A conventional triaxial test system and method for simulating residual stress in rock

Abstract

The present application relates to the technical field of rock mechanics test, and discloses a kind of conventional triaxial test system and method for simulating internal residual stress of rock, and the system includes the flexible bag of being placed into the vertical through hole of rock sample, and the two ends of flexible bag are sealed and connected with upper pressure head and lower pressure head respectively, and the first passage of upper pressure head is formed in upper pressure head, and one end of the first passage of upper pressure head is communicated with the inside of flexible bag, and the other end is communicated with outside through second stop valve, and the first passage of lower pressure head is formed in lower pressure head, and one end of the first passage of lower pressure head is communicated with the inside of flexible bag, and the other end is communicated with internal pressure hydraulic pump;The method is by internal pressure hydraulic pump to inject pressure medium into flexible bag, simulates the internal pressure of rock sample;The present application can introduce internal residual stress in conventional triaxial test frame, and more truly reflect the internal stress state that rock sample may still exist after rock mechanics characteristics and fracture evolution law research provide experimental means with higher physical reality.

Description

Technical Field

[0001] This invention belongs to the field of rock mechanics testing technology, specifically relating to a conventional triaxial testing system and method for simulating residual stress inside rocks. Background Technology

[0002] Rocks exist in complex geostress environments throughout geological evolution and engineering service, and their mechanical properties and fracture behavior are significantly influenced by stress state and loading history. To study the deformation characteristics, strength evolution, and failure mechanisms of rocks under stress conditions, laboratory rock mechanics testing methods are widely used. Among these, the conventional triaxial compression test is particularly effective because it can apply principal stress in the axial direction and isotropic confining pressure in the radial direction.

[0003] Existing conventional triaxial testing techniques typically apply axial loads to rock samples through upper and lower indenters and apply uniform confining pressure to the outer surface of the rock sample using a confining pressure chamber, thereby constructing a stress state where axial stress and radial confining pressure act together. Extensive research and related patents have explored improvements to the loading accuracy, sealing performance, and testing methods of conventional triaxial testing devices. For example, patent application CN102128741A proposes a triaxial rheological testing process and method for hard and brittle rocks; patent application CN106525598A discloses a simple triaxial compression testing instrument for rocks; and patent application CN107132127A provides a novel conventional triaxial compression testing device and method for rocks. These existing technologies are relatively mature in terms of external axial stress and confining pressure loading, but their testing concepts still mainly focus on the application and control of external stress conditions.

[0004] In existing conventional triaxial testing studies, a fundamental assumption is typically implicitly made: after a rock sample is taken from the original rock mass and processed into a regular shape, its internal stress has been completely released, and the rock sample can be considered to be in a stress-free state at the start of the test. However, considering the integrity of rock materials and stress release mechanisms, the stress release process often occurs first in the outer surface region of the specimen. Due to the encapsulation and constraint of the outer structure, the stress state inside the specimen may not be released synchronously and completely. Especially under the combined effects of rock heterogeneity, the development of structural planes, and disturbances during sampling and processing, a certain residual stress state may still remain inside the specimen. This residual stress manifests physically as the retention effect of internal stress under external constraints.

[0005] The above research indicates that rocks may have complex stress states under different loading histories and constraint conditions. Traditional triaxial testing methods that rely solely on external axial stress and confining pressure are insufficient for independently and controllably simulating and studying the residual stress inside rocks. Summary of the Invention

[0006] To address the problem that conventional triaxial testing methods commonly used in existing rock mechanics experiments are insufficient for simulating the residual stress state inside rock samples, especially after the rock sample has been removed from its original stress environment, as it may still retain certain residual stresses due to structural constraints and encapsulation effects. Existing conventional triaxial tests typically only consider external confining pressure and axial stress, making it difficult to independently and controllably simulate these internal stresses in a laboratory setting. The purpose of this invention is to provide a conventional triaxial testing system and method for simulating residual stress inside rocks. By setting an internal pressure loading system inside the rock sample, including a flexible bladder with sealed openings at both ends connecting to an upper and lower pressure head, and injecting a pressure medium into the flexible bladder using an internal pressure hydraulic pump, the residual stress inside the rock can be simulated, more realistically reproducing the mechanical response characteristics of the rock under its original stress environment.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A conventional triaxial testing system for simulating residual stress inside rock includes an axial pressure loading system, a confining pressure loading system, and an internal pressure loading system; The axial pressure loading system is used to apply axial stress to the rock sample 3 to be tested. ; The confining pressure loading system is used to apply a uniformly distributed radial confining pressure to the outer surface of the rock sample 3. ; The rock sample 3 has a cylindrical outer contour and an axial through hole 301; The internal pressure loading system is used to apply uniformly distributed internal pressure to the rock sample 3. The system includes a flexible bag 8 inserted into the axial through hole 301. The two ends of the flexible bag 8 are respectively sealed and connected to an upper pressure head 4 and a lower pressure head 1. The upper pressure head 4 and the lower pressure head 1 are respectively located at the upper and lower ends of the rock sample 3 and are used to transmit the axial stress applied by the axial pressure loading system to the end face of the rock sample 3. The upper pressure head 4 has an upper pressure head first channel 5 inside, one end of which is connected to the inside of the flexible bag 8, and the other end is connected to the outside through a second shut-off valve 23. The lower pressure head 1 has a lower pressure head first channel 9 inside, one end of which is connected to the inside of the flexible bag 8, and the other end is connected to an internal pressure hydraulic pump 24.

[0008] The flexible bag 8 is a cylindrical structure made of oil-resistant elastic material, and its dimensions are configured such that it can apply pressure to the inner wall of the rock sample 3 after the injection of the pressure medium. The internal pressure.

[0009] The upper pressure head 4 has a cylindrical protrusion 401 on its lower surface, and the lower pressure head 1 has a cylindrical protrusion 101 on its upper surface. The flexible bag 8 has openings at both ends that are respectively fitted onto the outer sides of the cylindrical protrusion 401 and the cylindrical protrusion 101. The dimensions and shapes of the upper pressure head cylindrical boss 401 and the lower pressure head cylindrical boss 101 are configured such that they can be inserted into the axial through hole 301 after the flexible bag 8 is fitted on them.

[0010] Both the upper pressure head cylindrical boss 401 and the lower pressure head cylindrical boss 101 have annular grooves on their outer peripheries. Annular sealing rings 29 are provided in the grooves, and the end of the flexible bag 8 is pressed into the annular groove area by the clamping ring 30, so that the flexible bag 8 is tightly attached to the annular sealing ring 29 to form an end sealing structure.

[0011] The upper pressure head 4 includes an upper pressure head cylindrical loading plate 402, and the lower pressure head 1 includes a lower pressure head cylindrical loading plate 102. The upper pressure head cylindrical boss 401 is connected to the lower surface of the upper pressure head cylindrical loading plate 402, and the lower pressure head cylindrical boss 101 is connected to the upper surface of the lower pressure head cylindrical loading plate 102. The cross-sections of the upper pressure head cylindrical loading plate 402 and the lower pressure head cylindrical loading plate 102 are adapted to the end face of the rock sample 3, for use in conjunction with the axial pressure loading system to transfer axial stress. Transferred to rock sample 3.

[0012] The axial pressure loading system includes an upper seat 14 and a base 26. The upper seat 14 is located above the upper pressure head 4, and the base 26 is located below the lower pressure head 1. The upper seat 14 has multiple through holes, and each through hole is equipped with a screw 12. The screw 12 is threadedly engaged with the base 26. The upper seat 14 includes a hydraulic chamber, in which a T-shaped piston 20 is movably disposed along the axial direction. The T-shaped piston 20 divides the hydraulic chamber into a first hydraulic chamber 13 and a second hydraulic chamber 17, and the lower end of the T-shaped piston 20 extends out of the lower wall of the hydraulic chamber. The T-shaped piston 20, the upper pressure head 4, the rock sample 3, the lower pressure head 1, and the base 26 are arranged coaxially along the same vertical center line. The T-shaped piston 20 is driven to engage with the upper pressure head 4. The T-shaped piston 20 has a stroke range. Within the first interval of the stroke range, the T-shaped piston 20 is driven to engage with the upper pressure head 4 to compress the upper pressure head 4. Within the second interval of the stroke range, the T-shaped piston 20 is disengaged from the upper pressure head 4. The upper seat 14 has an upper seat first channel 16 and an upper seat second channel 18 inside. One end of the upper seat first channel 16 is connected to the upper seat first hydraulic chamber 13, and the other end is connected to the upper seat first hydraulic pump 15. One end of the upper seat second channel 18 is connected to the upper seat second hydraulic chamber 17, and the other end is connected to the upper seat second hydraulic pump 19.

[0013] The confining pressure loading system includes a sealing sleeve 2, a confining pressure cavity wall 11, a first confining pressure cavity channel 27, and a second confining pressure cavity channel 21; The sealing sleeve 2 is fitted onto the outside of the rock sample 3. The sealing sleeve 2 is made of oil-resistant thermoplastic material, and its axial ends extend to the side walls of the upper pressure head 4 and the lower pressure head 1, respectively, for radial confinement pressure. A continuous external sealing and isolation structure is formed during the loading process; The confining cavity wall 11 is a cylindrical structure, coaxially arranged around the outer periphery of the cover 2. The lower surface of the upper seat 14 and the upper surface of the base 26 are both provided with a frustum adapted to the cylindrical structure. The confining cavity wall 11 is placed between the upper seat 14 and the base 26 and is snapped onto the frustum. The confining pressure cavity wall 11, upper seat 14, base 26 and sealing sleeve 2 together form a confining pressure cavity, which is used to apply uniform radial confining pressure to the rock sample 3. The first channel 27 of the confining pressure chamber is located inside the base 26, with one end connected to the confining pressure chamber and the other end connected to the confining pressure hydraulic pump 28. The second channel 21 of the confining pressure chamber is disposed on the wall 11 of the confining pressure chamber. One end is connected to the confining pressure chamber near the frustum of the lower surface of the upper seat 14, and the other end is connected to the outside through the first shut-off valve 22 for radial confining pressure. Venting or depressurization during the loading process.

[0014] The first channel 9 of the lower pressure head is connected to the internal pressure hydraulic pump 24 through the second channel 25 of the lower pressure head. The second channel 25 of the lower pressure head is located inside the base 26, with one end of the channel opening located at the center of the base 26 and connected to the first channel 9 of the lower pressure head through the first quick-change connector 10. The other end of the channel opening is connected to the internal pressure hydraulic pump 24. The first channel 5 of the upper pressure head is connected to the second shut-off valve 23 through the second channel 7 of the upper pressure head. The second channel 7 of the upper pressure head passes through the wall 11 of the confining pressure cavity. One end of the channel is connected to the first channel 5 of the upper pressure head through the second quick-connect connector 6, and the other end of the channel is connected to the outside through the second shut-off valve 23.

[0015] A conventional triaxial testing method for simulating residual stress inside rocks, implemented using a conventional triaxial testing system, includes the following steps: The flexible bag 8 is placed in the axial through hole 301 of the rock sample 3, and the two ends of the flexible bag 8 are respectively clamped to the annular sealing rings 29 in the annular grooves of the upper pressure head 4 and the lower pressure head 1 by the clamping ring 30 to form a sealed connection. The lower pressure head 1 is fixed to the base 26 through the first quick-change connector 10, so that the first channel 9 of the lower pressure head is connected to the second channel 25 of the lower pressure head; Open the second shut-off valve 23 and inject pressure medium into the flexible bag 8 through the internal pressure hydraulic pump 24. After the pressure medium flows out of the second shut-off valve 23, close the second shut-off valve 23 and continue to inject pressure medium into the flexible bag 8 through the internal pressure hydraulic pump 24 until the rock sample 3 reaches the set internal pressure. ; Axial stress is applied to the rock sample 3 through the axial pressure loading system. ; A uniformly distributed radial confining pressure is applied to the outer surface of the rock sample 3 by the confining pressure loading system. .

[0016] Axial stress is applied to the rock sample 3 through the axial pressure loading system. The method is as follows: The upper second hydraulic pump 19 delivers pressure medium to the upper second hydraulic chamber 17 through the upper second channel 18, while simultaneously controlling the upper first hydraulic pump 15 to release pressure medium from the upper first hydraulic chamber 13 through the upper first channel 16, causing the T-piston 20 to move downwards until the set axial stress is reached. ; A uniformly distributed radial confining pressure is applied to the outer surface of the rock sample 3 by the confining pressure loading system. The method is as follows: The first shut-off valve 22 is opened, and the confining pressure hydraulic pump 28 injects pressure medium into the confining pressure chamber through the first channel 27. After pressure medium flows out of the first shut-off valve 22, the first shut-off valve 22 is closed, and the confining pressure hydraulic pump 28 continues to inject hydraulic oil into the confining pressure chamber until the set radial confining pressure is reached. .

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention, through an axial pressure loading system, a confining pressure loading system, and an internal pressure loading system, can achieve repeatable and controllable simulation of residual stress inside rocks. Compared with the technical limitations of traditional true triaxial tests that cannot reflect the effect of residual stress inside rocks, this invention can study the deformation characteristics, strength evolution, and fracture behavior of rocks under different internal residual stress conditions, and improve the physical consistency between the test results and the mechanical behavior of the original rock.

[0018] 2. The present invention provides an upper pressure head cylindrical boss 401 and a lower pressure head cylindrical boss 101 on the upper pressure head 4 and the lower pressure head 1, respectively, and provides annular grooves on the upper pressure head cylindrical boss 401 and the lower pressure head cylindrical boss 101 in the circumferential direction, and provides annular sealing rings 29 in the annular grooves, and uses clamping rings 30 to make the flexible bag 8 tightly fit the annular sealing rings 29, so that the internal pressure loading system has a better sealing structure, and at the same time facilitates the disassembly and assembly of rock sample 3.

[0019] 3. The present invention provides a second shut-off valve 23 at the first channel 5 of the upper pressure head 4 and a first shut-off valve 22 at the second channel 21 of the confining pressure cavity wall 11, so that when the internal pressure hydraulic pump 24 injects pressure medium into the flexible bag 8, or when the confining pressure hydraulic pump 28 injects pressure medium into the confining pressure cavity, it is convenient to discharge the gas in the flexible bag 8 or the confining pressure cavity.

[0020] 4. The present invention provides a first quick-connect coupling 10 and a second quick-connect coupling 6, which facilitates the installation or disassembly of the internal pressure loading system, the axial pressure loading system, and the confining pressure loading system, thereby reducing the maintenance cost of the experimental system.

[0021] In summary, the experimental system described in this invention, combined with experimental methods, achieves repeatable and controllable simulations, and can systematically study different internal pressures. Axial stress and radial confining pressure This invention investigates the deformation characteristics, strength evolution, and fracture mechanisms of rocks under combined conditions, improving the physical consistency between experimental results and the mechanical behavior of the original rock. Utilizing a flexible capsule, multiple mechanical seals, and a rationally designed channel and quick-change connection, this invention ensures stable internal pressure application while remaining compatible with existing conventional triaxial testing systems. It also boasts low maintenance costs and excellent operability and engineering applicability. Attached Figure Description

[0022] Figure 1 This is a cross-sectional view of the overall structure of the conventional triaxial test system for simulating residual stress inside rocks according to the present invention.

[0023] Figure 2 This is a top-view cross-sectional schematic diagram of the conventional triaxial test system for simulating residual stress inside rocks according to the present invention.

[0024] Figure 3 This is a schematic diagram of the assembly of the internal pressure loading system components of the present invention.

[0025] Figure 4 This is a cross-sectional view of the internal pressure loading system components of the present invention.

[0026] Figure 5 This is a schematic diagram of the rock sample loading state in the conventional triaxial test method for simulating residual stress inside rocks according to the present invention.

[0027] In the figure, 1 is the lower pressure head; 101 is the cylindrical boss of the lower pressure head; 102 is the cylindrical loading plate of the lower pressure head; 2 is the sealing sleeve; 3 is the rock sample; 301 is the axial through hole; 4 is the upper pressure head; 401 is the cylindrical boss of the upper pressure head; 402 is the cylindrical loading plate of the upper pressure head; 5 is the first channel of the upper pressure head; 6 is the second quick-connect coupling; 7 is the second channel of the upper pressure head; 8 is the flexible bag; 9 is the first channel of the lower pressure head; 10 is the first quick-connect coupling; 11 is the confining pressure cavity wall; 12 is the screw; 13 is the first hydraulic cavity of the upper seat; 14 is the upper seat. ; 15 is the first hydraulic pump of the upper seat; 16 is the first channel of the upper seat; 17 is the second hydraulic chamber of the upper seat; 18 is the second channel of the upper seat; 19 is the second hydraulic pump of the upper seat; 20 is the T-type piston; 21 is the second channel of the confining pressure chamber; 22 is the first shut-off valve; 23 is the second shut-off valve; 24 is the internal pressure hydraulic pump; 25 is the second channel of the lower pressure head; 26 is the base; 27 is the first channel of the confining pressure chamber; 28 is the confining pressure hydraulic pump; 29 is the annular sealing ring; 30 is the clamping ring; 31 is the sensor control line; 32 is the processing control system. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings.

[0029] like Figure 1 , Figure 2 As shown, a conventional triaxial testing system for simulating residual stress inside rock is used to simulate the stress of the rock sample 3 to be tested. The system includes an axial pressure loading system, a confining pressure loading system, and an internal pressure loading system. The axial pressure loading system is used to apply axial stress to the rock sample 3 to be tested. ; The confining pressure loading system is used to apply a uniformly distributed radial confining pressure to the outer surface of the rock sample 3. ; like Figure 3 As shown, the rock sample 3 has a cylindrical outer contour and a flat outer surface, and has an axial through hole 301 for arranging the internal pressure loading system. like Figure 3 , Figure 4 As shown, the internal pressure loading system is used to apply uniformly distributed internal pressure to the rock sample 3. The flexible bag 8, which is inserted into the axial through hole 301, has its two ends sealed and connected to the upper pressure head 4 and the lower pressure head 1, respectively, for transmitting axial stress. The upper pressure head 4 and the lower pressure head 1 are respectively disposed at the upper and lower ends of the rock sample 3, and are used to transmit the axial stress applied by the axial pressure loading system to the end face of the rock sample 3. The upper pressure head 4 has an upper pressure head first channel 5 inside, one end of which is connected to the inside of the flexible bag 8, and the other end is connected to the outside through the second shut-off valve 23 for venting or depressurizing. The lower pressure head 1 has a lower pressure head first channel 9 inside, one end of which is connected to the inside of the flexible bag 8, and the other end is connected to an internal pressure hydraulic pump 24.

[0030] The flexible bag 8 has a cylindrical structure and is made of an oil-resistant elastic material. In this embodiment, fluororubber is used, but in other embodiments, nitrile rubber or thermoplastic polyurethane can also be used. The size of the flexible bag 8 is configured such that, after hydraulic oil is injected, it can apply pressure to the inner wall of the rock sample 3. The internal pressure.

[0031] The upper pressure head 4 has a cylindrical protrusion 401 on its lower surface, and the lower pressure head 1 has a cylindrical protrusion 101 on its upper surface. The flexible bag 8 has openings at both ends that are respectively fitted onto the outer sides of the cylindrical protrusion 401 and the cylindrical protrusion 101. The dimensions and shapes of the upper pressure head cylindrical boss 401 and the lower pressure head cylindrical boss 101 are configured such that they can be inserted into the axial through hole 301 after the flexible bag 8 is fitted on them.

[0032] Both the upper pressure head cylindrical boss 401 and the lower pressure head cylindrical boss 101 have annular grooves on their outer peripheries. Annular sealing rings 29 are installed in the grooves, and the end of the flexible bag 8 is pressed against the annular groove area by a clamping ring 30, so that the flexible bag 8 is tightly attached to the annular sealing ring 29 to form an end sealing structure. The matching design of the annular groove and the clamping ring 30 ensures that the outer wall remains basically flat with the rest of the parts after clamping, which facilitates the insertion of the whole structure into the axial through hole 301.

[0033] The upper pressure head 4 includes an upper pressure head cylindrical loading plate 402, and the lower pressure head 1 includes a lower pressure head cylindrical loading plate 102. The upper pressure head cylindrical boss 401 is connected to the lower surface of the upper pressure head cylindrical loading plate 402, and the lower pressure head cylindrical boss 101 is connected to the upper surface of the lower pressure head cylindrical loading plate 102. The cross-sections of the upper pressure head cylindrical loading plate 402 and the lower pressure head cylindrical loading plate 102 are adapted to the end face of the rock sample 3, for use in conjunction with the axial pressure loading system to transfer axial stress. Transferred to rock sample 3.

[0034] The axial pressure loading system includes an upper seat 14 and a base 26. The upper seat 14 is located above the upper pressure head 4, and the base 26 is located below the lower pressure head 1. The upper seat 14 has multiple vertical through holes, and each through hole is equipped with a screw 12. The screw 12 is threadedly engaged with the base 26. The upper seat 14 includes a hydraulic chamber, within which a T-shaped piston 20 is axially movable. The T-shaped piston 20 divides the hydraulic chamber into a first hydraulic chamber 13 and a second hydraulic chamber 17, with the lower end of the T-shaped piston 20 extending beyond the lower wall of the hydraulic chamber. The T-shaped piston 20, the upper pressure head 4, the rock sample 3, the lower pressure head 1, and the base 26 are coaxially arranged along the same vertical centerline. The T-shaped piston 20 is driven to engage with the upper pressure head 4, and the T-shaped piston 20 has a stroke range. Within the first interval of the stroke range, the T-shaped piston 20 is driven to engage with the upper pressure head 4 to compress it. Within the second interval of the stroke range, the T-shaped piston 20 disengages from the upper pressure head 4. By controlling the inlet and outlet states of the two hydraulic pumps, the up and down movement of the T-shaped piston 20 is achieved, thereby completing the axial stress. Loading and unloading.

[0035] The upper seat 14 has an upper seat first channel 16 and an upper seat second channel 18 inside. One end of the upper seat first channel 16 is connected to the upper seat first hydraulic chamber 13, and the other end is connected to the upper seat first hydraulic pump 15. One end of the upper seat second channel 18 is connected to the upper seat second hydraulic chamber 17, and the other end is connected to the upper seat second hydraulic pump 19.

[0036] The confining pressure loading system includes a sealing sleeve 2, a confining pressure cavity wall 11, a first confining pressure cavity channel 27, and a second confining pressure cavity channel 21; The sealing sleeve 2 is fitted onto the outside of the rock sample 3. The sealing sleeve 2 is made of an oil-resistant thermoplastic material. In this embodiment, cross-linked polyolefin heat-shrinkable material is used. In other embodiments, polyvinylidene fluoride heat-shrinkable material or other heat-shrinkable thermoplastic materials with oil-resistant sealing properties can also be used. The sealing sleeve 2 extends axially to the side walls of the upper pressure head 4 and the lower pressure head 1, respectively, for radial compression. During loading, a continuous external sealing and isolation structure is formed to prevent the confining hydraulic oil from seeping into the sample or leaking along the ends.

[0037] The confining pressure cavity wall 11 is a cylindrical structure, coaxially arranged around the outer periphery of the sleeve 2. The lower surface of the upper seat 14 and the upper surface of the base 26 are both provided with a frustum adapted to the cylindrical structure. The confining pressure cavity wall 11 is placed between the upper seat 14 and the base 26 and is snapped onto the frustum, so that the confining pressure cavity wall 11 forms a corresponding sleeve sealing structure with the base 26 and the upper seat 14 at the upper and lower ends of the axial direction, thereby improving the overall sealing performance and confining pressure loading stability of the confining pressure cavity.

[0038] The confining pressure cavity wall 11, upper seat 14, base 26 and sealing sleeve 2 together form a confining pressure cavity, which is used to apply uniform radial confining pressure to the rock sample 3. The first channel 27 of the confining pressure chamber is located inside the base 26, with one end connected to the confining pressure chamber and the other end connected to the confining pressure hydraulic pump 28. The second channel 21 of the confining pressure chamber is disposed on the wall 11 of the confining pressure chamber. One end is connected to the confining pressure chamber near the frustum of the lower surface of the upper seat 14, and the other end is connected to the outside through the first shut-off valve 22 for radial confining pressure. Venting or depressurization during the loading process.

[0039] The screw 12 is threaded into the base 26, which tightens and fixes the upper seat 14, the base 26, and the confining pressure cavity wall 11 as a whole in the axial direction. This structure can effectively resist the separation force generated during axial loading and confining pressure loading, and prevent the confining pressure cavity structure from axially loosening or separating.

[0040] The first channel 9 of the lower pressure head is connected to the internal pressure hydraulic pump 24 through the second channel 25 of the lower pressure head. The second channel 25 of the lower pressure head is located inside the base 26, with one end of the channel opening located at the center of the base 26 and connected to the first channel 9 of the lower pressure head through the first quick-change connector 10. The other end of the channel opening is connected to the internal pressure hydraulic pump 24. The first channel 5 of the upper pressure head is connected to the second shut-off valve 23 through the second channel 7 of the upper pressure head. The second channel 7 of the upper pressure head passes through the wall 11 of the confining pressure cavity. One end of the channel is connected to the first channel 5 of the upper pressure head through the second quick-connect connector 6, and the other end of the channel is connected to the outside through the second shut-off valve 23.

[0041] The upper first hydraulic pump 15, upper second hydraulic pump 19, internal pressure hydraulic pump 24 and confining pressure hydraulic pump 28 contain hydraulic sensors and are connected to a sufficient amount of external hydraulic oil according to actual working needs. The hydraulic sensors are connected to the processing control system 32 through the sensing control line 31. The processing control system 32 combines the pressure set value and the pressure value fed back by the hydraulic sensors in each hydraulic pump to control the operation of each hydraulic pump.

[0042] A conventional triaxial testing method for simulating residual stress inside rocks, implemented using a conventional triaxial testing system, includes the following steps: Step 1: Prepare rock sample 3 with axial through hole 301; Step 2: The upper end of the flexible bag 8 is fitted onto the outside of the cylindrical boss 401 of the upper pressure head, and the end of the flexible bag 8 is pressed and fixed by the clamping ring 30. Step 3: Insert the upper pressure head cylindrical boss 401 equipped with the flexible bag 8 into the upper end of the axial through hole 301 of the rock sample 3, so that the flexible bag 8 passes through the axial through hole 301 and exits from the bottom of the hole; then, put the lower end of the flexible bag 8 on the outside of the lower pressure head cylindrical boss 101 and fix it with the clamping ring 30. Step 4: Place the sealing sleeve 2 on the outside of the structure assembled in Step 3, and use a hot air blower to heat the sealing sleeve 2, so that it shrinks during the heating process and tightly covers the outer surface of the rock sample 3 and the adjacent area of ​​the upper pressure head 4 and the lower pressure head 1, thereby forming an outer seal. Step 5: Place the sample assembly assembled in Step 4 onto the base 26, and connect the first channel 9 of the lower pressure head and the second channel 25 of the lower pressure head through the first quick-connect connector 10 to complete the connection of the internal pressure channels. Step 6: Fit the lower inner wall of the confining cavity wall 11 onto the outer side of the central protruding truncated cone of the base 26; then connect the upper pressure head first channel 5 and the upper pressure head second channel 7 of the upper pressure head 4 through the second quick-connect coupling 6 for venting and depressurization during the internal pressure loading process. Step 7: Insert the truncated cone portion protruding at the lower end of the upper seat 14 into the upper inner wall of the confining cavity wall 11, and pass the screw 12 through the vertical through hole of the upper seat 14, and screw its lower end into the threaded round hole of the base 26 and tighten it, so that the upper seat 14, the base 26 and the confining cavity wall 11 form an axially tensioned integral structure. Step 8, follow as follows Figure 5 The load state shown applies internal pressure to simulate residual stress within the rock. First, open the second shut-off valve 23. The processing control system 32 then starts the internal pressure hydraulic pump 24, injecting hydraulic oil into the flexible bag 8 through the second channel 25 and the first channel 9 of the lower pressure head. When hydraulic oil continuously flows out of the second shut-off valve 23, it indicates that the air in the flexible bag 8 has been completely expelled and it is filled with hydraulic oil. At this point, close the second shut-off valve 23 and continue to pressurize the flexible bag 8 by the internal pressure hydraulic pump 24 until the set internal pressure is reached. ; Step 9, follow as follows Figure 5 The load state shown applies axial stress. and radial confining pressure : Among them, axial stress is applied At the same time, the processing control system 32 controls the start of the upper seat second hydraulic pump 19 to deliver hydraulic oil to the upper seat second hydraulic chamber 17 through the upper seat second channel 18, and simultaneously controls the upper seat first hydraulic pump 15 to discharge the hydraulic oil in the upper seat first hydraulic chamber 13 through the upper seat first channel 16, causing the T-shaped piston 20 to move downward until the set axial stress is reached. ; Apply radial confining pressure When the first shut-off valve 22 is opened, the control system 32 starts the confining pressure hydraulic pump 28, injecting hydraulic oil into the confining pressure chamber through the first channel 27. When hydraulic oil flows out of the first shut-off valve 22, the first shut-off valve 22 is closed, and the confining pressure hydraulic pump 28 continues to inject hydraulic oil into the confining pressure chamber until the set radial confining pressure is reached. This causes the outer surface of rock sample 3 to be subjected to uniform radial confining pressure. ; The internal pressure Axial stress and radial confining pressure They can be independently controlled; Step 10: After the test, unload in the reverse order of loading: unload the internal pressure. When the second shut-off valve 23 is opened, the hydraulic oil in the flexible bag 8 flows out through the second shut-off valve 23. Then, the processing control system 32 controls the start of the internal pressure hydraulic pump 24, which recovers the residual hydraulic oil in the flexible bag 8 through the second channel 25 of the lower pressure head and the first channel 9 of the lower pressure head. Unloading axial stress At the same time, the processing control system 32 controls the start of the upper seat first hydraulic pump 15 to deliver hydraulic oil to the upper seat first hydraulic chamber 13 through the upper seat first channel 16, and at the same time controls the upper seat second hydraulic pump 19 to discharge the hydraulic oil in the upper seat second hydraulic chamber 17 through the upper seat second channel 18, so that the T-shaped piston 20 moves upward. Unloading radial confining pressure When the first shut-off valve 22 is opened, the hydraulic oil in the confining pressure chamber is discharged through the first shut-off valve 22. Subsequently, the processing control system 32 controls the start of the confining pressure hydraulic pump 28 to recover the hydraulic oil in the confining pressure chamber. Step 11: After unloading is completed, remove the upper seat 14 and related loading components, take out the rock sample 3, and clean and reset the equipment.

[0043] Compared to existing conventional triaxial tests, this invention introduces internal pressure under conventional triaxial test conditions. The loading method introduces the residual stress inside the rock as an independent and controllable physical quantity into the test system, causing rock sample 3 to be subjected to axial stress. and radial confining pressure While functioning, it can withstand adjustable internal pressure, thus more realistically simulating the residual internal stress state that rocks may retain after excavation and unloading in the original rock stress environment. This invention uses a cylindrical rock sample 3 with an axially penetrating hole 301 as the specimen, combined with a flexible bag 8. This creates a stable and uniform internal pressure field without compromising the integrity of the specimen, effectively avoiding the loading instability problems caused by hole wall penetration, local stress concentration, or sealing failure in traditional tests. The synergistic sealing structure of the outer sealing sleeve and the confining pressure cavity wall improves the radial confining pressure. The uniformity and reliability of the loading ensure that the outer surface of the specimen is in a stable isotropic confining pressure environment during the loading process. This test system and method can achieve independent control of internal residual stress, axial stress and confining pressure within a conventional triaxial test framework. The loading path is flexible and has good repeatability, which is conducive to conducting research on the strength, deformation and fracture evolution of rocks under different internal residual stress levels and external stress combinations. It provides a more physically realistic experimental means for the stability analysis of deep rock mass engineering and related test method research.

[0044] In the description of this invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

Claims

1. A conventional triaxial testing system for simulating residual stress inside rock, characterized in that, This includes an axial pressure loading system, a confining pressure loading system, and an internal pressure loading system; The axial pressure loading system is used to apply axial stress to the rock sample (3) to be tested. ; The confining pressure loading system is used to apply a uniformly distributed radial confining pressure to the outer surface of the rock sample (3). ; The rock sample (3) has a cylindrical outer contour and an axial through hole (301). The internal pressure loading system is used to apply uniformly distributed internal pressure to the rock sample (3). The system includes a flexible bag (8) inserted into the axial through hole (301). The two ends of the flexible bag (8) are respectively sealed and connected to an upper pressure head (4) and a lower pressure head (1). The upper pressure head (4) and the lower pressure head (1) are respectively located at the upper end and the lower end of the rock sample (3) to transmit the axial stress applied by the axial pressure loading system to the end face of the rock sample (3). The upper pressure head (4) has an upper pressure head first channel (5) inside. One end of the upper pressure head first channel (5) is connected to the inside of the flexible bag (8), and the other end is connected to the outside through a second shut-off valve (23). The lower pressure head (1) has a lower pressure head first channel (9) inside. One end of the lower pressure head first channel (9) is connected to the inside of the flexible bag (8), and the other end is connected to an internal pressure hydraulic pump (24).

2. The conventional triaxial testing system according to claim 1, characterized in that, The flexible bag (8) is a cylindrical structure made of oil-resistant elastic material, and its dimensions are configured such that it can apply pressure to the inner wall of the rock sample (3) after the pressure medium is injected. The internal pressure.

3. The conventional triaxial testing system according to claim 1, characterized in that, The upper pressure head (4) has an upper pressure head cylindrical boss (401) on its lower surface, and the lower pressure head (1) has a lower pressure head cylindrical boss (101) on its upper surface. The flexible bag (8) has openings at both ends that are respectively fitted onto the outer sides of the upper pressure head cylindrical boss (401) and the lower pressure head cylindrical boss (101). The dimensions and shapes of the upper pressure head cylindrical boss (401) and the lower pressure head cylindrical boss (101) are configured such that they can be inserted into the axial through hole (301) after being fitted with a flexible bag (8).

4. The conventional triaxial testing system according to claim 3, characterized in that, The outer periphery of both the upper pressure head cylindrical boss (401) and the lower pressure head cylindrical boss (101) is provided with an annular groove, and an annular sealing ring (29) is provided in the groove. The end of the flexible bag (8) is pressed into the annular groove area by the clamping ring (30), so that the flexible bag (8) is tightly attached to the annular sealing ring (29) to form an end sealing structure.

5. The conventional triaxial testing system according to claim 3, characterized in that, The upper pressure head (4) includes an upper pressure head cylindrical loading plate (402), and the lower pressure head (1) includes a lower pressure head cylindrical loading plate (102); the upper pressure head cylindrical boss (401) is connected to the lower surface of the upper pressure head cylindrical loading plate (402), and the lower pressure head cylindrical boss (101) is connected to the upper surface of the lower pressure head cylindrical loading plate (102); the cross-sections of the upper pressure head cylindrical loading plate (402) and the lower pressure head cylindrical loading plate (102) are adapted to the end face of the rock sample (3) for use in conjunction with the axial pressure loading system to transfer axial stress. Transferred to rock sample (3).

6. The conventional triaxial testing system according to claim 1, characterized in that, The axial pressure loading system includes an upper seat (14) and a base (26). The upper seat (14) is located above the upper pressure head (4), and the base (26) is located below the lower pressure head (1). The upper seat (14) has multiple through holes, and each through hole is equipped with a screw (12). The screw (12) is threadedly engaged with the base (26). The upper seat (14) includes a hydraulic chamber, in which a T-shaped piston (20) is movably disposed along the axial direction. The T-shaped piston (20) divides the hydraulic chamber into a first hydraulic chamber (13) and a second hydraulic chamber (17) of the upper seat, and the lower end of the T-shaped piston (20) extends out of the lower wall of the hydraulic chamber. The T-shaped piston (20), the upper pressure head (4), the rock sample (3), the lower pressure head (1) and the base (26) are arranged coaxially along the same vertical center line. The T-shaped piston (20) is driven to cooperate with the upper pressure head (4). The T-shaped piston (20) has a stroke range. In the first interval of the stroke range, the T-shaped piston (20) is driven to connect with the upper pressure head (4) to squeeze the upper pressure head (4). In the second interval of the stroke range, the T-shaped piston (20) is disengaged from the upper pressure head (4). The upper seat (14) has an upper seat first channel (16) and an upper seat second channel (18) inside. One end of the upper seat first channel (16) is connected to the upper seat first hydraulic chamber (13), and the other end is connected to the upper seat first hydraulic pump (15). One end of the upper seat second channel (18) is connected to the upper seat second hydraulic chamber (17), and the other end is connected to the upper seat second hydraulic pump (19).

7. The conventional triaxial testing system according to claim 6, characterized in that, The confining pressure loading system includes a sealing sleeve (2), a confining pressure cavity wall (11), a first confining pressure cavity channel (27), and a second confining pressure cavity channel (21). The sealing sleeve (2) is fitted onto the outside of the rock sample (3). The sealing sleeve (2) is made of oil-resistant thermoplastic material, and its two axial ends extend to the side walls of the upper pressure head (4) and the lower pressure head (1), respectively, for radial confinement pressure. A continuous external sealing and isolation structure is formed during the loading process; The confining cavity wall (11) is a cylindrical structure and is coaxially arranged around the outer periphery of the cover (2). The lower surface of the upper seat (14) and the upper surface of the base (26) are both provided with a frustum adapted to the cylindrical structure. The confining cavity wall (11) is placed between the upper seat (14) and the base (26) and is snapped onto the frustum. The confining cavity wall (11), upper seat (14), base (26) and sealing sleeve (2) together form a confining cavity, which is used to apply uniform radial confining pressure to the rock sample 3; The first channel (27) of the confining pressure chamber is located inside the base (26), with one end connected to the confining pressure chamber and the other end connected to the confining pressure hydraulic pump (28). The second channel (21) of the confining pressure chamber is disposed on the wall (11) of the confining pressure chamber. One end is connected to the confining pressure chamber near the frustum of the lower surface of the upper seat (14), and the other end is connected to the outside through the first shut-off valve (22) for radial confining pressure. Venting or depressurization during the loading process.

8. The conventional triaxial testing system according to claim 7, characterized in that, The first channel (9) of the lower pressure head is connected to the internal pressure hydraulic pump (24) through the second channel (25) of the lower pressure head. The second channel (25) of the lower pressure head is located inside the base (26). One end of the channel is located at the center of the base (26) and is connected to the first channel (9) of the lower pressure head through the first quick-connect coupling (10). The other end of the channel is connected to the internal pressure hydraulic pump (24). The first channel (5) of the upper pressure head is connected to the second shut-off valve (23) through the second channel (7) of the upper pressure head. The second channel (7) of the upper pressure head passes through the wall (11) of the confining pressure cavity. One end of the channel is connected to the first channel (5) of the upper pressure head through the second quick-connect coupling (6), and the other end of the channel is connected to the outside through the second shut-off valve (23).

9. A conventional triaxial testing method for simulating residual stress inside rock, characterized in that, The conventional triaxial testing system described in any one of claims 1-8 is used, comprising the following steps: The flexible bag (8) is placed in the axial through hole (301) of the rock sample (3), and the two ends of the flexible bag (8) are respectively clamped to the annular sealing ring (29) in the annular groove of the upper pressure head (4) and the lower pressure head (1) by the clamping ring (30) to form a sealed connection; The lower pressure head (1) is fixed to the base (26) through the first quick-connect connector (10), so that the first channel (9) of the lower pressure head is connected to the second channel (25) of the lower pressure head; Open the second shut-off valve (23) and inject pressure medium into the flexible bag (8) through the internal pressure hydraulic pump (24). After the pressure medium flows out from the second shut-off valve (23), close the second shut-off valve (23) and continue to inject pressure medium into the flexible bag (8) through the internal pressure hydraulic pump (24) until the rock sample (3) reaches the set internal pressure. ; Axial stress is applied to the rock sample (3) by the axial pressure loading system. ; A uniformly distributed radial confining pressure is applied to the outer surface of the rock sample (3) by the confining pressure loading system. .

10. The conventional triaxial testing method according to claim 9, characterized in that, Axial stress is applied to the rock sample (3) by the axial pressure loading system. The method is as follows: The upper second hydraulic pump (19) delivers pressure medium to the upper second hydraulic chamber 17 through the upper second channel (18), while simultaneously controlling the upper first hydraulic pump (15) to release the pressure medium from the upper first hydraulic chamber (13) through the upper first channel (16), causing the T-piston (20) to move downward until the set axial stress is reached. ; A uniformly distributed radial confining pressure is applied to the outer surface of the rock sample (3) by the confining pressure loading system. The method is as follows: Open the first shut-off valve (22), and inject pressure medium into the confining pressure chamber through the first channel (27) of the confining pressure chamber via the confining pressure hydraulic pump (28). After pressure medium flows out of the first shut-off valve (22), close the first shut-off valve (22), and the confining pressure hydraulic pump (28) continues to inject hydraulic oil into the confining pressure chamber until the set radial confining pressure is reached. .

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