Pneumatic shearing type in-situ soil shear strength testing device and method

Abstract

The present invention belongs to the technical field of engineering geological exploration, and specifically discloses a pneumatic shearing type in-situ soil shear strength test device and method, the device includes a lateral force structure, an extension structure and a retractable pneumatic shearing structure; the lateral force structure is fixedly connected to the extension structure and is located at the annular soil in the borehole, and is used to apply a horizontal normal force to the annular soil; the pneumatic shearing structure is fixedly connected to the bottom end of the extension structure, and is used to apply a vertical upward shear force to the annular soil subjected to the horizontal normal force; the extension structure is used to drive the lateral force structure and the pneumatic shearing structure to synchronously move to the next layer or layers of annular soil deep in the borehole, so as to obtain the shear strength of each layer of annular soil under the horizontal normal force that increases layer by layer. The present invention can obtain the shear strength of soil at different depths in the same soil layer under different horizontal normal forces in one test process, and has a simple structure, convenient operation, and is easy to carry and install.

Description

Technical Field

[0001] The invention discloses a gas pressure shearing type in-situ soil shear strength testing device and method, belonging to the technical field of engineering geological exploration. Background Art

[0002] During the construction process, soil shear strength is an important parameter in the engineering geological survey stage, which affects the selection and design of the later foundation treatment plan. At present, there are two main methods for determining soil shear strength parameters: indoor shear test and in-situ shear test. Indoor tests often use direct shear test and triaxial test. The direct shear test has the advantages of simple equipment, convenient soil sample preparation and test operation, but it cannot strictly control the drainage conditions, resulting in inaccurate data results when measuring collapsible soil; triaxial test can better simulate the stress condition of soil in the stratum, and can accurately measure the change of pore water pressure during shear process, but the sample preparation is complicated and the operation is difficult, and the common pseudo-triaxial test is also difficult to imitate the stratum conditions well.

[0003] Compared with indoor shear tests, in-situ shear tests have the advantages of strong representativeness, low disturbance, and can truly and accurately reflect the actual situation of the project, which can greatly meet the needs of engineering design and disaster management. At present, the in-situ shear tests for determining the shear strength parameters of soil mainly include two methods: soil column shear method and in-hole pull-out method. The soil column shear method requires digging a test pit and leaving a soil column for shear test, which is time-consuming and labor-intensive, and can only test the surface soil, and cannot perform shear strength tests on collapsible soils at different depths; the in-hole pull-out method is to put the shear device close to the inner wall of the borehole, use the corresponding pressure device to apply normal stress to the hole wall, and then pull the entire shear device to obtain the interface parameters. Although the in-hole pull-out method makes up for the problem that the soil column shear method is difficult to obtain the shear strength parameters of deep soil, the parameters obtained are the interface shear strength parameters between the shear device and the soil, which have a certain gap with the actual shear strength parameters of the soil; and the in-hole pull-out method generates huge pressure on the base outside the hole, which is not conducive to the stability of the device, and the shear rate is also difficult to guarantee. Summary of the invention

[0004] The purpose of the present invention is to provide a pneumatic shear type in-situ soil shear strength testing device and method to solve the technical problems of inaccurate shear strength parameters, difficult to ensure shear rate and unstable device existing in the in-situ shear device corresponding to the in-hole pulling method in the prior art.

[0005] The first aspect of the present invention provides a pneumatic shear type in-situ soil shear strength testing device, comprising a lateral force structure, an extension structure and a retractable pneumatic shear structure; the lateral force structure is fixedly connected to the extension structure and is located at the annular soil in the borehole, and is used to apply a horizontal normal force to the annular soil; the height of the annular soil is 5cm~7cm, and the ring width is 2cm~3cm; the pneumatic shear structure is fixedly connected to the bottom end of the extension structure, and is used to apply a vertical upward shear force to the annular soil subjected to the horizontal normal force; the extension structure is used to drive the lateral force structure and the pneumatic shear structure to move synchronously to the next layer or layers of annular soil deep in the borehole, so as to obtain each layer of annular soil under the increasing horizontal normal force layer by layer. shear strength, wherein the next layer or layers of annular soil are in the same soil layer as the current annular soil, for example, they are all sandy soil layers or all clay soil layers; also includes a retractable hole-forming structure; the hole-forming structure replaces the pneumatic shear structure and is fixedly connected to the bottom end of the extension structure, the hole-forming structure is used to cut the hole wall of the drill hole to obtain the annular soil; the hole-forming structure includes an upper hole-forming module and a lower hole-forming module arranged in sequence along the extension structure; the upper hole-forming module and the lower hole-forming module both include a hole-forming plate, a retractable blade fixed on the hole-forming plate and a hole-forming driver; the hole-forming driver is fixed on the hole-forming plate, the retractable blade is arranged around the hole-forming driver, and is fixedly connected to the hole-forming driver.

[0006] Preferably, the pneumatic shearing structure includes a shell, a driver and a plurality of retractable shearing modules; the outer wall of the shell is fixedly connected to the bottom end of the extension structure; the driver is arranged in the shell and fixedly connected to the center position of the shell; the plurality of retractable shearing modules are arranged around the driver with the driver as the center, and are fixedly connected to the driver, so as to extend or retract the shell at the same time under the drive of the driver.

[0007] Preferably, each retractable shearing module comprises an unfolding plate and a shearing rubber bag arranged on the upper surface of the unfolding plate; the unfolding plate is fixedly connected to the driver, and the shearing rubber bag on the unfolding plate is in contact with the lower surface of the annular soil body when the unfolding plate is in an extended state.

[0008] Preferably, each retractable shear module further includes a shear air pipe, a shear pressurizing bottle and a pressure controller; one end of the shear air pipe is connected to the shear pressurizing bottle, and the other end is connected to the shear rubber bag; the pressure controller is arranged on the shear air pipe, and is used to control the pressure in the shear rubber bag.

[0009] Preferably, the lateral force-applying structure comprises a limiting cylinder and a force-applying rubber bag; the extending structure passes through the limiting cylinder along the central axis and is fixedly connected to the limiting cylinder; the force-applying rubber bag is coated on the outer wall of the limiting cylinder.

[0010] Preferably, the lateral force structure also includes a force air supply pipe, a force pressurizing bottle and a pressure controller; one end of the force air supply pipe is connected to the force pressurizing bottle, and the other end is connected to the force rubber bag; the pressure controller is arranged on the force air supply pipe, and is used to control the pressure in the force rubber bag.

[0011] Preferably, the extension structure includes a bracket, an extension rod and an extension controller; the bracket is arranged on the ground where the drill hole is located; one end of the extension rod is fixedly connected to the bracket, and the other end extends into the drill hole and is located on the axis of the drill hole; the extension controller is connected to the extension rod and is used to control the extension amount of the extension rod.

[0012] A second aspect of the present invention provides a pneumatic shearing type in-situ soil shear strength testing method, comprising:

[0013] Step 1: Use the above-mentioned pneumatic shear type in-situ soil shear strength testing device to obtain the shear strength of the annular soil in the borehole under the horizontal normal force.

[0014] Step 2: Move the pneumatic shear type in-situ soil shear strength testing device down to the next layer of annular soil to obtain the shear strength of the current annular soil under the horizontal normal force after adding a preset increment.

[0015] Step 3: Repeat step 2 for a preset number of times to obtain multiple sets of horizontal normal forces and shear strengths.

[0016] Preferably, after step 3, the method further includes:

[0017] Step 4: Draw a relationship curve between horizontal normal force and shear strength based on multiple sets of horizontal normal force and shear strength.

[0018] Step 5: Determine the cohesion and internal friction angle of the soil layers corresponding to the plurality of annular soil bodies according to the relationship curve.

[0019] Preferably, the shear completion standard for obtaining the shear strength is that the air pressure of the shear rubber bag in the air pressure shear structure remains unchanged or the height change of the shear rubber bag is equal to a preset threshold; the height of the shear rubber bag is determined according to the volume and cross-sectional area of ​​the shear rubber bag.

[0020] Compared with the prior art, the pneumatic shearing type in-situ soil shear strength testing device and method of the present invention have the following beneficial effects:

[0021] The pneumatic shearing type in-situ soil shear strength testing device of the present invention can obtain the shear strength of soil at different depths in the same soil layer under different horizontal normal forces during one test. The present invention uses a pneumatic shearing structure to shear the annular soil, and the force is more uniform. At the same time, the shear rate can be accurately determined according to the inflation amount, which greatly improves the accuracy of the obtained shear strength. The structure is simple, the operation is convenient, and it is easy to carry and install. Furthermore, the pneumatic shearing structure does not need to rely on the extension structure to provide the pulling force, which greatly reduces the burden of the extension structure, prolongs the service life of the extension structure, reduces the requirements for the site use and the layout process of the extension structure, and the stability of the entire device is better, and it can be used under more working conditions.

[0022] The present invention can determine the internal friction angle and cohesion of the soil layer according to the shear strength of soil at different depths in the same soil layer under different horizontal normal forces, and can quickly and accurately obtain various types of soil parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the overall structure of a pneumatic shear type in-situ soil shear strength testing device according to an embodiment of the present invention.

[0024] Figure 2 It is a schematic diagram of the structure in which the shearing module is retracted into the housing in an embodiment of the present invention.

[0025] Figure 3 It is a schematic diagram of the structure in which the shearing module extends out of the housing in an embodiment of the present invention.

[0026] Figure 4 Schematic diagram of circuit connection when the shearing module extends out of the housing in an embodiment of the present invention.

[0027] Figure 5 Schematic diagram of the use status of the pneumatic shear structure in the embodiment of the present invention.

[0028] Figure 6 Schematic diagram of the lower hole-forming module in an embodiment of the present invention.

[0029] Figure 7 1 and 10 are stress-strain curves of the annular soil body 3 obtained by using the device of the present invention and the indoor experimental device respectively when the horizontal normal force is 50 kPa in the embodiment of the present invention.

[0030] Figure 8 1 and 10. The stress-strain curves of the annular soil body 3 obtained by using the device of the present invention and the indoor experimental device respectively when the horizontal normal force is 100 kPa in the embodiment of the present invention.

[0031] Fig. 91 and 10 are stress-strain curves of the annular soil body 3 obtained by using the device of the present invention and the indoor experimental device respectively when the horizontal normal force is 200 kPa in the embodiment of the present invention.

[0032] Fig.10 1 and 10 are stress-strain curves of the annular soil body 3 obtained by using the device of the present invention and the indoor experimental device respectively when the horizontal normal force is 400 kPa in the embodiment of the present invention.

[0033] Fig.11 The figure is a relationship diagram between normal stress and shear strength obtained by using the device of the present invention and the indoor experimental device.

[0034] In the figure: 1 is a drilling hole; 2 is a hole expansion; 3 is an annular soil body; 4 is a force-applying rubber bag; 5 is a limit cylinder; 6 is a pneumatic shearing structure; 6-1 is a shell; 6-2 is a shearing module; 7 is an extension controller; 8 is an extension rod; 9 is a bracket; 10-1 is a shearing pressurizing bottle; 10-2 is a force-applying pressurizing bottle; 11 is a pressure controller; 12-1 is a shearing air pipe; 12-2 is a force-applying air pipe; 13 is a data line; 14 is a hole-forming plate; 15 is a retractable blade. DETAILED DESCRIPTION

[0035] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0036] A first aspect of an embodiment of the present invention provides a pneumatic shearing in-situ soil shear strength testing device, such as Figures 1 to 6 As shown, it includes a lateral force structure, an extension structure and a retractable pneumatic shear structure 6; the lateral force structure is fixedly connected to the extension structure and is located at the annular soil 3 in the borehole 1, and is used to apply a horizontal normal force to the annular soil 3; the height of the annular soil is 5cm~7cm, preferably 5cm, and the ring width is 2cm~3cm, preferably 2cm. The annular soil in this size range is more applicable and can ensure the convenience of the test process of the test device of the present invention and the accuracy of the results obtained; the pneumatic shear structure 6 is fixedly connected to the bottom end of the extension structure, and is used to apply a vertical upward shear force to the annular soil 3 that is subjected to the horizontal normal force; the extension structure is used to drive the lateral force structure and the pneumatic shear structure 6 to move synchronously to the next layer or multiple layers of annular soil 3 deep in the borehole 1, so as to obtain the shear strength of each layer of annular soil 3 under the horizontal normal force that increases layer by layer. The next layer or multiple layers of annular soil 3 are located in the same soil layer as the current annular soil 3, for example, both are sandy soil layers or both are clay soil layers.

[0037] In order to ensure that the state of the annular soil body 3 is close to the original state to the greatest extent, the embodiment of the present invention also includes a retractable hole-forming structure; wherein the hole-forming structure replaces the pneumatic shear structure and is fixedly connected to the bottom end of the extension structure. The hole-forming structure is used to cut the hole wall of the borehole 1 to obtain the annular soil body 3, and then disassemble the hole-forming structure, assemble the pneumatic shear structure and perform shearing. The above-mentioned hole-forming structure includes an upper hole-forming module and a lower hole-forming module sequentially arranged along the extension structure; the upper hole-forming module and the lower hole-forming module both include a hole-forming plate 14, a retractable blade 15 fixed on the hole-forming plate 14 and a hole-forming driver, the hole-forming driver is fixed at the center of the hole-forming plate 14, the retractable blade 15 is arranged around the hole-forming driver and is fixedly connected to the hole-forming driver, and the hole-forming driver is used to drive the retractable blade 15 to rotate in a circle, such as Figure 6 The embodiment of the present invention uses the upper hole-forming module and the lower hole-forming module to cut simultaneously, which reduces the stress concentration that may be generated during single cutting, thereby reducing the impact on the soil.

[0038] The retractable blade 15 comprises a circumferential retractable structure and a plurality of blades surrounding the circumferential retractable structure and fixedly connected thereto, and the movement path of the blades is the radial direction of the circumferential retractable structure.

[0039] The pneumatic shearing type in-situ soil shear strength testing device of the present invention can obtain the shear strength of soil at different depths in the same soil layer in one test process. The present invention uses the pneumatic shearing structure 6 to shear the annular soil 3, and the force is more uniform. At the same time, the shear rate can be accurately determined according to the inflation amount, which greatly improves the accuracy of the obtained shear strength. The pneumatic shearing structure 6 has a simple structure, is easy to operate, and is easy to carry and install. Furthermore, the pneumatic shearing structure 6 does not need to rely on the extension structure to provide the pulling force, which greatly reduces the burden of the extension structure, prolongs the service life of the extension structure, reduces the site requirements and the layout process of the extension structure, and the stability of the entire device is better, and it can be used under more working conditions.

[0040] In order to ensure the stability and controllability of the shearing process, the air pressure shearing structure 6 of the embodiment of the present invention is as follows: Figures 2 to 4 As shown, it includes a shell 6-1, a driver and a plurality of retractable shearing modules 6-2; the center of the outer wall of the shell 6-1 is fixedly connected to the bottom end of the extension structure; the driver is arranged in the shell 6-1 and is fixedly connected to the center position of the shell 6-1; a plurality of retractable shearing modules 6-2 are arranged around the driver with the driver as the center, and are fixedly connected to the driver, and are used to extend or retract the shell 6-1 at the same time under the drive of the driver.

[0041] The embodiment of the present invention uses a driver to realize the extension and retraction of multiple retractable shear modules 6-2, wherein the purpose of retraction is to facilitate the movement of the pneumatic shear structure 6 in the borehole 1, and it is extended only at the corresponding annular soil body 3, so that the upper surface of the shear module 6-2 is in contact with the lower surface of the annular soil body 3 for shearing.

[0042] Each retractable shear module 6-2 includes an expansion plate and a shear rubber bag arranged on the upper surface of the expansion plate; one end of the expansion plate is fixedly connected to the driver, and the shear rubber bag on the expansion plate is connected to the lower surface of the annular soil body 3 when the expansion plate is in the extended state. Multiple expansion plates enclose the shape of the annular soil body 3, such as Figure 5 shown.

[0043] The present invention uses a retractable shearing module 6-2 composed of a shearing rubber bag and an unfolding plate, which has a simple structure, is easy to operate, and has controllable shearing force.

[0044] Each of the retractable shear modules 6-2 further includes a shear air pipe 12-1, a shear pressurizing bottle 10-1 and a pressure controller 11; one end of the shear air pipe 12-1 is connected to the shear pressurizing bottle 10-1, and the other end is connected to the shear rubber bag; the pressure controller 11 is arranged on the shear air pipe 12-1, and is used to control the pressure of the shear rubber bag. The present invention uses the pressure controller 11 to accurately control the inflation amount and the pressure in the shear rubber bag, thereby accurately controlling the magnitude of the shear force.

[0045] The lateral force-applying structure of the embodiment of the present invention comprises a limiting cylinder 5 and a force-applying rubber bag 4; the extension structure passes through the central axis of the limiting cylinder 5 and is fixedly connected to the limiting cylinder 5; the force-applying rubber bag 4 is coated on the outer wall of the limiting cylinder 5. The lower surface of the limiting cylinder 5 of the present invention is in the same horizontal plane as the lower surface of the corresponding annular soil body 3. The force-applying rubber bag 4 coated on the outside of the limiting cylinder 5 can play a role in limiting the force-applying rubber bag 4, thereby ensuring that the force-applying rubber bag 4 can accurately and effectively apply force to the inner ring side of the annular soil body 3 after being inflated.

[0046] The lateral force structure further includes a force air pipe 12-2, a force pressurizing bottle 10-2 and a pressure controller 11; one end of the force air pipe 12-2 is connected to the force pressurizing bottle 10-2, and the other end is connected to the force rubber bag 4; the pressure controller 11 is arranged on the force air pipe 12-2, and is used to control the pressure in the force rubber bag 4. The present invention uses the pressure controller 11 to accurately control the inflation volume and the pressure in the force rubber bag 4, thereby accurately controlling the magnitude of the horizontal normal force. The pressure controller 11 can be the same as the pressure controller 11 in the shear module 6-2, that is, the shear module 6-2 and the lateral force structure share a pressure controller 11.

[0047] In order to ensure the structural stability of the pneumatic shear type in-situ soil shear strength test device of the present invention, the extension structure of the embodiment of the present invention includes a bracket 9, an extension rod 8 and an extension controller 7; the bracket 9 is arranged on the ground where the borehole 1 is located; one end of the extension rod 8 is fixedly connected to the bracket 9, and the other end extends into the borehole 1 and is located on the axis of the borehole 1; the extension controller 7 is connected to the extension rod 8 and is used to control the extension amount of the extension rod 8. The extension and shortening of the extension rod 8 are controlled by the extension controller 7, wherein the extension controller 7 is also connected to the driver in the pneumatic shear structure 6 through the data line 13, so as to control the driver.

[0048] The pneumatic shearing type in-situ soil shear strength testing device of the present invention has a simple structure and is easy to operate, and can quickly obtain accurate soil layer shear strength.

[0049] A second aspect of the present invention provides a pneumatic shearing type in-situ soil shear strength testing method, comprising:

[0050] Step 1: using the above-mentioned pneumatic shear type in-situ soil shear strength testing device to obtain the shear strength of the annular soil 3 in the borehole 1 under the horizontal normal force, specifically comprising:

[0051] Step 1.1, generate a borehole 1 in a flat area, and set multiple annular soil bodies 3 along the depth direction of the borehole 1, and the multiple annular soil bodies 3 are located in the same soil layer, specifically: generate a borehole 1 in a flat area, arrange the extension structure above the borehole 1, and assemble the retractable hole-forming structure at the bottom of the extension structure. After the assembly is completed, ensure that the retractable blade 15 in the hole-forming structure is in a retracted state, and then use the extension structure to lower the hole-forming structure to the depth to be measured, extend the retractable blade 15, and make the retractable blade 15 rotate to cut the soil on the wall of the borehole 1. When cutting, control the hole-forming structure to move upward or downward along the axis of the borehole 1 to obtain an expanded hole 2 with a hole height of 3-5cm, and obtain an annular soil body 3. The upper surface of the annular soil body 3 is located at The depth and lower surface of Depth.

[0052] Along the depth direction of the borehole, multiple annular soil bodies located in the same soil layer and at different depths are obtained according to the above method.

[0053] Step 1.2: After obtaining multiple annular soil bodies 3, disassemble the hole-forming structure, assemble the pneumatic shearing structure at the bottom of the extension structure, use the extension structure to move the lateral force structure and the retractable pneumatic shearing structure 6 to the top annular soil body, and then use the lateral force structure to apply a horizontal normal force to the top annular soil body. For example, the horizontal normal force is 50 kPa. After the horizontal normal force is applied stably, extend the expansion plate in the pneumatic shearing structure 6, and inflate the shearing rubber bag covered by the expansion plate to shear the top annular soil body until the shearing is completed, and obtain the shear strength of the top annular soil body.

[0054] The standard for the above shearing to be completed is that the air pressure of the shearing rubber bag in the air pressure shearing structure 6 remains unchanged or the height change of the shearing rubber bag is equal to a preset threshold; the height of the shearing rubber bag is determined according to the volume and cross-sectional area of ​​the shearing rubber bag.

[0055] For example, the shearing rubber bag is inflated and pressurized, and the pressurization rate is controlled so that the shearing rate is maintained at 0.08 mm / min. When the pressure in the shearing rubber bag drops suddenly or remains unchanged or the height changes to 6 mm, it is considered to be sheared and the shearing is completed.

[0056] The height of the shear rubber bag is determined according to its volume and cross-sectional area.

[0057] (1)

[0058] In the formula, is the height of the shear rubber bag; is the volume of the shear rubber bag; is the cross-sectional area of ​​the shear rubber bladder.

[0059] In the above formula (1), Determined according to formula (2).

[0060] (2)

[0061] In the formula, is the amount of gas filled in the shear rubber bag, , is the volume of gas filled in the shear rubber bag, is the molar volume of the gas; is the molar gas constant; is temperature; is the pressure in the shear rubber bag.

[0062] Step 2: Move the pneumatic shear type in-situ soil shear strength test device down to the next layer of annular soil to obtain the shear strength of the current annular soil under the horizontal normal force after adding a preset increment.

[0063] Exemplarily, after the lateral force structure and the retractable pneumatic shear structure 6 are moved to the next layer of annular soil using the extension structure, the horizontal normal force is applied to the annular soil using the lateral force structure, and the horizontal normal force is 100 kPa. After the horizontal normal force is applied stably, the expansion plate in the pneumatic shear structure 6 is extended, and the shear rubber bag wrapped outside the expansion plate is inflated to shear the annular soil until the shearing is completed, thereby obtaining the shear strength of the annular soil layer.

[0064] Step 3: Repeat step 2 for a preset number of times to obtain multiple sets of horizontal normal forces and shear strengths.

[0065] The number of predictions in the embodiment of the present invention is 2 times, and the horizontal normal force applied each time is twice the previous horizontal normal force, that is, the horizontal normal force applied to the third layer of annular soil is 200kPa, and the horizontal normal force applied to the fourth layer of annular soil is 400kPa.

[0066] The present invention can obtain the shear strengths corresponding to multiple groups of gradually increasing horizontal normal forces in the same soil layer in a set of test processes, which is quick and convenient.

[0067] Furthermore, after step 3, the method further includes:

[0068] Step 4: Draw a relationship curve between horizontal normal force and shear strength based on multiple sets of horizontal normal force and shear strength.

[0069] Step 5: Determine the cohesion and internal friction angle of the corresponding soil layers of multiple annular soil bodies according to the relationship curve.

[0070] The relationship between horizontal normal stress, shear strength, cohesion and internal friction angle is:

[0071] (3)

[0072] In the formula, is the shear strength; is the horizontal normal stress; is the internal friction angle; For cohesion.

[0073] According to the above formula (3), it can be determined that the intersection of the above relationship curve and the ordinate is the cohesion, and the slope is the internal friction angle.

[0074] In order to verify the effect of the device and method of the present invention, the results obtained are compared with those obtained in the indoor test as shown in Table 1 and Figures 7 to 11 Table 1 shows the stress-strain curve data of the annular soil body 3 obtained by using the device of the present invention and the indoor experimental device; Figure 7When the horizontal normal force is 50 kPa, the stress-strain curves of the annular soil body 3 obtained by using the device of the present invention and the indoor experimental device respectively; Figure 8 When the horizontal normal force is 100 kPa, the stress-strain curves of the annular soil body 3 obtained by using the device of the present invention and the indoor experimental device respectively; Fig. 9 When the horizontal normal force is 200 kPa, the stress-strain curves of the annular soil body 3 obtained by using the device of the present invention and the indoor experimental device respectively; Fig.10 When the horizontal normal force is 400 kPa, the stress-strain curves of the annular soil body 3 obtained by using the device of the present invention and the indoor experimental device respectively; Fig.11 The figure is a relationship diagram between normal stress and shear strength obtained by using the device of the present invention and the indoor experimental device.

[0075] Table 1 Stress-strain curve data

[0076]

[0077] Note: The criterion for stopping recording of stress-strain curve is that the shear stress does not change with the shear strain or the shear strain reaches the threshold or some data is recorded after a sudden drop in stress. Therefore, there is no data in some parts of the above table because the shear stress does not change with the shear strain or a sudden drop has occurred.

[0078] It can be seen from the stress-strain curve that the soil in the indoor test is brittle and will be destroyed when the strain is small (about 5%). The soil in the gas pressure shear test of the present invention is plastic and the shear stress will decrease when the strain is large. Because the annular shear surface of gas pressure shear is large, the change of shear surface has little effect on the experimental data, so the plastic failure characteristics of the soil are obvious. At the same time, the stability of the structure and the uniformity of the shear rate during the shearing process can ensure the accuracy of the data. This accurately reflects the stress process of soil destruction in the project, which is helpful for accurate engineering design, disaster prevention and control, and saving money.

[0079] The present invention can determine the cohesion and internal friction angle of the soil layer according to the shear strength corresponding to multiple groups of gradually increasing horizontal normal forces in the same soil layer. The determination method is simple and can quickly and accurately obtain parameters of various types of soil bodies.

[0080] The invention has reasonable design, simple device, low cost and easy operation, can perform shear strength test on soil bodies at different depths and has wide applicability.

[0081] The above are only several embodiments of the present invention and are not intended to limit the present invention in any form. Although the present invention is disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, using the above disclosed technical content to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A pneumatic shearing in-situ soil shear strength testing device, characterized in that: It includes a lateral force application structure, an extension structure and a retractable gas pressure shearing structure; The lateral force applying structure is fixedly connected to the extension structure and is located at the annular soil body in the borehole, and is used to apply a horizontal normal force to the annular soil body; the height of the annular soil body is 5 cm to 7 cm, and the ring width is 2 cm to 3 cm; The pneumatic shearing structure is fixedly connected to the bottom end of the extension structure and is used to apply a vertical upward shearing force to the annular soil body subjected to the horizontal normal force; The extension structure is used to drive the lateral force application structure and the pneumatic shear structure to move synchronously toward the next layer or layers of annular soil in the depth of the borehole, so as to obtain the shear strength of each layer of annular soil under the horizontal normal force that increases layer by layer; Also included is a retractable pore-forming structure; The hole-forming structure replaces the gas pressure shearing structure and is fixedly connected to the bottom end of the extension structure, and the hole-forming structure is used to cut the hole wall of the drill hole to obtain the annular soil body; The hole-forming structure comprises an upper hole-forming module and a lower hole-forming module sequentially arranged along the extension structure; The upper hole-forming module and the lower hole-forming module each include a hole-forming plate, a retractable blade fixed on the hole-forming plate, and a hole-forming driver; The hole-forming driver is fixed on the hole-forming plate, and the retractable blade is arranged around the hole-forming driver and is fixedly connected to the hole-forming driver; The pneumatic shearing structure comprises a housing, a driver and a plurality of retractable shearing modules; The outer wall of the shell is fixedly connected to the bottom end of the extension structure; The driver is disposed in the housing and fixedly connected to the center of the housing; The plurality of retractable shearing modules are arranged around the driver with the driver as the center and are fixedly connected to the driver, and are used to extend or retract into the housing at the same time under the drive of the driver; Each retractable shearing module comprises an unfolding plate and a shearing rubber bag arranged on the upper surface of the unfolding plate; The expansion plate is fixedly connected to the driver, and the shear rubber bag on the expansion plate is in contact with the lower surface of the annular soil body when the expansion plate is in the extended state; The extension structure includes a bracket, an extension rod and an extension controller; The support is arranged on the ground where the drilling hole is located; One end of the extension rod is fixedly connected to the bracket, and the other end extends into the drill hole and is located on the axis of the drill hole; The extension controller is connected to the extension rod and is used to control the extension amount of the extension rod.

2. The pneumatic shearing type in-situ soil shear strength testing device according to claim 1 is characterized in that: The lateral force-applying structure comprises a limiting cylinder and a force-applying rubber bag; The extension structure passes through the center axis of the limiting cylinder and is fixedly connected to the limiting cylinder; The force-applying rubber bag is coated on the outer wall of the limiting cylinder.

3. A pneumatic shearing in-situ soil shear strength test method, characterized in that: include: Step 1: using the pneumatic shear type in-situ soil shear strength testing device as claimed in claim 1 or 2 to obtain the shear strength of the annular soil in the borehole under horizontal normal force; Step 2: Move the pneumatic shear type in-situ soil shear strength test device down to the next layer of annular soil to obtain the shear strength of the current annular soil under the horizontal normal force after adding a preset increment; Step 3: Repeat step 2 for a preset number of times to obtain multiple sets of horizontal normal forces and shear strengths.

4. The pneumatic shearing in-situ soil shear strength testing method according to claim 3 is characterized in that: After step 3, the method further includes: Step 4, drawing a relationship curve between horizontal normal force and shear strength according to multiple groups of horizontal normal force and shear strength; Step 5: Determine the cohesion and internal friction angle of the soil layers corresponding to the plurality of annular soil bodies according to the relationship curve.

5. The pneumatic shearing in-situ soil shear strength testing method according to claim 3, characterized in that: The shear completion standard when obtaining the shear strength is that the air pressure of the shear rubber bag in the air pressure shear structure remains unchanged or the height change of the shear rubber bag is equal to a preset threshold; The height of the shear rubber bag is determined according to the volume and cross-sectional area of ​​the shear rubber bag.

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