In-situ lateral pressure and shear composite test device and method

Abstract

The present invention discloses an in-situ pressure and shear composite test device and method. The device includes a pressure gauge, which applies the normal compressive stress required for the direct shear test to the side wall of the borehole; an annular upper horizontal plate is fixedly installed at the upper end of the pressure gauge, and a deformation expansion plate is installed at the lower end; a plurality of symmetrical lifting rings are provided on the upper surface of the upper horizontal plate, and traction is applied to the lifting rings through a traction device to provide the shear force required for the direct shear test; the deformation expansion plate includes an annular fixed box, which is fixedly installed at the lower end of the pressure gauge, and has a rotating part thereon. The end face of the rotating part is equipped with a plurality of metal blades distributed around the pressure gauge cavity, and the metal blades are expanded as the rotating part rotates to achieve radial annular cutting, and remain expanded after the rotation stops. The present invention can form a combined vertical and horizontal loading for on-site direct shear tests, with little disturbance to the in-situ soil, and can achieve the effect of one hole for multiple uses, saving site and time costs, and is suitable for in-situ strength property testing of soil.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil in-situ testing, and in particular relates to an in-situ lateral pressure and shear composite testing device and method for testing the strength characteristic indexes of in-situ soil. Background Art

[0002] The in-situ direct shear test is a commonly used in-situ test method in soil mechanics, which is used to determine the in-situ shear strength of soil. However, the traditional in-situ direct shear test method still has limitations in the application of in-situ soil testing. When conducting an in-situ direct shear test, the soil around the target specimen needs to be excavated. The overall workload of the test is large, the operation is complicated, and the cost is high. In addition, the excavation process is likely to disturb the in-situ soil and affect the accuracy of the test results. The lateral pressure test is a test method used to study the stress-strain relationship of foundation soil in the horizontal direction. This method inserts a cylindrical lateral pressure gauge vertically into the soil and uses the lateral expansion of the lateral pressure gauge to apply uniform pressure, thereby measuring the relationship between radial pressure and deformation. The results of the lateral pressure test combined with parameter inversion technology can determine the parameters of the stress-strain relationship constitutive model that can reflect the in-situ structural properties of the soil layer, and is widely used in geotechnical engineering testing.

[0003] Due to the limitations of the test methods, traditional in-situ direct shear tests are difficult to conduct in conjunction with other on-site in-situ tests (such as lateral pressure tests), resulting in low test site utilization. Summary of the Invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, obtain the in-situ parameters of the soil as comprehensively as possible, and improve the site utilization rate of the in-situ test, the present invention is based on the working principle of the lateral pressure tester, uses the lateral pressure device to provide positive pressure on the side wall of the borehole, proposes an in-situ lateral pressure and shear composite test device, and designs a supporting test method to form a vertical and horizontal combined loading for the on-site in-situ direct shear test; the test device is easy to operate, has little disturbance to the in-situ soil, and can achieve the effect of one hole for multiple uses, saving site and time costs, and is suitable for in-situ strength characteristic testing of soil.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] An in-situ pressure and shear composite test device includes a pressure gauge, which applies the positive compressive stress required for a direct shear test to the side wall of a borehole; an annular upper horizontal plate is fixedly installed at the upper end of the pressure gauge, and a deformation expansion plate is installed at the lower end; a plurality of symmetrical lifting rings are provided on the upper surface of the upper horizontal plate, and a traction force is applied to the lifting rings through a traction device to provide the shear force required for the direct shear test; the deformation expansion plate includes an annular fixed box, which is fixedly installed at the lower end of the pressure gauge and has a rotating part thereon. The end face of the rotating part is equipped with a plurality of metal blades distributed around the pressure gauge cavity, and the metal blades are expanded as the rotating part rotates to achieve radial annular cutting, and remain expanded after the rotation stops, and are retracted after the test is completed.

[0007] In one embodiment, the upper horizontal plate is a circular metal plate, fixedly mounted on the outer wall of the upper end of the pressure regulator and having no contact with the pressure regulator cavity.

[0008] In one embodiment, the traction device is connected to the lifting bail, and a tension sensor is provided at the connection point.

[0009] In one embodiment, the rotating part is composed of a plurality of vertical fixed tubes, each of which is arranged in a single ring around the pressure relief chamber. Each fixed tube can rotate around its tube axis driven by a motor in a fixed box. A metal blade is installed at the end of each fixed tube. Each fixed tube has the same rotation speed and direction. The rotation of each fixed tube drives the corresponding metal blade to expand and cut into the soil.

[0010] In one embodiment, the rotating part is a bearing structure installed between the inner ring of the fixed box and the pressure relief chamber. A plurality of metal blades are installed at the end of the bearing structure. The bearing structure rotates driven by the motor in the fixed box, and each metal blade is unfolded and cut into the soil as it rotates.

[0011] In one embodiment, the metal blade is arc-shaped, and its curvature, width and length are such that it exceeds the outer edge of the fixed box when unfolded, and does not exceed the outer edge of the fixed box when folded.

[0012] In one embodiment, the metal blades are stacked in sequence when unfolded to form a ring that extends beyond the outer edge of the fixed box, and the metal blades are stacked in sequence when folded to form a ring that does not extend beyond the outer edge of the fixed box and does not contact the fixed tube.

[0013] The present invention also provides a test method based on the in-situ lateral pressure and shear composite test device, which mainly includes the following steps:

[0014] Step 1: Using undisturbed soil as the test soil, excavate a test hole in the test soil, and expand the upper part of the test hole to the required depth for the test; the expanded hole diameter is slightly larger than the diameter of the upper horizontal plate;

[0015] Step 2: Lift the test device and bury it in the enlarged test hole, ensuring that the upper horizontal plate is in full contact with the bottom surface of the enlarged hole;

[0016] Step 3: Start the motor to drive the metal blades in the retracted state to rotate and expand to cut into the soil; after the metal blades are fully expanded, turn off the motor;

[0017] Step 4: Convert the normal compressive stress required for the direct shear test into the lateral pressure value provided by the lateral pressure gauge, use the lateral pressure gauge to pressurize the inner wall of the test hole, and record the relationship curve between lateral pressure and deformation during the loading process;

[0018] Step 5: Use the traction device to lift the entire test device upwards, set the pulling force to the sum of the gravity of the test device and the test soil, record this state as the initial state of the test, and the pulling force at this time as the initial pulling force;

[0019] Step 6: Apply tension to the test device in stages. The magnitude of each stage of tension is controlled according to a fixed ratio of the positive pressure. The tension applied at each stage and the corresponding pull-up height are recorded until a sharp increase in deformation occurs during the pull-up process or the pull-up height reaches a set threshold. This is considered to be soil failure, and the tension at this time is recorded as the failure tension.

[0020] Step 7: Release the pressure in the pressure transmitter;

[0021] Step 8: Pull the test device out of the ground, take photos of the soil failure surface, and check whether the metal blades are in the normal state of deployment to determine whether the test is valid.

[0022] Step 9: Remove the soil from the equipment, start the motor, and rotate it in the opposite direction to retract the metal blades; turn off the motor, and the test is over.

[0023] In one embodiment, the diameter of the expanded hole is 10 cm larger than the diameter of the upper transverse plate.

[0024] In one embodiment, the fixed ratio is 10%; the set threshold is 10% of the distance between the lower end of the upper transverse plate and the upper end of the deformable expansion plate.

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] 1) The in-situ lateral pressure and shear composite test is realized, which causes little disturbance to the in-situ soil and has high test accuracy.

[0027] 2) It can carry out combined borehole soil lateral pressure test and in-situ direct shear test, achieving the effect of multiple uses of one hole and comprehensive utilization of multiple tests with one set of equipment.

[0028] 3) The test cost is low, the operation is simple, and the control of each system is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the overall structure of the in-situ lateral pressure and shear composite test device of the present invention (with blades folded in).

[0030] Figure 2 It is a schematic diagram of the overall structure of the in-situ lateral pressure and shear composite test device of the present invention (with blades unfolded).

[0031] Figure 3 This is a schematic diagram of the deformed expansion plate structure of the present invention (blades folded in)

[0032] Figure 4 This is a schematic diagram of the deformed expansion plate structure of the present invention (with blades unfolded)

[0033] Figure 5 It is a schematic diagram of the folding and unfolding of a single blade on a deformable expansion plate of the present invention.

[0034] Figure 6 It is a schematic diagram of the folding of a single blade of the present invention.

[0035] Figure 7 It is a schematic structural diagram of the linkage of the fixed pipes in one embodiment of the present invention.

[0036] Figure 8 yes Figure 7 Schematic diagram of the structure of the single-piece fixed pipe connecting piece.

[0037] Figure 9 yes Figure 7 Schematic diagram of the connection between two adjacent fixed pipe connecting pieces. DETAILED DESCRIPTION

[0038] The embodiments of the present invention are described in detail below with reference to the accompanying drawings and examples.

[0039] In order to carry out in-situ direct shear tests and lateral pressure tests using the same device and the same borehole, the present invention provides an in-situ lateral pressure and shear composite test device. By improving and upgrading the existing lateral pressure test device, it can carry out direct shear tests on in-situ sand layers on the basis of its original function of completing the lateral pressure test.

[0040] The device of the present invention is deeply buried in the sand layer, and the overall structure diagram of the device is as follows Figure 1 and Figure 2 As shown, from the functional point of view, it includes three major parts: in-situ soil shear box mechanism, positive stress loading mechanism and shear force loading and testing mechanism. From the structural point of view, it mainly includes lateral pressure device 1, upper cross plate 2, lifting ring 4, deformation expansion plate 5, fixing box 6, metal blade 8, etc.

[0041] Among them, the upper horizontal plate 2, the outer wall of the lateral pressure device 1, and the deformation expansion plate 5 are the main components of the in-situ soil shear box mechanism. The in-situ soil shear box mechanism is mainly used to form a thin-walled cylindrical in-situ soil layer, providing a test object for the in-situ direct shear test.

[0042] The lateral pressure gauge 1 and its associated pressure device are the primary components of the positive stress loading mechanism, which is primarily used to provide the positive compressive stress required for direct shear testing. Specifically, the present invention utilizes the lateral pressure gauge 1 and its associated pressure device to apply the positive compressive stress required for direct shear testing to the borehole sidewall, consistent with the loading process of the lateral pressure test.

[0043] The upper horizontal plate 2, the deformation expansion plate 5, and the traction device and tension sensor acting on the lifting ring 4 are the main components of the shear force loading and testing mechanism. The main function of the shear force loading and testing mechanism is to provide the shear force required for the direct shear test and complete the direct shear test.

[0044] In the present invention, the upper horizontal plate 2 is an annular structure, fixedly mounted on the upper end of the pressure gauge 1. Specifically, it can be a circular metal plate, fixedly mounted on the outer wall of the upper end of the pressure gauge by bolts or other fixing methods, and has no contact with the pressure gauge cavity. The number of lifting rings 4 is preferably multiple (two are selected in this embodiment), and they are symmetrically arranged on the upper surface of the upper horizontal plate 2 to ensure uniform acceptance. By applying traction to the lifting rings 4 through a traction device, the shear force required for the direct shear test can be provided. The figure also shows the connection line interface 3 of the pressure gauge 1, which is used to connect the pressure gauge 1 and its attached loading and measuring device.

[0045] For example, the traction device can be directly connected to the lifting ring 4, and a tension sensor is provided at the connection point (typically between the ring and the traction rope). The function of the tension sensor is to monitor the magnitude of the traction force in real time.

[0046] In the present invention, the deformable expansion plate 5 is fixedly mounted on the lower end of the pressure transmitter 1 and is also not in contact with the pressure transmitter cavity. It mainly includes an annular fixed box 6, which is fixedly mounted on the lower end of the pressure transmitter 1. Its cross section is preferably annular, and the interior is used to install a motor. A rotating part is also mounted on the fixed box 6, and a plurality of metal blades 8 are mounted on the end face of the rotating part. Each metal blade 8 is evenly distributed in a single circle around the pressure transmitter cavity. The rotating part is driven to rotate by the motor inside the fixed box 6, and each metal blade 8 can be expanded with the rotation of the rotating part to achieve radial annular cutting (such as Figure 2 and Figure 4 As shown in the figure), a thin-walled cylindrical in-situ soil layer structure to be sheared is formed by radial annular cutting, and the structure is kept in an expanded state after the rotation stops, and is closed after the test is completed (as shown in the figure). Figure 1 and Figure 3As shown in FIG. 1 , the diameter of the side pressure device is close to that of the side pressure device in the folded state, and can be folded by inverting. The end surface here refers to the upper end surface or the lower end surface. In the embodiment of the present invention, the upper end surface is used.

[0047] According to the above structure, through the above three aspects of the structural system, the shear strength test of the original sand layer inside the borehole can be achieved.

[0048] The metal blades 8 of the present invention can be expanded and retracted in various ways, and two feasible solutions are provided in the embodiment of the present invention.

[0049] In the first embodiment, the rotating portion comprises multiple vertical fixed tubes 7, each arranged in a single annular loop around the pressure relief chamber and inserted into a fixed housing 6 for installation. Each tube 7 maintains a certain radial distance from both the pressure relief chamber and the outer edge of the fixed housing 6. The end of each tube 7 (the upper end in this embodiment) extends a certain distance beyond the end face of the fixed housing 6 and is fitted with a metal blade 8. Driven by a motor within the fixed housing 6, each tube 7 rotates about its own axis, with the same rotational speed and direction. The rotation of each tube 7 causes the corresponding metal blade 8 to expand and cut into the soil.

[0050] In the second scheme, the rotating part is a bearing structure installed between the inner ring of the fixed box 6 and the pressure relief chamber. The end of the bearing structure (the upper end in this embodiment) extends a certain distance from the fixed box 6 and is installed with multiple metal blades 8. The bearing structure rotates under the drive of the motor in the fixed box 6, and each metal blade 8 is unfolded and cuts into the soil as it rotates.

[0051] In the above solution, the metal blades 8 are arc-shaped, and their curvature, width and length are such that they extend beyond the outer edge of the fixed box 6 when extended, and do not extend beyond the outer edge of the fixed box 6 when retracted. When extended, the metal blades 8 are stacked one after another to form a ring that extends beyond the outer edge of the fixed box 6. When retracted, the metal blades 8 are stacked one after another to form a ring that does not extend beyond the outer edge of the fixed box 6 and does not collide or contact with the fixed tube 7. Figure 5 and Figure 6 As shown. The material stiffness of the metal blade 8 should be much greater than the soil stiffness to ensure that the metal blade does not deform significantly during loading. Steel can be selected. In solution 1, the fixed pipe 7 and the metal blade 8 can be an integrated structure.

[0052] The specific installation method of the metal blade 8 and the fixed tube 7 or the bearing structure is the existing technology. You can refer to the folding / expanding fan blades in the existing technology, such as patents CN206860502U, CN211666918U, CN204646788U, CN209261876U, etc., all of which can realize the blade expansion / contraction function of the present invention.

[0053] In one embodiment of the present invention, reference Figure 7 、 Figure 8 and Figure 9 As shown, Figure 7 The internal form of the deformed expansion plate 5 is shown. A fixed pipe connecting plate 9 is provided around the fixed pipes 7 arranged in a ring. The structure of the single-piece fixed pipe connecting plate 9 is as shown in FIG. Figure 8 As shown, it is an arc-shaped plate with both ends extending toward the center of the ring, with connecting holes provided at both ends, and the middle connecting part of the arc-shaped plate can be a broken line type, that is, Figure 8 The part shown is close to the center of the ring, while the other part is far away from the center of the ring, forming an asymmetrical shape. The two adjacent fixed pipe connecting plates 9 are connected by a support rod passing through the connecting holes at the adjacent ends. Figure 9 As shown. The support rod is parallel to the length direction of the fixed tube 7 and has a connection relationship. Therefore, when the fixed tube 7 rotates, it can drive the support rod to rotate, and at the same time drive the corresponding fixed tube connecting plate 9 to move, and finally realize linkage to ensure that each metal blade 8 moves neatly. It is worth noting that in the present invention, the fixed tube 7 only needs to rotate at a certain angle, and does not need to rotate a large range or even 360°. For example, the metal blade 8 is fixedly installed at one end of the fixed tube 7. When the fixed tube 7 is reset, that is, the rotation angle is 0, each metal blade 8 is in its first position, that is, the retracted position, as shown in FIG. Figure 3 When the fixed tube 7 is reset, that is, the rotation angle is α (such as 15 to 45 degrees), each metal blade 8 is in its second position, that is, the expanded position, as shown. Figure 4 、 Figure 5 Shown, this moment, fixed pipe 7 can be fixed, also is about to each metal blade 8 is fixed in its unfolded position. After this, when reversing α, fixed pipe 7 resets, and each metal blade 8 is positioned at its first position, also is the stowed position.

[0054] The specific steps of using the device of the present invention to conduct an in-situ lateral pressure and shear composite test are as follows:

[0055] Step 1: Use undisturbed soil as the test soil. Use drilling equipment to excavate a test hole in the test soil. Expand the upper part of the test hole to the required test depth and remove the excess soil at the bottom of the expanded hole. The expanded hole diameter should be slightly larger than the diameter of the upper cross plate 2, but not too large to avoid reducing the overburden stress of the surrounding soil and causing the test results to be smaller. For example, a 10 cm increase is sufficient. The test depth area should not overlap with the area of ​​the lateral pressure test that has been conducted, and it is necessary to ensure that the test soil is undisturbed.

[0056] 2. Connect the device to the lifting equipment through the lifting ring 2, lift the test device, and bury it in the expanded test hole, ensuring that the upper horizontal plate 2 of the device is in full contact with the bottom surface of the expanded hole.

[0057] 3. Start the motor to make the metal blade 8 rotate counterclockwise and expand to cut into the soil (see Figure 5 ). After each metal blade 8 is fully unfolded, the motor is turned off.

[0058] 4. Convert the direct shear normal stress required for the direct shear test into the lateral pressure value provided by the lateral pressure gauge 1. Use the lateral pressure gauge 1 to pressurize the inner wall of the test hole and record the relationship curve between the lateral pressure and deformation during the loading process.

[0059] 5. Use the traction device to lift the test device upward as a whole, set the pulling force to the sum of the gravity of the test device and the test soil, and record this state as the initial state of the test. The pulling force at this time is the initial pulling force.

[0060] 6. Apply a pulling force to the test device in stages. The magnitude of the pulling force at each stage is controlled according to a fixed proportion of the positive pressure (typically 10%). Record the pulling force applied at each stage and the corresponding pulling height. When the deformation increases sharply during the pulling process or the pulling height reaches the set threshold (typically 10% of the distance between the lower end of the upper cross plate 2 and the upper end of the deformation expansion plate 5), the soil is considered to be damaged, and the pulling force at this time is recorded as the damaging pulling force.

[0061] 7. Release the pressure in the bypass pressure vessel 1.

[0062] 8. Pull the test device out of the ground, take photos of the soil failure surface (i.e., the interface between the soil sheared out with the test device and the soil on the side wall of the test hole after the test), and check to confirm whether the deployment state of the metal blade 8 is normal to determine whether the test is valid.

[0063] 9. Remove the soil from the equipment (i.e., the soil between the upper horizontal plate 2, the outer wall of the lateral pressure device, and the deformation expansion plate 5, which was sheared and pulled out with the test device). Start the motor to rotate the blades clockwise and retract them into the deformation expansion plate. Turn off the motor, and the test is complete.

Claims

1. An in-situ lateral pressure and shear composite test device, characterized in that: The invention comprises a pressure gauge (1), wherein the pressure gauge (1) applies a normal compressive stress required for a direct shear test to the side wall of a borehole; an annular upper horizontal plate (2) is fixedly mounted on the upper end of the pressure gauge (1), and a deformation expansion plate (5) is mounted on the lower end; a plurality of symmetrical lifting rings (4) are provided on the upper surface of the upper horizontal plate (2), and a traction force is applied to the lifting rings (4) by a traction device to provide the shear force required for the direct shear test; the deformation expansion plate (5) comprises an annular fixed box (6), which is fixedly mounted on the lower end of the pressure gauge (1) and has a rotating part thereon, and a plurality of metal blades (8) distributed around the pressure gauge cavity are mounted on the end surface of the rotating part, and the metal blades (8) are expanded as the rotating part rotates to achieve radial annular cutting, and remain in an expanded state after the rotation stops, and are retracted after the test is completed; The rotating part is composed of a plurality of vertical fixed tubes (7), each fixed tube (7) is arranged in a single ring around the lateral pressure chamber, each fixed tube (7) can rotate around its tube axis under the drive of the motor in the fixed box (6), and a metal blade (8) is installed at the end of each fixed tube (7). Each fixed tube (7) has the same rotation speed and rotation direction, and the rotation of each fixed tube (7) drives each corresponding metal blade (8) to expand and cut into the soil; The metal blade (8) is arc-shaped, and its arc, width and length are such that it exceeds the outer edge of the fixed box (6) when unfolded, and does not exceed the outer edge of the fixed box (6) when folded; The metal blades (8) are stacked in sequence when unfolded to form a ring that extends beyond the outer edge of the fixed box (6); and the metal blades (8) are stacked in sequence when folded to form a ring that does not extend beyond the outer edge of the fixed box (6) and does not contact the fixed tube (7).

2. The in-situ lateral pressure and shear composite test device according to claim 1, characterized in that: The upper horizontal plate (2) is a circular metal plate, fixedly mounted on the outer wall of the upper end of the pressure transmitter, and has no contact with the pressure transmitter cavity.

3. The in-situ lateral pressure and shear composite test device according to claim 1 or 2, characterized in that: The traction device is connected to the lifting bail (4), and a tension sensor is provided at the connection.

4. The in-situ lateral pressure and shear composite test device according to claim 1, characterized in that: The rotating part is a bearing structure installed between the inner ring of the fixed box (6) and the pressure relief chamber. A plurality of metal blades (8) are installed at the end of the bearing structure. The bearing structure rotates under the drive of the motor in the fixed box (6). The metal blades (8) are unfolded and cut into the soil as they rotate.

5. The test method based on the in-situ lateral pressure and shear composite test device according to claim 1 is characterized in that: The steps include: Step 1: Using undisturbed soil as the test soil, excavate a test hole in the test soil, and expand the upper part of the test hole to the required depth for the test; the expanded hole diameter is slightly larger than the diameter of the upper horizontal plate (2); Step 2: Lift the test device and bury it in the expanded test hole, ensuring that the upper horizontal plate (2) is in full contact with the bottom surface of the expanded hole; Step 3: Start the motor to drive the metal blade (8) in the retracted state to rotate and expand to cut into the soil; after the metal blade (8) is fully expanded, turn off the motor; Step 4: Convert the normal compressive stress required for the direct shear test into the lateral pressure value provided by the lateral pressure gauge, use the lateral pressure gauge (1) to pressurize the inner wall of the test hole, and record the relationship curve between the lateral pressure and deformation during the loading process; Step 5: Use the traction device to lift the entire test device upwards, set the pulling force to the sum of the gravity of the test device and the test soil, record this state as the initial state of the test, and the pulling force at this time as the initial pulling force; Step 6: Apply tension to the test device in stages. The magnitude of each stage of tension is controlled according to a fixed ratio of the positive pressure. The tension applied at each stage and the corresponding pull-up height are recorded until a sharp increase in deformation occurs during the pull-up process or the pull-up height reaches a set threshold. This is considered to be soil failure, and the tension at this time is recorded as the failure tension. Step 7: Release the pressure in the pressure relief valve (1); Step 8: Pull the test device out of the ground, take photos of the soil damage surface, and check whether the metal blade (8) is in a normal state of deployment to determine whether the test is effective. Step 9: Remove the soil in the equipment, start the motor, and rotate it in the reverse direction to retract the metal blades (8); turn off the motor, and the test is over.

6. The test method according to claim 5, characterized in that: The diameter of the expanded hole is 10 cm larger than the diameter of the upper horizontal plate (2).

7. The test method according to claim 5, characterized in that: The fixed ratio is 10%; the set threshold is 10% of the distance between the lower end of the upper horizontal plate (2) and the upper end of the deformed expansion plate (5).

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