A system and method for testing in-situ borehole shear strength of rock mass of underground engineering

Abstract

The application discloses a kind of underground engineering rock mass in situ borehole shear strength test system and method, belong to rock mass mechanics in situ test technical field.It is formed in the rock mass to be measured sequentially connected first hole section, second hole section and third hole section, annular bearing surface is formed between second hole section and third hole section, annular rock mass to be sheared is formed in the radial outside of second hole section;The shearing component of test device can be retracted through second hole section, and after being unfolded in third hole section, it is abutted to annular bearing surface;Normal loading mechanism applies radial normal load to second hole section hole wall, axial driving mechanism applies axial shear load to annular rock mass to be sheared by shearing component and annular bearing surface;Determine the cohesion and internal friction angle of rock mass by normal force, axial load and displacement data obtained under different normal load conditions;The application can reduce the local crushing caused by the pre-embedded hole wall of shearing member, and make the shearing region and axial bearing path more explicit.

Description

Technical Field

[0001] This invention relates to the field of in-situ testing technology for rock mechanics, specifically to a system and method for testing the in-situ borehole shear strength of rock masses in underground engineering. Background Technology

[0002] The cohesion and internal friction angle of rock mass are important fundamental parameters for stability analysis and support design in underground engineering, mine roadways, tunnels, water conservancy and hydropower projects, slope engineering, and underground energy storage projects. Indoor rock mechanics tests usually require core sampling from the engineering site and processing into standard specimens. Rock samples are prone to unloading, disturbance, and changes in water content during sampling, transportation, and processing, which may lead to differences between the test results and the in-situ state of the rock mass in the engineering project.

[0003] Traditional in-situ direct shear tests typically require cutting or excavating large-sized rock specimens on the rock mass surface and setting up reaction frames, normal loading equipment, and shear loading equipment. This results in problems such as large construction workload, long test cycle, high testing cost, and difficulty in conducting tests inside deep surrounding rock.

[0004] Existing borehole shear testing methods typically involve pressing a shear plate, shear teeth, or loading head into the borehole wall, followed by axial lifting to create relative movement between the loading component and the borehole wall rock. The actual shear depth and shear area obtained using this method are easily affected by the degree of loading component penetration, borehole wall roundness, rock hardness, and borehole wall fracture condition. In hard rock masses, the loading component may fail to reach the predetermined embedding depth, while in soft or fractured rock masses, localized crushing may occur, resulting in unclear measured shear area and failure boundaries.

[0005] Other techniques involve creating in-situ specimens by grooving the borehole wall, enlarging the borehole, or retaining rock columns. However, the in-hole loading devices of these techniques often struggle to penetrate the intermediate diameter reduction section and apply loads from the deep end face of the rock mass to be sheared. Furthermore, it is difficult to simultaneously apply controllable radial normal loads and axial shear loads to the rock mass to be sheared in small-diameter engineering boreholes. In addition, when different normal loads are repeatedly applied to the same section of the borehole wall for shear tests, the previous loading and failure can damage and disturb the subsequent test area, reducing the comparability of multi-level normal load test data.

[0006] Therefore, there is a need for an in-situ testing system and method that can sequentially prepare independent annular rock masses to be sheared along the borehole depth direction in the same borehole, establish a clear axial bearing path after the device is in place, apply a controllable radial normal load, and simultaneously acquire normal force, shear force, and displacement data. Summary of the Invention

[0007] Based on the above analysis, the present invention aims to provide an in-situ borehole shear strength testing system and method for underground engineering rock masses, in order to solve the problems in the prior art.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: This invention provides an in-situ borehole shear strength testing system for underground engineering rock masses, comprising a variable-diameter borehole formed within the rock mass to be tested and a testing device that cooperates with the variable-diameter borehole. The variable-diameter borehole is formed sequentially from the borehole opening to the bottom of the borehole along the borehole axis into a first borehole segment, a second borehole segment, and a third borehole segment. The inner diameter of the first borehole segment is larger than the inner diameter of the second borehole segment, and the inner diameter of the third borehole segment is larger than the inner diameter of the second borehole segment. An annular bearing surface is formed between the second borehole segment and the third borehole segment, and the rock mass to be tested radially outside the second borehole segment forms an annular rock mass to be sheared. The testing device includes: a central bearing seat, located within the second borehole section during testing; a shearing assembly, disposed on the central bearing seat and capable of switching between a retracted state and an extended state, capable of passing through the second borehole section when retracted and forming a bearing contact with the annular bearing surface when extended; an extension drive mechanism, movably disposed along the axial direction of the variable-diameter borehole, used to push the shearing assembly to extend it; an axial drive mechanism, connected to the central bearing seat, used to drive the central bearing seat to move along the borehole axial direction, so as to apply an axial shear load to the annular rock mass to be sheared through the extended shearing assembly and the annular bearing surface; and a normal loading mechanism, disposed on the central bearing seat and capable of moving radially outward, used to abut against the inner wall of the second borehole section and apply a radial normal load to the annular rock mass to be sheared.

[0009] Furthermore, the axial drive mechanism includes a traction rod and a support seat disposed on the orifice side of the first hole section. The support seat has a hollow channel through which the traction rod passes axially and can apply an axial load to the traction rod. The end of the central bearing seat opposite to the shearing assembly is detachably connected to a connecting seat, and the extension end of the traction rod is connected to the connecting seat.

[0010] Furthermore, the shearing assembly includes multiple shearing arms spaced apart circumferentially along the central support base. Each shearing arm has a force-bearing end, a shearing bearing end, and a rotating connection between the force-bearing end and the shearing bearing end. The central support base has multiple shearing arm supports spaced apart circumferentially. The rotating connection of each shearing arm is mounted to the corresponding shearing arm support via a rotating shaft. The force-bearing end and the shearing bearing end are located on opposite sides of the rotating connection, so that the shearing arm forms a lever structure with the rotating connection as the fulcrum. After the multiple shearing arms are deployed, the multiple shearing bearing ends are spaced apart circumferentially along the annular support surface. The inner diameter of the third hole section is larger than the maximum radial outer envelope diameter of the multiple shearing arms when they are in the deployed state, so as to provide radial space for the multiple shearing arms to deploy within the third hole section and rotate to the retracted state.

[0011] Furthermore, the unfolding drive mechanism includes an axial telescopic rod, one end of which is provided with a push plate, and the other end with a limiting part; the central bearing seat is provided with an axially connected axial limiting cavity and an axial hydraulic cavity, the rod is axially movable and passes through the axial limiting cavity, the limiting part is slidably connected to the inner cavity of the axial hydraulic cavity and can abut against the axial end face of the axial hydraulic cavity to limit the axial movement stroke of the axial telescopic rod; the axial hydraulic cavity is connected to a first oil circuit, when the first oil circuit supplies oil, the hydraulic pressure acts on the limiting part, pushing the axial telescopic rod to move in the direction of the shear arm, so that the push plate pushes against multiple force-bearing ends; after the first oil circuit is depressurized, the continuous pushing action of the push plate on the multiple force-bearing ends is released.

[0012] Furthermore, the normal loading mechanism includes multiple normal loading members spaced apart circumferentially along the central bearing seat. Each normal loading member includes an abutment portion, a guide rod portion, and a limiting head disposed at the radially inner end of the guide rod portion. The abutment portion is threaded to the radially outer end of the guide rod portion. The radially outer side of the abutment portion is provided with an arc-shaped abutment surface extending circumferentially along the second hole segment and adapted to its inner wall. When the multiple shear arms are in the extended state and the multiple normal loading members are in the radial loading position, the side of each shear bearing end facing the corresponding abutment portion and the side of the corresponding abutment portion facing the shear bearing end fit together to form a spliced ​​structure distributed circumferentially along the central bearing seat.

[0013] The central support is provided with a plurality of radially extending radial guide holes and limiting grooves that communicate with the radially inner ends of the plurality of radial guide holes respectively. Each radially outer end of the radial guide hole is threaded with a limiting ring. The limiting ring has a through hole in the middle that is coaxially connected with the radial guide hole. The guide rod portion movably passes through the middle of the limiting ring and is inserted into the radial guide hole. The limiting head is sealed and slidably disposed in the limiting groove and can abut against the end of the limiting ring facing the limiting groove to limit the maximum stroke of the normal loading member moving radially outward.

[0014] Furthermore, the mating end faces of the central bearing seat and the connecting seat are provided with an annular connecting groove, which is connected to a second oil passage; the central bearing seat is provided with a plurality of branch channels distributed circumferentially, one end of each branch channel is connected to the annular connecting groove, and the other end is connected to the corresponding limiting groove; the limiting head forms a piston pressure surface facing the side of the corresponding branch channel. When the second oil passage is pressurized, the pressure medium passes through the annular connecting groove and the plurality of branch channels in sequence into the corresponding limiting groove, and acts on the corresponding limiting head to push the plurality of normal loading members to move radially outward, so that the plurality of abutting parts abut against the inner wall of the second hole section.

[0015] Furthermore, the traction rod is movable in the direction toward the orifice; when the traction rod moves in the direction toward the orifice, the plurality of shear bearing ends abut against the annular bearing surface and apply axial shear load to the annular rock mass to be sheared through the annular bearing surface.

[0016] This invention also provides a method for testing the in-situ borehole shear strength of underground engineering rock mass, using the aforementioned in-situ borehole shear strength testing system for underground engineering rock mass, comprising the following steps: S1, a first hole segment is formed in the rock mass to be tested, and a second hole segment is formed by continuing to process along the drilling axis at the bottom of the first hole segment. A third hole segment is formed by post-expansion on the bottom side of the second hole segment, so that the inner diameter of the first hole segment is larger than the inner diameter of the second hole segment, and the inner diameter of the third hole segment is larger than the inner diameter of the second hole segment. An annular bearing surface is formed between the second hole segment and the third hole segment, and an annular rock mass to be sheared is formed on the radially outer side of the second hole segment. S2, put the multiple shear arms in a retracted state, send the test device into the variable diameter borehole, place the central bearing seat in the second borehole section, and allow the multiple shear arms to enter the third borehole section; S3, oil is supplied to the axial hydraulic chamber through the first oil circuit, pushing the axial telescopic rod to move along the axial direction, causing the top push plate to push against multiple force-bearing ends, and the multiple shear arms rotate around the corresponding rotating connection to the unfolded state, and the multiple shear bearing ends abut against the annular bearing surface; S4, the second oil passage pushes multiple normal loading members to move radially outward, so that multiple abutting parts abut against the inner wall of the second hole section, and applies a predetermined radial normal load to the annular rock mass to be sheared; S5, while maintaining the radial normal load, drive the traction rod to move towards the orifice, so that the central bearing seat drives multiple shear arms to move towards the orifice, and apply axial shear load to the annular rock mass to be sheared through the annular bearing surface until the annular rock mass to be sheared undergoes shear failure along its outer periphery. S6. During the execution of steps S4 and S5, the radial normal load, the axial load borne by the traction rod, and the axial displacement of the traction rod are collected simultaneously.

[0017] Before conducting the formal shear test, a pre-test annular rock mass to be sheared is first prepared at the bottom of the current hole. The test device is then sent into the variable diameter borehole, so that multiple normal loading elements abut against the inner wall of the second hole section. The radial normal load is gradually increased, and the pre-test annular rock mass to be sheared is made to undergo compressive failure without axial shear loading. The radial normal load corresponding to the occurrence of compressive failure is determined as the compressive ultimate load. After the pressure failure test is completed, the normal loading mechanism is depressurized and the multiple shear arms are rotated to the retracted state to remove the test device from the variable diameter borehole. Using a drill bit that matches the inner diameter D1 of the first borehole section, the pre-test annular rock mass to be sheared, which has already undergone pressure failure, and the adjacent disturbed rock mass are removed, and the bottom of the main borehole is pushed deeper to the deep boundary of the original third borehole section. After the new hole is advanced, a small-diameter coaxial hole with an inner diameter of D2 is machined along the borehole axis at the bottom of the new hole. Then, the diameter is expanded at the bottom of the small-diameter coaxial hole to form a new third hole segment with an inner diameter of D3, thereby forming a new annular bearing surface and a new complete annular rock mass to be sheared at the current hole bottom. The testing device was reinserted into the borehole to conduct a formal shear test on the newly formed annular rock mass to be sheared, wherein the radial normal load used in the formal shear test was not greater than the bearing capacity limit load. Each annular rock mass to be sheared for the formal shear test is subjected to only one destructive shear test. After each formal shear test, the axial shear load is removed in sequence, the normal loading mechanism is depressurized, multiple shear arms are rotated to the retracted state and the test device is removed. Then, the annular rock mass to be sheared that has been tested and destroyed and the adjacent disturbed rock mass are swept away, and a new annular rock mass to be sheared is prepared to continue to the depth of the borehole. By changing the radial normal load level corresponding to different formal shear tests, at least three sets of mutually independent formal shear test data are obtained.

[0018] Furthermore, based on the total radial normal force applied by multiple normal loading elements and the pre-obtained normal load calibration relationship, the equivalent normal stress σ on the predetermined shear failure region is determined. ni ;

[0019] Equivalent normal stress σ ni Determined according to the following formula: σ ni =K n ； Among them, K n The normal load transfer factor, F, can be obtained through standard ring specimens, indoor calibration tests, or numerical analysis. ni Let A be the total normal force corresponding to the i-th formal shear test. s Let be the shear area of ​​the i-th test group; Peak shear stress τ i Determined according to the following formula: τ i = ; Among them, F f F is the correction value for the no-load friction of the device. si The peak shear force of the i-th test group; Let D be the equivalent diameter of the predetermined shear failure zone of the annular rock mass to be sheared corresponding to the i-th formal shear test. s The axial length is L s Then the effective shear area A s According to A s =πD s L s Sure.

[0020] The peak shear stress τ obtained from at least three sets of formal shear tests i and equivalent normal stress σ ni Substituting into the Mohr-Coulomb relation τ = c + σ n Linear fitting was performed using tanφ to obtain the cohesion c and internal friction angle φ of the rock mass under test; the compressive failure data of the pre-tested annular rock mass under shearing was not included in the linear fitting.

[0021] Compared with the prior art, the present invention can achieve the following beneficial effects: 1. This invention constructs a variable-diameter borehole with enlarged ends and reduced diameter in the middle by forming a first, second, and third borehole segment; and utilizes the annular bearing surface between the second and third borehole segments and the rock mass radially outside the second borehole segment to form a geometrically defined annular rock mass to be sheared; compared with the testing method that relies on shearing teeth or shear plates to embed into the borehole wall of ordinary boreholes, this invention does not require determining the shearing area with an uncontrollable embedding depth, which can reduce the impact of local crushing of weak borehole walls, insufficient embedding of hard borehole walls, and borehole wall roundness errors on the test results, making the axial load transmission path, the predetermined shearing area, and the shearing area more clearly defined.

[0022] 2. This invention configures multiple shear arms as a retractable and deployable lever structure. After the shear arms are retracted, they can pass through the second hole section with a smaller diameter. After entering the third hole section, the axial telescopic rod and the jacking plate simultaneously push against multiple force-bearing ends, causing multiple shear bearing ends to unfold and abut against each other at circumferential intervals along the annular bearing surface. Compared with the existing in-hole loading devices, which have difficulty passing through the narrow-diameter hole section or loading from the deep end face of the rock mass, this invention takes into account both the device's small-diameter hole section passage capacity and deep end face bearing capacity, and can disperse and transmit axial shear loads through multiple shear bearing ends, reducing the risk of local crushing and skew damage caused by single-position bearing.

[0023] 3. This invention applies radial normal loads to the inner wall of the second borehole section by multiple normal loading elements spaced circumferentially along the central bearing seat, and utilizes annular connecting grooves and multiple branch channels to achieve synchronous pressure supply of multiple normal loading elements; simultaneously, only one annular rock mass to be sheared is prepared at the current bottom of the borehole each time in the same borehole, and each annular rock mass to be sheared is subjected to only one destructive test; after the test is completed, the already damaged annular rock mass to be sheared and the adjacent disturbed rock mass are removed, and new complete annular rock masses to be sheared are prepared to continue to the depth of the borehole, so that the shear data obtained under different radial normal load levels are respectively from relatively independent original rock mass areas, thereby reducing the interference of the previous compaction, cracking and shear failure on the subsequent test data, and improving the reliability and comparability of the fitting results of rock mass cohesion and internal friction angle. Attached Figure Description

[0024] Figure 1 This is a three-dimensional structural diagram of the testing device of the present invention; Figure 2 This is a schematic axial cross-sectional view of the testing device of the present invention installed in a variable diameter borehole; Figure 3 This is a schematic axial cross-sectional view of the test device when the shear arm of the present invention is in the retracted state; Figure 4 This is an axial cross-sectional schematic diagram of the testing device and its oil circuit when the shear arm of the present invention is in the deployed state; Figure 5 This is an exploded structural diagram of the central support base and the connecting base of the present invention; Figure 6 This is a cross-sectional schematic diagram of the internal cavity and oil passage of the central support seat of the present invention; Figure 7 This is a schematic diagram of the axial telescopic rod of the present invention; Figure 8 This is a schematic diagram of the structure of the normal loading component of the present invention; Figure 9 This is a schematic diagram of the shear arm of the present invention; Figure 10 This is a partial cross-sectional schematic diagram of the variable diameter borehole and the annular rock mass to be sheared according to the present invention; Figure 11 This is a schematic diagram illustrating the hole-forming, installation, and testing process of the present invention; Figure 12 This is a schematic diagram of the variable-diameter drilling model in the numerical simulation of this invention; Figure 13 This is a schematic diagram of the test device during installation in the numerical simulation of this invention; Figure 14 This is the minimum principal stress contour plot in the numerical simulation of this invention; Figure 15 This is the maximum principal stress contour plot in the numerical simulation of this invention; Figure 16 This is the X-axis displacement contour map in the numerical simulation of this invention.

[0025] In the diagram, 1. First borehole section; 2. Second borehole section; 3. Third borehole section; 4. Annular bearing surface; 5. Annular rock mass to be sheared; 6. Traction rod; 7. Central bearing seat; 8. Shear arm; 9. Axial telescopic rod; 10. Normal loading component; 11. First oil passage; 12. Second oil passage; 61. Support seat; 71. Connecting seat; 81. Force-bearing end; 82. Shear bearing end; 83. Rotating connection part; 84. Shear arm support; 91. Push plate; 92. Limiting part; 93. Axial limiting cavity; 94. Axial hydraulic cavity; 95. Limiting ring; 101. Abutment part; 102. Guide rod part; 103. Limiting head; 104. Radial guide hole; 105. Limiting groove; 121. Annular connecting groove; 122. Branch channel. Detailed Implementation

[0026] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0027] Example 1 This embodiment provides an in-situ borehole shear strength testing system for underground engineering rock masses; such as... Figures 1 to 10As shown, the system consists of a variable-diameter borehole formed in the rock mass to be tested and a testing device that works in conjunction with the variable-diameter borehole; the variable-diameter borehole forms a first borehole section 1, a second borehole section 2 and a third borehole section 3 in sequence from the borehole opening to the bottom of the borehole along the borehole axis.

[0028] In this embodiment, the inner diameters of the first borehole segment 1 and the third borehole segment 3 are both larger than the inner diameter of the second borehole segment 2; the second borehole segment 2 constitutes a small-diameter borehole segment located between the two large-diameter borehole segments; an annular bearing surface 4 is formed between the second borehole segment 2 and the third borehole segment 3, facing the third borehole segment 3; the rock mass to be tested, located between the first borehole segment 1 and the third borehole segment 3 and radially outside the second borehole segment 2, forms an annular rock mass to be sheared 5.

[0029] With this configuration, the first borehole section 1 can provide a large passage space for the insertion, positioning and retraction of the testing device; the second borehole section 2 can retain the continuous annular rock mass 5 to be sheared and provide a radial loading position for the normal loading member 10; the third borehole section 3 can provide space for the deployment and axial movement of the shear arm 8; and the annular bearing surface 4 can transfer the axial load of the shear arm 8 to the deep end face of the annular rock mass 5 to be sheared, thereby establishing a clear axial load transfer path.

[0030] In this embodiment, the inner diameter of the first hole segment 1 is denoted as D1, the inner diameter of the second hole segment 2 is denoted as D2, and the inner diameter of the third hole segment 3 is denoted as D3, where D1>D2 and D3>D2. The third hole segment 3 is mainly used to provide operating space for the unfolding, axial movement, and rotation to the retracted state of the multiple shear arms 8, so D3 is not required to be equal to D1; preferably, D3≥D1. For example, D1 can be 70mm, D2 can be 50mm, and D3 can be 70mm, 72mm, or 75mm.

[0031] In one embodiment where the equivalent diameter Ds of the predetermined shear failure zone is determined according to the inner diameter D1 of the first borehole section 1, the equivalent radial thickness t of the annular rock mass 5 to be sheared is determined according to t = (D1 - D2) / 2; the axial length of the second borehole section 2 is denoted as L2, which is determined according to the properties of the rock mass to be tested, the radial thickness of the annular rock mass 5 to be sheared, and the predetermined shear failure zone, so that the annular rock mass 5 to be sheared has an axial length and radial thickness that meet the requirements of the shear test.

[0032] Furthermore, the inner diameter of the third hole segment 3 is greater than the maximum radial outer envelope diameter when the plurality of shear arms 8 are in the deployed state, so as to provide radial space within the third hole segment 3 for the deployment and de-deployment of the plurality of shear arms 8; the inner diameter of the first hole segment 1 meets the axial passage requirements of the testing device when the shear arms 8 are in the retracted state.

[0033] This configuration allows for clearance for drilling errors, shear arm machining errors, and coaxiality errors between the testing device and the borehole. During axial loading or device retraction, the shear arm 8 will not continuously abut against the circumferential wall of the first hole section 1 or the third hole section 3. This reduces the possibility of the shear arm scraping or getting stuck against the hole wall and minimizes the interference of hole wall contact on axial load transmission.

[0034] In this embodiment, variable diameter drilling can first drill a through-hole, and then use a deployable reamer to ream the first hole segment 1 and the third hole segment 3 respectively; it can also be done by staged drilling, reverse reaming, reaming with a cutter behind the hole, or other hole-forming methods that can retain the intermediate small-diameter hole segments; during hole formation, the axial position of each hole segment can be controlled by the drill rod depth mark, the mechanical limit of the reamer, or the hole opening positioning sleeve, and the reaming diameter can be controlled by the diameter limiting sleeve, the maximum unfolding angle of the reamer, or the diameter measuring device.

[0035] Post-expansion can be achieved using a retractable reamer. The reamer enters the bottom of the hole through the second hole section 2 in a retracted state, unfolds the cutter at the predetermined expansion position and performs rotational cutting to form the third hole section 3 with an inner diameter of D3. After the expansion is completed, the cutter retracts and exits through the second hole section 2.

[0036] It should be noted that after the hole is formed, a borehole inspection instrument or a diameter gauge can be used to check the inner diameter of the first hole section 1, the second hole section 2 and the third hole section 3, the axial length of the second hole section 2, the integrity of the annular bearing surface 4 and the state of hole wall breakage; at the same time, rock cuttings and accumulated water in the hole should be removed to avoid rock cuttings getting stuck between the shear bearing end 82 and the annular bearing surface 4, affecting the bearing contact and test results.

[0037] Furthermore, the testing device includes a central bearing seat 7; during testing, the central bearing seat 7 is located within the second hole section 2; the central bearing seat 7 provides a mounting base for the shearing assembly, the unfolding drive mechanism, and the normal loading mechanism, and undertakes the transmission of axial and radial loads.

[0038] In this embodiment, the axial drive mechanism includes a traction rod 6 and a support seat 61 disposed on the orifice side of the first borehole section 1; the support seat 61 has a hollow channel extending along the borehole axis, through which the traction rod 6 can move axially; a connecting seat 71 is detachably connected to one end of the central bearing seat 7 away from the shearing assembly, and the extended end of the traction rod 6 is connected to the connecting seat 71.

[0039] Furthermore, in this embodiment, the support base 61 can be a hollow hydraulic jack; the hollow hydraulic jack forms a reaction force support with the rock mass to be measured around the borehole through a pressure plate or a reaction frame, the traction rod 6 passes through the hollow channel of the hollow hydraulic jack, and the loading end of the hollow hydraulic jack is connected to the traction rod 6 through a clamp, nut or connecting sleeve; when the hollow hydraulic jack is in operation, it applies an axial force toward the borehole to the traction rod 6 with the rock mass to be measured as the reaction force basis.

[0040] With this configuration, the support base 61 can provide an axial loading foundation for the traction rod 6 on the borehole side, and the hollow structure can keep the traction rod 6 arranged along the borehole axis. The reaction force generated during the axial loading process can be transmitted to the rock mass to be tested around the borehole through the pressure plate or reaction frame, and the axial shear load can be transmitted to multiple shear arms 8 through the traction rod 6, the connecting base 71 and the central bearing base 7.

[0041] Furthermore, the traction rod 6 can be composed of multiple rod segments connected sequentially along the axial direction; adjacent rod segments can be connected by threads; the rod segment at the extension end is connected to the connecting seat 71; the threaded connection position can be equipped with a lock nut, anti-loosening washer, radial locking screw or threaded locking structure.

[0042] This setup allows for the increase or decrease of the number of tie rod sections based on the actual depth of the current test location. At the same time, the anti-loosening structure reduces the possibility of loosening of the threaded connection during repeated axial loading, thereby maintaining the continuity of axial force transmission between the traction tie rod 6, the connecting seat 71, and the central bearing seat 7.

[0043] Furthermore, the shearing assembly includes multiple shearing arms 8 spaced apart circumferentially along the central support 7; each shearing arm 8 is provided with a force-bearing end 81, a shearing bearing end 82, and a rotating connection part 83; the rotating connection part 83 is located between the force-bearing end 81 and the shearing bearing end 82; a plurality of shearing arm supports 84 are provided at one end of the central support 7 facing the third hole section 3; each rotating connection part 83 is mounted on the corresponding shearing arm support 84 via a rotating shaft.

[0044] In this embodiment, the force-bearing end 81 and the shear bearing end 82 are located on both sides of the rotating connection part 83, respectively; the shear arm 8 forms a lever structure with the rotating connection part 83 as the fulcrum; when the force-bearing end 81 is subjected to axial thrust, the shear bearing end 82 rotates in a direction away from the central axis of the device.

[0045] With this configuration, only a small axial displacement is needed at the force-bearing end 81 to achieve a corresponding radial expansion displacement at the shear bearing end 82; multiple shear arms 8 can be synchronously driven by a single axial telescopic rod 9, eliminating the need for separate radial drive cylinders; this reduces the number of in-hole drive structures and helps to reduce the radial dimensions of the testing device.

[0046] Furthermore, when the multiple shear arms 8 are in the retracted state, their radial outer envelope diameter is less than or equal to the inner diameter of the second hole section 2; the multiple shear arms 8 can pass through the first hole section 1 and the second hole section 2 in sequence, and allow the multiple shear bearing ends 82 to enter the third hole section 3.

[0047] In this embodiment, after the multiple shear arms 8 are deployed, the multiple shear bearing ends 82 are distributed circumferentially along the annular bearing surface 4; the shear bearing ends 82 are provided with bearing contact surfaces facing the annular bearing surface 4; the non-bearing edges of the shear bearing ends 82 can be rounded.

[0048] With this configuration, multiple shear bearing ends 82 can distribute and transmit axial loads at different circumferential positions on the annular bearing surface 4, avoiding the concentration of all loads on a single local position on the annular bearing surface 4; the arc transition can reduce the possibility of the shear bearing ends 82 scraping against the hole wall during the insertion and retraction of the test device.

[0049] Furthermore, the unfolding drive mechanism includes an axial telescopic rod 9; one end of the axial telescopic rod 9 is provided with a push plate 91, and the other end is provided with a limiting part 92; the central bearing seat 7 is provided with an axial limiting cavity 93 and an axial hydraulic cavity 94 that are connected along the axial direction; the rod is axially movable and passes through the axial limiting cavity 93; the limiting part 92 is slidably and sealingly disposed in the axial hydraulic cavity 94.

[0050] In this embodiment, the radial dimension of the push plate 91 is greater than the radial dimension of the area enclosed by the inner sides of the multiple force-bearing ends 81; the push plate 91 can simultaneously cover and push against the multiple force-bearing ends 81; the limiting part 92 can abut against the axial end face of the axial hydraulic cavity 94 to limit the maximum axial movement stroke of the axial telescopic rod 9.

[0051] With this configuration, the push plate 91 can synchronously drive multiple shear arms 8 to unfold, reducing the problem of inconsistent unfolding degree of each shear arm 8; the limiting part 92 cooperates with the axial end face of the axial hydraulic cavity 94 to prevent excessive movement of the axial telescopic rod 9 and to limit the maximum unfolding degree of the shear arm 8, avoiding interference between the shear arm 8 and the hole wall.

[0052] Furthermore, the axial hydraulic chamber 94 is connected to the first oil circuit 11; when the first oil circuit 11 supplies oil, the pressure medium acts on the limiting part 92, pushing the axial telescopic rod 9 to move toward the shear arm 8; the push plate 91 pushes against multiple force-bearing ends 81, causing multiple shear arms 8 to rotate around the corresponding rotating connection part 83 to the unfolded state.

[0053] In this embodiment, the first oil circuit 11 can adopt a one-way pressure supply structure; a control valve, a shut-off valve and a hydraulic lock can be installed on the first oil circuit 11; when the shear arm 8 is extended to the predetermined position, the control valve can be closed or the hydraulic lock can be used to maintain the pressure in the axial hydraulic chamber 94, so that the push plate 91 continuously supports the force-bearing end 81.

[0054] It should be noted that in this embodiment, the shear arm 8 is not provided with an elastic reset member for automatic retraction; after the first oil circuit 11 is depressurized, only the continuous pushing action of the push plate 91 on the multiple force-bearing ends 81 is released, and it is not required that the multiple shear arms 8 immediately return to the initial fully retracted state in the borehole; during the process of the test device retracting towards the borehole opening, the shear bearing end 82, under the pushing and guiding action of the annular bearing surface 4 and the borehole wall of the second borehole section 2, drives the shear arm 8 to rotate around the rotating connection part 83 toward the central axis, so that the multiple shear arms 8 are at least retracted to the state that can pass through the second borehole section 2; after the test device enters the first borehole section 1, approaches the borehole opening, or moves out of the variable diameter borehole, the operator then rotates the multiple shear arms 8 completely back to the initial retracted position.

[0055] Furthermore, the normal loading mechanism includes a plurality of normal loading members 10 distributed circumferentially along the central bearing seat 7; the number of normal loading members 10 can be three, four, six, eight or other suitable numbers; in this embodiment, the normal loading members 10 are preferably set to six, and the included angle between the center lines of two adjacent normal loading members 10 is 60°.

[0056] With this configuration, multiple normal loading elements 10 can form multiple spaced loading areas in the circumference of the second hole section 2. Compared with a single or two oppositely arranged loading elements, circumferential multi-point loading can make the radial normal load distribution on the annular rock mass 5 to be sheared more balanced and can reduce the local stress concentration at a single loading position.

[0057] Furthermore, each normal loading member 10 is provided with an abutment portion 101, a guide rod portion 102, and a limiting head 103; the abutment portion 101 is threaded to the radial outer end of the guide rod portion 102; the limiting head 103 is provided at the radial inner end of the guide rod portion 102; the radial outer side of the abutment portion 101 is provided with an arc-shaped abutment surface that extends circumferentially along the second hole segment 2 and is adapted to its inner wall.

[0058] It should be noted that the abutment part 101 and the guide rod part 102 are connected by threads, which makes it easy to replace the abutment part 101 with different radii of curvature or different contact areas according to the inner diameter of the second hole section 2. With this configuration, the arc-shaped abutment surface can increase the contact area between the abutment part 101 and the inner wall of the second hole section 2, so that the normal load changes from a point or line action to a surface action. This can improve the stability of the normal load and reduce the possibility of the abutment part 101 causing local crushing of the hole wall in the early stage of loading.

[0059] When the multiple shear arms 8 are in the extended state, each shear arm 8 and the corresponding abutment part 101 are axially adjacent to each other to form a circumferentially distributed splicing structure; the splicing structure is used to reduce the axial gap between the shear arm 8 and the abutment part 101, while not restricting the radial extension and retraction movement of the abutment part 101.

[0060] Furthermore, the central bearing seat 7 is provided with a plurality of radially extending radial guide holes 104; the radial inner end of each radial guide hole 104 is connected to the corresponding limiting groove 105; the radial outer end of each radial guide hole 104 is threadedly connected to a limiting ring 95; the middle part of the limiting ring 95 is provided with a through hole coaxially connected to the radial guide hole 104.

[0061] In this embodiment, the inner diameter of the through hole in the middle of the limiting ring 95 is the same as or substantially the same as that of the radial guide hole 104; the guide rod 102 movably passes through the middle of the limiting ring 95 and is inserted into the radial guide hole 104; the limiting head 103 is slidably and sealed within the limiting groove 105.

[0062] With this configuration, the radial guide hole 104 and the central through hole of the limiting ring 95 together provide radial guidance for the guide rod portion 102, which can reduce the possibility of the normal loading member 10 tilting or swinging during the extension process; the limiting ring 95 is threadedly connected to the central bearing seat 7, which facilitates the installation or removal of the normal loading member 10 from the outside of the central bearing seat 7.

[0063] Furthermore, when the normal loading member 10 moves radially outward to the maximum extension position, the limiting head 103 abuts against the end of the limiting ring 95 facing the limiting groove 105; the limiting ring 95 prevents the limiting head 103 from continuing to move outward, thereby limiting the maximum radial extension stroke of the normal loading member 10.

[0064] With this configuration, the limiting head 103 will not come out of the limiting groove 105, and the guide rod 102 will not come off the central bearing seat 7. At the same time, the maximum extension stroke of the normal loading member 10 can be adjusted by adjusting the installation depth of the limiting ring 95 or by replacing the limiting ring 95 with one of different axial thicknesses, so as to adapt to the hole forming error of the second hole section 2.

[0065] Furthermore, the mating end faces of the central bearing seat 7 and the connecting seat 71 are provided with an annular connecting groove 121; the annular connecting groove 121 is connected to the second oil passage 12; the central bearing seat 7 is provided with a plurality of branch channels 122 distributed circumferentially; one end of each branch channel 122 is connected to the annular connecting groove 121, and the other end is connected to the corresponding limiting groove 105.

[0066] With this configuration, the second oil circuit 12 only needs to supply pressure medium to the annular connecting groove 121 through a single pressure inlet; the annular connecting groove 121 can distribute pressure medium along the circumference of the central bearing seat 7; multiple branch channels 122 then respectively supply pressure medium to the corresponding limiting grooves 105; thereby reducing the number of independent oil pipes and enabling multiple normal loading elements 10 to be synchronously driven by the same pressure source.

[0067] Furthermore, the limiting head 103 forms a piston pressure surface on the side facing the corresponding branch channel 122; when the second oil circuit 12 supplies pressure, the pressure medium passes through the annular connecting groove 121 and multiple branch channels 122 in sequence into the corresponding limiting groove 105 and acts on the corresponding limiting head 103; the limiting head 103 pushes the guide rod 102 and the abutment part 101 to move radially outward.

[0068] With this configuration, the limiting head 103 simultaneously serves as both the radial drive piston and the stroke limiting component, eliminating the need for a separate piston to be installed in the limiting groove 105. This reduces the number of parts in the normal loading mechanism and helps to reduce the radial dimension of the central bearing seat 7.

[0069] In this embodiment, the second oil circuit 12 can adopt a unidirectional pressure supply structure; after the second oil circuit 12 is depressurized, the radial thrust of the pressure medium on the limiting head 103 is released.

[0070] Furthermore, in this embodiment, the normal loading member 10 is not provided with an elastic reset member for automatic retraction; after the second oil circuit 12 is depressurized, only the radial thrust of the pressure medium on the limiting head 103 is released, and the normal loading member 10 is not required to immediately return to the initial fully retracted position in the borehole; when the test device retracts towards the borehole opening, the abutment part 101, under the pushing action of the borehole wall of the second borehole section 2, drives the guide rod part 102 and the limiting head 103 to retract radially inward, so that the radial outer envelope size of the multiple normal loading members 10 is reduced to be able to pass through the second borehole section 2; after the test device enters the first borehole section 1, approaches the borehole opening, or moves out of the variable diameter borehole, the operator pushes the multiple normal loading members 10 completely back to the initial retracted position.

[0071] Furthermore, in another optional embodiment, a first elastic reset member is provided between each shear arm 8 and the corresponding shear arm support 84. The first elastic reset member is used to drive the shear arm 8 to rotate toward the retracted state after the first oil circuit 11 is depressurized. A second elastic reset member is provided between each normal loading member 10 and the central bearing seat 7. The second elastic reset member is used to drive the normal loading member 10 to move radially inward after the second oil circuit 12 is depressurized. The first elastic reset member and the second elastic reset member are only used to provide reset force and do not bear axial load or radial normal loading during the shearing test.

[0072] Optionally, the first elastic reset member is a torsion spring disposed at the rotating connection portion 83, and the second elastic reset member is a compression spring disposed between the limiting head 103 and the limiting ring 95.

[0073] Furthermore, the testing device is also equipped with a normal force detection component, an axial force detection component, a displacement detection component, and a data acquisition and processing unit. The normal force detection component can be a pressure sensor installed on the second oil circuit 12, and the total normal force is determined based on the hydraulic pressure of the second oil circuit 12, the effective pressure-bearing area of ​​the limiting head 103, and the number of normal loading components 10. The axial force detection component can be connected in series between the loading end of the support base 61 and the traction rod 6. The displacement detection component can be installed between the traction rod 6 and the fixed reference on the orifice side.

[0074] This setup allows for the simultaneous acquisition of radial normal load, axial shear load, and axial displacement. The peak shear force, initial shear stiffness, and residual bearing characteristics after failure can be determined through the axial load-displacement curve. The cohesion and internal friction angle of the rock mass under test can be further determined through test results at different normal load levels.

[0075] The working process of this embodiment is as follows: First, the first oil passage 11 and the second oil passage 12 are depressurized, the multiple shear arms 8 are retracted, and the multiple normal loading members 10 are positioned to pass through the second hole section 2; then, the test device is sent from the first hole section 1 into the variable diameter borehole until the central bearing seat 7 is located in the second hole section 2, and the multiple shear arms 8 enter the third hole section 3.

[0076] Furthermore, oil is supplied to the axial hydraulic chamber 94 through the first oil passage 11; the limiting part 92 drives the axial telescopic rod 9 to move toward the shearing arm 8 under the action of hydraulic pressure; the push plate 91 simultaneously pushes against multiple force-bearing ends 81; the multiple shearing arms 8 rotate outward around the corresponding rotating connection part 83 until the multiple shearing bearing ends 82 enter the radially outer region of the second hole section 2.

[0077] Furthermore, the traction rod 6 can be slightly pulled towards the orifice; when the multiple shear bearing ends 82 come into contact with the annular bearing surface 4, the axial resistance of the traction rod 6 changes; this change can help determine whether the test device has reached the predetermined axial position; then the pressure of the first oil circuit 11 is maintained to keep the multiple shear arms 8 in the extended state.

[0078] Furthermore, pressure is supplied through the second oil passage 12; the pressure medium enters each limiting groove 105 through the annular connecting groove 121 and the branch channel 122; multiple normal loading members 10 move outward radially in sync until the arc-shaped contact surfaces of multiple contact parts 101 contact the inner wall of the second hole section 2; the pressure of the second oil passage 12 is further increased so that the annular rock mass 5 to be sheared is subjected to a radial normal load of a predetermined size.

[0079] In this embodiment, pressure is maintained after the target radial normal load is reached; when the detected radial normal load meets the predetermined stability condition, it is determined that the radial normal load has reached a stable state; the data acquisition and processing unit synchronously acquires the radial normal load, axial load and axial displacement according to the predetermined sampling frequency.

[0080] Furthermore, while maintaining a basically constant radial normal load, the hollow hydraulic jack in the support seat 61 is axially loaded, causing the loading end of the hollow hydraulic jack to drive the traction rod 6 to move towards the orifice; the traction rod 6 drives the central bearing seat 7 and multiple unfolded shear arms 8 to move towards the orifice through the connecting seat 71; multiple shear bearing ends 82 abut against the annular bearing surface 4, and apply axial shear load to the deep end face of the annular rock mass 5 to be sheared through the annular bearing surface 4.

[0081] Furthermore, while maintaining the radial normal load basically stable, the hollow hydraulic jack in the support 61 is controlled to perform axial loading at a predetermined loading rate, so that the loading end of the hollow hydraulic jack drives the traction rod 6 to move towards the orifice; during the loading process, the total normal force, axial shear load and axial displacement are recorded simultaneously; when the axial shear load reaches its peak and then decreases significantly, or when the axial displacement reaches the predetermined termination condition, the shear loading is stopped.

[0082] It should be noted that in this embodiment, it is not necessary to use shearing teeth, shearing plates or pressure heads to pre-insert into the hole wall of the second hole section 2 to establish the axial force transmission relationship; the shear bearing end 82 applies load to the end face of the annular rock mass 5 to be sheared through the annular bearing surface 4; therefore, the present invention can reduce the local crushing, spalling or loosening of the weak or broken hole wall before the formal shear loading.

[0083] Furthermore, after the test is completed, the axial shear load, the radial normal load in the second oil circuit 12, and the unfolding load in the first oil circuit 11 are removed in sequence; after the first oil circuit 11 is depressurized, the push plate 91 releases its continuous pushing action on the multiple force-bearing ends 81; after the second oil circuit 12 is depressurized, the pressure medium releases its radial pushing action on the multiple limit heads 103; then the operator pulls the traction rod 6 at the orifice side to retract the test device towards the orifice.

[0084] During the retraction process, multiple shear arms 8 partially retract under the pushing and guiding action of the annular bearing surface 4 and the hole wall of the second hole section 2, and multiple normal loading elements 10 retract radially inward under the pushing action of the hole wall of the second hole section 2; the in-hole reset process does not require the shear arms 8 and normal loading elements 10 to return to the initial fully retracted state or fully retracted state, it is only necessary to reduce the radial outer envelope size of the test device to be able to pass through the second hole section 2.

[0085] After the testing device enters the first hole section 1 through the second hole section 2 or is moved out of the hole, the operator resets the shearing arms 8 and the normal loading members 10, so that the multiple shearing arms 8 return to the initial retracted position and the multiple normal loading members 10 return to the initial retracted position, so as to perform device inspection and the next test.

[0086] It should be noted that before the next test, the annular rock mass 5 that has been tested and damaged, as well as the adjacent disturbed rock mass, is removed using a drill bit that matches the inner diameter D1 of the first borehole section 1, and the main borehole is continued to advance to a deeper level. Then, the second borehole section 2 is re-processed at the bottom of the new borehole, and a new third borehole section 3, annular bearing surface 4, and a new complete annular rock mass 5 are formed by using a post-expansion method.

[0087] In this embodiment, a ring-shaped rock mass 5 with clearly defined geometric dimensions is pre-formed by a three-section variable-diameter borehole; a shearing arm 8 that can be retracted and extended accommodates both passage in the small-diameter borehole section and bearing load on the deep end face; a radially distributed normal load is applied to the borehole wall of the second borehole section 2 by multiple normal loading elements 10; and a clear axial load transmission path is established by the annular bearing surface 4. This improves the feasibility of in-situ borehole shear testing and the comparability of test results.

[0088] Example 2 Based on Example 1, this embodiment prepares multiple independent annular rock masses 5 along the depth direction in the same borehole, conducts shear tests under different radial normal load levels, and determines the cohesion and internal friction angle of the rock masses based on multiple sets of formal shear test data.

[0089] Before the formal shear test, a pre-test annular rock mass 5 to be sheared is first prepared at the bottom of the current hole; the test device is sent into the variable diameter borehole, so that the central bearing seat 7 is located in the second hole section 2, and multiple shear arms 8 enter the third hole section 3; multiple normal loading members 10 are driven to move radially outward through the second oil passage 12, so that multiple abutment parts 101 abut against the inner wall of the second hole section 2.

[0090] Subsequently, the radial normal load is gradually increased, and a radial bearing failure test is conducted on the pre-test annular rock mass 5 without axial shear loading. When the pre-test annular rock mass 5 exhibits at least one of the following phenomena: obvious local crushing, cracking, significant increase in radial deformation, or the radial normal load reaching its peak and then no longer steadily increasing, it can be determined that it has undergone bearing failure; the radial normal load corresponding to the occurrence of bearing failure is determined as the bearing ultimate load Fn,max.

[0091] After the pressure failure test is completed, the second oil circuit 12 is depressurized, the radial normal load applied by multiple normal loading elements 10 is released, and multiple shear arms 8 are rotated to the retracted state; then the test device is taken out from the borehole.

[0092] Using a drill bit that matches the inner diameter D1 of the first borehole section 1, the pre-test annular rock mass 5 that has already undergone pressure failure and the adjacent disturbed rock mass are removed, and the bottom of the main borehole is advanced to the deep boundary of the original third borehole section 3. At the bottom of the new borehole after advancement, a second borehole section 2 with an inner diameter of D2 is machined using a small-diameter drill bit, and then a retractable reaming tool is used to perform post-diameter expansion on the bottom side of the second borehole section 2 to form a new third borehole section 3 with an inner diameter of D3, thereby forming a new annular bearing surface 4 and a new complete annular rock mass 5 to be sheared.

[0093] The testing device is reinserted into the borehole, and a first target radial normal load not exceeding the bearing capacity load Fn,max is selected to conduct the first formal shear test on the newly formed annular rock mass 5 to be sheared. After the radial normal load reaches the predetermined stability condition, the traction rod 6 is driven to move towards the borehole opening according to the predetermined loading rate, so that multiple shear bearing ends 82 apply axial shear load to the annular rock mass 5 through the annular bearing surface 4, and the total normal force, axial shear load and axial displacement are collected simultaneously until the shear test is completed.

[0094] After the first formal shear test is completed, the axial shear load and radial normal load are removed in sequence, and the test device is taken out. The annular rock mass 5 that has been tested and damaged and the adjacent disturbed rock mass are swept away again using a drill bit that matches the inner diameter D1 of the first hole section 1. The drilling continues to advance to the depth of the borehole, the second hole section 2 is reprocessed and the diameter is expanded afterward to form the next new complete annular rock mass 5 to be sheared.

[0095] Subsequent formal shear tests used different target radial normal loads, and each target radial normal load was no greater than the bearing capacity ultimate load Fn,max; each newly formed annular rock mass to be sheared 5 was subjected to only one destructive shear test. By repeating the above process of sample preparation, testing, cleaning and continuing to prepare samples at a deeper level, at least three sets of mutually independent formal shear test data were obtained.

[0096] For the i-th formal shear test, the displacement detection device obtains the axial displacement of the traction rod 6 relative to the rock mass under test. Based on the total radial normal force applied by multiple normal loading devices and the pre-obtained normal load calibration relationship, the equivalent normal stress σ on the predetermined shear failure region is determined. ni ; Equivalent normal stress σ ni Determined according to the following formula: σ ni =K n ； Among them, K n The normal load transfer factor, F, can be obtained through standard ring specimens, indoor calibration tests, or numerical analysis. ni Let A be the total normal force corresponding to the i-th formal shear test. s Let be the shear area of ​​the i-th test group; Peak shear stress τ i Determined according to the following formula: τ i = ; Among them, F f F is the correction value for the no-load friction of the device. si denoted as the peak shear force of the i-th test group.

[0097] Let D be the equivalent diameter of the predetermined shear failure zone of the annular rock mass 5 corresponding to the i-th formal shear test. s The axial length is L s Then the effective shear area A s According to A s =πD s L s Sure.

[0098] The peak shear stress τ obtained from at least three sets of formal shear tests i and equivalent normal stress σ ni Substituting into the Mohr-Coulomb relation τ = c + σ n Linear fitting was performed using tanφ to obtain the cohesion c and internal friction angle φ of the rock mass under test; the compressive failure data of the pre-test annular rock mass 5 to be sheared were not included in the linear fitting.

[0099] For formal shear test data that show obvious crushing of the annular bearing surface 4, overall splitting of the annular rock mass to be sheared 5, oblique failure, or local collapse without forming the expected shear failure area, they can be marked as abnormal data and not included in the fitting.

[0100] By using the above testing method, each formal shear test uses a newly prepared complete annular rock mass 5 to be sheared, which can reduce the influence of cracks, loose areas and stress release areas formed by the previous failure on the subsequent test results, thereby improving the independence and comparability of test data under different radial normal load levels.

[0101] Example 3 This embodiment, based on Embodiment 1, performs numerical simulation verification of the variable-diameter drilling structure, normal loading position, and axial shear load transfer process. Furthermore, as... Figures 12 to 16 As shown, FLAC3D or other geotechnical numerical analysis software can be used to numerically simulate the hole formation, normal loading and axial shear loading process of variable diameter boreholes; the numerical model is established according to the actual geometric relationship of the first hole segment 1, the second hole segment 2 and the third hole segment 3; the annular rock mass to be sheared 5 is located on the radial outer side of the second hole segment 2.

[0102] In this embodiment, the rock mass to be tested can be modeled using the Mohr-Coulomb elastoplastic constitutive model; for rock masses with well-developed joints and fissures or significant anisotropy, a joint model, a damage model, or anisotropic constitutive model can also be used; the testing device can be modeled according to the actual structure, or the shear arm 8 and the normal loading element 10 can be simplified to an equivalent loading region.

[0103] Furthermore, the numerical simulation first establishes a three-section variable diameter borehole model; then, a radial loading region corresponding to multiple abutment parts 101 is set on the inner wall of the second borehole section 2; an axial loading region corresponding to multiple shear bearing ends 82 is set on the annular bearing surface 4; and then radial normal load and axial displacement or axial load are applied sequentially.

[0104] In this embodiment, the numerical simulation outputs the maximum principal stress cloud map, minimum principal stress cloud map, shear strain cloud map, and displacement cloud map. By observing the stress transmission near the annular bearing surface 4, the stress concentration around the second borehole section 2, and the displacement concentration in the outer periphery of the annular rock mass to be sheared 5, it is determined whether the selected borehole size and loading position can form the expected shear failure trend.

[0105] With this setup, when the maximum principal stress, minimum principal stress, and displacement concentration area are mainly distributed near the predetermined cylindrical shear failure area on the outer periphery of the annular rock mass 5 to be sheared, it indicates that the dimensional relationship, normal loading position, and axial load transmission path of the first hole segment 1, the second hole segment 2, and the third hole segment 3 are relatively reasonable. If the stress is mainly concentrated in a local area of ​​the annular bearing surface 4, the axial length of the second hole segment 2, the thickness of the annular rock mass 5 to be sheared, or the circumferential distribution of the shear bearing end 82 can be appropriately adjusted.

[0106] It should be noted that the numerical simulation is used to assist in determining the hole segment size, normal load level, axial loading rate, and number of shear arms; the simulation results do not replace the in-situ test results and do not constitute a limitation on the scope of protection of this invention.

[0107] Through the above numerical simulation, the axial load transmission near the annular bearing surface 4, the stress distribution around the second borehole section 2, and the displacement concentration in the outer periphery of the annular rock mass 5 to be sheared can be observed. When the stress and displacement concentration areas are mainly distributed near the predetermined cylindrical shear failure area on the outer periphery of the annular rock mass 5 to be sheared, it indicates that the adopted three-section variable diameter borehole size relationship, normal loading position, and axial shear load transmission path can form the expected shear failure trend, thus providing a reference for determining the borehole size and loading parameters in the in-situ shear test.

[0108] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. An in-situ borehole shear strength testing system for underground engineering rock masses, comprising a variable-diameter borehole formed within the rock mass to be tested and a testing device that cooperates with the variable-diameter borehole, characterized in that, The variable-diameter borehole is formed sequentially from the borehole opening to the bottom of the borehole along the borehole axis as a first borehole segment (1), a second borehole segment (2), and a third borehole segment (3). The inner diameter of the first borehole segment (1) is larger than the inner diameter of the second borehole segment (2), and the inner diameter of the third borehole segment (3) is larger than the inner diameter of the second borehole segment (2). An annular bearing surface (4) is formed between the second borehole segment (2) and the third borehole segment (3). The rock mass to be tested on the radially outer side of the second borehole segment (2) forms an annular rock mass to be sheared (5). The testing apparatus includes: The central support (7) is located within the second hole section (2) during testing; The shearing component is set on the central support seat (7) and can switch between a retracted state and an unfolded state. When retracted, it can pass through the second hole segment (2), and when unfolded, it can form a bearing contact with the annular support surface (4). An unfolding drive mechanism is movably disposed along the axial direction of the variable diameter borehole and is used to push against the shearing assembly to unfold it; An axial drive mechanism, connected to the central bearing seat (7), is used to drive the central bearing seat (7) to move along the borehole axis to apply an axial shear load to the annular rock mass (5) to be sheared through the unfolded shear assembly and the annular bearing surface (4). The normal loading mechanism is located on the central bearing seat (7) and can move radially outward to abut against the inner wall of the second hole section (2) and apply a radial normal load to the annular rock mass to be sheared (5).

2. The in-situ borehole shear strength testing system for underground engineering rock mass according to claim 1, characterized in that, The axial drive mechanism includes a traction rod (6) and a support seat (61) disposed on the orifice side of the first hole section (1). The support seat (61) is provided with a hollow channel through which the traction rod (6) passes axially and can apply axial loading to the traction rod (6). The central bearing seat (7) is detachably connected to a connecting seat (71) at one end away from the shear assembly. The extended end of the traction rod (6) is connected to the connecting seat (71).

3. The in-situ borehole shear strength testing system for underground engineering rock mass according to claim 2, characterized in that, The shearing assembly includes a plurality of shearing arms (8) spaced apart circumferentially along the central support (7). Each shearing arm (8) is provided with a force-bearing end (81), a shearing bearing end (82), and a rotating connection part (83) located between the force-bearing end (81) and the shearing bearing end (82). The central support (7) is provided with a plurality of shearing arm supports (84) spaced apart circumferentially. The rotating connection part (83) of each shearing arm (8) is mounted on the corresponding shearing arm support (84) via a rotating shaft. The force-bearing end (81) and the shearing bearing end (82) are located on both sides of the rotating connection part (83), so that the shearing arm (8) forms a lever structure with the rotating connection part (83) as the fulcrum. After the multiple shear arms (8) are deployed, the multiple shear bearing ends (82) are distributed circumferentially along the annular bearing surface (4); the inner diameter of the third hole section (3) is greater than the maximum radial outer envelope diameter of the multiple shear arms (8) when they are deployed, so as to provide radial space for the multiple shear arms (8) to deploy in the third hole section (3) and rotate to the retracted state.

4. The in-situ borehole shear strength testing system for underground engineering rock mass according to claim 3, characterized in that, The unfolding drive mechanism includes an axial telescopic rod (9), one end of which is provided with a push plate (91) and the other end with a limiting part (92); the central bearing seat (7) is provided with an axial limiting cavity (93) and an axial hydraulic cavity (94) that are connected along the axial direction; the rod is axially movable and passes through the axial limiting cavity (93); the limiting part (92) is sealed and slidably connected to the inner cavity of the axial hydraulic cavity (94) and can abut against the axial end face of the axial hydraulic cavity (94) to limit the axial movement stroke of the axial telescopic rod (9); The axial hydraulic chamber (94) is connected to the first oil passage (11). When the first oil passage (11) supplies oil, the hydraulic pressure acts on the limiting part (92), pushing the axial telescopic rod (9) to move in the direction of the shear arm (8), so that the push plate (91) pushes against the multiple force-bearing ends (81). After the first oil passage (11) is depressurized, the continuous pushing action of the push plate (91) on the multiple force-bearing ends (81) is released.

5. The in-situ borehole shear strength testing system for underground engineering rock mass according to claim 3, characterized in that, The normal loading mechanism includes a plurality of normal loading members (10) distributed circumferentially along the central bearing seat (7). Each normal loading member (10) includes an abutment part (101), a guide rod part (102), and a limiting head (103) disposed at the radial inner end of the guide rod part (102). The abutment part (101) is threaded to the radial outer end of the guide rod part (102). The radial outer side of the abutment part (101) is provided with an arc-shaped abutment surface that extends circumferentially along the second hole section (2) and is adapted to its inner wall. When the multiple shear arms (8) are in the unfolded state and the multiple normal loading members (10) are in the radial loading position, the side of each shear bearing end (82) facing the corresponding abutment (101) and the side of the corresponding abutment (101) facing the shear bearing end (82) fit together to form a splicing structure distributed circumferentially along the central bearing seat (7). The central support (7) is provided with a plurality of radially extending radial guide holes (104) and limiting grooves (105) that are respectively connected to the radial inner ends of the plurality of radial guide holes (104). Each radial guide hole (104) is threaded to a limiting ring (95). The middle part of the limiting ring (95) is provided with a through hole that is coaxially connected to the radial guide hole (104). The guide rod (102) movably passes through the middle of the limiting ring (95) and is inserted into the radial guide hole (104). The limiting head (103) is sealed and slidably disposed in the limiting groove (105) and can abut against one end of the limiting ring (95) facing the limiting groove (105) to limit the maximum stroke of the normal loading member (10) moving radially outward.

6. The in-situ borehole shear strength testing system for underground engineering rock mass according to claim 5, characterized in that, The mating end faces of the central bearing seat (7) and the connecting seat (71) are provided with an annular connecting groove (121), and the annular connecting groove (121) is connected to the second oil passage (12); the central bearing seat (7) is provided with a plurality of branch channels (122) distributed circumferentially, one end of each branch channel (122) is connected to the annular connecting groove (121), and the other end is connected to the corresponding limiting groove (105); The limiting head (103) forms a piston pressure surface on the side facing the corresponding branch channel (122). When the second oil circuit (12) supplies pressure, the pressure medium passes through the annular connecting groove (121) and multiple branch channels (122) in sequence into the corresponding limiting groove (105) and acts on the corresponding limiting head (103) to push multiple normal loading members (10) to move radially outward, so that multiple abutting parts (101) abut against the inner wall of the second hole section (2).

7. The in-situ borehole shear strength testing system for underground engineering rock mass according to claim 3, characterized in that, The traction rod (6) can move in the direction toward the orifice; When the traction rod (6) moves in the direction toward the orifice, the plurality of shear bearing ends (82) abut against the annular bearing surface (4) and apply an axial shear load to the annular rock mass (5) to be sheared through the annular bearing surface (4).

8. A testing method using the in-situ borehole shear strength testing system for underground engineering rock mass according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1, a first hole segment (1) is formed in the rock mass to be tested, and a second hole segment (2) is formed at the bottom of the first hole segment (1) along the drilling axis. A third hole segment (3) is formed by post-expansion on the bottom side of the second hole segment (2), so that the inner diameter of the first hole segment (1) is greater than the inner diameter of the second hole segment (2), and the inner diameter of the third hole segment (3) is greater than the inner diameter of the second hole segment (2). An annular bearing surface (4) is formed between the second hole segment (2) and the third hole segment (3), and an annular rock mass to be sheared (5) is formed on the radially outer side of the second hole segment (2). S2, so that the multiple shear arms (8) are in a retracted state, the test device is sent into the variable diameter borehole, the central bearing seat (7) is located in the second hole section (2), and the multiple shear arms (8) enter the third hole section (3). S3, oil is supplied to the axial hydraulic chamber (94) through the first oil passage (11), pushing the axial telescopic rod (9) to move along the axial direction, so that the push plate (91) pushes against multiple force-bearing ends (81), and multiple shear arms (8) rotate around the corresponding rotating connection part (83) to the unfolded state, and multiple shear bearing ends (82) abut against the annular bearing surface (4). S4, the second oil passage (12) pushes multiple normal loading members (10) to move radially outward, so that multiple abutting parts (101) abut against the inner wall of the second hole section (2), and applies a predetermined radial normal load to the annular rock mass to be sheared (5); S5, under the condition of maintaining the radial normal load, drive the traction rod (6) to move towards the orifice, so that the central bearing seat (7) drives multiple shear arms (8) to move towards the orifice, and apply axial shear load to the annular rock mass (5) through the annular bearing surface (4) until the annular rock mass (5) undergoes shear failure along its outer periphery. S6. During the execution of steps S4 and S5, the radial normal load, the axial load borne by the traction rod (6), and the axial displacement of the traction rod (6) are collected simultaneously.

9. The method for testing the in-situ shear strength of rock mass in underground engineering according to claim 8, characterized in that, Before conducting the formal shear test, a pre-test annular rock mass (5) to be sheared is first prepared at the bottom of the current hole. The test device is sent into the variable diameter borehole so that multiple normal loading elements (10) abut against the inner wall of the second hole section (2) and the radial normal load is gradually increased. Under the condition of not performing axial shear loading, the pre-test annular rock mass (5) to be sheared is subjected to compressive failure. The radial normal load corresponding to the compressive failure is determined as the compressive ultimate load. After the pressure failure test is completed, the normal loading mechanism is depressurized and the multiple shear arms (8) are rotated to the retracted state to remove the test device from the variable diameter borehole. Using a drill bit that matches the inner diameter D1 of the first borehole section (1), the pre-test annular rock mass (5) that has already undergone pressure failure and the adjacent disturbed rock mass are removed, and the bottom of the main borehole is pushed deeper to the deep boundary of the original third borehole section (3). After the new hole is advanced, a small-diameter coaxial hole with an inner diameter of D2 is machined along the borehole axis, and the hole bottom side of the small-diameter coaxial hole is expanded to form a new third hole segment with an inner diameter of D3 (3), thereby forming a new annular bearing surface (4) and a new complete annular rock mass to be sheared (5) at the current hole bottom. The testing device was reinserted into the borehole to conduct a formal shear test on the newly formed annular rock mass to be sheared (5), wherein the radial normal load used in the formal shear test was not greater than the bearing capacity limit load. Each annular rock mass (5) used for formal shear testing is subjected to only one destructive shear test. After each formal shear test is completed, the axial shear load is removed in sequence, the normal loading mechanism is depressurized, multiple shear arms (8) are rotated to the retracted state and the test device is removed. Then, the annular rock mass (5) that has been tested and destroyed and the adjacent disturbed rock mass are removed, and a new annular rock mass (5) is prepared to be re-prepared at the depth of the borehole. By changing the radial normal load level corresponding to different formal shear tests, at least three sets of mutually independent formal shear test data are obtained.

10. The method for testing the in-situ shear strength of rock mass in underground engineering according to claim 9, characterized in that, Based on the total radial normal force applied by multiple normal loading elements and the pre-obtained normal load calibration relationship, the equivalent normal stress σ on the predetermined shear failure region is determined. ni ; Equivalent normal stress σ ni Determined according to the following formula: s ni =K n ； Among them, K n The normal load transfer factor, F, can be obtained through standard ring specimens, indoor calibration tests, or numerical analysis. ni Let A be the total normal force corresponding to the i-th formal shear test. s Let be the shear area of ​​the i-th test group; Peak shear stress τ i Determined according to the following formula: t i = ; Among them, F f F is the correction value for the no-load friction of the device. si The peak shear force of the i-th test group; Let D be the equivalent diameter of the predetermined shear failure zone of the annular rock mass (5) corresponding to the i-th formal shear test. s The axial length is L s Then the effective shear area A s According to A s =πD s L s Sure; The peak shear stress τ obtained from at least three sets of formal shear tests i and equivalent normal stress σ ni Substituting into the Mohr-Coulomb relation τ = c + σ n Linear fitting was performed using tanφ to obtain the cohesion c and internal friction angle φ of the rock mass to be tested; the compressive failure data of the pre-tested annular rock mass to be sheared (5) did not participate in the linear fitting.

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