A step-variable-diameter rock direct shear test machine and method

Abstract

This invention discloses a stepped variable-diameter direct shear testing machine and method for rock testing, belonging to the technical field of direct shear testing equipment. Through the stepped structure of the left and right shear boxes, this invention allows the sample to form multiple potential shear surfaces during the shearing process. That is, the contact surface of each step is a potential shear surface, allowing the rock sample to fail along its natural weak points rather than being forcibly confined to a single fixed interface, conforming to the actual failure law of rocks. Simultaneously, the variable-diameter structure ensures a gradual, stepped transition in the effective shear area during shearing, avoiding stress fluctuations caused by abrupt changes in effective area, improving stress distribution uniformity, and enhancing the accuracy of rock testing.

Description

Technical Field

[0001] This invention belongs to the technical field of direct shear testing equipment, and particularly relates to a step-type variable diameter rock direct shear testing machine and method. Background Technology

[0002] The shear strength parameters of rocks include the internal friction angle and cohesion, which are core basic data in geotechnical engineering design, geological disaster prevention and control, and stability assessment of underground engineering. As a key device for measuring these parameters, the direct shear testing machine has been widely used in engineering scenarios such as water conservancy and hydropower, tunnels and bridges, and mining, as well as in geotechnical mechanics research.

[0003] The existing rock direct shear testing machine mainly consists of a main frame, a loading system, a shear box system, and a measurement and control system. It obtains shear strength parameters by applying a fixed normal stress to the rock sample and then applying a horizontal shear force until the sample fails. The loading system provides vertical pressure and horizontal shear thrust. The shear box system includes an upper shear box for fixing the upper part of the sample and a lower shear box that can move horizontally. The lower shear box and the upper shear box form a shear surface. The measurement and control system measures shear displacement and vertical deformation data and realizes automatic loading, data acquisition and processing through a micro-control system.

[0004] However, current direct shear testing machines use upper and lower shear boxes with the same inner diameter, and the shear surface is forcibly limited to the interface between the upper and lower boxes. This interface is not the natural weak surface of the rock sample, which makes the test results unable to truly reflect the actual shear resistance of the rock in the engineering environment. This error is more significant for rocks containing joints, fissures or clay interlayers, thus affecting the accuracy of rock shear strength determination. Summary of the Invention

[0005] The purpose of this invention is to provide a stepped variable-diameter rock shear testing machine, which utilizes the stepped structure of the left and right shear boxes to form multiple potential shear surfaces in the sample during the shearing process, thereby improving the accuracy of rock shear strength determination.

[0006] The present invention is achieved through the following technical solutions.

[0007] The present invention provides a stepped variable diameter rock direct shear testing machine, including a base, on which a height-adjustable support platform is installed, and an alignment line for limiting the placement position of the rock is provided on the support platform; A frame is fixed to the upper surface of the base. A first hydraulic cylinder is installed at the upper end of the frame. A pressure block for applying vertical pressure to the support platform is installed at the telescopic end of the first hydraulic cylinder. The shear box body includes a left shear box and a right shear box with a stepped variable diameter structure; A horizontal adjustment mechanism is installed on one side of the frame, and the left shear box is detachably connected to the horizontal adjustment mechanism through a first connecting mechanism; The second hydraulic cylinder is installed on the other side of the frame, and the right shear box is connected to the telescopic end of the second hydraulic cylinder through the second connecting mechanism.

[0008] Preferably, both the left and right shear boxes contain at least two concentric steps. The number of steps in the left and right shear boxes can be adjusted, and the steps of the left and right shear boxes complement each other. The mating surfaces of each step form a shearing surface during the shearing process.

[0009] Preferably, the right shear box includes a first fixed cylinder, a first middle cylinder, and an inner cylinder. The diameters of the inner cylinder, the first middle cylinder, and the first fixed cylinder increase sequentially to form a three-stage stepped variable diameter structure. The first fixed cylinder, the first middle cylinder, and the inner cylinder are located on the same axis. The first middle cylinder and the inner cylinder are inserted into the interior of the first fixed cylinder, and the first middle cylinder and the inner cylinder are connected to the first fixed cylinder by a first long bolt.

[0010] Preferably, the first middle cylinder and the inner cylinder have an integrally formed first protrusion on the side wall of the insertion end, and the first fixed cylinder has an annular groove inside for the insertion of the first middle cylinder, the inner cylinder and the first protrusion. The first fixed cylinder, the first middle cylinder and the inner cylinder all have a first mounting hole for the first long bolt to pass through, and the first long bolt passes through the first mounting hole and is threaded with a nut.

[0011] Preferably, the left shear box includes a second fixed cylinder with one open end, a second middle cylinder with both open ends, and an inner rod. The diameters of the inner rod, the second middle cylinder, and the second fixed cylinder increase sequentially to form a three-stage stepped variable diameter structure. The second middle cylinder and the inner rod are inserted into the interior of the second fixed cylinder and connected by a second long bolt.

[0012] Preferably, the second fixed cylinder, the second middle cylinder, and the inner rod are all provided with a second mounting hole for the second long bolt to pass through. The second long bolt passes through the second mounting hole and is threaded with a nut. The outer wall of one end of the second middle cylinder and the outer wall of one end of the inner rod are integrally formed with a second protrusion. The interior of the second fixed cylinder is provided with a mounting groove for the second middle cylinder, the inner rod, and the second protrusion to be inserted.

[0013] Preferably, a lifting mechanism is installed at the lower end of the support platform, and a transmission mechanism for driving the lifting mechanism to perform lifting actions is installed inside the base. One end of the transmission mechanism is equipped with a drive mechanism with a locking function, and the drive mechanism is installed on one side of the base.

[0014] Preferably, the lifting mechanism includes a U-shaped plate fixed to the lower surface of the support platform and an adjusting rod rotatably connected to the upper surface of the base. The U-shaped plate is slidably connected to the base, and the lower end of the U-shaped plate is located inside the base. The base has a sliding hole for the U-shaped plate to slide. The upper outer wall of the adjusting rod is provided with an external thread section, and the lower surface of the support platform has a screw hole for the upper end of the adjusting rod to be screwed in.

[0015] Preferably, the transmission mechanism includes a driving rod, a first driven rod, and two second driven rods rotatably connected to the inner wall of the base, as well as toothed plates fixed to the inner walls on both sides of the U-shaped plate. A first gear is fixed on the driving rod and the first driven rod, and the two first gears mesh with each other, and each of the two first gears meshes with the toothed plates on the U-shaped plate. A second gear is fixed on the second driven rod, and the second gear on one of the second driven rods meshes with the first gear on the driving rod. A bevel gear is fixed to the lower end of the adjusting rod and both ends of the other second driven rod, and the bevel gear on the adjusting rod meshes with the bevel gear on the second driven rod. One end of the driving rod extends to the outside of the base and is connected to the drive mechanism.

[0016] Preferably, the driving mechanism includes a limiting sleeve fixed to the outer wall of the base and a plug rod slidably inserted into the end of the driving rod. One end of the plug rod is fixed with a limiting block that matches the limiting sleeve. The limiting block can be inserted into the interior of the limiting sleeve. One end of the limiting block is fixed with a turntable. The end of the driving rod is located inside the limiting sleeve and is not connected to the limiting sleeve. The end of the driving rod has an insertion hole for the other end of the plug rod to be inserted into. The side wall of the insertion hole has a moving groove. The other end of the plug rod has a limiting rod fixed to the side wall that slides in the moving groove.

[0017] Preferably, the leveling mechanism includes a screw threaded to one side of the frame, one end of the screw is fixed with an adjusting hand disc, a limiting mechanism for limiting the rotational position of the adjusting hand disc is installed on the outer wall of one side of the frame, and the first connecting mechanism is installed at the other end of the screw.

[0018] Preferably, the limiting mechanism includes a cylinder fixed to the outer wall of the frame, a spring fixed inside the cylinder, a movable rod fixed to one end of the spring, one end of the movable rod sliding inside the cylinder, and a stop block rotatably connected to the other end of the movable rod. An L-shaped rod is fixed to one end of the stop block, and a stop bar is fixed to the outer wall of the cylinder near the stop block. When the spring is not compressed, the stop block passes through the adjusting hand disc, and the stop bar is separated from the L-shaped rod. When the spring is compressed, the stop block moves away from the adjusting hand disc, and rotating the stop block engages the L-shaped rod with the stop bar.

[0019] Preferably, the first connecting mechanism includes a fixed base for connecting with a horizontal adjustment mechanism and an insert block fixed on the left shear box. One end of the fixed base has a slot for inserting the insert block. The insert block is connected to the fixed base by a hand-tightening bolt. The insert block has a through hole for the hand-tightening bolt connection.

[0020] A method for using a stepped variable-diameter rock testing machine includes the following steps: S1. Based on the characteristics of the rock sample, assemble the left shear box and the right shear box so that the steps of the left shear box and the steps of the right shear box complement each other to form at least two potential shear surfaces. The left shear box is detachably connected to the horizontal adjustment mechanism and the right shear box is detachably connected to the telescopic end of the second hydraulic cylinder through the first connecting mechanism and the second connecting mechanism, respectively. S2. Adjust the height of the bearing platform according to the height of the rock sample so that the shear box body is adapted to be clamped in the middle of the rock sample. After adjustment, lock the height of the bearing platform. S3. Place the rock sample on the alignment line of the bearing platform, so that the center of the sample coincides with the axis of the pressure block and the main body of the shear box. Rotate the horizontal adjustment mechanism to push the left shear box closer to the sample, and cooperate with the right shear box to achieve stable clamping of the rock sample. S4. Start the first hydraulic cylinder to apply a preset vertical normal stress and maintain stability; S5. Start the second hydraulic cylinder to apply an increasing horizontal shear force, and collect shear force, displacement and vertical deformation data in real time until the sample fails. S6. Observe and record the morphology of the failure surface, calculate the shear strength by combining the collected data with the effective shear area, fit the test results under multiple sets of different vertical stresses, and obtain the internal friction angle and cohesion of the rock.

[0021] The beneficial effects of this invention are as follows: 1. This invention utilizes a stepped structure of left and right shear boxes to create multiple potential shear surfaces for the sample during shearing. Each step's contact surface is a potential shear surface, allowing the rock sample to break along its natural weak points rather than being forced into a single fixed interface, thus conforming to the actual failure characteristics of rocks. Simultaneously, the variable diameter structure ensures a gradual, stepped transition in the effective shear area during shearing, avoiding stress fluctuations caused by abrupt changes in effective area, improving stress distribution uniformity, and enhancing the accuracy of rock measurements.

[0022] 2. The present invention uses a height-adjustable support platform. When measuring rocks of different heights, the position of the shear box body clamping the rock can be adjusted by adjusting the position of the support platform, so as to provide a horizontal force to the middle of the rock and improve the force balance of the rock test.

[0023] 3. Both the left and right shear boxes of this invention are modular assembly configurations, which can adjust the number of steps in the stepped variable diameter structure according to actual usage needs, thereby improving the flexibility of use. Attached Figure Description

[0024] Figure 1 A schematic diagram of the structure according to an embodiment of the present invention is shown; Figure 2 A schematic diagram of the internal structure of the base according to an embodiment of the present invention is shown; Figure 3 A schematic diagram of a U-shaped plate structure according to an embodiment of the present invention is shown; Figure 4 A schematic diagram of the transmission mechanism structure according to an embodiment of the present invention is shown; Figure 5 A schematic diagram of the drive mechanism structure according to an embodiment of the present invention is shown; Figure 6 A schematic diagram of the cross-sectional structure of the left shear box according to an embodiment of the present invention is shown; Figure 7 A schematic diagram of the exploded structure of the left shear box according to an embodiment of the present invention is shown; Figure 8 An exploded view of the left shear box and the first connecting mechanism according to an embodiment of the present invention is shown; Figure 9 A schematic diagram of the cross-sectional structure of the right shear box according to an embodiment of the present invention is shown; Figure 10 An exploded view of the right shear box and the second connecting mechanism according to an embodiment of the present invention is shown. Figure 11 A schematic diagram of the exploded structure of the right shear box according to an embodiment of the present invention is shown; Figure 12 An exploded view of the limiting mechanism according to an embodiment of the present invention is shown.

[0025] In the diagram: 1. Base; 2. Frame; 3. Support platform; 4. First hydraulic cylinder; 5. Pressure block; 6. Second hydraulic cylinder; 7. Right shear box; 71. First fixed cylinder; 72. First middle cylinder; 73. Inner cylinder; 74. First long bolt; 75. First protrusion; 76. First mounting hole; 77. Annular groove; 8. Left shear box; 81. Second fixed cylinder; 82. Second middle cylinder; 83. Inner rod; 84. Second protrusion; 85. Second mounting hole; 86. Second long bolt; 87. Nut; 88. Mounting groove; 9. Adjusting hand disc; 10. Limiting mechanism; 101. Cylinder; 102. Moving rod; 103. Spring; 104. 105. Stop bar; 106. L-shaped rod; 11. Drive mechanism; 1101. Turntable; 1102. Limiting block; 1103. Insert rod; 1104. Limiting rod; 1105. Limiting sleeve; 1106. Moving groove; 12. Lifting mechanism; 121. U-shaped plate; 122. Tooth plate; 123. Adjusting rod; 124. Transmission mechanism; 1241. First driven rod; 1242. First gear; 1243. Driving rod; 1244. Second driven rod; 1245. Second gear; 1246. Bevel gear; 125. Screw hole; 13. Fixed seat; 14. Inserting block; 15. Slot; 16. Hand-tightening bolt. Detailed Implementation

[0026] The technical solution of the present invention is further described below, but the scope of protection is not limited to what is described.

[0027] Example: like Figures 1 to 12 As shown, a stepped variable-diameter rock direct shear testing machine includes a base 1, a frame 2, a shear box body, a horizontal adjustment mechanism, and a second hydraulic cylinder 6. The base 1 is equipped with a height-adjustable support platform 3, which has alignment lines to limit the placement of the rock. Figure 1 As shown, the alignment line includes multiple rectangular lines and multiple circular lines. The multiple rectangular lines and multiple circular lines are concentrically set, and the number of rectangular lines and circular lines decreases from the outside to the inside. This can be used for preliminary positioning of rocks of different shapes, so that when the pressure block 5 is pressed down, the pressing accuracy of the rock is improved and the pressure deviation is prevented. The lower end of the support platform 3 is equipped with a lifting mechanism 12, and the base 1 is equipped with a transmission mechanism 124 for driving the lifting mechanism 12 to perform lifting and lowering actions. One end of the transmission mechanism 124 is equipped with a drive mechanism 11 with a locking function. The drive mechanism 11 is installed on one side of the base 1, so that the drive mechanism 11 can drive the transmission mechanism 124 to perform lifting and lowering actions, thereby adjusting the position of the support platform 3, so that the shear box body can apply a horizontal shearing force to the middle of the rock sample. The lifting mechanism 12 includes a U-shaped plate 121 fixed to the lower surface of the support platform 3 and an adjusting rod 123 rotatably connected to the upper surface of the base 1. The U-shaped plate 121 is slidably connected to the base 1, and the lower end of the U-shaped plate 121 is located inside the base 1. The base 1 has a sliding hole for the U-shaped plate 121 to slide on the base 1. The upper outer wall of the adjusting rod 123 is provided with an external thread section. The lower surface of the support platform 3 has a screw hole 125 for the upper end of the adjusting rod 123 to be screwed in. There are two adjusting rods 123. At the center of the support platform 3, the adjusting rod 123 and the U-shaped plate 121 provide support from all sides of the support platform 3, ensuring the stability of the support platform 3 and preventing it from tilting when pressure is applied. By rotating the adjusting rod 123 and using the constraint of the U-shaped plate 121, the length of the adjusting rod 123 screwed into the screw hole 125 is adjusted to drive the lifting rod to rise or fall. When measuring rocks at different heights, the position of the shear box body clamping the rock is adjusted by adjusting the position of the support platform 3, so as to provide a horizontal force to the center of the rock and improve the force balance of the rock test. The transmission mechanism 124 includes a driving rod 1243 rotatably connected to the inner wall of the base 1, a first driven rod 1241, and two second driven rods 1244, as well as toothed plates 122 fixed to the inner walls of both sides of the U-shaped plate 121. A first gear 1242 is fixed to the driving rod 1243 and the first driven rod 1241. The two first gears 1242 mesh, and each of the two first gears 1242 meshes with a toothed plate 122 on the U-shaped plate 121. A second gear 1244 is fixed to the second driven rod 1244. Two gears 1245, one of which is a second gear 1245 on a second driven rod 1244 that meshes with a first gear 1242 on a driving rod 1243. The lower end of the adjusting rod 123 and both ends of the other second driven rod 1244 are fixed with bevel gears 1246, and the bevel gears 1246 on the adjusting rod 123 mesh with the bevel gears 1246 on the second driven rod 1244. One end of the driving rod 1243 extends to the outside of the base 1 and is connected to the drive mechanism 11. The drive mechanism 11 drives the active rod 1243 to rotate, which in turn drives the U-shaped plate 121 to rise or fall via the first gear 1242. At the same time, the first gear 1242 and the second gear 1245 drive the second driven rod 1244 to rotate, which in turn drives the adjusting rod 123 to rotate via the bevel gear 1246. As the U-shaped plate 121 rises or falls, the adjusting rod 123 can shorten or lengthen its length within the thread, causing the support plate to rise or fall. By utilizing the cooperation between the second driven rod 1244 and the second gear 1245 and the first gear 1242, the rotational force of the active rod 1243 can be transmitted to the middle position of the support platform 3, ensuring the stability of the support platform 3 during measurement.

[0028] The driving mechanism 11 includes a limiting sleeve 1105 fixed to the outer wall of the base 1 and an insert rod 1103 slidably inserted into the end of the driving rod 1243. One end of the insert rod 1103 is fixed with a limiting block 1102 that matches the limiting sleeve 1105. Both the limiting block 1102 and the limiting sleeve 1105 are polygonal in shape. The limiting block 1102 can be inserted into the interior of the limiting sleeve 1105. One end of the limiting block 1102 is fixed with a turntable 1101. The driving rod 1243... The end of 243 is located inside the limiting sleeve 1105 and is not connected to the limiting sleeve 1105. The end of the active rod 1243 is provided with a hole for the other end of the insertion rod 1103 to be inserted. The side wall of the insertion hole is provided with a moving groove 1106. The other side wall of the insertion rod 1103 is fixed with a limiting rod 1104 that slides in the moving groove 1106. By sliding the limiting rod 1104 in the moving groove 1106, the limiting block 1102 can be prevented from being pulled out excessively and detached from the active rod 1243. When the drive rod 1243 rotates, the turntable 1101 is pulled outward to disengage the limiting block 1102. Rotating the turntable 1101 causes the transfer to drive the drive rod 1243 to rotate through the limitation of the limiting rod 1104. When the drive rod 1243 is locked, the turntable 1101 pushes the limiting block 1102 towards the drive rod 1243, causing the limiting block 1102 to insert into the limiting sleeve 1105 and lock the turntable 1101. At this time, the transfer cannot rotate, achieving the effect of automatically limiting the drive rod 1243 after rotation.

[0029] The frame 2 is fixed on the upper surface of the base 1. A first hydraulic cylinder 4 is installed at the upper end of the frame 2. A pressure block 5 for applying vertical pressure to the support platform 3 is installed at the telescopic end of the first hydraulic cylinder 4. The pressure block 5 is driven to press down by the first hydraulic cylinder 4, so that the pressure block 5 applies vertical pressure to the rock on the support platform 3. The pressure block 5 is cylindrical, and the center of the pressure block 5 is on the same horizontal line as the center of the support platform 3, so that the pressure block 5 can apply pressure from the middle of the support platform 3. The shear box body includes a left shear box 8 and a right shear box 7 with a stepped variable diameter structure. The left shear box 8 and the right shear box 7 each contain at least two concentric steps. The number of steps of the left shear box 8 and the right shear box 7 can be adjusted. The steps of the left shear box 8 and the steps of the right shear box 7 complement each other. The mating surface of each step forms a shearing surface during the shearing process. Furthermore, the right shear box 7 includes a first fixed cylinder 71, a first middle cylinder 72, and an inner cylinder 73. The diameters of the inner cylinder 73, the first middle cylinder 72, and the first fixed cylinder 71 increase sequentially, forming a three-stage stepped variable diameter structure. The first fixed cylinder 71, the first middle cylinder 72, and the inner cylinder 73 are located on the same axis. The first middle cylinder 72 and the inner cylinder 73 are inserted into the interior of the first fixed cylinder 71, and the first middle cylinder 72 and the inner cylinder 73 are connected to the first fixed cylinder 71 by a first long bolt 74. The ends of the first fixed cylinder 71, the first middle cylinder 72, and the inner cylinder 73 are flush. The first fixed cylinder 71 is a cylindrical shape with one open end, while the first middle cylinder 72 and the inner cylinder 73 are cylindrical shapes with both open ends. The insertion and connection of the first fixed cylinder 71 and the inner cylinder 73 with the first fixed cylinder 71 improves the ease of assembly of the right shear box 7. Furthermore, when the components of the right shear box 7 are deformed or worn, they can be disassembled and replaced individually, improving the convenience of maintenance.

[0030] The first middle cylinder 72 and the inner cylinder 73 are integrally formed with a first protrusion 75 on the side wall of the insertion end. The first fixed cylinder 71 has an annular groove 77 for the insertion of the first middle cylinder 72, the inner cylinder 73 and the first protrusion 75, which facilitates the quick insertion of the first middle cylinder 72 and the inner cylinder 73 into the first fixed cylinder 71. The first fixed cylinder 71, the first middle cylinder 72 and the inner cylinder 73 are all provided with a first mounting hole 76 for the first long bolt 74 to pass through. The first long bolt 74 passes through the first mounting hole 76 and is threaded with a nut 87 to improve the connection force between the first middle cylinder 72 and the inner cylinder 73 and the first fixed cylinder 71.

[0031] The left shear box 8 includes a second fixed cylinder 81 with one open end, a second middle cylinder 82 with both open ends, and an inner rod 83. The diameters of the inner rod 83, the second middle cylinder 82, and the second fixed cylinder 81 increase sequentially, forming a three-stage stepped diameter-changing structure. The second middle cylinder 82 and the inner rod 83 are inserted into the interior of the second fixed cylinder 81 and connected by a second long bolt 86. The second fixed cylinder 81, the second middle cylinder 82, and the inner rod 83 are all provided with second mounting holes 85 for the second long bolt 86 to pass through. The hole 85 is threaded with a nut 87. The outer wall of one end of the second middle cylinder 82 and the outer wall of one end of the inner rod 83 are integrally formed with a second protrusion 84. The interior of the second fixed cylinder 81 is provided with an installation groove 88 for the second middle cylinder 82, the inner rod 83 and the second protrusion 84 to be inserted, so that the second middle cylinder 82 and the inner rod 83 are detachable, which is convenient for assembly and disassembly according to actual needs. At the same time, the second middle cylinder 82 or the inner rod 83 can also be assembled in the second fixed cylinder 81 to form a two-stage stepped variable diameter structure according to actual use needs, which improves the flexibility of use.

[0032] The inner rod 83 has the same diameter as the inner cylinder 73, the second middle cylinder 82 has the same inner diameter as the inner cylinder 73, the second middle cylinder 82 has the same outer diameter as the first middle cylinder 72, the first middle cylinder 72 has the same outer diameter as the first fixed cylinder 71, and the second fixed cylinder 81 has the same inner diameter as the first fixed cylinder 71. This allows the left shear box 8 to be set with a three-stage convex step that matches the inner diameter of the right shear box 7, forming a mutually supportive mating structure. The mating surface of each step is a potential shear surface, allowing the rock sample to be damaged along its own natural weak surface, rather than being forcibly confined to a single fixed interface. This conforms to the actual failure law of rocks. At the same time, the variable diameter structure makes the change of the effective shear area during shearing a step-like smooth transition, avoiding normal stress fluctuations caused by abrupt changes in the effective area and improving the uniformity of stress distribution.

[0033] The horizontal adjustment mechanism is installed on one side of the frame 2, and the left shear box 8 is detachably connected to the horizontal adjustment mechanism through the first connecting mechanism; The horizontal adjustment mechanism includes a screw threaded to one side of the frame 2. One end of the screw is fixed with an adjustment hand disc 9. A limiting mechanism 10 for limiting the rotational position of the adjustment hand disc 9 is installed on the outer wall of one side of the frame 2. The first connecting mechanism is installed at the other end of the screw. By rotating the adjustment hand disc 9, the length of the screw between the frame 2 and the adjustment hand disc 9 is adjusted by utilizing the threaded engagement between the screw and the frame 2. This allows the screw to push the left shear box 8 to move. When measuring rocks of different sizes, the left shear box 8 is preferentially adjusted to fit against the rock surface. This limits the position of the rock on the support platform 3 through the support platform 3 and the left shear box 8, further improving the accuracy of the pressure applied to the rock by the pressure block 5.

[0034] The limiting mechanism 10 includes a cylinder 101 fixed to the outer wall of the frame 2. A spring 103 is fixed inside the cylinder 101. A moving rod 102 is fixed to one end of the spring 103. One end of the moving rod 102 slides inside the cylinder 101. A stop block 105 is rotatably connected to the other end of the moving rod 102. An L-shaped rod 106 is fixed to one end of the stop block 105. A stop rod 104 is fixed to the outer wall of the cylinder 101 near the stop block 105. When the spring 103 is not compressed, the stop block 105 passes through the adjusting hand plate 9, and the stop rod 104 is separated from the L-shaped rod 106. The insertion of the moving rod 102 into the adjusting hand plate 9 restricts the rotation of the adjusting hand plate 9, thereby locking the adjusting hand plate 9. When the spring 103 is compressed, the stop block 105 moves away from the adjusting hand plate 9, and rotating the stop block 105 engages the L-shaped rod 106 with the stop rod 104, thereby releasing the restriction on the adjusting hand plate 9 and allowing the adjusting hand plate 9 to drive the screw to rotate.

[0035] The first connecting mechanism includes a fixed base 13 for connecting with the horizontal adjustment mechanism and an insert block 14 fixed on the left shear box 8. One end of the fixed base 13 has a slot 15 for inserting the insert block 14. The insert block 14 is connected to the fixed base 13 by a hand-tightening bolt 16. The insert block 14 has a through hole for the hand-tightening bolt 16 to be connected, so that the left shear box 8 and the horizontal adjustment mechanism are detachable. Different left shear boxes 8 can be replaced according to actual use needs, providing flexibility in the use of the equipment.

[0036] The second hydraulic cylinder 6 is installed on the other side of the frame 2. The right shear box 7 is connected to the telescopic end of the second hydraulic cylinder 6 through the second connecting mechanism, and is used to provide horizontal thrust to the rock.

[0037] The structure of the second connecting mechanism is the same as that of the first connecting mechanism. The second connecting mechanism uses a detachable connection between the right shear box 7 and the second hydraulic cylinder 6, which makes it easy to replace different right shear boxes 7 according to actual usage requirements.

[0038] It should be noted that the direct shear testing machine also includes a measurement system. The measurement system includes sensors for real-time acquisition of the vertical normal stress applied by the first hydraulic cylinder 4, the horizontal shear force applied by the second hydraulic cylinder 6, and the shear displacement and vertical deformation during the shearing process. According to the actual measurement requirements, slots for sensor installation can be opened on the equipment. This invention only improves the structure of the testing machine. The measurement system is used to realize data acquisition and control of the first hydraulic cylinder 4 and the second hydraulic cylinder 6. It is a well-known technology in the field, so it will not be described in detail here.

[0039] During operation, the rock sample is placed on the bearing platform 3 through the alignment line. The drive mechanism 11 drives the transmission mechanism 124 to work, thereby driving the lifting mechanism 12 to raise the bearing platform 3, so that the center of the rock sample is aligned with the axis of the pressure block 5 and the shear box body. Then, the adjustment hand plate 9 is rotated to push the left shear box 8 closer to the rock sample and make contact with the surface of the rock sample. The limiting mechanism 10 is then used to lock the adjustment hand plate 9 to ensure that the position of the left shear box 8 is fixed, providing stable boundary conditions for the shearing process. The first hydraulic cylinder 4 is activated, which drives the pressure block 5 to apply downward pressure. The vertical pressure acts directly on the top of the rock sample. Combined with the relative force of the bearing platform 3, the vertical pressure is evenly transmitted to the sample, forming a preset stable normal stress. Then, the second hydraulic cylinder 6 is activated, which drives the right shear box 7 to move horizontally to the left, applying a continuously increasing horizontal shear force to the rock sample. Combined with the left shear box 8, a shear force mode of right-push and left-fixed is formed. Since the left shear box 8 and the right shear box 7 are stepped variable diameter structures, the contact surfaces of each step constitute potential shear surfaces. Under the action of horizontal shear force, the sample will be damaged along its own natural weak surface, such as joints, fissures, and clay interlayers, rather than being forcibly confined to a fixed interface, which is completely in line with the actual failure law of rocks. The stepped variable diameter structure of the left shear box 8 and the right shear box 7 ensures that the effective shear area transitions smoothly in a stepped manner during the shearing process, avoiding the normal stress fluctuation caused by abrupt changes in the shear area in traditional equipment. At the same time, the concentric stepped design of the left shear box 8 and the right shear box 7 ensures that the horizontal shear force is evenly distributed along the height of the sample, solving the technical problem of edge stress concentration.

[0040] This invention also provides a method for determining the diameter of variable rocks, using a stepped direct shear testing machine for determining variable-diameter rocks as described above, comprising the following steps: S1. Based on the characteristics of the rock sample, assemble the left shear box 8 and the right shear box 7 so that the steps of the left shear box 8 and the steps of the right shear box 7 complement each other to form at least two potential shear surfaces. The left shear box 8 is detachably connected to the horizontal adjustment mechanism and the right shear box 7 is detachably connected to the telescopic end of the second hydraulic cylinder 6 through the first connecting mechanism and the second connecting mechanism, respectively. S2. Adjust the height of the support platform 3 according to the height of the rock sample so that the shear box body is adapted to be clamped in the middle position of the rock sample. After adjustment, lock the height of the support platform 3. That is, drive the transmission mechanism 124 through the drive mechanism 11 with locking function, and then control the lifting mechanism 12 to adjust the height of the support platform 3 so that the shear box body can be accurately clamped in the middle position of the sample, ensuring that the horizontal shearing force acts on the sample in the force-balanced area, avoiding test errors caused by clamping position deviation. After adjustment, fix the height of the support platform 3 through the locking function of the drive mechanism 11 to prevent the support platform 3 from shifting during the test. S3. Place the rock sample on the alignment line of the bearing platform 3, aligning the center of the sample with the axis of the pressure block 5 and the shear box body to avoid bias or shear force deviation. Rotate the horizontal adjustment mechanism to push the left shear box 8 closer to the sample, cooperating with the right shear box 7 to achieve stable clamping of the rock sample. Specifically, determine the number of steps (at least two) according to the test requirements, ensuring that the steps of the left shear box 8 and the steps of the right shear box 7 are completely interlocked, with each step's contact surface forming a potential shear surface. Detachably connect the left shear box 8 to the horizontal adjustment mechanism through the first connecting mechanism. Rotate the adjusting component of the horizontal adjustment mechanism to push the left shear box 8 to one side of the sample until the steps of the left shear box 8 are in contact with the sample surface. Fix the right shear box 7 to the telescopic end of the second hydraulic cylinder 6 through the second connecting mechanism. Adjust the position of the right shear box 7 so that the steps of the right shear box 7 are in contact with the other side of the sample, completing the stable clamping of the sample. The clamping force should be such that the sample does not loosen or produce pre-shear deformation. S4. Start the first hydraulic cylinder 4 to apply the preset vertical normal stress and keep it stable. That is, apply the preset vertical normal stress to the rock sample on the bearing platform 3 through the pressure block 5. The loading process is slow and uniform to avoid the impact load causing the sample to fail prematurely. When the vertical pressure reaches the preset value, keep the pressure stable. The constant normal stress can be maintained by the equipment control system to provide stable boundary stress conditions for subsequent shear tests. S5. Activate the second hydraulic cylinder 6 to apply an increasing horizontal shear force, and collect shear force, displacement, and vertical deformation data in real time until the sample fails. That is, apply a horizontal shear thrust to the sample through the right shear box 7. The loading rate must meet the rock mechanics testing standards and increase slowly to ensure that the sample deformation and stress response are synchronized. During the test, record key data in real time: the magnitude of the horizontal shear force, the amount of shear displacement, and the amount of vertical deformation. Pay special attention to the curve characteristics of the shear force changing with displacement until the sample fails. This is manifested by the shear force reaching its peak and then dropping sharply, or the displacement continuing to increase while the shear force no longer increases. Observe the sample failure process and record which step of the contact surface (or its own natural weak surface) the sample fails along to verify the test logic of non-forced single shear surface. S6. Observe and record the morphology of the failure surface, calculate the shear strength by combining the collected data with the effective shear area, fit the test results under multiple sets of different vertical stresses, and obtain the internal friction angle and cohesion of the rock. It should be noted that after the sample is damaged, the horizontal loading of the second hydraulic cylinder 6 is stopped, and the vertical pressure of the first hydraulic cylinder 4 is gradually unloaded to avoid sudden pressure drop that could cause equipment impact. Adjust the position of the left shear box 8 in the opposite direction by adjusting the horizontal adjustment mechanism, loosen the sample clamp, disassemble the connection between the left / right shear box 7 and the sample, take out the damaged sample, observe and record the morphology of the damaged surface, such as whether it is a natural joint surface or a fracture surface. Reset the equipment: Return the bearing platform 3, pressure block 5, shear box, and hydraulic cylinder extension end to their initial positions, and turn off the equipment power; Shear strength parameter calculation: Based on the peak horizontal shear force or shear force at failure recorded during the test, the preset vertical normal stress, and the effective shear area of ​​the shear box, i.e. the smooth transition area of ​​the stepped variable diameter structure, the rock shear strength is calculated according to the rock shear strength formula: Shear strength τ = peak shear force F / effective shear area A. Combining multiple sets of test data under different vertical normal stresses (the above steps need to be repeated to change the vertical stress value for multiple tests), the internal friction angle and cohesion of the rock are obtained by fitting through the Mohr-Coulomb strength theory, thus completing the determination of the rock shear strength parameters.

Claims

1. A stepped variable-diameter rock testing machine for direct shear testing, characterized in that: Includes a base (1), on which a height-adjustable support platform (3) is installed, and the support platform (3) is provided with alignment lines for limiting the placement position of the rock; The frame (2) is fixed on the upper surface of the base (1). A first hydraulic cylinder (4) is installed at the upper end of the frame (2). A pressure block (5) for applying vertical pressure to the support platform (3) is installed at the telescopic end of the first hydraulic cylinder (4). The shear box body includes a left shear box (8) and a right shear box (7) with a stepped variable diameter structure. A horizontal adjustment mechanism is installed on one side of the frame (2), and the left shear box (8) is detachably connected to the horizontal adjustment mechanism through a first connecting mechanism; The second hydraulic cylinder (6) is installed on the other side of the frame (2), and the right shear box (7) is connected to the telescopic end of the second hydraulic cylinder (6) through the second connecting mechanism.

2. The stepped variable diameter rock testing machine as described in claim 1, characterized in that: The left shear box (8) and the right shear box (7) each contain at least two concentric steps. The number of steps in the left shear box (8) and the right shear box (7) can be adjusted. The steps of the left shear box (8) and the steps of the right shear box (7) complement each other. The mating surface of each step forms a shearing surface during the shearing process.

3. The stepped variable-diameter rock testing machine as described in claim 1, characterized in that: The right shear box (7) includes a first fixed cylinder (71), a first middle cylinder (72) and an inner cylinder (73). The diameters of the inner cylinder (73), the first middle cylinder (72) and the first fixed cylinder (71) increase sequentially to form a three-stage stepped variable diameter structure. The first fixed cylinder (71), the first middle cylinder (72) and the inner cylinder (73) are on the same axis. The first middle cylinder (72) and the inner cylinder (73) are inserted into the inside of the first fixed cylinder (71). The first middle cylinder (72) and the inner cylinder (73) are connected to the first fixed cylinder (71) by a first long bolt (74).

4. The stepped variable diameter rock testing machine as described in claim 3, characterized in that: The first middle cylinder (72) and the inner cylinder (73) have an integrally formed first protrusion (75) on the side wall of the insertion end. The first fixed cylinder (71) has an annular groove (77) for the insertion of the first middle cylinder (72), the inner cylinder (73) and the first protrusion (75). The first fixed cylinder (71), the first middle cylinder (72) and the inner cylinder (73) are provided with a first mounting hole (76) for the first long bolt (74) to pass through. The first long bolt (74) passes through the first mounting hole (76) and is threaded with a nut (87).

5. The stepped variable diameter rock testing machine as described in claim 1, characterized in that: The left shear box (8) includes a second fixed cylinder (81) with one end open, a second middle cylinder (82) with both ends open, and an inner rod (83). The diameters of the inner rod (83), the second middle cylinder (82), and the second fixed cylinder (81) increase sequentially to form a three-stage stepped variable diameter structure. The second middle cylinder (82) and the inner rod (83) are inserted into the interior of the second fixed cylinder (81) and connected by a second long bolt (86).

6. The stepped variable diameter rock testing machine as described in claim 5, characterized in that: The second fixed cylinder (81), the second middle cylinder (82) and the inner rod (83) are all provided with a second mounting hole (85) for the second long bolt (86) to pass through. The second long bolt (86) passes through the second mounting hole (85) and is threaded with a nut (87). The outer wall of one end of the second middle cylinder (82) and the outer wall of one end of the inner rod (83) are integrally formed with a second protrusion (84). The interior of the second fixed cylinder (81) is provided with a mounting groove (88) for the second middle cylinder (82), the inner rod (83) and the second protrusion (84) to be inserted.

7. The stepped variable-diameter rock testing machine as described in claim 1, characterized in that: The lower end of the support platform (3) is equipped with a lifting mechanism (12), and the base (1) is equipped with a transmission mechanism (124) for driving the lifting mechanism (12) to perform lifting actions. One end of the transmission mechanism (124) is equipped with a drive mechanism (11) with a locking function, and the drive mechanism (11) is installed on one side of the base (1).

8. A stepped variable-diameter rock testing machine as described in claim 7, characterized in that: The lifting mechanism (12) includes a U-shaped plate (121) fixed on the lower surface of the support platform (3) and an adjusting rod (123) rotatably connected to the upper surface of the base (1). The U-shaped plate (121) is slidably connected to the base (1). The lower end of the U-shaped plate (121) is located inside the base (1). The base (1) has a sliding hole for the U-shaped plate (121) to slide. The upper outer wall of the adjusting rod (123) is provided with an external thread section. The lower surface of the support platform (3) has a screw hole (125) for the upper end of the adjusting rod (123) to be screwed.

9. A stepped variable-diameter rock testing machine as described in claim 7, characterized in that: The transmission mechanism (124) includes a driving rod (1243), a first driven rod (1241), and two second driven rods (1244) rotatably connected to the inner wall of the base (1), and toothed plates (122) fixed to the inner walls on both sides of the U-shaped plate (121). A first gear (1242) is fixed to the driving rod (1243) and the first driven rod (1241), and the two first gears (1242) mesh with each other, respectively, and each first gear (1242) meshes with a toothed plate (122) on the U-shaped plate (121). A first gear (1242) is fixed to the second driven rod (1244). Two gears (1245), one of which is a second gear (1245) on a second driven rod (1244) meshing with a first gear (1242) on a driving rod (1243), the lower end of the adjusting rod (123) and both ends of the other second driven rod (1244) are fixed with bevel gears (1246), and the bevel gear (1246) on the adjusting rod (123) meshes with the bevel gear (1246) on the second driven rod (1244), and one end of the driving rod (1243) extends to the outside of the base (1) and is connected to the drive mechanism (11).

10. A stepped variable-diameter rock testing machine as described in claim 7, characterized in that: The drive mechanism (11) includes a limiting sleeve (1105) fixed to the outer wall of the base (1) and a plug rod (1103) slidably inserted into the end of the drive rod (1243). One end of the plug rod (1103) is fixed with a limiting block (1102) that matches the limiting sleeve (1105). The limiting block (1102) can be inserted into the interior of the limiting sleeve (1105). One end of the limiting block (1102) is fixed with a rotating... The end of the active rod (1243) is located inside the limiting sleeve (1105) and is not connected to the limiting sleeve (1105). The end of the active rod (1243) is provided with a insertion hole for the other end of the insertion rod (1103) to be inserted. The side wall of the insertion hole is provided with a moving groove (1106). The other side wall of the insertion rod (1103) is fixed with a limiting rod (1104) that slides in the moving groove (1106).

11. A stepped variable-diameter rock testing machine as described in claim 1, characterized in that: The horizontal adjustment mechanism includes a screw threaded to one side of the frame (2), one end of which is fixed with an adjustment hand plate (9), and a limiting mechanism (10) for limiting the rotation position of the adjustment hand plate (9) is installed on the outer wall of one side of the frame (2). The first connecting mechanism is installed at the other end of the screw.

12. The stepped variable-diameter rock testing machine as described in claim 11, characterized in that: The limiting mechanism (10) includes a cylinder (101) fixed to the outer wall of the frame (2). A spring (103) is fixed inside the cylinder (101). A moving rod (102) is fixed to one end of the spring (103). One end of the moving rod (102) slides inside the cylinder (101). A stop block (105) is rotatably connected to the other end of the moving rod (102). An L-shaped rod (105) is fixed to one end of the stop block (105). 06), a stop bar (104) is fixed on the outer wall of the end of the cylinder (101) near the stop block (105). When the spring (103) is not compressed, the stop block (105) passes through the adjusting hand plate (9), and the stop bar (104) is separated from the L-shaped rod (106). When the spring (103) is compressed, the stop block (105) moves away from the adjusting hand plate (9), and rotating the stop block (105) hooks the L-shaped rod (106) with the stop bar (104).

13. A stepped variable-diameter rock testing machine as described in claim 1, characterized in that: The first connecting mechanism includes a fixed base (13) for connecting with the horizontal adjustment mechanism and an insert (14) fixed on the left shear box (8). One end of the fixed base (13) is provided with a slot (15) for inserting the insert (14). The insert (14) and the fixed base (13) are connected by a hand-tightening bolt (16). The insert (14) is provided with a through hole for connecting the hand-tightening bolt (16).

14. A method of using the stepped variable diameter rock testing machine as described in claim 1, characterized in that, Includes the following steps: S1. Based on the characteristics of the rock sample, assemble the left shear box (8) and the right shear box (7) so that the steps of the left shear box (8) and the steps of the right shear box (7) complement each other to form at least two potential shear surfaces. The left shear box (8) is detachably connected to the horizontal adjustment mechanism and the right shear box (7) is detachably connected to the telescopic end of the second hydraulic cylinder (6) through the first connecting mechanism and the second connecting mechanism, respectively. S2. Adjust the height of the support platform (3) according to the height of the rock sample so that the shear box body is adapted to be clamped in the middle of the rock sample. After adjustment, lock the height of the support platform (3). S3. Place the rock sample on the alignment line of the bearing platform (3) so that the center of the sample coincides with the axis of the pressure block (5) and the shear box body. Rotate the horizontal adjustment mechanism to push the left shear box (8) closer to the sample, and cooperate with the right shear box (7) to achieve stable clamping of the rock sample. S4. Start the first hydraulic cylinder (4) to apply the preset vertical normal stress and maintain stability; S5. Start the second hydraulic cylinder (6) to apply an increasing horizontal shear force, and collect shear force, displacement and vertical deformation data in real time until the sample is destroyed. S6. Observe and record the morphology of the failure surface, calculate the shear strength by combining the collected data with the effective shear area, fit the test results under multiple sets of different vertical stresses, and obtain the internal friction angle and cohesion of the rock.

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