A method and apparatus for loading and unloading cyclic testing of rock specimens with varying principal stress directions.

Abstract

This invention belongs to the field of rock engineering and provides a method and apparatus for cyclic loading and unloading tests of rock specimens with varying principal stress directions. The method includes: Step 1, specimen preparation: preparing a complete cubic rock specimen; Step 2, cyclic loading: subjecting the rock specimen to... x, y, z The stresses in the three directions are respectively σ x , σ y , σ z Step 3: Adjust the pressure in different directions sequentially to form... x - and - z, ox - z The cracks on the plane; Step 4, increase the pressure and repeat Step 3 until the rock sample is destroyed and three sets of "X"-shaped conjugate shear joint models are generated; This invention mainly simulates the geological history evolution process of the rock sample area, which is subjected to tectonic stress changes of different directions and different levels, as well as vertical stress changes caused by tectonic erosion or deposition. Under these conditions, three sets of "X"-shaped conjugate shear joints are often formed. It can be combined with local earthquake monitoring and on-site geological exploration to provide suggestions for engineering excavation.

Description

Technical Field

[0001] This invention belongs to the field of rock engineering, specifically relating to a method and apparatus for loading and unloading cyclic testing of rock samples with varying principal stress directions. 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 testing device for a model of three sets of conjugate "X"-shaped joint fractures is currently lacking. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a method and apparatus for loading and unloading cyclic testing of rock samples with varying principal stress directions, thereby addressing the problems in the prior art. The technical solution adopted by the present invention is as follows:

[0006] A method for cyclic loading and unloading tests of rock specimens with varying principal stress directions includes the following steps:

[0007] Step 1, Sample preparation: Prepare a complete cubic rock sample;

[0008] Step 2, Cyclic Loading: Six loading devices are set up and distributed on the six faces of the rock sample; the rock sample is subjected to pressure by the loading devices. x、y、z The stresses in the three directions are respectively s x , s y , sz The initial damage critical stress value of the rock sample is s c By adjusting the output pressure of the loading device, s x = s y = s z = s c ;

[0009] Step 3: Adjust the output pressure of the loading device to... s z Adjusted to , s x Adjusted to Rock samples z The direction is the maximum principal stress. x The direction is the minimum principal stress, and the rock sample is in x - y Cracks appeared on the surface;

[0010] Adjust the output pressure of the loading device to s x Stress adjustment in direction , s y Stress adjustment in direction rock samples x The direction is the maximum principal stress. y The direction is the minimum principal stress, and the rock sample is in y - z Cracks appeared on the surface;

[0011] Adjust the output pressure of the loading device to s y Stress adjustment in direction , s z Stress adjustment in direction ， rock sample y The direction is the maximum principal stress. z The direction is the minimum principal stress, and the rock sample is in x - z Cracks appeared on the surface;

[0012] Step 4, Increment Size, and repeat step three until the rock sample is broken and three sets of “X”-shaped conjugate shear joint models are produced.

[0013] A cyclic loading and unloading test device for rock specimens with varying principal stress directions, the test device comprising: a loading device, a base plate, side plates, a top plate, and a bearing support;

[0014] The support bracket is fixedly connected to the base plate. The support bracket is used to place the rock sample. The loading device is provided on all six sides of the rock sample, and the loading devices on opposite sides are symmetrically arranged. The loading device below the rock sample is located below the support bracket. The top of the loading device above the rock sample is fixedly connected to the top plate. The outer ends of the loading devices around the rock sample are fixedly connected to the side plates. The tops of the two side plates are detachably connected to the two ends of the top plate, and the bottoms of the side plates are fixedly connected to the base plate.

[0015] The loading device is used to apply pressure to the wall of the rock sample.

[0016] 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;

[0017] 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.

[0018] 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.

[0019] Furthermore, the limiting structure includes a vertical rod, a protrusion, a stop block, a second limiting block, an intermediate plate, and a cover plate;

[0020] 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.

[0021] 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.

[0022] 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;

[0023] 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 applied by the pressure plate, achieving adjustment. The function.

[0024] Furthermore, the limiting structure also includes a first limiting block, a transmission block, a telescopic rod, and a lifting mechanism;

[0025] 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.

[0026] 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;

[0027] 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.

[0028] Furthermore, the lifting mechanism includes a crossbar, a rotating ring, a spring, a sliding sleeve, a fixed ring plate, a plug-in piece, a wedge-shaped bottom surface, an arc-shaped groove, and a vertical rod;

[0029] The upright has a third oblong through hole, through which the crossbar passes. The third oblong through hole is slidably located within it. The crossbar is positioned below the second limiting block. One end of the crossbar is fixedly connected to the telescopic rod, and the other end is fixedly connected to the outer ring of the rotating ring. The inner ring of the rotating ring is rotatably fitted onto the sliding sleeve. The sliding sleeve is slidably fitted onto the lead screw. The sliding sleeve and the lead screw are circumferentially constrained by a spline. A compressed spring is provided at the bottom of the sliding sleeve. The spring is fitted onto the lead screw. The top and bottom of the spring abut against the bottom of the sliding sleeve and the top of the rotating seat, respectively. A fixed ring plate is provided above the sliding sleeve. The lead screw passes through the fixed ring plate. The bottom of the fixed ring plate is fixedly connected to the top of the vertical rod. The bottom of the vertical rod is fixedly connected to the top of the connecting plate. The vertical rod is located between the upright and the lead screw. A fourth oblong hole is provided on the vertical rod, through which the crossbar passes.

[0030] The top end face of the sliding sleeve is provided with the arc-shaped groove, the bottom surface of the arc-shaped groove is the wedge-shaped bottom surface, the matching plug-in piece is provided in the arc-shaped groove, the top of the plug-in piece is fixedly connected to the fixing ring plate, and the bottom of the plug-in piece is adapted to the wedge-shaped bottom surface;

[0031] When the lead screw drives the sliding sleeve to rotate, the sliding sleeve is raised and lowered through the cooperation of the plug-in piece and the wedge-shaped bottom surface, thereby raising and lowering the first limiting block.

[0032] Furthermore, the connecting rod is fixedly connected to the transition plate, and the transition plate is rotatably connected to the pressure plate.

[0033] Furthermore, the side of the threaded sleeve is fixedly connected to the connecting rod by a support rod.

[0034] Furthermore, the fixing plates of the six loading devices are respectively fixedly connected to the bottom plate, the top plate, and the four side plates.

[0035] Furthermore, multiple limiting structures are arranged around the lead screw.

[0036] The present invention has the following beneficial effects: The present invention mainly simulates the geological history evolution process of the rock sample area, which is subjected to tectonic stress changes of different directions and different orders, as well as vertical stress changes caused by tectonic erosion or deposition. Under these conditions, three sets of "X"-shaped conjugate shear joints are often formed, providing a basis for the verification of the proposed theoretical model and the self-developed program; At the same time, it can also simulate the formation and evolution process of "X"-shaped conjugate shear joints of different orders in intact rocks under the action of earthquake, excavation unloading, and engineering loading; It can provide suggestions for engineering excavation by combining local earthquake monitoring and on-site geological exploration. Attached Figure Description

[0037] Figure 1 This is a schematic diagram illustrating the generation of the three sets of conjugate "X" cracks in this invention;

[0038] Figure 2 This is a schematic diagram of the overall structure of the experimental device of the present invention;

[0039] Figure 3 This is a top view of the experimental setup;

[0040] Figure 4 This is a schematic diagram of the initial state of the loading device;

[0041] Figure 5 This is a schematic diagram of the loading device under maximum pressure.

[0042] Figure 6 This is a schematic diagram showing the contact between the first and second limit blocks;

[0043] Figure 7 This is a top view of the connection relationship of the second limiting block;

[0044] Figure 8 This is a top view of the sliding sleeve connection relationship;

[0045] Figure 9 This is a schematic diagram of the connector connection relationship. Detailed Implementation

[0046] The following will be based on embodiments of the present invention. Figure 1-Figure 9 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.

[0047] like Figure 1 A method for loading and unloading cyclic testing of rock specimens with varying principal stress directions includes the following steps:

[0048] Step 1, Sample preparation: Prepare a complete cubic rock sample 2: The sample preparation involves drilling a complete, unjointed, and fracture-free cubic sample from rock mass I or II; the size of rock sample 2 is 150 mm to 300 mm.

[0049] Step 2, Cyclic Loading: Six loading devices 6 are set up and distributed on the six faces of the rock sample 2; the rock sample 2 is subjected to pressure by the loading devices 6. x、y、z The stresses in the three directions are respectively s x , s y , s z The initial damage critical stress value of rock sample 2 is s c By adjusting the output pressure of the loading device 6, s x = s y = s z = s c， The corresponding Mohr stress circle is a point, in ( s c At point 0, the sample's condition corresponds to the initial damage critical value of the stress state of an intact rock mass that has not been disturbed and has not been subjected to seismic forces. s c It can be obtained through consulting materials and conducting actual experiments, and is a fixed value;

[0050] Step 3: Adjust the output pressure of loading device 6 to... s z Adjusted to , s x Adjusted to Rock sample 2 z The direction is the maximum principal stress. x The direction is the minimum principal stress, and rock sample 2 is in x - y Cracks appear on the surface; corresponding to x Directional unloading or z Operating conditions such as directional seismic waves;

[0051] Adjust the output pressure of loading device 6 to s x Stress adjustment in direction , s y Stress adjustment in direction Rock sample 2 x The direction is the maximum principal stress. y The direction is the minimum principal stress, and rock sample 2 is in y - z Cracks appear on the surface; corresponding to y Directional unloading or x Operating conditions such as directional seismic waves;

[0052] Adjust the output pressure of loading device 6 to s y Stress adjustment in direction , s z Stress adjustment in direction ， Rock sample 2 y The direction is the maximum principal stress. z The direction is the minimum principal stress, and rock sample 2 is in x - z Cracks appear on the surface; corresponding to z Directional unloading or y Operating conditions such as directional seismic waves;

[0053] The three steps in step three above can be performed in any order;

[0054] Step 4, Increment Size, and repeat step three until rock sample 2 is broken and three sets of "X"-shaped conjugate shear joint models are produced; typically, the stress increment is 2. 3 4 … n 。

[0055] In the method of this invention, the loading device 6 can be the loading device 6 proposed in this invention, or it can be a jack or other equipment. When the loading device 6 applies pressure, x、y、z Two loading devices 6 in the same direction load together.

[0056] This invention primarily simulates the geological history evolution of rock samples in different regions, where they are subjected to tectonic stress changes of different directions and sequences, as well as vertical stress changes caused by tectonic erosion or deposition. These stresses often lead to the formation of three sets of "X"-shaped conjugate shear joints, providing a basis for the proposed theoretical model and the verification of the self-developed program. It can also simulate the formation and evolution of "X"-shaped conjugate shear joints of different sequences in intact rocks under seismic action, excavation unloading, and engineering loading. Combined with local earthquake monitoring and on-site geological surveys, it can provide suggestions for engineering excavation.

[0057] It should be noted that in this invention... x、y、z The three directions refer to the vertical, horizontal, and front-back directions that are perpendicular to each other and intersect at a point.

[0058] like Figure 2 A cyclic loading and unloading test device for rock specimens with varying principal stress directions, the test device comprising: a loading device 6, a bottom plate 1, a side plate 3, a top plate 4, and a bearing support 5;

[0059] The supporting bracket 5 is fixedly connected to the base plate 1. The supporting bracket 5 is used to place the rock sample 2. The rock sample 2 is provided with the loading device 6 on all six sides. The loading devices 6 on opposite sides are symmetrically arranged. The loading device 6 located below the rock sample 2 is located below the supporting bracket 5. The top of the loading device 6 located above the rock sample 2 is fixedly connected to the top plate 4. The outer ends of the loading devices 6 located around the rock sample 2 are respectively fixedly connected to the side plates 3. The tops of the two side plates 3 are detachably connected to the two ends of the top plate 4. The bottom of the side plates 3 is fixedly connected to the base plate 1.

[0060] The loading device 6 is used to apply pressure to the wall of the rock sample 2.

[0061] There are a total of six loading devices 6. This embodiment of the invention uses the loading device 6 located below the support bracket 5 as an example to illustrate its structure. The upper and lower positions of each component are referenced to this loading device 6, that is... Figure 4 The location within.

[0062] There are a total of four side plates 3, which are distributed on the four sides of the rock sample 2. The tops of the two opposite side plates 3 can be connected to the top plate 4 by bolts. In practice, the rock sample 2 is first placed on the support bracket 5, and then the top plate 4 is installed. Figure 3 In the initial state of the invention, there is a gap between the rock sample 2 and the pressure plate 611. This gap is the initial gap, and the gap distance between each surface of the rock sample 2 is equal.

[0063] like Figure 4-Figure 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] The intermediate plate 616 is slidably located in the second waist-shaped through hole. The cover plate 617 and the upright 612 are constrained in vertical height by teeth 600. The inner side of the cover plate 617 and the outer side of the upright 612 are respectively provided with meshing teeth 600 to generate vertical constraint and facilitate precise adjustment of the vertical height of the cover plate 617 and the second limiting block 615.

[0071] 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.

[0072] 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.

[0073] Furthermore, the limiting structure also includes a first limiting block 618, a transmission block 619, a telescopic rod 620, and a lifting mechanism;

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] The pressurization process of this invention is as follows:

[0079] 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 until the pressure reaches the specified value. s c or During this process, the second limit block 615 abuts against the stop block 614 to form a circumferential constraint, preventing the stop block 614 from rotating. When the pressure value reaches... s c or At that time, 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 as shown in the figure. 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.

[0080] The procedure for releasing pressure (reset procedure) of this invention is as follows:

[0081] like Figure 5 When 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] like Figure 4 , Figure 8 and Figure 9 The lifting mechanism includes a crossbar 621, a rotating ring 622, a spring 623, a sliding sleeve 624, a fixed ring plate 625, a plug-in piece 626, a wedge-shaped bottom surface 627, an arc-shaped groove 628, and a vertical bar 629.

[0087] The upright 612 is provided with a third oblong through hole, through which the crossbar 621 passes. The third oblong through hole is slidably located within the third oblong through hole. The crossbar 621 is located below the second limiting block 615. One end of the crossbar 621 is fixedly connected to the telescopic rod 620, and the other end is fixedly connected to the outer ring of the rotating ring 622. The inner ring of the rotating ring 622 is rotatably fitted onto the sliding sleeve 624. The sliding sleeve 624 is slidably fitted onto the lead screw 606. The sliding sleeve 624 and the lead screw 606 are circumferentially constrained by a spline. The bottom of the sliding sleeve 624... A spring 623 in a compressed state is provided, and the spring 623 is sleeved on the lead screw 606. The top and bottom of the spring 623 abut against the bottom of the sliding sleeve 624 and the top of the rotating seat 605, respectively. A fixed ring plate 625 is provided above the sliding sleeve 624. The lead screw 606 passes through the fixed ring plate 625. The bottom of the fixed ring plate 625 is fixedly connected to the top of the vertical rod 629. The bottom of the vertical rod 629 is fixedly connected to the top of the connecting plate 604. The vertical rod 629 is located between the upright rod 612 and the lead screw 606. A fourth waist-shaped hole is provided on the vertical rod 629, and the horizontal rod 621 passes through the fourth waist-shaped hole.

[0088] The top end face of the sliding sleeve 624 is provided with the arc-shaped groove 628, the bottom surface of the arc-shaped groove 628 is the wedge-shaped bottom surface 627, the arc-shaped groove 628 is provided with the matching plug piece 626, the top of the plug piece 626 is fixedly connected to the fixing ring plate 625, and the bottom of the plug piece 626 is adapted to the wedge-shaped bottom surface 627;

[0089] When the lead screw 606 drives the sliding sleeve 624 to rotate, the sliding sleeve 624 is raised and lowered through the cooperation of the plug-in piece 626 and the wedge-shaped bottom surface 627, thereby causing the first limiting block 618 to rise and fall.

[0090] The rotating ring 622, sliding sleeve 624, fixed ring plate 625, and lead screw 606 are coaxially arranged. The spline between the sliding sleeve 624 and the lead screw 606 allows for sliding while simultaneously forming a circumferential constraint. A spline can be provided at the lower end of the lead screw 606, and a thread is provided at the upper end of the lead screw 606 to connect to the threaded sleeve 607. A corresponding spline groove is provided on the inner side of the sliding sleeve 624. The bottom of the insert piece 626 is preferably wedge-shaped, adapted to the wedge-shaped bottom surface 627. The insert piece 626 is arc-shaped and adapted to the arc-shaped groove 628. Multiple insert pieces 626 and arc-shaped grooves 628 are arranged circumferentially around the lead screw 606. The rotating ring 622 and fixed ring plate 625 are components that never rotate. The sliding sleeve 624 rotates with the lead screw 606 and its height changes. The rotating ring 622 can be connected to the sliding sleeve 624 via a bearing, achieving a rotatable connection and allowing the sliding sleeve 624 to drive the rotating ring 622 to rise and fall.

[0091] During the pressurization phase, as the drive device 603 slowly rotates forward, the insert piece 626 moves towards the lower end of the wedge-shaped bottom surface 627. Under the action of the spring 623, the sliding sleeve 624 rises, causing the first limiting block 618 to rise via the crossbar 621 and the telescopic rod 620, thus creating a gap between the first limiting block 618 and the second limiting block 615. The insert piece 626 then moves to abut against the wall of the arc-shaped groove 628. In the circumferential direction of the sliding sleeve 624, the insert piece 626 rotates along with it, maintaining the height of the sliding sleeve 624. During pressure release, the drive device 603 slowly reverses, and the insert piece 626 moves towards the higher end of the wedge-shaped bottom surface 627. The sliding sleeve 624 descends, causing the first limiting block 618 to descend until it contacts the second limiting block 615 via the crossbar 621 and the telescopic rod 620.

[0092] The lifting mechanism of the present invention can make full use of the power source of the drive device 603 itself and utilize the characteristic of the lead screw 606 to generate different movements in different directions, so as to raise and lower the first limit block 618, thereby fully cooperating with the movement of the stop block 614 during the pressurization and pressure release stages.

[0093] 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).

[0094] Furthermore, the side of the threaded sleeve 607 is fixedly connected to the connecting rod 609 via a support rod 608.

[0095] Furthermore, the fixing plates 601 of the six loading devices 6 are respectively fixedly connected to the bottom plate 1, the top plate 4 and the four side plates 3.

[0096] Furthermore, multiple limiting structures are arranged around the lead screw 606; specifically, the stops 614 of the multiple limiting structures can disperse the circumferential torque, making the overall structure more stable and reliable. Among the multiple limiting structures, the sliding sleeve 624, rotating ring 622, fixed ring plate 625 and connecting components located in the middle are all provided in one, that is, multiple limiting structures share the same space. Meanwhile, the components on the outer side, such as the upright 612, protrusion 613, stop 614, first limiting block 618, second limiting block 615, etc., are arranged in multiple ways around the lead screw 606.

[0097] 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. A cyclic loading and unloading test device for rock specimens with varying principal stress directions, characterized in that, The test apparatus includes: a loading device (6), a base plate (1), a side plate (3), a top plate (4), and a load-bearing support (5); The support bracket (5) is fixedly connected to the base plate (1). The support bracket (5) is used to place the rock sample (2). The loading device (6) is provided on all six sides of the rock sample (2). The loading devices (6) on opposite sides are symmetrically arranged. The loading device (6) below the rock sample (2) is located below the support bracket (5). The top of the loading device (6) above the rock sample (2) is fixedly connected to the top plate (4). The outer ends of the loading devices (6) around the rock sample (2) are fixedly connected to the side plates (3). The tops of the two side plates (3) are detachably connected to the two ends of the top plate (4). The bottom of the side plates (3) is fixedly connected to the base 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 movement of the threaded sleeve (607), and thus adjusting the maximum pressure value applied by the pressure plate (611), achieving adjustment. The function.

2. The rock specimen variable principal stress direction loading and unloading cyclic test device 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).

3. The cyclic loading and unloading test device for rock specimens with varying principal stress directions according to claim 2, characterized in that, The lifting mechanism includes a crossbar (621), a rotating ring (622), a spring (623), a sliding sleeve (624), a fixed ring plate (625), a plug-in piece (626), a wedge-shaped bottom surface (627), an arc groove (628), and a vertical bar (629). The upright (612) is provided with a third oblong through hole, and the crossbar (621) passes through the third oblong through hole. The third oblong through hole is slidably located inside the third oblong through hole. The crossbar (621) is located below the second limiting block (615). One end of the crossbar (621) is fixedly connected to the telescopic rod (620), and the other end of the crossbar (621) is fixedly connected to the outer ring of the rotating ring (622). The inner ring of the rotating ring (622) is rotatably sleeved on the sliding sleeve (624). The sliding sleeve (624) is slidably sleeved on the lead screw (606). The sliding sleeve (624) and the lead screw (606) are circumferentially constrained by a spline. The bottom of the sliding sleeve (624) is provided with a pressure-shaped... The spring (623) in its compressed state is sleeved on the lead screw (606). The top and bottom of the spring (623) abut against the bottom of the sliding sleeve (624) and the top of the rotating seat (605) respectively. The fixed ring plate (625) is provided above the sliding sleeve (624). The lead screw (606) passes through the fixed ring plate (625). The bottom of the fixed ring plate (625) is fixedly connected to the top of the vertical rod (629). The bottom of the vertical rod (629) is fixedly connected to the top of the connecting plate (604). The vertical rod (629) is located between the upright rod (612) and the lead screw (606). The vertical rod (629) is provided with a fourth waist-shaped hole. The horizontal rod (621) passes through the fourth waist-shaped hole. The top end face of the sliding sleeve (624) is provided with the arc-shaped groove (628), the bottom surface of the arc-shaped groove (628) is the wedge-shaped bottom surface (627), the arc-shaped groove (628) is provided with the matching plug-in piece (626), the top of the plug-in piece (626) is fixedly connected to the fixing ring plate (625), and the bottom of the plug-in piece (626) is adapted to the wedge-shaped bottom surface (627); When the lead screw (606) drives the sliding sleeve (624) to rotate, the sliding sleeve (624) is raised and lowered through the cooperation of the plug-in piece (626) and the wedge-shaped bottom surface (627), thereby raising and lowering the first limiting block (618).

4. The cyclic loading and unloading test device for rock specimens with varying principal stress directions according to claim 1, characterized in that, 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).

5. The cyclic loading and unloading test device for rock specimens with varying principal stress directions according to claim 1, characterized in that, The side of the threaded sleeve (607) is fixedly connected to the connecting rod (609) by a support rod (608).

6. The cyclic loading and unloading test device for rock specimens with varying principal stress directions according to claim 1, characterized in that, The fixing plates (601) of the six loading devices (6) are respectively fixedly connected to the bottom plate (1), the top plate (4) and the four side plates (3).

7. A cyclic loading and unloading test apparatus for rock specimens with varying principal stress directions according to any one of claims 1-6, characterized in that, The limiting structure is provided in multiple ways around the lead screw (606).

8. A method for cyclic loading and unloading of rock specimens with varying principal stress directions, applied to the cyclic loading and unloading test apparatus for rock specimens with varying principal stress directions as described in claim 1, characterized in that, Includes the following steps: Step 1, Sample preparation: Prepare a complete cubic rock sample (2); Step 2, cyclic loading: Six loading devices (6) are set up and distributed on the six faces of the rock sample (2); the rock sample (2) is subjected to pressure by the loading devices (6). x, y, z The stresses in the three directions are respectively σ x , σ y , σ z The initial damage critical stress value of rock sample (2) is σ c By adjusting the output pressure of the loading device (6), σ x = σ y = σ z = σ c ; Step 3: Adjust the output pressure of the loading device (6) to... σ z Adjusted to , σ x Adjusted to Rock sample (2) z The direction is the maximum principal stress. x The direction is the minimum principal stress, and the rock sample (2) is in x - y Cracks appeared on the surface; Adjust the output pressure of the loading device (6) to σ x Stress adjustment in direction , σ y Stress adjustment in direction Rock sample (2) x The direction is the maximum principal stress. y The direction is the minimum principal stress, and the rock sample (2) is in y - z Cracks appeared on the surface; Adjust the output pressure of the loading device (6) to σ y Stress adjustment in direction , σ z Stress adjustment in direction ， rock sample (2) y The direction is the maximum principal stress. z The direction is the minimum principal stress, and the rock sample (2) is in x - z Cracks appeared on the surface; Step 4, Increment Size, and repeat step three until the rock sample (2) is broken and three sets of "X"-shaped conjugate shear joint models are produced.

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