A method and equipment for testing variable principal stress in rocks with multiple sets of conjugate joints

Abstract

This invention belongs to the field of rock engineering and provides a method and equipment for testing the variable principal stress of rocks with multiple sets of conjugate joints. The method includes: Step 1, sample processing; Step 2, placing the rock sample on a support frame; Step 3, simultaneously applying pressure from three loading devices, and keeping the pressure constant, loading to, unloading to, and stabilizing before resetting; keeping the pressure constant, loading to, unloading to, and stabilizing before resetting; keeping the pressure constant, continuing to load to, unloading to, and stabilizing before resetting; Step 4, incrementally increasing and repeating Step 3 until the rock sample is destroyed. This invention simulates the stress and failure process of rock masses with multiple sets of "X"-shaped conjugate joints under complex stress environments in real-world conditions through a variable principal stress direction loading and unloading cyclic experimental method, thereby enabling effective experimental analysis of rock masses containing large conjugate joints.

Description

Technical Field

[0001] This invention belongs to the field of rock engineering, specifically relating to an experimental method and equipment for variable principal stress in rocks with multiple sets of conjugate joints. Background Technology

[0002] Due to long-term and complex geological movements, rocks in nature inevitably contain natural defects such as microcracks, faults, and cavities. The initiation, propagation, and connection of cracks within fractured rock masses are contributing factors to engineering accidents.

[0003] Structural planes in rock masses often exist in the form of joints, exhibiting varying lengths, angles, and orientations. Joints, fissures, cleavage surfaces, and weak interlayers within jointed rock masses can all compromise their integrity. Under the compressive and shear forces of external loads, the opening and propagation of wing-shaped cracks at joint tips often lead to rock mass instability and failure. The geometric characteristics of joints, including joint length, dip angle, and continuity, are the main factors influencing the mechanical properties of jointed rock masses. In engineering, conjugate "X"-shaped joints play a controlling role in rock mass stability. Simultaneously, secondary joints also influence rock mass strength; when primary and secondary joints have the same dip direction, the peak strength of a single-jointed rock mass is significantly higher than that of an "X"-shaped jointed rock mass.

[0004] Current research primarily suggests the existence of a set of conjugate "X"-shaped joint fractures in rock masses. Furthermore, cracks in materials are typically simplified into types such as opening, sliding, and tearing. In engineering, joints are rarely simplified to three sets of conjugate "X"-shaped joint fractures. However, in actual engineering projects, factors such as earthquakes and blasting can cause rock masses to exhibit three sets of conjugate "X"-shaped joint fractures in three-dimensional space. Based on these issues, a suitable experimental setup for a model of three sets of conjugate "X"-shaped joint fractures is currently lacking. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method and apparatus for testing variable principal stress in multi-group conjugate jointed rocks, thereby resolving the issues in the prior art. The technical solution adopted by this invention is as follows:

[0006] A method for testing variable principal stress in rocks with multiple sets of conjugate joints, including:

[0007] Step 1, Sample preparation: Prepare rock samples;

[0008] Step 2: Place the rock sample on the support bracket. The support bracket consists of three plates. The three plates are fixedly connected and wrap around one of the top corners of the bottom of the rock sample, so that the rock sample is exposed on three sides. Loading devices are set on the three exposed surfaces respectively. The two opposite sides of the rock sample are the loading devices and the plates respectively.

[0009] Step 3: Apply pressure to the rock sample using a loading device:

[0010] (a) Three loading devices simultaneously apply pressure , and and make ;

[0011] (b) Maintain Constant, Loading to ,uninstall to ,make It becomes the maximum principal stress. The minimum principal stress is reached; after it stabilizes, it is restored. ;

[0012] (c) Maintain Constant, Loading to ,uninstall to ,make It becomes the maximum principal stress. The minimum principal stress is reached; after it stabilizes, it is restored. ;

[0013] (d) Maintain Constant, continue loading to ,uninstall to ,make It becomes the maximum principal stress. The minimum principal stress is reached; after it stabilizes, it is restored. ;

[0014] Step 4, Increment Repeat step three until the rock sample is destroyed.

[0015] An experimental apparatus for variable principal stress in multi-group conjugate jointed rocks, the apparatus comprising: a loading device, a base plate, side plates, a top plate, and a load-bearing support;

[0016] The base plate is connected to the support bracket, which is used to place the rock sample. The support bracket includes three plates, which are fixedly connected and located on three mutually perpendicular spatial planes. The three plates together form a square opening groove, which covers the bottom and top corners of the rock sample, covering three sides of the rock sample and exposing the other three sides. The loading device is respectively set on the three exposed sides, and the two opposite sides of the rock sample are the loading device and the plate respectively.

[0017] A top plate is fixedly connected to the top of the loading device located above the rock sample, and the side plates are fixedly connected to the outer ends of the loading devices located on both sides of the rock sample, with the bottom of the side plates connected to the bottom plate.

[0018] The loading device is used to apply pressure to the wall of the rock sample.

[0019] Furthermore, four side plates are provided, two of which are connected to the loading device, and the other two adjacent side plates are fixedly connected to the plate body by support columns.

[0020] Furthermore, a lifting plate is fixedly connected to the bottom of the four side plates. The lifting plate is located above the base plate. An inclined connecting rod is provided at both ends of the lifting plate. The top of the connecting rod is rotatably connected to the end of the lifting plate, and the bottom of the connecting rod is rotatably connected to a sliding plate. The sliding plate is slidably connected to the base plate.

[0021] A limiting sleeve is fixedly connected to the bottom of the plate located at the bottom. A top rod can slide through the lifting plate, and the top of the top rod can slide through the limiting sleeve. A through hole adapted to the top rod is provided on the plate located at the bottom. The through hole is coaxially arranged with the limiting sleeve. The bottom of the top rod is connected to the bottom plate.

[0022] The top of the top plate is rotatably connected to the top of the sliding rod at both ends. The two opposite side plates are provided with through holes adapted to the sliding rod, through which the sliding rod can slide. The bottom plate is provided with positioning holes adapted to the sliding rod, and the bottom of the sliding rod passes through the lifting plate and the sliding plate in sequence and is located in the positioning hole.

[0023] The positioning hole is fixedly connected to the protrusion, and the bottom of the slide rod is provided with an annular groove that matches the protrusion. The annular groove has a notch, and the protrusion is used to pass through the notch and rotate to engage in the annular groove to form an axial constraint on the slide rod.

[0024] The slide bar is used to slide upwards to disengage from the slide plate, thereby causing the lifting plate to descend under its own weight, and causing the top rod to lift the rock sample.

[0025] Furthermore, the loading device includes a fixed plate, a driving device, a connecting plate, a rotating seat, a lead screw, a threaded sleeve, a connecting rod, a pressure plate, and a limiting structure;

[0026] The fixed plate and the connecting plate are arranged side by side. The driving device is installed between the fixed plate and the connecting plate. The output end of the driving device passes through the connecting plate and is fixedly connected to the rotating seat. The rotating seat is rotatably mounted on the connecting plate. One end of the rotating seat away from the driving device is fixedly connected to one end of the lead screw. The other end of the lead screw is threadedly connected to the threaded sleeve. The side of the threaded sleeve is connected to the connecting rod. The connecting rod is parallel to the axis of the lead screw. The end of the connecting rod away from the connecting plate is connected to the pressure plate.

[0027] The driving device is used to drive the rotating seat to rotate, causing the lead screw to rotate; the side of the connecting rod is connected to the limiting structure, which is used to limit the rotation of the connecting rod around the lead screw, thereby causing the threaded sleeve to move along the lead screw, and the pressure plate to face the wall of the rock sample.

[0028] Furthermore, the limiting structure includes a vertical rod, a protrusion, a stop block, a second limiting block, an intermediate plate, and a cover plate;

[0029] The upright and the connecting rod are parallel and spaced apart. The upright is located on the side of the connecting rod away from the lead screw. One end of the upright is fixedly connected to the connecting plate. The upright is provided with a second waist-shaped through hole. The middle plate is located in the second waist-shaped through hole. The end of the middle plate facing the connecting rod is fixedly connected to the second limiting block. The end of the middle plate away from the connecting rod is detachably connected to the cover plate.

[0030] The connecting rod is fixedly connected to the protrusion on its side, and the end of the protrusion is detachable from the stop. The second limiting block is located on the rotation path of the stop and is used to abut against the stop to form a circumferential constraint.

[0031] The intermediate plate is slidably located within the second waist-shaped through hole, and the cover plate and the upright are connected by teeth to constrain the vertical height;

[0032] By adjusting the height of the second limiting block, the stroke of the stop block disengaging from the second limiting block is changed, thereby adjusting the movement of the threaded sleeve and thus adjusting the maximum pressure value applied by the pressure plate.

[0033] Furthermore, the limiting structure also includes a first limiting block, a transmission block, a telescopic rod, and a lifting mechanism;

[0034] The upright has a first oblong through hole, and the transmission block is disposed in the first oblong through hole. The end of the transmission block facing the connecting rod is fixedly connected to the first limiting block. The first limiting block is located above the second limiting block. The end of the transmission block away from the connecting rod is fixedly connected to the telescopic rod. The telescopic rod is parallel to the upright. The end of the telescopic rod away from the transmission block is connected to the lifting mechanism for lifting the first limiting block.

[0035] When the lead screw rotates and moves the pressure plate toward the rock sample, the first limiting block moves to its highest height, and the bottom of the first limiting block and the top of the second limiting block form a gap; when the stop block disengages from the second limiting block, the stop block enters the gap above the second limiting block;

[0036] When the lead screw rotates and moves the pressure plate away from the rock sample, the first limiting block moves to its lowest height, and the bottom of the first limiting block is in contact with the top of the second limiting block; the stop block abuts against the lower end of the first limiting block and moves onto the second limiting block.

[0037] Furthermore, the lifting mechanism includes a linear drive device;

[0038] The linear pusher is mounted on the connecting plate, and the output end of the linear pusher is fixedly connected to the bottom of the telescopic rod. The linear pusher is used to push the telescopic rod up and down.

[0039] Furthermore, the fixing plates of the three loading devices are respectively fixedly connected to the top plate and the two side plates.

[0040] The present invention has the following beneficial effects: The present invention uses a variable principal stress direction loading and unloading cyclic test method to simulate the stress and failure process of rock masses with multiple sets of "X"-shaped conjugate joints under complex stress environment in real nature, thereby conducting effective experimental analysis on rock masses containing large conjugate joints. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the experimental method of the present invention;

[0042] Figure 2 This is a schematic diagram of the overall structure of the experimental apparatus of the present invention;

[0043] Figure 3 This is a diagram illustrating the sliding bar detaching from the sliding plate;

[0044] Figure 4 This is a schematic diagram of the initial state of the loading device;

[0045] Figure 5This is a schematic diagram of the loading device under maximum pressure.

[0046] Figure 6 This is a schematic diagram showing the contact between the first and second limit blocks;

[0047] Figure 7 This is a top view of the connection relationship of the second limiting block;

[0048] Figure 8 This is a top view of the support frame;

[0049] Figure 9 This is a schematic diagram showing the protrusion located inside the annular groove and offset from the notch.

[0050] Figure 10 This is a schematic diagram of the protrusion aligning with the notch. Detailed Implementation

[0051] The following will be based on embodiments of the present invention. Figures 1-10 The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0052] like Figure 1 A method for testing variable principal stress in rocks with multiple sets of conjugate joints, comprising:

[0053] Step 1, Sample Preparation: Rock sample 2 is prepared using 3D printing to create a rock specimen with three discontinuous "X"-shaped conjugate joints on three sides. This means that rock sample 2 contains three-sided conjugate joints. The dimensions of rock sample 2 are 150 mm to 300 mm.

[0054] Step 2: Place the rock sample 2 on the support bracket 5. The support bracket 5 includes three plates. The three plates are fixedly connected and wrap around one top corner of the bottom of the rock sample 2, so that the rock sample 2 is exposed on three surfaces. Loading devices 6 are respectively set on the three exposed surfaces. The two opposite surfaces of the rock sample 2 are the loading devices 6 and the plates, respectively.

[0055] Step 3: Apply pressure to rock sample 2 using loading device 6:

[0056] (a) Three loading devices 6 simultaneously apply pressure , and and make ;

[0057] (b) Maintain Constant, Loading to ,uninstall to ,make It becomes the maximum principal stress. The minimum principal stress is reached; after it stabilizes, it is restored. ;

[0058] (c) Maintain Constant, Loading to ,uninstall to ,make It becomes the maximum principal stress. The minimum principal stress is reached; after it stabilizes, it is restored. ;

[0059] (d) Maintain Constant, continue loading to ,uninstall to ,make It becomes the maximum principal stress. The minimum principal stress is reached; after it stabilizes, it is restored. ;

[0060] Steps (b), (c), and (d) in step three can be interchanged in any order;

[0061] Step 4, incrementally increasing Repeat step three until rock sample 2 is destroyed.

[0062] The shear failure process of rock specimen 2 follows the Mohr-Coulomb criterion:

[0063] ,

[0064] In the formula: For cohesion, It is the internal friction angle. This refers to shear strength.

[0065] In the method of the present invention, the loading device 6 may be the loading device 6 proposed in the present invention, or it may be a jack or other equipment.

[0066] This invention uses a variable principal stress direction loading and unloading cyclic test method to simulate the stress and failure process of rock masses with multiple sets of "X"-shaped conjugate joints under complex stress conditions in real nature, thereby enabling effective experimental analysis of rock masses containing large conjugate joints.

[0067] like Figure 2 An experimental device for variable principal stress in multi-group conjugate jointed rocks, the experimental device includes: a loading device 6, a bottom plate 1, a side plate 3, a top plate 4 and a bearing support 5;

[0068] The base plate 1 is connected to the support bracket 5, which is used to place the rock sample 2. The support bracket 5 includes three plates, which are fixedly connected and located on three mutually perpendicular spatial planes. The three plates together form a square opening groove, which covers the bottom and top corners of the rock sample 2, covering three sides of the rock sample 2 and exposing the other three sides. The loading device 6 is respectively arranged on the three exposed surfaces, and the two opposite sides of the rock sample 2 are the loading device 6 and the plate respectively.

[0069] The top plate 4 is fixedly connected to the top of the loading device 6 located above the rock sample 2, and the side plates 3 are fixedly connected to the outer ends of the loading device 6 located on both sides of the rock sample 2, and the bottom of the side plates 3 is connected to the bottom plate 1.

[0070] The loading device 6 is used to apply pressure to the wall of the rock sample 2.

[0071] Furthermore, four side plates 3 are provided, two of which are connected to the loading device 6, and the other two adjacent side plates 3 are fixedly connected to the plate body by support columns 301.

[0072] There are a total of three loading devices 6 in this embodiment of the invention. Figure 4 The loading device 6 in the example illustrates its structure, and the upper and lower positions of each component are referenced to this loading device 6, that is... Figure 4 The location in the middle, Figure 2 , Figure 3 The orientation of the loading device 6 in the middle can be based on Figure 4 And transformation.

[0073] There are a total of four side plates 3, which are distributed around the rock sample 2. The top of the two opposite side plates 3 are connected to the top plate 4. Figure 3 In the initial state of the invention, there is a uniform interval between the rock sample 2 and each pressure plate 611.

[0074] like Figure 2 , Figure 8 The three plates of the support bracket 5 are attached to the three mutually perpendicular surfaces of the rock sample 2, with each pair of plates being perpendicular to the others, thus forming a square opening groove that encloses the bottom corner of the rock sample 2. When the loading device 6 applies pressure to the exposed surface of the rock sample 2, the opposite wall surface of the rock sample 2 is supported by the plates, support columns 301, and side plates 3.

[0075] Furthermore, a lifting plate 7 is fixedly connected to the bottom of the four side plates 3. The lifting plate 7 is located above the base plate 1. An inclined connecting rod 701 is provided at both ends of the lifting plate 7. The top of the connecting rod 701 is rotatably connected to the end of the lifting plate 7, and the bottom of the connecting rod 701 is rotatably connected to the sliding plate 702. The sliding plate 702 is slidably connected to the base plate 1.

[0076] A limiting sleeve 704 is fixedly connected to the bottom of the plate body located at the bottom. A top rod 704 slidably passes through the lifting plate 7. The top of the top rod 704 slidably passes through the limiting sleeve 704. A through hole adapted to the top rod 704 is provided on the plate body located at the bottom. The through hole is coaxially arranged with the limiting sleeve 704. The bottom of the top rod 704 is connected to the bottom plate 1.

[0077] The top of the top plate 4 is rotatably connected to the top of the slide rod 401 at both ends. The two opposite side plates 3 are provided with through holes adapted to the slide rod 401. The slide rod 401 slides through the through holes. The bottom plate 1 is provided with positioning holes adapted to the slide rod 401. The bottom of the slide rod 401 passes through the lifting plate 7 and the sliding plate 702 in sequence and is located in the positioning hole.

[0078] The protrusion 402 is fixedly connected inside the positioning hole. The bottom of the slide rod 401 is provided with an annular groove that is adapted to the protrusion 402. A notch is provided on the annular groove. The protrusion 402 is used to pass through the notch and rotate to engage in the annular groove, so as to form an axial constraint on the slide rod 401.

[0079] The slide bar 401 is used to slide upward to disengage from the slide plate 702, thereby causing the lifting plate 7 to descend under its own weight, and causing the top rod 704 to lift the rock sample 2.

[0080] The lifting plate 7 is parallel to the base plate 1, and the bottom of the connecting rod 701 is inclined outward. The two connecting rods 701 are symmetrical. The sliding plate 702 can be connected to the base plate 1 via a slide rail. The bottom of the top rod 704 is fixedly connected to the base 705. The height of the base 705 is adjustable and connected to the base plate 1. The height of the base 705 can be adjusted by means of threads or lifting bolts, thereby adjusting the height at which the top rod 704 lifts the rock sample 2.

[0081] The specific implementation process is as follows:

[0082] like Figure 3 Before conducting the experiment, the two sliding rods 401 are moved upwards, raising the top plate 4 to a certain height to facilitate the placement of the rock sample 2. The lifting plate 7 decreases in height under its own weight, causing the connecting rod 701 to rotate and the sliding plate 702 to slide. Then, the rock sample 2 is placed, forming a... Figure 3 In this state, rock sample 2 is supported to a certain height by top rod 704. Then, push the two sliding plates 702 inward, the lifting plate 7 moves upward, and after the sliding plates 702 are in place, move the two sliding rods 401 downward, so that the sliding rods 401 pass through the lifting plate 7 and the sliding plates 702 and are located in the positioning hole. During this process, the protrusion 402 passes through the notch. Finally, rotate the sliding rod 401 so that the protrusion 402 is engaged in the annular groove to form an axial constraint on the sliding rod 401, ultimately forming Figure 2 The state in.

[0083] When the rock sample 2 needs to be removed after the experiment, rotate the slide rod 401 so that the protrusion 402 aligns with the notch. Then, raise the slide rod 401. After the slide rod 401 disengages from the sliding plate 702, the lifting plate 7 descends under its own weight, lowering the height of the support bracket 5, thereby allowing the top rod 704 to lift the rock sample 2. This invention utilizes the weight of the lifting plate 7 to lift the rock sample 2, facilitating the removal and placement of the rock sample 2. The weight of the lifting plate 7 is much greater than that of the rock sample 2.

[0084] For further reference Figure 9 , Figure 10 Multiple protrusions 402 and notches can be provided and arranged circumferentially around the slide bar 401.

[0085] Furthermore, such as Figures 4-6 The loading device 6 includes a fixed plate 601, a driving device 603, a connecting plate 604, a rotating seat 605, a lead screw 606, a threaded sleeve 607, a connecting rod 609, a pressure plate 611, and a limiting structure.

[0086] The fixed plate 601 and the connecting plate 604 are arranged side by side. The driving device 603 is installed between the fixed plate 601 and the connecting plate 604. The output end of the driving device 603 passes through the connecting plate 604 and is fixedly connected to the rotating seat 605. The rotating seat 605 is rotatably mounted on the connecting plate 604. One end of the rotating seat 605 away from the driving device 603 is fixedly connected to one end of the lead screw 606. The other end of the lead screw 606 is threadedly connected to the threaded sleeve 607. The side of the threaded sleeve 607 is connected to the connecting rod 609. The connecting rod 609 is parallel to the axis of the lead screw 606. The end of the connecting rod 609 away from the connecting plate 604 is connected to the pressure plate 611.

[0087] The driving device 603 is used to drive the rotating seat 605 to rotate, causing the lead screw 606 to rotate; the side of the connecting rod 609 is connected to the limiting structure, which is used to limit the rotation of the connecting rod 609 around the lead screw 606, thereby causing the threaded sleeve 607 to move along the lead screw 606, and the pressure plate 611 to face the wall of the rock sample 2.

[0088] The drive device 603 is existing technology and can be an electric motor, hydraulic motor, or other similar equipment. The connecting plate 604 and the fixing plate 601 are parallel, and the lead screw 606 is perpendicular to the connecting plate 604. The lead screw 606 and the threaded sleeve 607 constitute a transmission structure, converting the rotation of the lead screw 606 into the movement of the threaded sleeve 607 along the axial direction of the lead screw 606.

[0089] Furthermore, the limiting structure includes a pole 612, a protrusion 613, a stop block 614, a second limiting block 615, an intermediate plate 616, and a cover plate 617.

[0090] The upright 612 is parallel to and spaced apart from the connecting rod 609. The upright 612 is located on the side of the connecting rod 609 away from the lead screw 606. One end of the upright 612 is fixedly connected to the connecting plate 604. The upright 612 is provided with a second waist-shaped through hole. The intermediate plate 616 is located in the second waist-shaped through hole. The end of the intermediate plate 616 facing the connecting rod 609 is fixedly connected to the second limiting block 615. The end of the intermediate plate 616 away from the connecting rod 609 is detachably connected to the cover plate 617.

[0091] The connecting rod 609 is fixedly connected to the protrusion 613 on its side. The end of the protrusion 613 is detachable from the stop 614. The second limiting block 615 is located on the rotation path of the stop 614. The second limiting block 615 is used to abut against the stop 614 to form a circumferential constraint.

[0092] The intermediate plate 616 is slidably located in the second waist-shaped through hole, and the cover plate 617 and the upright 612 are constrained in vertical height by teeth 600;

[0093] By adjusting the height of the second limiting block 615, the stroke of the stop block 614 disengaging from the second limiting block 615 is changed, thereby adjusting the movement of the threaded sleeve 607, and thus adjusting the maximum pressure value applied by the pressure plate 611, achieving adjustment. The function.

[0094] The intermediate plate 616 can move up and down within the second oblong through hole to adjust the height of the second limiting block 615. The cover plate 617 is connected to the intermediate plate 616 by bolts. The protrusion 613 and the stop 614 are located on the radial side of the connecting rod 609. The stop 614 can be connected to the protrusion 613 by threads or screws. The depth of the stop 614 can be adjusted, thereby adjusting the amount of interference when the stop 614 and the second limiting block 615 collide. Damaged stop 614 can also be replaced.

[0095] Furthermore, the limiting structure also includes a first limiting block 618, a transmission block 619, a telescopic rod 620, and a lifting mechanism;

[0096] The upright 612 is provided with a first waist-shaped through hole, and the transmission block 619 is provided in the first waist-shaped through hole. The end of the transmission block 619 facing the connecting rod 609 is fixedly connected to the first limiting block 618. The first limiting block 618 is located above the second limiting block 615. The end of the transmission block 619 away from the connecting rod 609 is fixedly connected to the telescopic rod 620. The telescopic rod 620 is parallel to the upright 612. The end of the telescopic rod 620 away from the transmission block 619 is connected to the lifting mechanism for lifting the first limiting block 618.

[0097] When the lead screw 606 rotates and the pressure plate 611 moves toward the rock sample 2, the first limiting block 618 moves to its highest height, and the bottom of the first limiting block 618 forms a gap with the top of the second limiting block 615; when the stop block 614 disengages from the second limiting block 615, the stop block 614 enters the gap above the second limiting block 615.

[0098] When the lead screw 606 rotates and the pressure plate 611 moves away from the rock sample 2, the first limiting block 618 moves to its lowest height and the bottom of the first limiting block 618 is in contact with the top of the second limiting block 615; the stop block 614 abuts against the lower end of the first limiting block 618 and moves onto the second limiting block 615.

[0099] Specifically, a groove is provided on the side of the upright 612 facing the connecting rod 609, and the first limiting block 618 and the second limiting block 615 are both located in the groove.

[0100] The pressurization process of this invention is as follows:

[0101] like Figure 4 This is the initial state. When pressurization begins, the drive device 603 rotates forward, causing the threaded sleeve 607 to move the pressure plate 611 toward the rock sample 2, thereby generating extrusion force; during this process, the second limiting block 615 abuts against the stop block 614 to form a circumferential constraint, preventing the stop block 614 from rotating. When the pressure reaches its maximum value, the stop block 614 just disengages from the top of the second limiting block 615 and enters the gap between the second limiting block 615 and the first limiting block 618, forming a... Figure 5 In the state of being unrestrained, the stop block 614 is unconstrained, and the friction between the threaded sleeve 607 and the lead screw 606 causes the threaded sleeve 607 to rotate with the lead screw 606.

[0102] The procedure for releasing pressure (reset procedure) of this invention is as follows:

[0103] like Figure 5When the pressure plate 611 has moved to its maximum travel, the drive device 603 slowly reverses. At this time, the lifting mechanism lowers the telescopic rod 620 and the first limiting block 618, causing the top of the second limiting block 615 to contact the bottom of the first limiting block 618. The stop block 614 then reverses to abut against the junction of the top of the second limiting block 615 and the bottom of the first limiting block 618, thus forming a circumferential constraint on the stop block 614. Figure 6 In the state of rotation of the lead screw 606, the threaded sleeve 607 moves downward, thereby causing the stop block 614 to return to the coverage area of ​​the second limit block 615.

[0104] When pressure is reapplied, the drive unit 603 slowly rotates forward, and the lifting mechanism pushes the first limit block 618 up to form a gap between the first limit block 618 and the second limit block 615.

[0105] When adjusting ， When adjusting the maximum pressure, the movement of the threaded sleeve 607 is adjusted by adjusting the height of the second limiting block 615, thereby accommodating the maximum stroke of the threaded sleeve 607 to adjust the maximum pressure. Additionally, the length of the telescopic rod 620 is adjusted so that the distance between the first limiting block 618 and the second limiting block 615 is a fixed value. The telescopic rod 620 is existing technology.

[0106] In addition, a scale line can be set on the outside of the upright 612 to reflect the movement of the cover plate 617, thereby progressively adjusting the height of the second limit block 615 to form a progressive adjustment function for the maximum pressure.

[0107] This invention utilizes the adjustable stroke of the second limiting block 615 to adjust the movement stroke of the threaded sleeve 607, thereby adjusting the maximum pressure. It can achieve the function of progressively adjusting the maximum pressure, and the stroke change can be intuitively reflected by the scale line. There is a definite conversion relationship between the stroke and the pressure, which can be directly obtained by setting a pressure sensor on the pressure plate 611 and calculating the linear relationship between the pressure and the stroke. It can accurately adjust and control the maximum pressure.

[0108] Furthermore, the lifting mechanism includes a linear pusher 621; the linear pusher 621 is mounted on the connecting plate 604, and the output end of the linear pusher 621 is fixedly connected to the bottom of the telescopic rod 620. The linear pusher 621 is used to push the telescopic rod 620 up and down.

[0109] The linear actuator 621 is existing technology, such as a cylinder, hydraulic cylinder, linear guide, etc. During the pressure application phase, the linear actuator 621 pushes the first limit block 618 to its maximum stroke; during the pressure release phase, the linear actuator 621 pushes the first limit block 618 to its minimum stroke.

[0110] Furthermore, the fixing plates 601 of the three loading devices 6 are respectively fixedly connected to the top plate 4 and the two side plates 3.

[0111] Furthermore, the connecting rod 609 is fixedly connected to the transition plate 610, and the transition plate 610 is rotatably connected to the pressure plate 611. When the stop block 614 is within the interval, the friction between the pressure plate 611 and the rock sample 2 keeps the pressure plate 611 relatively stationary, while the transition plate 610 and the threaded sleeve 607 rotate relative to each other, which can prevent the threaded sleeve 607 from continuing to move axially under the action of this friction (the friction between the pressure plate 611 and the rock sample 2).

[0112] Furthermore, the side of the threaded sleeve 607 is fixedly connected to the connecting rod 609 via a support rod 608.

[0113] Furthermore, multiple limiting structures are provided around the lead screw 606.

[0114] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, alterations, substitutions, or variations made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention shall fall within the protection scope defined by the claims of the present invention.

Claims

1. An experimental apparatus for variable principal stress in multi-set conjugate jointed rocks, characterized in that, The experimental equipment includes: a loading device (6), a base plate (1), a side plate (3), a top plate (4), and a support bracket (5); The base plate (1) is connected to the support bracket (5), and the support bracket (5) is used to place the rock sample (2). The support bracket (5) includes three plates, which are fixedly connected and located on three mutually perpendicular spatial surfaces. The three plates together form a square opening groove, which covers the bottom corner of the rock sample (2), covering three sides of the rock sample (2) and exposing the other three sides. The loading device (6) is respectively set on the three exposed surfaces. The two opposite sides of the rock sample (2) are the loading device (6) and the plate. The top plate (4) is fixedly connected to the top of the loading device (6) located above the rock sample (2), and the side plates (3) are fixedly connected to the outer ends of the loading device (6) located on both sides of the rock sample (2). The bottom of the side plate (3) is connected to the bottom plate (1). The loading device (6) is used to apply pressure to the wall of the rock sample (2); The loading device (6) includes a fixed plate (601), a driving device (603), a connecting plate (604), a rotating seat (605), a lead screw (606), a threaded sleeve (607), a connecting rod (609), a pressure plate (611), and a limiting structure; The fixed plate (601) and the connecting plate (604) are arranged side by side. The driving device (603) is installed between the fixed plate (601) and the connecting plate (604). The output end of the driving device (603) passes through the connecting plate (604) and is fixedly connected to the rotating seat (605). The rotating seat (605) is rotatably mounted on the connecting plate (604). One end of the rotating seat (605) away from the driving device (603) is fixedly connected to one end of the lead screw (606). The other end of the lead screw (606) is threadedly connected to the threaded sleeve (607). The side of the threaded sleeve (607) is connected to the connecting rod (609). The connecting rod (609) is parallel to the axis of the lead screw (606). One end of the connecting rod (609) away from the connecting plate (604) is connected to the pressure plate (611). The driving device (603) is used to drive the rotating seat (605) to rotate, causing the lead screw (606) to rotate; the side of the connecting rod (609) is connected to the limiting structure, which is used to limit the rotation of the connecting rod (609) around the lead screw (606), thereby causing the threaded sleeve (607) to move along the lead screw (606), and the pressure plate (611) to face the wall of the rock sample (2); The limiting structure includes a pole (612), a protrusion (613), a stop (614), a second limiting block (615), an intermediate plate (616), and a cover plate (617). The upright (612) is parallel to and spaced apart from the connecting rod (609). The upright (612) is located on the side of the connecting rod (609) away from the lead screw (606). One end of the upright (612) is fixedly connected to the connecting plate (604). The upright (612) is provided with a second waist-shaped through hole. The intermediate plate (616) is located in the second waist-shaped through hole. The end of the intermediate plate (616) facing the connecting rod (609) is fixedly connected to the second limiting block (615). The end of the intermediate plate (616) away from the connecting rod (609) is detachably connected to the cover plate (617). The connecting rod (609) is fixedly connected to the protrusion (613) on its side. The end of the protrusion (613) is detachable from the stop (614). The second limiting block (615) is located on the rotation path of the stop (614). The second limiting block (615) is used to abut against the stop (614) to form a circumferential constraint. The intermediate plate (616) is slidably located in the second waist-shaped through hole, and the cover plate (617) and the upright (612) are connected by teeth (600) to constrain the vertical height; By adjusting the height of the second limiting block (615), the stroke of the stop block (614) disengaging from the second limiting block (615) is changed, thereby adjusting the amount of movement of the threaded sleeve (607) and thus adjusting the maximum pressure value applied by the pressure plate (611).

2. The experimental apparatus for variable principal stress in multi-set conjugate jointed rocks according to claim 1, characterized in that, The side plates (3) are provided in four parts, two of which are connected to the loading device (6), and the other two are fixedly connected to the plate body by support columns (301).

3. The experimental apparatus for variable principal stress in multi-set conjugate jointed rocks according to claim 2, characterized in that, The bottom of the four side plates (3) is fixedly connected to the lifting plate (7), which is located above the base plate (1). The two ends of the lifting plate (7) are respectively provided with inclined connecting rods (701). The top of the connecting rod (701) is rotatably connected to the end of the lifting plate (7), and the bottom of the connecting rod (701) is rotatably connected to the sliding plate (702). The sliding plate (702) is slidably connected to the base plate (1). A limiting sleeve is fixedly connected to the bottom of the plate at the bottom. A top rod can slide through the lifting plate (7). The top of the top rod can slide through the limiting sleeve. A through hole adapted to the top rod is provided on the plate at the bottom. The through hole is coaxially arranged with the limiting sleeve. The bottom of the top rod is connected to the bottom plate (1). The top of the top plate (4) is rotatably connected to the top of the sliding rod (401) at both ends. The two opposite side plates (3) are provided with through holes adapted to the sliding rod (401). The sliding rod (401) slides through the through holes. The bottom plate (1) is provided with positioning holes adapted to the sliding rod (401). The bottom of the sliding rod (401) passes through the lifting plate (7) and the sliding plate (702) in sequence and is located in the positioning hole. The positioning hole is fixedly connected to the protrusion (402), and the bottom of the slide rod (401) is provided with an annular groove that matches the protrusion (402). The annular groove is provided with a notch. The protrusion (402) is used to pass through the notch and rotate before being engaged in the annular groove to form an axial constraint on the slide rod (401). The slide bar (401) is used to slide upward to disengage from the slide plate (702), thereby causing the lifting plate (7) to descend under its own weight, and causing the top rod to lift the rock sample (2).

4. The experimental apparatus for variable principal stress in multi-set conjugate jointed rocks according to claim 1, characterized in that, The limiting structure also includes a first limiting block (618), a transmission block (619), a telescopic rod (620), and a lifting mechanism; The upright (612) is provided with a first waist-shaped through hole, and the transmission block (619) is provided in the first waist-shaped through hole. The end of the transmission block (619) facing the connecting rod (609) is fixedly connected to the first limiting block (618). The first limiting block (618) is located above the second limiting block (615). The end of the transmission block (619) away from the connecting rod (609) is fixedly connected to the telescopic rod (620). The telescopic rod (620) is parallel to the upright (612). The end of the telescopic rod (620) away from the transmission block (619) is connected to the lifting mechanism for lifting the first limiting block (618). When the lead screw (606) rotates and the pressure plate (611) moves toward the rock sample (2), the first limiting block (618) moves to its highest height, and the bottom of the first limiting block (618) and the top of the second limiting block (615) form a gap; when the stop block (614) disengages from the second limiting block (615), the stop block (614) enters the gap above the second limiting block (615); When the lead screw (606) rotates and moves the pressure plate (611) away from the rock sample (2), the first limiting block (618) moves to its lowest height and the bottom of the first limiting block (618) is in contact with the top of the second limiting block (615); the stop block (614) abuts against the lower end of the first limiting block (618) and moves to the second limiting block (615).

5. The experimental apparatus for variable principal stress in multi-set conjugate jointed rocks according to claim 4, characterized in that, The lifting mechanism includes a linear drive device (621). The linear push device (621) is mounted on the connecting plate (604). The output end of the linear push device (621) is fixedly connected to the bottom of the telescopic rod (620). The linear push device (621) is used to push the telescopic rod (620) up and down.

6. The experimental apparatus for variable principal stress in multi-set conjugate jointed rocks according to claim 1, characterized in that, The fixing plates (601) of the three loading devices (6) are respectively fixedly connected to the top plate (4) and the two side plates (3).

7. A method for testing variable principal stress in rocks with multiple sets of conjugate joints, applied to the experimental apparatus for testing variable principal stress in rocks with multiple sets of conjugate joints as described in claim 1, characterized in that, The following steps are involved: Step 1, Sample preparation: Prepare rock samples (2); Step 2: Place the rock sample (2) on the support bracket (5). The support bracket (5) includes three plates. The three plates are fixedly connected and wrap around one of the top corners of the bottom of the rock sample (2), so that the rock sample (2) is exposed on three surfaces. Loading devices (6) are respectively set on the three exposed surfaces. The two opposite surfaces of the rock sample (2) are the loading device (6) and the plate. Step 3: Apply pressure to the rock sample (2) using the loading device (6): (a) Three loading devices (6) simultaneously apply pressure , and and make ; (b) Maintain Constant, Loading to ,uninstall to ,make It becomes the maximum principal stress. The minimum principal stress is reached; after it stabilizes, it is restored. ; (c) Maintain Constant, Loading to ,uninstall to ,make It becomes the maximum principal stress. The minimum principal stress is reached; after it stabilizes, it is restored. ; (d) Maintain Constant, continue loading to ,uninstall to ,make It becomes the maximum principal stress. The minimum principal stress is reached; after it stabilizes, it is restored. ; Step 4, Increment And repeat step three until the rock sample (2) is destroyed.

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