unsaturated soil, using the above-mentioned unsaturated soil tensile strength testing device, and the method for testing the tensile strength of unsaturated soil includes:

[0043] After the clay plate is saturated, the soil to be tested is fixed to the soil fixing mechanism to limit the soil to be tested from lateral deformation;

[0044] Controlling the load mechanism to apply a load to the soil to be tested to a target load amount;

[0045] After applying a load to the soil to be tested, the regulating mechanism is controlled to gradually adjust the pore water pressure and pore air pressure of the soil to be tested, exhaust the bubbles at the bottom of the clay plate, and perform water absorption, dehydration and compression tests on the soil to be tested.

[0046] The beneficial effects of the present application are as follows: a clay plate is arranged between the soil to be tested and the water source in the soil fixing mechanism, and the pore air pressure and pore water pressure of the soil to be tested can be controlled separately by utilizing the boundary effect of the fully saturated clay plate on the pore air pressure and pore water pressure of the soil to be tested, so as to control the matrix suction level of the soil to be tested; at the same time, a load mechanism that can apply a vertical load and a stretching mechanism that applies a horizontal tension are configured, and the vertical load and / or the horizontal tension can be configured respectively according to actual needs to carry out the required type of test, and the influence of the suction change of the soil under the actual dry and wet path on the corresponding soil properties can be considered, so as to improve the test accuracy of the soil tensile strength test. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the planar structure of the unsaturated soil tensile strength test device provided in an embodiment of the present application.

[0048] Figure 2 It is a partial front view structural schematic diagram of an unsaturated soil tensile strength test device provided in an embodiment of the present application.

[0049] Figure 3It is a partial side structural schematic diagram of an unsaturated soil tensile strength test device provided in an embodiment of the present application.

[0050] Figure 4 It is a schematic diagram of the planar structure of the sample preparation mechanism provided in the embodiment of the present application.

[0051] Figure 5 It is a side structural schematic diagram of the sample preparation piston provided in an embodiment of the present application.

[0052] Figure 6 It is a flow chart of the unsaturated soil tensile strength test method provided in the first embodiment of the present application.

[0053] Figure 7 This is a flow chart of the unsaturated soil tensile strength test method provided in the second embodiment of the present application.

[0054] Figure 8 This is a flow chart of the unsaturated soil tensile strength test method provided in the third embodiment of the present application. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0056] It should be noted that, although the functional modules are divided in the device schematic diagram and the logical order is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than the module division in the device or the order in the flowchart. The terms "first", "second", etc. in the specification, claims and the above drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein are only for the purpose of describing the embodiments of this application and are not intended to limit this application.

[0058] An embodiment of the present application provides an unsaturated soil tensile strength test device.

[0059] Combined with reference Figure 1 and Figure 2 In one embodiment, the unsaturated soil tensile strength test device includes a closed chamber 1, a soil fixing mechanism 2, a loading mechanism 3, a stretching mechanism 4 and an adjusting mechanism 5.

[0060] The soil fixing mechanism 2 is arranged in the closed chamber 1. The soil fixing mechanism 2 can accommodate the soil to be tested and access the external water source, and is provided with a clay plate 6 spaced between the soil to be tested and the external water source. Specifically, the soil to be tested is placed in the soil fixing mechanism 2 for testing, and the soil fixing mechanism 2 isolates the soil to be tested from the external water source through the clay plate 6. The clay plate 6 has water-permeable and air-isolating properties, and the external water source can pass through the clay plate 6 and contact the soil to be tested, so that the pore water pressure and pore air pressure of the soil to be tested can be set independently, and the pore air pressure of the soil to be tested can be set by adjusting the air pressure in the closed chamber 1, and the pore water pressure of the soil to be tested can be set by adjusting the water pressure of the external water source.

[0061] The load mechanism 3 is configured to apply a vertical load to the soil to be tested. Specifically, the load mechanism 3 applies a load to the soil to be tested by applying pressure to the soil to be tested in the vertical direction, so that the soil to be tested is subjected to pressure and produces a corresponding amount of compression. The load mechanism 3 can apply loads to the soil to be tested step by step to test the amount of compression produced by the soil to be tested at different levels of loads.

[0062] The stretching mechanism 4 is connected to the soil fixing mechanism 2, and the stretching mechanism 4 is configured to stretch and cooperate with the soil fixing mechanism 2 to apply tension to the soil to be tested in the horizontal direction. Specifically, the soil to be tested clamps the soil to be tested, and the stretching mechanism 4 stretches the soil fixing mechanism 2 in the horizontal direction, thereby applying tension to the soil to be tested in the horizontal direction. The stretching mechanism 4 can apply tension to the soil to be tested step by step until the soil to be tested breaks, thereby testing the tensile strength of the soil to be tested.

[0063] The regulating mechanism 5 connects the closed chamber 1, the soil fixing mechanism 2 and the stretching mechanism 4. The regulating mechanism 5 is configured to adjust the pore water pressure and pore air pressure of the soil to be tested so that the soil to be tested has the target matrix suction, and is configured to adjust the magnitude and change rate of the tension applied to the soil to be tested by the stretching mechanism 4. Specifically, the regulating mechanism 5 adjusts the pore air pressure of the soil to be tested by adjusting the air pressure in the closed chamber 1, and sets the pore water pressure of the soil to be tested by adjusting the water pressure of the external water source flowing into the soil fixing mechanism 2, so that the pore water pressure and pore air pressure of the soil to be tested have a corresponding pressure difference, which is the target matrix suction. For example, the pore water pressure and pore air pressure of the soil to be tested are adjusted by adjusting the pressure valve set on the pipeline. On the other hand, the regulating mechanism 5 adjusts the magnitude and change rate of the tension applied to the soil to be tested by the stretching mechanism 4 by adjusting the horizontal displacement distance and horizontal displacement speed of the soil fixing mechanism 2 pulled by the stretching mechanism 4.

[0064] In actual application, the clay plate 6 is first placed in a fully saturated state. The pore air pressure and pore water pressure of the soil to be tested can be controlled separately by utilizing the boundary effect of the fully saturated clay plate 6 on the pore air pressure and pore water pressure of the soil to be tested. Then, the prepared soil to be tested is fixed in the soil fixing mechanism 2. The type of test to be carried out is determined according to the test requirements, and the corresponding test operation is carried out based on the determined test type. The pore air pressure of the soil to be tested, the pore water pressure of the soil to be tested, the load applied to the soil to be tested by the load mechanism 3, the tension of the stretching mechanism 4 and / or the tension change rate of the stretching mechanism 4 are adjusted to carry out the required type of test, for example, a soil tensile test with constant normal load and matrix suction, a soil compression test with constant matrix suction, and a soil-water characteristic curve test with constant vertical stress.

[0065] Optionally, the clay board 6 can be fully saturated by using a back pressure technique, specifically setting the water pressure of the external water source flowing to the clay board 6 to 20 kPa-30 kPa, so that the external water source overflows from the surface of the clay board 6 until a bubble-free water film is formed on the surface of the clay board 6. If this process lasts for more than 8 hours, the clay board 6 can be considered to be fully saturated.

[0066] Combined with reference Figure 1 and Figure 2 In one embodiment, the soil fixing mechanism 2 specifically includes a fixed seat 21, a sliding seat 22, a first clamp 23, a second clamp 24 and a water outlet trough 25. The fixed seat 21 is fixedly arranged in the closed chamber 1 and embedded with the clay plate 6, the sliding seat 22 can reciprocate in the closed chamber 1 along the horizontal direction and embed the clay plate 6, the first clamp 23 is fixed to the fixed seat 21, the second clamp 24 is fixed to the sliding seat 22, the second clamp 24 is connected to the first clamp 23 when the fixed seat 21 and the sliding seat 22 are attached, and the second clamp 24 forms a clamp cavity 26 when the first clamp 23 is connected, and the water outlet trough 25 is opened in the fixed seat 21 and the sliding seat 22, and the water outlet trough 25 can discharge water to the side of the clay plate 6 away from the clamp cavity 26.

[0067] Specifically, the fixed seat 21 is fixedly arranged on the bottom surface of the inner cavity of the closed chamber 1, and the first clamp 23 and the embedded clay plate 6 are fixedly arranged on the upper surface of the fixed seat 21. The clay plate 6 embedded in the fixed seat 21 is within the covering range of the first clamp 23 and can contact the soil to be tested. The fixed seat 21 is provided with a water outlet 25 to discharge water to the clay plate 6 embedded in the fixed seat 21. The sliding seat 22 is slidably arranged on the bottom surface of the inner cavity of the closed chamber 1 through a low-friction guide rod, and the second clamp 24 and the embedded clay plate 6 are fixedly arranged on the upper surface of the sliding seat 22. The clay plate 6 embedded in the sliding seat 22 is within the covering range of the second clamp 24 and can contact the soil to be tested. The sliding seat 22 is provided with a water outlet 25 to discharge water to the clay plate 6 embedded in the fixed seat 21. When the fixed seat 21 and the sliding seat 22 are connected, the first clamp 23 and the second clamp 24 are connected to form a clamp cavity 26 for accommodating the soil to be tested.

[0068] In actual application, the relative distance between the fixed seat 21 and the sliding seat 22 is adjusted so that the first clamp 23 and the second clamp 24 are connected and the clay plate 6 is in a fully saturated state, and the pre-prepared soil to be tested is placed in the clamp cavity 26. The first clamp 23 and the second clamp 24 respectively clamp and position the soil to be tested. After the water pressure of the water outlet 25 and the air pressure in the closed chamber 1 are adjusted so that the soil to be tested has a target matrix suction, the stretching mechanism 4 can be used to pull the sliding seat 22 so that the sliding seat 22 moves in a horizontal direction away from the fixed seat 21. The soil to be tested is stretched under the clamping action of the first clamp 23 and the second clamp 24 to carry out a soil tensile strength test.

[0069] Combined with reference Figure 4 and Figure 5 In one embodiment, the unsaturated soil tensile strength test device further includes a sample preparation mechanism 7, which includes a sample preparation mold 71 and a sample preparation piston 72. The sample preparation mold 71 has a sample pressing cavity 73 adapted to the fixture cavity 26, and the sample preparation piston 72 is adapted to the sample pressing cavity 73. The sample preparation piston 72 can be embedded in the sample pressing cavity 73 to statically press the soil in the sample pressing cavity 73, and a limit portion 74 for limiting the embedding depth is provided.

[0070] Specifically, the sample preparation mold 71 is provided with a sample pressing cavity 73, and the shape and volume of the sample pressing cavity 73 are the same as the mold and volume of the fixture cavity 26, and the shape and volume of the sample preparation piston 72. The sample preparation piston 72 is provided with a plurality of limiting portions 74 located at different heights, which are used to limit the depth of the sample preparation piston 72 embedded in the sample pressing cavity 73. In this embodiment, the limiting portion 74 is a through hole provided in the sample preparation piston 72, which, by cooperating with an external latch, plays a role in limiting the depth of the sample preparation piston 72 embedded in the sample pressing cavity 73.

[0071] In actual application, an appropriate amount of soil is placed in the sample pressing cavity 73 of the sample preparation mold 71, and the sample preparation piston 72 is embedded in the sample pressing cavity 73 to statically press the soil for sampling. The limit portion 74 of the sample preparation piston 72 limits the downward pressing depth of the sample preparation piston 72. When the sample preparation piston 72 reaches the limited downward pressing depth, the preset static pressing sampling condition is achieved, the soil to be tested is obtained, and the soil to be tested is transferred from the sample preparation mold 71 to the soil fixing mechanism 2.

[0072] Combined with reference Figure 1 , Figure 2 and Figure 3 In one embodiment, the load mechanism 3 specifically includes a loading arm 31, a pressure arm 32 and a connecting frame 33. The loading arm 31 is arranged at the bottom of the closed chamber 1, the loading arm 31 is connected to a weight plate 34, the pressure arm 32 is partially inserted into the closed chamber 1, one end of the pressure arm 32 inserted into the closed chamber 1 is provided with a pressure transmission component 35, and one end of the pressure arm 32 outside the closed chamber 1 is provided with a vertical displacement sensor 36 for detecting the vertical displacement distance of the pressure arm 32, and the connecting frame 33 connects the loading arm 31 and the pressure arm 32, so that the loading arm 31 drives the pressure arm 32 to apply a vertical load to the soil to be tested through the pressure transmission component 35.

[0073] Specifically, the connecting frame 33 is arranged around the periphery of the closed chamber 1, and the pressure arm 32 penetrates from the top of the closed chamber 1 to the interior of the closed chamber 1 and is slidably connected to the closed chamber 1. The end of the pressure arm 32 that penetrates into the interior of the closed chamber 1 applies a vertical load to the test soil through the pressure transmission component 35. The pressure transmission component 35 may include a pressure transmission cap connected to the pressure arm 32 and a pressure transmission plate arranged on the side of the pressure transmission cap away from the pressure arm 32. The end of the pressure arm 32 outside the closed chamber 1 is connected to the upper half of the connecting frame 33, and the upper half of the connecting frame 33 is connected to one end of the loading arm 31. The other end of the loading arm 31 is connected to the weight plate 34 through a hook.

[0074] In actual application, it is first necessary to determine the size of the load to be applied in the vertical direction. The lever ratio of the loading arm 31 determines the weight of the weight to be added. The weights of corresponding weights are placed on the weight plate 34. Through the connection relationship between the loading arm 31, the pressure arm 32 and the connecting frame 33, the pressure arm 32 can apply the target load to the test soil in the vertical downward direction through the pressure transmission component 35. When the target load is reached, the value of the vertical displacement sensor 36 on the pressure arm 32 remains stable.

[0075] Combined with reference Figure 1 and Figure 2In one embodiment, the stretching mechanism 4 specifically includes a stretching arm 41 and a stretching driver 42. The stretching arm 41 is connected to the soil fixing mechanism 2, and the stretching arm 41 is provided with a tension sensor 43 for detecting the horizontal tension applied by the stretching arm 41 to the soil to be tested and a horizontal displacement sensor 44 for detecting the horizontal displacement distance of the stretching arm 41. The stretching driver 42 is in transmission cooperation with the stretching arm 41, so that the stretching arm 41 applies horizontal tension to the soil to be tested in the soil fixing mechanism 2 when in transmission cooperation.

[0076] Specifically, the stretching arm 41 penetrates from one side of the closed chamber 1 into the interior of the closed chamber 1, and the end of the stretching arm 41 that penetrates into the interior of the closed chamber 1 is connected to the sliding seat 22 and is equipped with a tension sensor 43. The tension sensor 43 is used to detect the horizontal tension applied by the stretching arm 41 to the sliding seat 22. The end of the stretching arm 41 outside the closed chamber 1 is connected to the stretching driver 42 through a rotating shaft. The stretching arm 41 is rotatably connected to the rotating shaft and is equipped with a horizontal displacement sensor 44. The stretching driver 42 and the rotating shaft are transmission-coordinated (for example, screw-coordinated), so that the rotating shaft can generate a horizontal displacement during the transmission-coordinated process, thereby driving the stretching arm 41 to generate a horizontal displacement. The horizontal displacement sensor 44 is used to detect the horizontal displacement of the stretching arm 41.

[0077] In actual application, the stretching driver 42 drives the rotating shaft to rotate, so that the rotating shaft produces a horizontal displacement, and the rotating shaft drives the stretching arm 41 to produce the same horizontal displacement. The rotating shaft pulls the sliding seat 22 to move away from the fixed seat 21, and the test soil is stretched under the clamping action of the first clamp 23 and the second clamp 24, so as to achieve the application of horizontal tension to the test soil.

[0078] See also Figure 1 In one embodiment, the regulating mechanism 5 specifically includes an air pressure controller 51, a water pressure controller 52 and a flushing pipe 53. The air pressure controller 51 is connected to an air pressure regulating valve 54, and is configured to set the internal air pressure of the closed chamber 1 through the air pressure regulating valve 54 to adjust the pore air pressure of the soil to be tested. The water pressure controller 52 is connected to a water pressure regulating valve 55, and is configured to set the water pressure of the external water source through the water pressure regulating valve 55 to adjust the pore water pressure of the soil to be tested. The flushing pipe 53 connects the soil fixing mechanism 2 and the external water source. The flushing pipe 53 can introduce the external water source into the soil fixing mechanism 2 under the pressure of an external force or suck out the external water source in the soil fixing mechanism 2 when the external force disappears.

[0079] The closed chamber 1 is provided with an air inlet, which is connected to an external air source through an air pipe, and an air pressure regulating valve 54 is arranged on the air pipe. In actual application, the air pressure controller 51 controls the opening degree of the air pressure regulating valve 54, thereby setting the internal air pressure of the closed chamber 1, and then adjusting the pore air pressure of the soil to be tested. The closed chamber 1 is provided with a water inlet, which is connected to an external water source through a water pipe and introduces the external water source into the water outlet 25 of the soil fixing mechanism 2 through the water pipe. The water pressure regulating valve 55 is arranged on the water pipe. In actual application, the water pressure controller 52 controls the opening degree of the water pressure regulating valve 55, thereby setting the water output of the water outlet 25, and then adjusting the pore water pressure of the soil to be tested. The closed chamber 1 is provided with a flushing port, which is connected to the flushing pipe 53 and the water outlet trough 25 of the soil fixing mechanism 2 through the water pipe. In actual application, by repeatedly applying external force to squeeze the flushing pipe 53 or canceling the external force applied to the flushing pipe 53, the water in the flushing pipe 53 repeatedly enters the water outlet trough 25 of the soil fixing mechanism 2 or is discharged from the water outlet trough 25 of the soil fixing mechanism 2, thereby achieving the effect of flushing the bubbles in the water outlet trough 25 of the soil fixing mechanism 2.

[0080] See also Figure 1 In one embodiment, the unsaturated soil tensile strength test device also includes a control mechanism 8, which is configured to control the adjustment mechanism 5 to adjust the pore water pressure and pore air pressure of the soil to be tested and to adjust the magnitude and change rate of the tension applied by the stretching mechanism 4, as well as to collect the magnitude and change rate of the target matrix suction, load and tension.

[0081] The embodiment of the present application also provides an unsaturated soil tensile strength test method using the above-mentioned unsaturated soil tensile strength test device.

[0082] See also Figure 6 , Figure 6 is a flow chart of the unsaturated soil tensile strength test method provided in the first embodiment of the present application. In some embodiments, Figure 6 The method may specifically include but is not limited to steps S601 to S603. Figure 6 These three steps are introduced in detail.

[0083] Step S601, after the clay plate is saturated, the soil to be tested is fixed to the soil fixing mechanism, and the regulating mechanism is controlled to adjust the pore water pressure and pore air pressure of the soil to be tested so that the soil to be tested has a target matrix suction.

[0084] Step S602: Control the load mechanism to apply a load to the soil to be tested to a target load amount.

[0085] Step S603, after applying the load to the soil body to be tested, the control regulating mechanism adjusts the magnitude and the rate of change of the tensile force applied by the tensile mechanism to the soil body to be tested, so as to perform a tensile strength test on the soil body to be tested.

[0086] The unsaturated soil tensile strength test method provided in this embodiment is used to test the tensile strength of the soil to be tested under different conditions.

[0087] Before starting the test, first determine whether a uniaxial tensile test or a plane strain tensile test with a vertical load is required, that is, determine the size of the load to be applied, set the target load, and then determine the required target matrix suction. Based on this, determine the pore air pressure and pore water pressure of the soil to be tested. Prepare the soil to be tested according to the sample preparation method provided in the above embodiment, prepare the soil to be tested with a certain dry density and water content, and make the clay board in a saturated state.

[0088] In step S601 to step S603, the soil to be tested is fixed in the soil fixing mechanism (filter paper is placed above the clay plate in advance), and then the loading mechanism and the soil to be tested are aligned, the closed chamber is closed, and the regulating mechanism is controlled to gradually increase the pore water pressure and pore air pressure of the soil to be tested until the difference between the pore water pressure and the pore air pressure reaches the target matrix suction, and a load in the vertical direction is applied to the soil to be tested through the loading mechanism, and the loading mechanism is controlled to apply a load to the soil to be tested to a target load amount, and finally the regulating mechanism is controlled to adjust the magnitude and change rate of the tensile force applied by the tensile mechanism to the soil to be tested, so as to test the tensile strength performance of the soil to be tested.

[0089] See also Figure 7 , Figure 7 is a flow chart of the unsaturated soil tensile strength test method provided in the second embodiment of the present application. In some embodiments, Figure 7 The method may specifically include but is not limited to steps S701 to S703. Figure 7 These three steps are introduced in detail.

[0090] Step S701, after the clay plate is saturated, the soil to be tested is fixed to a soil fixing mechanism, so that the soil to be tested cannot be deformed in the horizontal direction.

[0091] Step S702: controlling the regulating mechanism to regulate the pore water pressure and pore air pressure of the soil body to be tested so that the soil body to be tested has a target matrix suction.

[0092] Step S703, after obtaining the target matrix suction, controlling the load mechanism to apply load to the test soil body step by step, so as to perform a compression test on the test soil body.

[0093] The unsaturated soil tensile strength test method provided in this embodiment is suitable for testing the compression deformation of an unsaturated soil body to be tested.

[0094] Before starting the test, the required target matrix suction is first determined, based on which the pore air pressure and pore water pressure of the soil to be tested are determined, and the soil to be tested is prepared according to the sample preparation method provided in the above embodiment to obtain a soil to be tested having a certain dry density and water content, and then the clay board is placed in a saturated state.

[0095] In step S701 to step S703, the soil to be tested is fixed in the soil fixing mechanism (filter paper is placed above the clay plate in advance), and then the first clamp and the second clamp of the soil fixing mechanism are fixed by a hoop. In the lateral confinement compression test, the test clamp is fixed by the rectangular hoop to limit the soil to be tested from deforming in the horizontal direction. The load mechanism and the soil to be tested are aligned, and the closed chamber is closed. The regulating mechanism is controlled to gradually increase the pore water pressure and pore air pressure of the soil to be tested until the difference between the pore water pressure and the pore air pressure reaches the target matrix suction. After obtaining the target matrix suction, the load mechanism is controlled to gradually apply a vertical load to the soil to be tested. When the moisture desorption of the soil to be tested is stable under the current level of load, the load mechanism is controlled to apply the next level of load to the soil to be tested, and the compression amount of the soil to be tested under each level of load is recorded to obtain the compression curve of the soil to be tested at the suction level.

[0096] See also Figure 8 , Figure 8 Flow chart of the unsaturated soil tensile strength test method provided in the third embodiment of the present application. In some embodiments, Figure 8 The method may specifically include but is not limited to steps S801 to S803. Figure 8 These three steps are introduced in detail.

[0097] Step S801, after the clay plate is saturated, the soil to be tested is fixed to a soil fixing mechanism to limit the soil to be tested from lateral deformation.

[0098] Step S802, controlling the load mechanism to apply a load to the soil to be tested to a target load amount.

[0099] Step S803, after applying load to the soil to be tested, the control regulating mechanism is used to gradually adjust the pore water pressure and pore air pressure of the soil to be tested, to discharge the bubbles at the bottom of the clay plate, and to perform water absorption, dehydration and compression tests on the soil to be tested at multiple suction levels.

[0100] The unsaturated soil tensile strength test method provided in this embodiment is suitable for an unsaturated soil dehumidification test under a constant vertical stress.

[0101] Before starting the test, the soil to be tested is prepared according to the sample preparation method provided in the above embodiment to obtain a soil to be tested with a certain dry density and water content, so that the clay board is in a saturated state, and then the load required to be applied is determined and the target load is set.

[0102] In step S801 to step S803, the soil to be tested is fixed in the soil fixing mechanism (filter paper is placed above the clay plate in advance), and then the load mechanism and the soil to be tested are aligned, the closed chamber is closed, the load mechanism is controlled to apply a load to the soil to be tested to a target load, and then the regulating mechanism is controlled to change the pore water pressure and pore air pressure of the soil to be tested step by step, so that the soil to be tested completes the dehumidification process, and the flushing mechanism is used to timely discharge the bubbles at the bottom of the clay plate, and the water absorption, volume and compression of the soil to be tested under each suction condition are recorded. After the test, the water content of the soil to be tested is measured, and the mass water content or volume water content of the soil to be tested under the corresponding suction level can be inversely calculated by combining the dehumidification and compression of the soil to be tested under each matrix suction condition, and the dehumidification curve of the soil to be tested, that is, the soil-water characteristic curve of the soil to be tested, can be obtained.

[0103] In summary, the unsaturated soil tensile strength test device and test method provided in the embodiment of the present application are provided with a clay plate spaced between the soil to be tested and the water source in the soil fixing mechanism, and the pore air pressure and pore water pressure of the soil to be tested are controlled separately by utilizing the boundary effect of the fully saturated clay plate on the pore air pressure and pore water pressure of the soil to be tested. At the same time, a load mechanism that can apply a vertical load and a stretching mechanism that applies a horizontal tension are configured. The vertical load and / or the horizontal tension can be configured separately according to actual needs to carry out the required type of test, and the influence of the suction change of the soil under the actual dry and wet path on the corresponding soil properties can be considered to improve the test accuracy of the soil tensile strength test.

[0104] It should be understood that in the present application, "at least one (item)" means one or more, and "plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" can mean: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally indicates that the objects associated before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0105] The preferred embodiments of the present invention are described above with reference to the accompanying drawings, but the scope of the rights of the present invention is not limited thereto. Any modification, equivalent substitution and improvement made by a person skilled in the art without departing from the scope and essence of the present invention should be within the scope of the rights of the present invention.

Claims

1. An unsaturated soil tensile strength test device, characterized in that: include: Closed chamber; A soil fixing mechanism is arranged in the closed chamber, can accommodate the soil to be tested and is connected to an external water source, and is provided with a clay plate spaced between the soil to be tested and the external water source; A loading mechanism, configured to apply a vertical load to the soil to be tested; A stretching mechanism, connected to the soil fixing mechanism, and configured to cooperate with the soil fixing mechanism in a stretching manner so as to apply a tensile force to the soil to be tested in a horizontal direction; as well as an adjusting mechanism, connecting the closed chamber, the soil fixing mechanism and the stretching mechanism, configured to adjust the pore water pressure and pore air pressure of the soil to be tested so that the soil to be tested has a target matrix suction, and configured to adjust the magnitude and change rate of the tension applied by the stretching mechanism to the soil to be tested; The soil fixing mechanism comprises: A fixing seat, fixedly disposed in the sealed chamber, and embedded with the clay plate; A sliding seat, which can reciprocate in the horizontal direction in the closed chamber and embed the clay plate; A first clamp, fixed to the fixing seat; a second fixture, fixed to the sliding seat, connected to the first fixture when the fixed seat and the sliding seat are in contact, and forming a fixture cavity when connected to the first fixture; and A water outlet trough is provided on the fixed seat and the sliding seat, and can discharge water to a side of the clay plate away from the fixture cavity; The unsaturated soil tensile strength test device also includes a sample preparation mechanism; The sample preparation mechanism comprises: A sample preparation mold, having a sample pressing cavity adapted to the fixture cavity; and The sample preparation piston is matched with the sample pressing cavity and can be embedded in the sample pressing cavity to statically press the soil in the sample pressing cavity for sampling. A limiting part for limiting the embedding depth is provided.

2. The unsaturated soil tensile strength test device according to claim 1 is characterized in that: The load mechanism comprises: A loading arm is disposed at the bottom of the closed chamber and is connected to a weight plate; A pressure arm partially penetrates into the sealed chamber, one end of which is provided with a pressure transmission component, and one end outside the sealed chamber is provided with a vertical displacement sensor for detecting the vertical displacement distance of the pressure arm; and A connecting frame connects the loading arm and the pressure arm, so that the loading arm drives the pressure arm to apply a vertical load to the soil to be tested through the pressure transmission assembly.

3. The unsaturated soil tensile strength test device according to claim 1, characterized in that: The stretching mechanism comprises: a stretching arm connected to the soil fixing mechanism and provided with a tension sensor for detecting the horizontal tension applied by the stretching arm to the soil to be tested and a horizontal displacement sensor for detecting the horizontal displacement distance of the stretching arm; and The stretching driver cooperates with the stretching arm in transmission, so that the stretching arm applies a horizontal pulling force to the soil to be tested in the soil fixing mechanism when the stretching arm cooperates in transmission.

4. The unsaturated soil tensile strength test device according to claim 1, characterized in that: The regulating mechanism comprises: An air pressure controller connected to an air pressure regulating valve and configured to set the internal air pressure of the closed chamber through the air pressure regulating valve to adjust the pore air pressure of the soil to be tested; a water pressure controller connected to a water pressure regulating valve and configured to set the water pressure of the external water source through the water pressure regulating valve to adjust the pore water pressure of the soil body to be tested; and A flushing pipe is connected to the soil fixing mechanism and the external water source, and can introduce the external water source into the soil fixing mechanism under the pressure of external force or suck out the external water source in the soil fixing mechanism when the external force disappears.

5. The unsaturated soil tensile strength test device according to claim 1, characterized in that: The unsaturated soil tensile strength test device also includes a control mechanism; The control mechanism is configured to control the regulating mechanism to regulate the pore water pressure and pore air pressure of the soil to be tested and to regulate the magnitude and change rate of the tension applied by the stretching mechanism, and to collect the magnitude and change rate of the target matrix suction, the load and the tension.

6. A method for testing the tensile strength of unsaturated soil, using the unsaturated soil tensile strength testing device according to any one of claims 1 to 5, characterized in that: The unsaturated soil tensile strength test method comprises: After the clay plate is saturated, the soil to be tested is fixed to the soil fixing mechanism, and the regulating mechanism is controlled to adjust the pore water pressure and pore air pressure of the soil to be tested so that the soil to be tested has the target matrix suction; Controlling the load mechanism to apply a load to the soil to be tested to a target load amount; After the load is applied to the soil body to be tested, the adjusting mechanism is controlled to adjust the magnitude and the rate of change of the tensile force applied by the stretching mechanism to the soil body to be tested, so as to perform a tensile strength test on the soil body to be tested.

7. A method for testing the tensile strength of unsaturated soil, using the unsaturated soil tensile strength testing device according to any one of claims 1 to 6, characterized in that: The unsaturated soil tensile strength test method comprises: After the clay plate is saturated, the soil to be tested is fixed to the soil fixing mechanism, so that the soil to be tested cannot be deformed in the horizontal direction; Controlling the regulating mechanism to regulate the pore water pressure and pore air pressure of the soil body to be tested so that the soil body to be tested has the target matrix suction; After the target matrix suction is obtained, the load mechanism is controlled to apply loads step by step to the soil body to be tested, so as to perform a compression test on the soil body to be tested.

8. A method for testing the tensile strength of unsaturated soil, using the unsaturated soil tensile strength testing device according to any one of claims 1 to 5, characterized in that: The unsaturated soil tensile strength test method comprises: After the clay plate is saturated, the soil to be tested is fixed to the soil fixing mechanism to limit the soil to be tested from lateral deformation; Controlling the load mechanism to apply a load to the soil to be tested to a target load amount; After applying a load to the soil to be tested, the regulating mechanism is controlled to gradually adjust the pore water pressure and pore air pressure of the soil to be tested, exhaust the bubbles at the bottom of the clay plate, and perform water absorption, dehydration and compression tests on the soil to be tested.

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