Rock sample variable principal stress direction loading and unloading cyclic test method and device

Abstract

The invention belongs to the field of rock mass engineering, and provides a rock sample variable principal stress direction loading and unloading cyclic test method and device, the method comprises the following steps: 1, sample processing: processing a complete cubic rock sample; step 2, cyclic loading: the rock sample is subjected to stresses in x, y and z directions, and the stresses are sigma x, sigma y and sigma z respectively; step 3; sequentially adjusting the pressures in different directions to form fractures on x-y, y-z and x-z planes; 4, increasing the pressure, and repeating the step 3 until the rock sample is damaged and three groups of X-shaped conjugated shear joint models are generated; the device is mainly used for simulating that three groups of X-shaped conjugated shear joints are often formed under the action of tectonic stress changes in different directions and different orders and vertical ground stress changes caused by tectonic denudation or deposition in the geological historical evolution process of an area where a rock sample is located; and suggestions can be provided for engineering excavation in combination with local earthquake monitoring and on-site geological exploration.

Description

Technical Field

[0001] The invention belongs to the field of rock mass engineering, and in particular relates to a method and a device for a rock sample loading and unloading cycle test with a variable principal stress direction. Background Art

[0002] Natural rocks inevitably have natural defects such as microcracks, faults and holes due to long-term and complex geological movements. The initiation, expansion and penetration of cracks inside the fractured rock mass are the causes of engineering accidents.

[0003] The structural planes of rock mass space often exist in the form of joints with different lengths, angles and orientations. The joints, fissures, cleavage planes and weak interlayers in the jointed rock mass will destroy the integrity of the rock mass. The cracking and expansion of the wing-shaped cracks generated at the joint tips under the compression and shearing action of external loads often lead to the instability and destruction of the rock mass. The geometric characteristics of the joints mainly include the length of the joints, the inclination of the joints, and the degree of penetration, which are the main factors affecting the mechanical properties of the jointed rock mass. In engineering, the conjugate "X" type joint fissures play a controlling role in the stability of the rock mass. At the same time, the secondary joints also have a certain influence on the strength of the rock mass. When the inclination of the primary and secondary joints is the same, the peak strength of the single jointed rock mass is significantly higher than that of the X-type jointed rock mass.

[0004] At present, the main view of research is that there is a group of conjugate "X" type joints and fissures in the rock mass. In addition, the cracks in the material are usually simplified into several types such as opening type, sliding type, and tearing type. In engineering, joints are rarely simplified into three groups of conjugate "X" type joints and fissures. However, in actual engineering, due to factors such as earthquakes and blasting, three groups of conjugate "X" type joints and fissures appear in the rock mass in three-dimensional space. Based on the above problems, there is currently a lack of a device for testing the three groups of conjugate "X" type joints and fissures model. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method and device for a rock sample loading and unloading cycle test with variable principal stress direction to solve the problems in the prior art. The technical solution adopted by the present invention is: A method for loading and unloading cyclic testing of rock samples with variable principal stress direction comprises the following steps: Step 1: Sample processing: processing a complete cubic rock sample; Step 2: Cyclic loading: a total of six loading devices are set up, distributed on the six faces of the rock sample; the rock sample is pressurized by the loading devices. x、y、z The stresses in three directions are s x , s y , s z The initial damage critical stress value of the rock sample is sc By adjusting the output pressure of the loading device, s x = s y = s z = s c ; Step 3: Adjust the output pressure of the loading device. s z Adjust to , s x Adjust to , rock samples z The direction is the maximum principal stress, x The direction is the minimum principal stress, and the rock sample is x - y Cracks appear on the plane; Adjust the output pressure of the loading device to s x The stress in the direction is adjusted to , s y The stress in the direction is adjusted to , rock samples x The direction is the maximum principal stress, y The direction is the minimum principal stress, and the rock sample is y - z Cracks appear on the plane; Adjust the output pressure of the loading device to s y The stress in the direction is adjusted to , s z The stress in the direction is adjusted to ， Rock samples y The direction is the maximum principal stress, z The direction is the minimum principal stress, and the rock sample is x - z Cracks appear on the plane; Step 4: Increment size, and repeat step 3 until the rock specimen is destroyed and three sets of “X”-type conjugate shear joint models are generated.

[0006] A rock sample variable principal stress direction loading and unloading cycle test device, the test device comprises: a loading device, a bottom plate, a side plate, a top plate and a bearing bracket; The bottom plate is fixedly connected to the bearing bracket, and the bearing bracket is used to place the rock sample. The six faces of the rock sample are all provided with the loading devices, and the loading devices on the two opposite faces are symmetrically arranged; wherein the loading device below the rock sample is located below the bearing bracket, the top of the loading device above the rock sample is fixedly connected to the top plate, and the outer ends of the loading devices around the rock sample are respectively fixedly connected to the side plates, wherein 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 bottom plate; The loading device is used to apply pressure to the wall surface of the rock sample.

[0007] Furthermore, the loading device includes a fixing plate, a driving device, a connecting plate, a rotating seat, a screw rod, a threaded sleeve, a connecting rod, a pressing plate and a limiting structure; The fixing plate and the connecting plate are arranged side by side, the driving device is installed between the fixing 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 arranged on the connecting plate, one end of the rotating seat away from the driving device is fixedly connected to one end of the screw rod, the other end of the screw rod is threadedly connected to the threaded sleeve, the side surface of the threaded sleeve is connected to the connecting rod, the connecting rod is parallel to the axis of the screw rod, and the end of the connecting rod away from the connecting plate is connected to the pressing plate; The driving device is used to drive the rotating seat to rotate, so that the screw rod rotates; the side of the connecting rod is connected to the limiting structure, which is used to limit the connecting rod to rotate around the screw rod, so that the threaded sleeve moves along the screw rod and the pressure plate faces the wall of the rock sample.

[0008] Furthermore, the limiting structure includes a vertical rod, a protrusion, a stopper, a second limiting block, an intermediate plate and a cover plate; The vertical rod is parallel to the connecting rod and is arranged at an interval. The vertical rod is located on a side of the connecting rod away from the screw rod. One end of the vertical rod is fixedly connected to the connecting plate. A second waist-shaped through hole is provided on the vertical rod. The middle plate is located in the second waist-shaped through hole. One end of the middle plate facing the connecting rod is fixedly connected to the second limit block. One end of the middle plate away from the connecting rod is detachably connected to the cover plate. The side of the connecting rod is fixedly connected to the protrusion, the end of the protrusion can remove the stopper, the second limit block is located on the rotation path of the stopper, and the second limit block is used to abut against the stopper to form a circumferential constraint; The middle plate is slidable up and down in the second waist-shaped through hole, and the cover plate and the vertical pole are provided with teeth to restrict the vertical height; By adjusting the height of the second limit block, the travel of the stopper to separate from the second limit block is changed to adjust the movement of the threaded sleeve, thereby adjusting the maximum pressure value applied by the pressure plate to achieve adjustment. function.

[0009] Furthermore, the limiting structure also includes a first limiting block, a transmission block, a telescopic rod and a lifting mechanism; The vertical rod is provided with a first waist-shaped through hole, the transmission block is arranged in the first waist-shaped through hole, the transmission block is fixedly connected to the first limit block at one end facing the connecting rod, the first limit block is located above the second limit block, the transmission block is fixedly connected to the telescopic rod at one end away from the connecting rod, the telescopic rod is parallel to the vertical rod, and the telescopic rod is connected to the lifting mechanism at one end away from the transmission block for lifting the first limit block; When the screw is rotated to make the pressing plate move toward the rock sample, the first limit block moves to the highest height, and a gap is formed between the bottom of the first limit block and the top of the second limit block; when the stop block is separated from the second limit block, the stop block enters the gap above the second limit block; When the screw rotates to move the pressure plate away from the rock sample, the first limit block moves to the lowest height, and the bottom of the first limit block fits with the top of the second limit block; the stop block abuts the lower end of the first limit block and moves onto the second limit block.

[0010] Further, the lifting mechanism includes a crossbar, a rotating ring, a spring, a sliding sleeve, a fixed ring plate, a plug-in sheet, a wedge-shaped bottom surface, an arc-shaped groove and a vertical rod; The third waist-shaped through hole is provided on the vertical rod, and the cross bar passes through the third waist-shaped through hole, and the third waist-shaped through hole can slide up and down and is located in the third waist-shaped through hole, and the cross bar is located below the second limit block, and one end of the cross bar is fixedly connected to the telescopic rod, and the other end of the cross bar is fixedly connected to the outer ring of the rotating ring, and the inner ring of the rotating ring is rotatably sleeved on the sliding sleeve, and the sliding sleeve can be slidably sleeved on the screw rod, and the sliding sleeve and the screw rod are circumferentially constrained by splines; the spring in a compressed state is provided at the bottom of the sliding sleeve, and the spring is sleeved on the screw rod, and the top and bottom of the spring respectively abut against the bottom of the sliding sleeve and the top of the rotating seat, and the fixing ring plate is provided above the sliding sleeve, and the screw rod passes through the fixing ring plate, and the bottom of the fixing ring plate is fixedly connected to the top of the vertical rod, and the bottom of the vertical rod is fixedly connected to the top of the connecting plate, and the vertical rod is located between the vertical rod and the screw rod. A fourth waist-shaped hole is provided on the vertical rod, and the cross bar passes through the fourth waist-shaped hole; The top end surface of the sliding sleeve is provided with the arc groove, the bottom surface of the arc groove is the wedge-shaped bottom surface, the matching plug-in piece is provided in the arc groove, the top of the plug-in piece is fixedly connected to the fixed ring plate, and the bottom of the plug-in piece is matched with the wedge-shaped bottom surface; When the screw rod drives the sliding sleeve to rotate, the sliding sleeve is lifted and lowered by the cooperation between the plug-in piece and the wedge-shaped bottom surface, thereby causing the first limiting block to be lifted and lowered.

[0011] Furthermore, the connecting rod is fixedly connected to the transition plate, and the transition plate is rotatably connected to the pressure plate.

[0012] Furthermore, the side surface of the threaded sleeve is fixedly connected to the connecting rod via a support rod.

[0013] Furthermore, the six fixing plates of the loading devices are respectively fixedly connected to the bottom plate, the top plate and the four side plates.

[0014] Furthermore, a plurality of the limiting structures are arranged around the screw rod.

[0015] The present invention has the following beneficial effects: the present invention mainly simulates the geological history evolution process of the area where the rock sample is located, and under the action of tectonic stress changes of different directions and orders, as well as vertical ground stress changes caused by tectonic erosion or sedimentation, three groups of "X"-shaped conjugate shear joints are often formed, providing a basis for the verification of the proposed theoretical model and the self-compiled program; at the same time, the present invention can also simulate the formation evolution process of "X"-shaped conjugate shear joints of rocks of different orders under the action of earthquake, excavation unloading and engineering loading of intact rocks; and can provide suggestions for engineering excavation in combination with local earthquake monitoring and on-site geological surveys. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the generation of three groups of conjugated "X" cracks of the present invention; Figure 2 It is a schematic diagram of the overall structure of the test device of the present invention; Figure 3 is a top view schematic diagram of the test device; Figure 4 is a schematic diagram of the initial state of the loading device; Figure 5 is a schematic diagram of the loading device being loaded to the maximum pressure state; Figure 6 is a schematic diagram when the first and second limit blocks are in contact; Figure 7 is a top view schematic diagram of the connection relationship of the second limit block; Figure 8 1. It is a top view schematic diagram of the connection relationship of the sliding sleeve; Figure 9It is a schematic diagram of the connection relationship of the plug-in piece. DETAILED DESCRIPTION

[0017] The following will be combined with the embodiments of the present invention Figure 1-Figure 9 , the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0018] like Figure 1 A method for loading and unloading cyclic testing of rock samples with variable principal stress direction comprises the following steps: Step 1, sample processing: processing a complete cubic rock sample 2: the sample processing is to drill a complete cubic sample without joints and cracks on the rock mass I or II; the size of the rock sample 2 is 150 mm to 300 mm; Step 2: Cyclic loading: a total of six loading devices 6 are provided, distributed on the six faces of the rock sample 2; the rock sample 2 is pressurized by the loading devices 6. x、y、z The stresses in three directions are 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 at ( s c , 0), the state of the sample corresponds to the stress state of the intact rock mass when it is undisturbed and not subjected to earthquake action. The initial damage critical stress value s c It can be obtained by consulting materials and actual experiments, and is a fixed value; Step 3: Adjust the output pressure of the loading device 6. s z Adjust to , s x Adjust 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 x -y The plane has cracks; the corresponding x Direction unloading or z Directional seismic waves and other working conditions; Adjust the output pressure of the loading device 6 to s x The stress in the direction is adjusted to , s y The stress in the direction is adjusted to , 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 y - z The plane has cracks; the corresponding y Direction unloading or x Directional seismic waves and other working conditions; Adjust the output pressure of the loading device 6 to s y The stress in the direction is adjusted to , s z The stress in the direction is adjusted to ， 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 x - z The plane has cracks; the corresponding z Direction unloading or y Directional seismic waves and other working conditions; The three steps in step 3 above can be performed in any order you choose; Step 4: Increment size, and repeat step 3 until rock sample 2 is destroyed and three sets of "X" type conjugate shear joint models are generated; usually, the stress increment is 2 , 3 , 4 … n 。

[0019] In the method of the present invention, the loading device 6 can be the loading device 6 proposed in the present invention, or 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.

[0020] The present invention mainly simulates the geological history evolution process of the area where the rock sample is located, and the three groups of "X"-shaped conjugate shear joints are often formed under the action of tectonic stress changes of different directions and orders, as well as vertical stress changes caused by tectonic erosion or sedimentation, providing a basis for the verification of the proposed theoretical model and the self-compiled program; at the same time, it can also simulate the formation evolution process of "X"-shaped conjugate shear joints of rocks of different orders under the action of earthquake, excavation unloading and engineering loading of intact rocks; it can provide suggestions for engineering excavation in combination with local earthquake monitoring and on-site geological surveys.

[0021] It should be noted that the present invention x、y、z The three directions refer to the up-down, left-right, and front-back directions that are perpendicular to each other and intersect at one point.

[0022] like Figure 2 , a rock sample variable principal stress direction loading and unloading cycle test device, the test device comprises: a loading device 6, a bottom plate 1, a side plate 3, a top plate 4 and a bearing bracket 5; The bottom plate 1 is fixedly connected to the bearing bracket 5, and the bearing bracket 5 is used to place the rock sample 2. The six faces of the rock sample 2 are all provided with the loading devices 6, and the loading devices 6 on the two opposite faces are symmetrically arranged; wherein the loading device 6 below the rock sample 2 is located below the bearing bracket 5, and the top of the loading device 6 above the rock sample 2 is fixedly connected to the top plate 4, and the outer ends of the loading devices 6 around the rock sample 2 are respectively fixedly connected to the side plates 3, wherein the tops of the two side plates 3 are detachably connected to the two ends of the top plate 4, and the bottoms of the side plates 3 are fixedly connected to the bottom plate 1; The loading device 6 is used to apply pressure to the wall surface of the rock sample 2 .

[0023] There are six loading devices 6 in total. In the embodiment of the present invention, the loading device 6 below the supporting bracket 5 is used as an example to illustrate its structure, wherein the upper and lower positions of each component are all referred to this loading device 6, that is, Figure 4 The position in.

[0024] There are four side panels 3 in total, which are distributed on the four surfaces of the rock sample 2. The tops of two opposite side panels 3 can be connected to the top panel 4 by bolts. In specific implementation, the rock sample 2 is first placed on the bearing bracket 5, and then the top panel 4 is installed. Figure 3 This is the initial state of the invention. There is a gap between the rock sample 2 and the pressure plate 611. The gap is the initial gap, and the gap distances on each surface of the rock sample 2 are equal.

[0025] like Figure 4-Figure 6The loading device 6 includes a fixing plate 601, a driving device 603, a connecting plate 604, a rotating seat 605, a screw rod 606, a threaded sleeve 607, a connecting rod 609, a pressing plate 611 and a limiting structure; The fixing plate 601 and the connecting plate 604 are arranged side by side, the driving device 603 is installed between the fixing 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 arranged 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 screw rod 606, the other end of the screw rod 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 screw rod 606, and the end of the connecting rod 609 away from the connecting plate 604 is connected to the pressing plate 611; The driving device 603 is used to drive the rotating seat 605 to rotate, so that the screw rod 606 rotates; the side of the connecting rod 609 is connected to the limiting structure, which is used to limit the connecting rod 609 to rotate around the screw rod 606, so that the threaded sleeve 607 moves along the screw rod 606, and the pressure plate 611 faces the wall of the rock sample 2.

[0026] The driving device 603 is a prior art device, which can be a motor, a hydraulic motor, etc. The connecting plate 604 is parallel to the fixing plate 601, and the screw rod 606 is perpendicular to the connecting plate 604. The screw rod 606 and the threaded sleeve 607 form a transmission structure, which converts the rotation of the screw rod 606 into the movement of the threaded sleeve 607 along the axial direction of the screw rod 606.

[0027] Furthermore, the limiting structure includes a vertical rod 612, a protrusion 613, a stopper 614, a second limiting block 615, an intermediate plate 616 and a cover plate 617; The vertical rod 612 is parallel to the connecting rod 609 and is arranged at intervals. The vertical rod 612 is located on a side of the connecting rod 609 away from the screw rod 606. One end of the vertical rod 612 is fixedly connected to the connecting plate 604. A second waist-shaped through hole is provided on the vertical rod 612. The middle plate 616 is located in the second waist-shaped through hole. One end of the middle plate 616 facing the connecting rod 609 is fixedly connected to the second limit block 615. One end of the middle plate 616 away from the connecting rod 609 is detachably connected to the cover plate 617. The side of the connecting rod 609 is fixedly connected to the protrusion 613, and the end of the protrusion 613 can remove the stopper 614. The second limit block 615 is located on the rotation path of the stopper 614, and the second limit block 615 is used to resist the stopper 614 to form a circumferential constraint; The middle plate 616 can slide up and down in the second waist-shaped through hole, and the cover plate 617 and the vertical pole 612 are provided with a tooth portion 600 to constrain the vertical height; the inner side surface of the cover plate 617 and the outer side surface of the vertical pole 612 are respectively provided with meshing teeth 600 to produce vertical constraints and facilitate precise adjustment of the upper and lower heights of the cover plate 617 and the second limit block 615.

[0028] By adjusting the height of the second limit block 615, the travel of the stop block 614 to disengage from the second limit block 615 is changed to adjust the movement of the threaded sleeve 607, thereby adjusting the maximum pressure value applied by the pressure plate 611 to achieve adjustment. function.

[0029] The middle plate 616 can move up and down in the second waist-shaped through hole to adjust the height of the second stopper 615. The cover plate 617 is connected to the middle plate 616 by bolts. The protrusion 613 and the stopper 614 are located on the radial side of the connecting rod 609. The stopper 614 can be connected to the protrusion 613 by means of threads or screws. The depth of the stopper 614 can be adjusted, thereby adjusting the interference amount when the stopper 614 collides with the second stopper 615, and the damaged stopper 614 can be replaced.

[0030] Furthermore, the limiting structure also includes a first limiting block 618, a transmission block 619, a telescopic rod 620 and a lifting mechanism; The vertical rod 612 is provided with a first waist-shaped through hole, in which the transmission block 619 is provided, and one end of the transmission block 619 facing the connecting rod 609 is fixedly connected to the first limit block 618, and the first limit block 618 is located above the second limit block 615, and one end of the transmission block 619 away from the connecting rod 609 is fixedly connected to the telescopic rod 620, and the telescopic rod 620 is parallel to the vertical rod 612, and one end of the telescopic rod 620 away from the transmission block 619 is connected to the lifting mechanism for lifting the first limit block 618; When the screw rod 606 rotates to make the pressing plate 611 move toward the rock sample 2, the first limit block 618 moves to the highest height, and a gap is formed between the bottom of the first limit block 618 and the top of the second limit block 615; when the stop block 614 is separated from the second limit block 615, the stop block 614 enters the gap above the second limit block 615; When the screw rod 606 rotates to move the pressure plate 611 away from the rock sample 2, the first limit block 618 moves to the lowest height, and the bottom of the first limit block 618 fits with the top of the second limit block 615; the stop block 614 abuts against the lower end of the first limit block 618 and moves onto the second limit block 615.

[0031] Specifically, a slide groove is provided on one side of the vertical rod 612 facing the connecting rod 609 , and the first limiting block 618 and the second limiting block 615 are both located in the slide groove.

[0032] The pressurization process of the present invention is as follows: like Figure 4 , which is the initial state. When the pressure is applied, the driving device 603 rotates forward, so that the threaded sleeve 607 drives the pressing plate 611 to move toward the rock sample 2, thereby generating an extrusion force until the pressure reaches s c or During this process, the second limit block 615 abuts against the stop block 614 to form a circumferential constraint to prevent the stop block 614 from rotating. s c or When the stopper 614 is just separated from the top of the second stopper 615, it enters the gap between the second stopper 615 and the first stopper 618, forming a Figure 5 In the middle state, the stopper 614 is not constrained, and the friction between the threaded sleeve 607 and the screw rod 606 causes the threaded sleeve 607 to rotate along with the screw rod 606.

[0033] The process of releasing pressure (resetting process) of the present invention is as follows: like Figure 5 When the pressure plate 611 moves to the farthest stroke, the driving device 603 slowly reverses, and the lifting mechanism causes the telescopic rod 620 and the first limit block 618 to descend, so that the top of the second limit block 615 fits with the bottom of the first limit block 618, and then the stopper 614 reverses to abut against the junction of the top of the second limit block 615 and the bottom of the first limit block 618, thereby forming a circumferential constraint on the stopper 614, forming Figure 6 In the state, under the rotation of the screw rod 606, the threaded sleeve 607 moves downward, so that the stopper 614 returns to the coverage range of the second limit block 615.

[0034] When the pressure is re-applied, the driving device 603 slowly rotates forward, and the lifting mechanism pushes the first limit block 618 to rise, so as to form a gap between the first limit block 618 and the second limit block 615 .

[0035] When adjusting ， That is, when adjusting the maximum pressure, the movement of the threaded sleeve 607 is adjusted by adjusting the height of the second limit block 615, so as to adjust the maximum movement stroke of the threaded sleeve 607. In addition, the length of the telescopic rod 620 is adjusted so that the spacing distance between the first limit block 618 and the second limit block 615 is a fixed value. The telescopic rod 620 is a prior art.

[0036] In addition, scale lines may be provided on the outer side of the vertical rod 612 to reflect the movement of the cover plate 617 , thereby progressively adjusting the height of the second limit block 615 to form a function of progressively adjusting the maximum pressure.

[0037] The present invention utilizes the adjustable stroke of the second limit block 615 to adjust the movement stroke of the threaded sleeve 607, thereby adjusting the maximum pressure, and can realize the function of progressively adjusting the maximum pressure. The stroke change can be intuitively reflected through the scale line. There is a definite conversion relationship between the stroke and pressure, which can be directly obtained by setting a pressure sensor on the pressure plate 611 and calculating the linear relationship between the stroke, so that the maximum pressure can be accurately adjusted and controlled.

[0038] 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 groove 628 and a vertical rod 629; The vertical rod 612 is provided with a third waist-shaped through hole, and the cross bar 621 passes through the third waist-shaped through hole. The third waist-shaped through hole can slide up and down in the third waist-shaped through hole, and the cross bar 621 is located below the second limit block 615. One end of the cross bar 621 is fixedly connected to the telescopic rod 620, and the other end of the cross bar 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, and the sliding sleeve 624 is slidably sleeved on the screw rod 606. The sliding sleeve 624 and the screw rod 606 are circumferentially constrained by splines; the bottom of the sliding sleeve 624 The spring 623 in a compressed state is provided, and the spring 623 is sleeved on the screw rod 606. The top and bottom of the spring 623 respectively abut against the bottom of the sliding sleeve 624 and the top of the rotating seat 605. The fixing ring plate 625 is provided above the sliding sleeve 624. The screw rod 606 passes through the fixing ring plate 625. The bottom of the fixing 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 vertical rod 612 and the screw rod 606. A fourth waist-shaped hole is provided on the vertical rod 629, and the cross bar 621 passes through the fourth waist-shaped hole. The top end surface of the sliding sleeve 624 is provided with the arc groove 628, the bottom surface of the arc groove 628 is the wedge-shaped bottom surface 627, the arc 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 matched with the wedge-shaped bottom surface 627; When the screw rod 606 drives the sliding sleeve 624 to rotate, the sliding sleeve 624 is lifted or lowered by the cooperation between the plug-in piece 626 and the wedge-shaped bottom surface 627 , thereby causing the first limiting block 618 to be lifted or lowered.

[0039] The rotating ring 622, the sliding sleeve 624, the fixed ring plate 625 and the screw 606 are coaxially arranged. The spline between the sliding sleeve 624 and the screw 606 can realize sliding and form a circumferential constraint at the same time. The spline can be set at the lower end of the screw 606, and the upper end of the screw 606 is provided with a thread to connect the threaded sleeve 607. The inner side of the sliding sleeve 624 is provided with a corresponding spline groove. The bottom of the plug-in piece 626 is preferably a wedge-shaped structure, which is adapted to the wedge-shaped bottom surface 627. The plug-in piece 626 is arc-shaped and adapted to the arc groove 628. The plug-in piece 626 and the arc groove 628 are arranged in multiple directions around the screw 606. The rotating ring 622 and the fixed ring plate 625 are components that never rotate, and the sliding sleeve 624 rotates with the screw 606 and changes in height. The rotating ring 622 can be connected to the sliding sleeve 624 through a bearing to achieve a rotating connection and enable the sliding sleeve 624 to drive the rotating ring 622 to rise and fall.

[0040] In the pressurizing stage, when the driving device 603 rotates forward slowly, the plug-in piece 626 moves toward the lower end of the wedge-shaped bottom surface 627, and then the sliding sleeve 624 rises in height under the action of the spring 623, and the first limit block 618 rises through the cross bar 621 and the telescopic rod 620, so that a gap is formed between the first limit block 618 and the second limit block 615. The plug-in piece 626 moves to abut against the wall surface of the arc groove 628, and the plug-in piece 626 rotates along with it in the circumferential direction of the sliding sleeve 624, so as to maintain the height of the sliding sleeve 624. When releasing the pressure, the driving device 603 slowly reverses, and the plug-in piece 626 moves toward the higher end of the wedge-shaped bottom surface 627, and the sliding sleeve 624 drops in height, and the first limit block 618 drops to contact the second limit block 615 through the cross bar 621 and the telescopic rod 620.

[0041] The lifting mechanism of the present invention can make full use of the power source of the driving device 603 itself and the characteristics of the screw rod 606 rotating in different directions to produce different movements, so as to lift the first limit block 618, thereby fully cooperating with the movement of the stop block 614 during the pressurization and pressure release stages.

[0042] Furthermore, the connecting rod 609 is fixedly connected to the transition plate 610, and the transition plate 610 is rotatably connected to the pressing plate 611. When the stopper 614 is in the interval, the friction between the pressing plate 611 and the rock sample 2 makes the pressing plate 611 relatively stationary, while the transition plate 610 and the threaded sleeve 607 rotate relatively, which can prevent the threaded sleeve 607 from continuing to move axially under the action of the friction (friction between the pressing plate 611 and the rock sample 2).

[0043] Furthermore, the side surface of the threaded sleeve 607 is fixedly connected to the connecting rod 609 via a support rod 608 .

[0044] 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 .

[0045] Furthermore, the limiting structures are arranged in plurality around the screw rod 606; specifically, the stoppers 614 of the plurality of limiting structures can disperse the circumferential torque, making the overall structure more stable and reliable. Among the plurality of limiting structures, the sliding sleeve 624, the rotating ring 622, the fixed ring plate 625 and the connected parts located in the middle are arranged in one, that is, the plurality of limiting structures are shared. The components located on the outside, such as the vertical rod 612, the protrusion 613, the stopper 614, the first limiting block 618, the second limiting block 615, etc., are arranged in plurality around the screw rod 606.

[0046] The embodiments described above are only descriptions of the preferred modes of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations, modifications, and substitutions made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for loading and unloading cyclic testing of rock specimens with variable principal stress direction, characterized in that: The following steps are involved: Step 1: Sample processing: processing a complete cubic rock sample (2); Step 2: cyclic loading: a total of six loading devices (6) are provided, distributed on the six surfaces of the rock sample (2); the rock sample (2) is pressurized by the loading devices (6). x, y, z The stresses in three directions are 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) σ z Adjust to , σ x Adjust to , rock samples (2) z The direction is the maximum principal stress, x The direction is the minimum principal stress, and the rock sample (2) is x - y Cracks appear on the plane; Adjust the output pressure of the loading device (6) to σ x The stress in the direction is adjusted to , σ y The stress in the direction is adjusted to , 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 y - z Cracks appear on the plane; Adjust the output pressure of the loading device (6) to σ y The stress in the direction is adjusted to , σ z The stress in the direction is adjusted to ， Rock samples (2) y The direction is the maximum principal stress, z The direction is the minimum principal stress, and the rock sample (2) is x - z Cracks appear on the plane; Step 4: Increment size, and repeat step 3 until the rock specimen (2) is destroyed and three sets of "X" type conjugate shear joint models are generated.

2. A rock sample variable principal stress direction loading and unloading cycle test device, using the test method of claim 1, characterized in that: The test device comprises: a loading device (6), a bottom plate (1), a side plate (3), a top plate (4) and a load-bearing bracket (5); The bottom plate (1) is fixedly connected to the bearing bracket (5), and the bearing bracket (5) is used to place the rock sample (2). The six surfaces of the rock sample (2) are all provided with the loading devices (6), and the loading devices (6) on two opposite surfaces are symmetrically arranged; wherein the loading device (6) below the rock sample (2) is located below the bearing bracket (5), the top of the loading device (6) above the rock sample (2) is fixedly connected to the top plate (4), and the outer ends of the loading devices (6) around the rock sample (2) are respectively fixedly connected to the side plates (3), wherein the tops of the two side plates (3) are detachably connected to the two ends of the top plate (4), and the bottoms of the side plates (3) are fixedly connected to the bottom plate (1); The loading device (6) is used to apply pressure to the wall surface of the rock sample (2).

3. A rock sample variable principal stress direction loading and unloading cycle test device according to claim 2, characterized in that: The loading device (6) comprises a fixing plate (601), a driving device (603), a connecting plate (604), a rotating seat (605), a screw rod (606), a threaded sleeve (607), a connecting rod (609), a pressing 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 arranged 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 screw rod (606), the other end of the screw rod (606) is threadedly connected to the threaded sleeve (607), the side surface of the threaded sleeve (607) is connected to the connecting rod (609), the connecting rod (609) is parallel to the axis of the screw rod (606), and one end of the connecting rod (609) away from the connecting plate (604) is connected to the pressing plate (611); The driving device (603) is used to drive the rotating seat (605) to rotate, thereby rotating the screw rod (606); the side surface of the connecting rod (609) is connected to the limiting structure, which is used to limit the connecting rod (609) to rotate around the screw rod (606), so that the threaded sleeve (607) moves along the screw rod (606) and the pressure plate (611) faces the wall surface of the rock sample (2).

4. A rock sample variable principal stress direction loading and unloading cycle test device according to claim 3, characterized in that: The limiting structure comprises a vertical rod (612), a protrusion (613), a stopper (614), a second limiting block (615), an intermediate plate (616) and a cover plate (617); The vertical rod (612) is parallel to the connecting rod (609) and is arranged at an interval. The vertical rod (612) is located on a side of the connecting rod (609) away from the screw rod (606). One end of the vertical rod (612) is fixedly connected to the connecting plate (604). A second waist-shaped through hole is provided on the vertical rod (612). The middle plate (616) is located in the second waist-shaped through hole. One end of the middle plate (616) facing the connecting rod (609) is fixedly connected to the second limit block (615). One end of the middle plate (616) away from the connecting rod (609) is detachably connected to the cover plate (617). The side of the connecting rod (609) is fixedly connected to the protrusion (613); the end of the protrusion (613) can remove the stopper (614); the second limit block (615) is located on the rotation path of the stopper (614); the second limit block (615) is used to abut against the stopper (614) to form a circumferential constraint; The middle plate (616) is slidable up and down and is located in the second waist-shaped through hole, and a tooth portion (600) is provided between the cover plate (617) and the vertical rod (612) to constrain the vertical height; By adjusting the height of the second limit block (615), the stroke of the stop block (614) disengaging from the second limit block (615) is changed to adjust the movement amount of the threaded sleeve (607), thereby adjusting the maximum pressure value applied by the pressure plate (611), thereby achieving adjustment. function.

5. A rock sample variable principal stress direction loading and unloading cycle test device according to claim 4, characterized in that: The limiting structure further comprises a first limiting block (618), a transmission block (619), a telescopic rod (620) and a lifting mechanism; The vertical rod (612) is provided with a first waist-shaped through hole, the transmission block (619) is arranged in the first waist-shaped through hole, one end of the transmission block (619) facing the connecting rod (609) is fixedly connected to the first limit block (618), the first limit block (618) is located above the second limit block (615), one 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 vertical rod (612), and one end of the telescopic rod (620) away from the transmission block (619) is connected to the lifting mechanism for lifting the first limit block (618); When the screw rod (606) rotates to cause the pressing plate (611) to move toward the rock sample (2), the first limit block (618) moves to the highest height, and a gap is formed between the bottom of the first limit block (618) and the top of the second limit block (615); when the stop block (614) is separated from the second limit block (615), the stop block (614) enters the gap above the second limit block (615); When the screw rod (606) rotates to move the pressure plate (611) away from the rock sample (2), the first limit block (618) moves to the lowest height, and the bottom of the first limit block (618) fits with the top of the second limit block (615); the stop block (614) abuts against the lower end of the first limit block (618) and moves onto the second limit block (615).

6. A rock sample variable principal stress direction loading and unloading cycle test device according to claim 5, characterized in that: The lifting mechanism comprises a crossbar (621), a rotating ring (622), a spring (623), a sliding sleeve (624), a fixed ring plate (625), a plug-in plate (626), a wedge-shaped bottom surface (627), an arc-shaped groove (628) and a vertical rod (629); The vertical rod (612) is provided with a third waist-shaped through hole, the cross rod (621) passes through the third waist-shaped through hole, the third waist-shaped through hole can slide up and down in the third waist-shaped through hole, the cross rod (621) is located below the second limit block (615), one end of the cross rod (621) is fixedly connected to the telescopic rod (620), and the other end of the cross rod (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 screw rod (606), and the sliding sleeve (624) and the screw rod (606) are circumferentially constrained by a spline; the bottom of the sliding sleeve (624) is provided with a compression The spring (623) is in a contracted state, the spring (623) is sleeved on the screw rod (606), the top and bottom of the spring (623) respectively abut against the bottom of the sliding sleeve (624) and the top of the rotating seat (605), the fixing ring plate (625) is arranged above the sliding sleeve (624), the screw rod (606) passes through the fixing ring plate (625), the bottom of the fixing 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 vertical rod (612) and the screw rod (606), the vertical rod (629) is provided with a fourth waist-shaped hole, and the cross rod (621) passes through the fourth waist-shaped hole; The top end surface 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 matching plug-in piece (626) is provided in the arc-shaped groove (628), the top of the plug-in piece (626) is fixedly connected to the fixed ring plate (625), and the bottom of the plug-in piece (626) is matched with the wedge-shaped bottom surface (627); When the screw rod (606) drives the sliding sleeve (624) to rotate, the sliding sleeve (624) is lifted or lowered through the cooperation between the plug-in piece (626) and the wedge-shaped bottom surface (627), thereby causing the first limiting block (618) to lift or lower.

7. The rock sample variable principal stress direction loading and unloading cycle test device according to claim 3 is 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 pressing plate (611).

8. The rock sample variable principal stress direction loading and unloading cycle test device according to claim 3 is characterized in that: The side surface of the threaded sleeve (607) is fixedly connected to the connecting rod (609) via a supporting rod (608).

9. The rock sample variable principal stress direction loading and unloading cycle test device according to claim 3 is 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).

10. A rock sample variable principal stress direction loading and unloading cycle test device according to any one of claims 3 to 9, characterized in that: A plurality of the limiting structures are arranged around the screw rod (606).

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