Air pressure shear type soil strength testing device and method for drilling experiment

Abstract

The present invention belongs to the technical field of engineering geological exploration, and specifically discloses a pneumatic shearing soil strength testing device and method for drilling experiments, wherein the device comprises an extension component and a shearing component slidably connected to the extension component, wherein the shearing component comprises a plurality of limiting cylinders, a pneumatic shearing structure corresponding to the number of limiting cylinders, and a retractable lateral force application structure; the extension component extends into the borehole; each limiting cylinder is slidably connected to the extension component and is located at the annular soil body in the borehole; each lateral force application structure is arranged on the outer wall of the limiting cylinder, and is used to cut the annular soil body into blocks to be sheared when in the extended state and to apply a horizontal normal force to the blocks to be sheared; each pneumatic shearing structure is arranged below the corresponding block to be sheared, and is used to apply a vertical shearing force to the block to be sheared that bears the horizontal normal force, and the plurality of pneumatic shearing structures shear each block to be sheared one by one under the gradually increasing horizontal normal force. The present invention can quickly and accurately obtain the shear strength parameters of the soil body.

Description

Technical Field

[0001] The invention discloses a gas pressure shearing type soil strength testing device and method for drilling experiments, 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 soil strength testing device and method for drilling experiments, so as 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 soil strength testing device for drilling experiments, comprising an extension component and a shear component slidably connected to the extension component, the shear component comprising a plurality of limit cylinders, a pneumatic shear structure corresponding to the number of the limit cylinders, and a retractable lateral force structure; the extension component extends into the borehole along the axis of the borehole; each limit cylinder is slidably connected to the extension component and is located at the annular soil in the borehole; each lateral force structure is arranged on the outer wall of the limit cylinder, and is used to cut the annular soil into blocks to be sheared and apply horizontal normal force to the blocks to be sheared when in an extended state; each pneumatic shear structure is arranged below the corresponding block to be sheared, and is used to apply a vertical shear force to the corresponding block to be sheared that is subjected to the horizontal normal force, and the plurality of pneumatic shear structures shear each block to be sheared one by one under a gradually increasing horizontal normal force.

[0006] Preferably, the lateral force structure includes a retractable limit member and a lateral force member; the retractable limit member is arranged on the outer wall of the limit cylinder and is retracted along the outer wall of the limit cylinder, and is used to cut the annular soil into blocks to be cut when it is in an extended state; the lateral force member is arranged at one end of the limit cylinder close to the annular soil body, and is used to apply a horizontal normal force to the blocks to be cut.

[0007] Preferably, the retractable limiting member includes a driving member, two side limiting plates and an upper limiting plate; the plate surfaces of the two side limiting plates are parallel to the axis of the drilled hole; the plate surface of the upper limiting plate is perpendicular to the axis of the drilled hole; the two side limiting plates are connected to the upper limiting plate to form a three-sided encirclement structure and cover the limiting cylinder when in the retracted state; the driving member is fixed on the outer wall of the limiting cylinder, and the driving end of the driving member is connected to the encirclement structure, which is used to drive the encirclement structure to retract and retract along the outer wall of the limiting cylinder.

[0008] Preferably, the lateral force applying member includes a lateral pressure bottle and a lateral rubber bag; the lateral pressure bottle is connected to the lateral rubber bag and is used to inflate the lateral rubber bag; the lateral rubber bag is located in the three-sided enclosed structure in the extended state, and is used to apply horizontal normal force to the block to be sheared.

[0009] Preferably, the pneumatic shearing structure comprises a vertical pressurized bottle and a vertical rubber bag; the vertical pressurized bottle is connected to the vertical rubber bag for inflating the vertical rubber bag; the vertical rubber bag is arranged below the corresponding block to be sheared, for applying a vertical shearing force to the corresponding block to be sheared that is subjected to a horizontal normal force.

[0010] Preferably, it also includes a retractable hole-forming component; the hole-forming component replaces the shearing component and is fixedly connected to the extension component, and the hole-forming component is used to cut the hole wall of the drill hole to obtain the annular soil body.

[0011] Preferably, the hole-forming assembly comprises an upper hole-forming structure and a lower hole-forming structure sequentially arranged along the extension assembly; the upper hole-forming structure and the lower hole-forming structure comprise a hole-forming plate, a retractable blade fixed on the hole-forming plate, and a hole-forming driver;

[0012] 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.

[0013] A second aspect of the present invention provides a pneumatic shearing soil strength testing method for a drilling experiment. The method is based on the pneumatic shearing soil strength testing device for a drilling experiment, and comprises:

[0014] Step 1: Cut the annular soil into a plurality of blocks to be sheared, and apply an equal horizontal normal force to each of the blocks to be sheared.

[0015] Step 2: Apply shear force to one of the blocks to be sheared until the shearing is completed.

[0016] Step 3: Apply a horizontal normal force equal to and greater than the previous one to each of the blocks to be sheared, then apply a shear force to the next block to be sheared until shearing is completed, and repeat this step until shearing of all blocks to be sheared is completed.

[0017] Preferably, after step 3, the method further comprises:

[0018] Step 4: Draw a relationship curve between horizontal normal stress and shear strength based on the corresponding horizontal normal stress and the obtained shear strength after all the blocks to be sheared are sheared.

[0019] Step 5: Determine the cohesion and internal friction angle of the annular soil body according to the relationship curve.

[0020] Preferably, the criterion for determining the completion of shearing in step 3 is that the pressure of the vertical rubber bag remains unchanged or the height change of the vertical rubber bag is equal to a preset threshold; the height of the vertical rubber bag is determined according to the volume and cross-sectional area of ​​the vertical rubber bag.

[0021] Compared with the prior art, the pneumatic shear type soil strength testing device and method for drilling experiments of the present invention have the following beneficial effects:

[0022] The shearing assembly of the present invention is composed of a plurality of shearing units, each of which includes a stopper, a pneumatic shearing structure and a retractable lateral force application structure. The plurality of shearing units are symmetrically arranged around the extension assembly, thereby ensuring that in the process of shearing each block to be sheared one by one under a gradually increasing horizontal normal force, each application of the horizontal normal force can achieve a balance, thereby ensuring the stability of the entire test device and thus ensuring the accuracy of the obtained shearing parameters.

[0023] The testing device of the present invention can obtain accurate shear parameters of the same soil layer under different horizontal normal forces, and then determine the internal friction angle and cohesion of the soil according to the shear parameters, and can quickly and accurately obtain various types of soil parameters.

[0024] The present invention uses an extension component to drive the shearing component to move to the annular soil body in the borehole for subsequent shearing operations. It has a simple structure and good stability and can obtain shearing parameters of annular soil bodies corresponding to soil layers at different depths, which is convenient and quick. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic structural diagram of a pneumatic shear type soil strength testing device for drilling experiments using a shear assembly according to an embodiment of the present invention.

[0026] Figure 2 It is a schematic structural diagram of a pneumatic shear type soil strength testing device for drilling experiments using a drilling assembly according to an embodiment of the present invention.

[0027] Figure 3 It is a schematic diagram of the enclosed structure in a retracted state in an embodiment of the present invention.

[0028] Figure 4 It is a schematic diagram of the enclosed structure in an extended state according to an embodiment of the present invention.

[0029] Figure 5 Schematic diagram of the lower hole-forming structure in an embodiment of the present invention.

[0030] In the figure: 1 is a limit cylinder; 2 is a drill hole; 3 is an annular soil body; 4 is a supporting structure; 5 is a main controller; 6 is an extension rod; 7 is a side limit plate; 8 is an upper limit plate; 9 is a lateral pressure bottle; 10 is a lateral rubber bag; 11 is a pressure controller; 12 is a vertical pressure bottle; 13 is a vertical rubber bag; 14 is an upper hole-forming structure; 15 is a lower hole-forming structure; 16 is a hole-forming plate; 17 is a retractable blade; 18 is a shear plate; 19 is a block to be sheared. DETAILED DESCRIPTION

[0031] 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.

[0032] A first aspect of an embodiment of the present invention provides a Figures 1 to 5 The pneumatic shear type soil strength testing device for drilling experiments shown in the figure comprises an extension component and a shear component slidably connected to the extension component, wherein the shear component comprises a plurality of limit cylinders 1, a pneumatic shear structure corresponding to the number of the limit cylinders 1, and a retractable lateral force structure; the extension component extends into the borehole 2 along the axis of the borehole 2; each limit cylinder 1 is slidably connected to the extension component and is located at the annular soil 3 in the borehole 2; each lateral force structure is arranged on the outer wall of the limit cylinder 1, and is used to cut the annular soil 3 into blocks to be sheared 19 and apply horizontal normal force to the blocks to be sheared 19 when in the extended state; each pneumatic shear structure is arranged below the corresponding block to be sheared 19, and is used to apply vertical shear force to the corresponding block to be sheared 19 that is subjected to the horizontal normal force, and the plurality of pneumatic shear structures shear each block to be sheared 19 one by one under the gradually increasing horizontal normal force.

[0033] The extension assembly includes a support structure 4 and an extension structure, wherein the support structure 4 is arranged at the borehole 2, and the extension structure is arranged on the support structure 4. The extension structure includes a master controller 5 and an extension rod 6, and the extension rod 6 extends into the borehole 2 and coincides with the axis of the borehole 2, and the shear assembly is slidably connected to the extension rod 6.

[0034] The embodiment of the present invention uses an extension component to drive the shearing component to move to the annular soil 3 in the borehole 2 for subsequent shearing operations. It has a simple structure, good stability, and can obtain the shearing parameters of the annular soil 3 corresponding to soil layers at different depths, which is convenient and fast. The shearing component of the embodiment of the present invention is composed of a plurality of shearing units, each of which includes a limit cylinder 1, a pneumatic shearing structure, and a retractable lateral force structure. For example, the number of shearing units can be 4 to 6, preferably 4. The above-mentioned multiple shearing units are symmetrically arranged around the extension component, so as to ensure that in the process of shearing each block 19 to be sheared one by one under the gradually increasing horizontal normal force, each application of the horizontal normal force can achieve balance, ensure the stability of the entire test device, and then ensure the accuracy of the obtained shearing parameters. The test device of the embodiment of the present invention can obtain accurate shearing parameters of the same soil layer under different horizontal normal forces, and then determine the internal friction angle and cohesion of the soil according to the shearing parameters, and can quickly and accurately obtain various types of parameters of the soil.

[0035] The lateral force structure in the embodiment of the present invention includes a retractable limit member and a lateral force member; wherein the retractable limit member is arranged on the outer wall of the limit cylinder 1, and is retracted along the outer wall of the limit cylinder 1, and is used to cut the annular soil body 3 into blocks to be cut 19 when it is in the extended state; the lateral force member is arranged at one end of the limit cylinder 1 close to the annular soil body 3, and is used to apply a horizontal normal force to the blocks to be cut 19.

[0036] Exemplarily, the limiting cylinder 1 is placed horizontally so that the axis of the limiting cylinder 1 is in a horizontal state. At this time, the telescopic limiting member is set on the outer wall of the limiting cylinder 1. When the telescopic limiting member extends along the outer wall of the limiting cylinder 1, the annular soil body 3 is cut into the block 19 to be cut. At this time, the telescopic limiting member is kept stationary. Since the lateral force member is set at one end of the limiting cylinder 1 close to the annular soil body 3, the lateral force member can only apply a horizontal normal force to the block 19 to be cut, and then the pneumatic shear structure can be combined to perform shearing. In the lateral force structure of the embodiment of the present invention, the telescopic limiting member and the lateral force member cooperate with each other to obtain the best cutting and force application effect.

[0037] The above-mentioned retractable limit member includes a driving member, two side limit plates 7 and an upper limit plate 8; wherein the plate surfaces of the two side limit plates 7 are parallel to the axis of the drill hole 2, and the plate surface of the upper limit plate 8 is perpendicular to the axis of the drill hole 2, and the two side limit plates 7 are connected to the upper limit plate 8 to form a three-sided encirclement structure and cover the limit tube 1 when in the retracted state; wherein the driving member is fixed on the outer wall of the limit tube 1, and the driving end of the driving member is connected to the encirclement structure, which is used to drive the encirclement structure to retract and retract along the outer wall of the limit tube 1.

[0038] In order to minimize the impact on the annular soil body 3 during the cutting process, the enclosing structure of the embodiment of the present invention is provided with a blade angle on one side close to the annular soil body 3 .

[0039] The present invention uses a three-sided enclosed structure to cut the annular soil body 3, and when the block to be sheared 19 is obtained and the pneumatic shearing structure is used, the block to be sheared 19 can be protected. The shearing assembly of the present application is slidably connected to the extension assembly, so during the shearing process, the limit cylinder 1, the retractable lateral force structure and the block to be sheared 19 will be displaced as a whole or the pressure of the pneumatic shearing structure will remain unchanged, thereby completing the shearing.

[0040] The lateral force applying member of the embodiment of the present invention comprises a lateral pressure bottle 9 and a lateral rubber bag 10; the lateral pressure bottle 9 is arranged on the ground around the borehole 2, and the lateral pressure bottle 9 is connected to the lateral rubber bag 10, and is used to inflate the lateral rubber bag 10; the lateral rubber bag 10 is located in the three-sided enclosed structure in the extended state, and is used to apply a horizontal normal force to the block to be sheared 19. Exemplarily, when there are 4 shearing units, the shape of the lateral rubber bag 10 of the embodiment of the present invention is an octagonal ring, which matches the shape of the corresponding block to be sheared 19.

[0041] The pneumatic shearing structure of the embodiment of the present invention comprises a vertical pressurizing bottle 12 and a vertical rubber bag 13; the vertical pressurizing bottle 12 is arranged on the ground around the borehole 2, and the vertical pressurizing bottle 12 is connected to the vertical rubber bag 13, and is used to inflate the vertical rubber bag 13; the vertical rubber bag 13 is arranged below the corresponding block to be sheared 19, and is used to apply a vertical upward shearing force to the corresponding block to be sheared 19 that bears the horizontal normal force. Exemplarily, when there are 4 shearing units, the shape of the lateral rubber bag 10 of the embodiment of the present invention is an octagonal ring, which matches the shape of the corresponding block to be sheared 19.

[0042] The embodiment of the present invention uses a pressure controller to control the inflation amount of the lateral pressure bottle 9 and the vertical pressure bottle 12 to the corresponding rubber bag.

[0043] The present invention uses the vertical rubber bag 13 to apply shear force to the block to be sheared 19, and the force is applied more evenly and stably, thereby improving the accuracy of the obtained shear parameters. In order to further improve the accuracy and stability of the force applied by the vertical rubber bag 13, the embodiment of the present invention also provides a shear plate 18 at the bottom of the limiting cylinder 1 to limit the vertical rubber bag 13 laterally.

[0044] 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 component; wherein the hole-forming component replaces the shearing component and is fixedly connected to the extension component, and the hole-forming component is used to cut the hole wall of the borehole 2 to obtain the annular soil body 3, and then the hole-forming component is disassembled, and the shearing component is assembled to perform shearing. The above-mentioned hole-forming component includes an upper hole-forming structure 14 and a lower hole-forming structure 15 arranged in sequence along the extension component; the upper hole-forming structure 14 and the lower hole-forming structure 15 both include a hole-forming plate 16, a retractable blade 17 fixed on the hole-forming plate 16, and a hole-forming driver, such as Figure 5 The hole forming driver is fixed at the center of the hole forming plate 16, and the retractable blade 17 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 17 to rotate in a circle.

[0045] The embodiment of the present invention uses the upper hole-forming structure 14 and the lower hole-forming structure 15 to cut simultaneously, thereby reducing stress concentration that may be generated during single cutting, thereby reducing the impact on the soil.

[0046] The retractable blade 17 comprises a circumferential telescopic structure and a plurality of blades surrounding the circumferential telescopic structure and fixedly connected thereto, and the movement path of the blades is the radial direction of the circumferential telescopic structure.

[0047] A second aspect of the present invention provides a pneumatic shearing soil strength testing method for a drilling experiment. The method is based on the pneumatic shearing soil strength testing device for a drilling experiment, and comprises:

[0048] Step 1: Cut the annular soil body 3 into a plurality of blocks 19 to be sheared, and apply an equal horizontal normal force to each block 19 to be sheared.

[0049] The method for obtaining the annular soil body 3 in the embodiment of the present invention is as follows: generate a borehole 2 in a flat area, arrange the extension component above the borehole 2, and assemble the retractable hole-forming component and the extension component. After the assembly is completed, ensure that the retractable blade 17 in the hole-forming component is in a retracted state, and then lower the hole-forming component to the depth to be measured with the help of the extension component, extend the retractable blade 17, and make the retractable blade 17 rotate to cut the soil body on the wall of the borehole 2. When cutting, control the hole-forming component to move upward or downward along the axis of the borehole 2 to expand the hole. The hole height is 3-5 cm, and an annular soil body 3 is obtained. The upper surface of the annular soil body 3 is located at The depth and lower surface of Depth.

[0050] After obtaining the annular soil body 3, disassemble the hole forming assembly, assemble the shear assembly and the extension assembly, and lower the shear assembly to The depth of the limiting cylinder 1 is set so that the upper and lower surfaces of the limiting cylinder 1 are kept level with the upper and lower surfaces of the annular soil body 3, and then a plurality of retractable limiting members are used to cut the annular soil body 3 into a plurality of blocks 19 to be cut and a plurality of lateral rubber bags 10 are inflated and pressurized to 50 kPa to apply a horizontal normal force to the corresponding blocks 19 to be cut.

[0051] Step 2: Apply shearing force to one of the blocks to be sheared 19 until the shearing is completed.

[0052] Exemplarily, the first vertical rubber bag is inflated and pressurized, and the pressurization rate is controlled so that the shear rate is maintained at 0.08 mm / min. When the pressure in the first vertical rubber bag drops suddenly or remains unchanged or the height changes by 6 mm, it is considered that the first block to be sheared is cut and the shearing is completed.

[0053] The height of the first vertical rubber bag is determined according to its volume and the area of ​​its cross section.

[0054] (1)

[0055] In the formula, is the height of the first vertical rubber bag; is the volume of the first vertical rubber bag; is the cross-sectional area of ​​the first vertical rubber bag.

[0056] In the above formula (1), Determined according to formula (2).

[0057] (2)

[0058] In the formula, is the amount of gas filled into the first vertical rubber bag, , is the volume of gas filled in the first vertical rubber bag, is the molar volume of the gas; is the molar gas constant; is temperature; is the pressure in the first vertical rubber bag.

[0059] Step 3: Apply a horizontal normal force equal to and greater than the previous one to each block 19 to be sheared, then apply a shear force to the next block 19 to be sheared until shearing is completed, and repeat this step until shearing of all blocks 19 to be sheared is completed.

[0060] Exemplarily, when there are 4 blocks 19 to be cut, step 3 is specifically as follows:

[0061] The four lateral rubber bags 10 are inflated and pressurized to 100 kPa, thereby applying a horizontal normal force of 100 kPa to the corresponding blocks 19 to be sheared.

[0062] The second vertical rubber bag is inflated and pressurized, and the pressurization rate is controlled so that the shear rate is maintained at 0.08mm / min. When the pressure in the second vertical rubber bag drops suddenly or remains unchanged or the height changes by 6mm, it is considered that the second block to be sheared is cut and the shearing is completed.

[0063] Then, the four lateral rubber bags 10 are inflated and pressurized to 200 kPa, thereby applying a horizontal normal force of 200 kPa to the corresponding blocks 19 to be sheared.

[0064] The third vertical rubber bag is inflated and pressurized, and the pressurization rate is controlled so that the shear rate is maintained at 0.08mm / min. When the pressure in the third vertical rubber bag drops suddenly or remains unchanged or the height changes by 6mm, it is considered that the third block to be sheared is cut and the shearing is completed.

[0065] Finally, the four lateral rubber bags 10 are inflated and pressurized to 400 kPa, thereby applying a horizontal normal force of 400 kPa to the corresponding blocks 19 to be sheared.

[0066] The fourth vertical rubber bag is inflated and pressurized, and the pressurization rate is controlled so that the shear rate is maintained at 0.08mm / min. When the pressure in the fourth vertical rubber bag drops suddenly or remains unchanged or the height changes by 6mm, it is considered that the fourth block to be sheared is cut and the shearing is completed.

[0067] The embodiment of the present invention adopts this shearing method, which can obtain accurate shear strength of the same soil layer under different horizontal normal forces while ensuring the stability of the device. It is easy to operate and has wide applicability.

[0068] The embodiment of the present invention further includes, after step 3:

[0069] Step 4: Draw a relationship curve between horizontal normal stress and shear strength according to the corresponding horizontal normal stress and the obtained shear strength after all the blocks 19 to be sheared are sheared.

[0070] Exemplarily, a relationship curve between the two is drawn based on 4 sets of horizontal normal stress and shear strength.

[0071] Step 5: Determine the cohesion and internal friction angle of the annular soil body 3 according to the relationship curve.

[0072] The relationship between horizontal normal stress, shear strength, cohesion and internal friction angle is:

[0073] (3)

[0074] In the formula, is the shear strength; is the horizontal normal stress; is the internal friction angle; For cohesion.

[0075] 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.

[0076] In the embodiment of the present invention, the above steps 1-5 can be repeated at different depths, so as to obtain the shear strength of soil at different depths, and then obtain the internal friction angle and cohesion of the corresponding soil.

[0077] 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.

[0078] 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 shear type soil strength testing device for drilling experiments, characterized in that: It comprises an extension component and a shearing component slidably connected to the extension component, wherein the shearing component comprises a plurality of limiting cylinders, a pneumatic shearing structure corresponding to the number of the limiting cylinders, and a retractable lateral force application structure; The extension assembly extends into the borehole along the axis of the borehole; Each limiting cylinder is slidably connected to the extension assembly and is located at the annular soil body in the borehole; Each lateral force-applying structure is arranged on the outer wall of the limiting cylinder, and is used to cut the annular soil into blocks to be cut and apply a horizontal normal force to the blocks to be cut when in an extended state; Each pneumatic shearing structure is arranged below the corresponding block to be sheared, and is used to apply a vertical shearing force to the corresponding block to be sheared which is subjected to a horizontal normal force. The multiple pneumatic shearing structures shear each block to be sheared one by one under a gradually increasing horizontal normal force. The lateral force applying structure includes a telescopic limiting member and a lateral force applying member; The retractable limiting member is arranged on the outer wall of the limiting cylinder and is retracted along the outer wall of the limiting cylinder, and is used to cut the annular soil body into blocks to be cut when in the extended state; The lateral force applying member is arranged at one end of the limiting cylinder close to the annular soil body, and is used to apply a horizontal normal force to the block to be sheared; The retractable limiting member comprises a driving member, two side limiting plates and an upper limiting plate; The plate surfaces of the two side limit plates are parallel to the axis of the drilled hole; The plate surface of the upper limit plate is perpendicular to the axis of the drill hole; The two side limit plates are connected to the upper limit plate to form a three-sided enclosed structure and cover the limit cylinder in the retracted state; The driving member is fixed on the outer wall of the limiting cylinder, and the driving end of the driving member is connected to the enclosing structure, and is used to drive the enclosing structure to extend and retract along the outer wall of the limiting cylinder; The lateral force applying member includes a lateral pressure bottle and a lateral rubber bag; The lateral pressure bottle is connected to the lateral rubber bag and is used to inflate the lateral rubber bag; The lateral rubber bag is located in the three-sided enclosed structure in the extended state, and is used to apply a horizontal normal force to the block to be sheared.

2. The pneumatic shear type soil strength testing device for drilling experiment according to claim 1 is characterized in that: The pneumatic shearing structure includes a vertical pressurizing bottle and a vertical rubber bag; The vertical pressurizing bottle is connected to the vertical rubber bag and is used to inflate the vertical rubber bag; The vertical rubber bag is arranged below the corresponding block to be sheared, and is used to apply a vertical shear force to the corresponding block to be sheared that bears the horizontal normal force.

3. The pneumatic shear type soil strength testing device for drilling experiments according to any one of claims 1 to 2, characterized in that: Also included is a retractable hole-forming assembly; The hole-forming component replaces the shearing component and is fixedly connected to the extension component. The hole-forming component is used to cut the hole wall of the drill hole to obtain the annular soil body.

4. The pneumatic shear type soil strength testing device for drilling experiment according to claim 3 is characterized in that: The hole-forming assembly comprises an upper hole-forming structure and a lower hole-forming structure sequentially arranged along the extension assembly; The upper hole-forming structure and the lower hole-forming structure 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, and the retractable blade is arranged around the hole-forming driver and is fixedly connected to the hole-forming driver.

5. A pneumatic shear soil strength test method for drilling experiments, characterized in that: The pneumatic shear type soil strength testing device for drilling experiments according to claim 2 comprises: Step 1: cutting the annular soil into a plurality of blocks to be sheared, and applying an equal horizontal normal force to each of the blocks to be sheared; Step 2, applying shear force to one of the blocks to be sheared until shearing is completed; Step 3, applying an equal horizontal normal force with a value greater than the previous one to each of the blocks to be sheared, and then applying a shear force to the next block to be sheared until the shearing is completed, and repeating this step until the shearing of all the blocks to be sheared is completed; Step 4: Draw a relationship curve between horizontal normal stress and shear strength according to the corresponding horizontal normal stress and the obtained shear strength after all the blocks to be sheared are sheared; Step 5: determining the cohesion and internal friction angle of the annular soil body according to the relationship curve; The standard for determining the completion of shearing in step 3 is that the vertical rubber bag pressure remains unchanged or the vertical rubber bag height change is equal to a preset threshold; The height of the vertical rubber bag is determined according to the volume and cross-sectional area of ​​the vertical rubber bag.

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