A True Triaxial Compression-Tension Fixture for Deep Hard Rock and Its Experimental Method

Abstract

The present invention discloses a deep hard rock true triaxial compression and tension fixture and an experimental method. The fixture includes: an upper loading plate, a lower loading plate, side loading plates, end loading plate pads, and side loading plate pads. A plurality of side loading plates are connected to form an integral body, forming a cuboid-shaped space for placing a rock specimen. The upper loading plate and the lower loading plate are attached to the upper and lower surfaces of the rock specimen. The present invention uses a true triaxial testing machine to apply uniform pressure or tension to six surfaces of the rock specimen from three directions through the fixture. The pressure is applied by the oil cylinder pushing the corresponding direction loading plate towards the center of the rock specimen, and the tension is applied by the oil cylinder pulling the loading plate bonded to the rock specimen towards a direction away from the center of the rock specimen, realizing an indoor simulation test of the true triaxial stress state of deep hard rock compression and tension.

Description

Technical Field

[0001] The present invention relates to the technical field of deep rock mass engineering, and particularly to a deep hard rock true triaxial compression and tension fixture and an experimental method. Background Art

[0002] The stress state of rocks in actual engineering is very complex and generally in a triaxial unequal stress state. Most previous studies have focused on rock compression. However, after entering the deep part, the rocks that are originally under high stress will generate unloading stress waves due to the excavation unloading effect after excavation, resulting in tensile stress. Especially when using the blasting method for excavation, due to the propagation and refraction of stress waves, tensile stress will be generated in the rock mass. In addition, for general rock engineering, since the in-situ stress is not a uniform hydrostatic pressure, there will be areas of compressive stress and tensile stress concentration. Generally speaking, rocks in in-situ actual engineering are in a true triaxial stress state and there is tensile stress therein.

[0003] Rocks, especially hard rocks, are typical hard and brittle geological materials. Their remarkable feature is that the compressive strength is much higher than the tensile strength, and the compressive strength of hard rocks depends on confining pressure. That is to say, under true triaxial conditions, the confining pressure (if the intermediate and minimum compressive stresses are equal, usually called conventional triaxial) has a significant strengthening effect on the strength of rocks. However, the effects of the intermediate stress and the minimum stress are different. The minimum stress has the strongest effect on enhancing the strength of rocks, which is why most current rock strength criteria only consider the influence of the minimum stress. The intermediate stress has an enhancing effect on the strength of rocks, but the effect is limited, not as good as the minimum stress, and when the intermediate stress exceeds a certain limit, the strength will instead decrease. The above studies all assume that the rocks are under true triaxial compression conditions. It can be seen that when the minimum stress is compressive, it is most beneficial for improving the strength of rocks. Through the above analysis, it can be known that it is a favorable condition for the minimum and intermediate stresses to be compressive. On the contrary, if the minimum stress is tensile, the rock will be more easily damaged and its strength will be lower. Following the idea that tensile stress is an unfavorable factor, then under true triaxial stress conditions, there are four cases: 1) true triaxial tensile stress state; 2) one direction is tensile stress and the other two directions are compressive stresses; 3) one direction is compressive stress and the other two directions are tensile stresses; 4) all three directions are compressive stresses.

[0004] At present, most of the fixtures of experimental devices for deep hard rock only focus on the compressive stress state of the true triaxial of hard rock, and it is difficult to carry out experimental research on the remaining tensile-compressive true triaxial stress states mentioned above. Moreover, when designing the experimental fixtures that currently focus on the compressive stress state of the true triaxial of hard rock, the surface of the loading plate is designed to have the same size as the surface of the rock specimen. As a result, when applying compressive stress to the rock specimen, the rock specimen deforms, and at this time, the surface size of the rock changes, resulting in an easy existence of a certain gap deviation between the edge of the loading plate and the rock specimen, thereby triggering the corner effect, leading to significant stress concentration at the gap during the pressurization process, and the rock at this place is damaged, thus changing the failure mode of the rock specimen, affecting the properties such as the distribution of shear bands inside the specimen and the lateral deformation characteristics, and affecting the accuracy of rock strength determination. Summary of the Invention

[0005] The purpose of the present invention is to provide a tensile-compressive true triaxial fixture and experimental method for deep hard rock, which can respectively carry out hard rock deformation failure tests under four tensile-compressive true triaxial stress states, and truly reflect the deformation failure conditions of actual deep hard rock under general tensile-compressive true triaxial stress conditions.

[0006] The technical solution of the present invention is as follows:

[0007] A tensile-compressive true triaxial fixture for deep hard rock, comprising: four side loading plates, which are the same in size and are all vertically arranged rectangular plate bodies. The four side loading plates are connected end to end to form a square tube space structure, and two adjacent side loading plates are movably connected through a connecting piece. The side end face of the previous side loading plate is connected to the edge of the plate surface of the next side loading plate. Among the four side loading plates, taking two adjacent side loading plates as a side loading plate group, and the other two adjacent side loading plates as another side loading plate group. And the upper end faces of the two side loading plates in each side loading plate group are aligned, and the two side loading plate groups are arranged in a staggered manner in the height direction, so that there is a height distance staggered between the upper end face and the lower end face of the two side loading plate groups; the staggered height distance is the thickness of the upper loading plate; an upper loading plate, the plate surface of which is hermetically connected to one end of the square tube space structure, is located at the height distance where the upper end faces of the two side loading plate groups are staggered, and can move along the height direction of the square tube space structure; a lower loading plate, which has the same size as the upper loading plate, the plate surface of which is hermetically connected to the other end of the square tube space structure, is located at the height distance where the lower end faces of the two side loading plate groups are staggered, and can move along the height direction of the square tube space structure. The upper loading plate, the lower loading plate and multiple side loading plates enclose a cuboid space, and the inside of the cuboid space is used to place a rock specimen and wrap the rock specimen.

[0008] Further, bolt through-holes are provided at the central positions of the side surfaces of the end loading plate pads and the side loading plate pads that are away from the outer sidewalls of the cuboid-shaped space. The loading plate pads are connected to the tension connection device through the bolt through-holes, and the tension connection device is used when the testing machine applies tension to the fixture. The tension connection device includes: a short bolt, one end of which is connected to the bolt through-hole on the loading plate pad; a pull rod, one end of which is connected to the other end of the short bolt; a connection head, which is connected to the other end of the pull rod. A plurality of threaded holes are provided on the circumferential side of the connection head, and long bolts are arranged on each of the threaded holes. The push head of the testing machine is inserted into the connection head and clamped and fixed by the long bolts.

[0009] Further, the connecting piece includes: a U-shaped bolt and a fixing bolt. Bolt holes are provided on the circumferential side surfaces of the end loading plate pads of the upper loading plate, and bolt holes are provided on one end face of the side loading plate pad. A U-shaped bolt is provided on the other side surface opposite to the end face where the bolt hole of the side loading plate pad is provided. U-shaped bolts are provided around the end loading plate pads of the lower loading plate. The fixing bolt is threadedly connected to the threaded hole, and the nut of the fixing bolt abuts against the outer side surface of the U-shaped bolt. The U-shaped bolt is mainly used to accommodate the movement of the fixing bolt caused by the deformation of the rock specimen after being stressed.

[0010] Further, the top surface of the upper loading plate is flush with the outer sidewall of the square pipe space structure, and the bottom surface of the lower loading plate is flush with the outer sidewall of the square pipe space structure.

[0011] An experimental method for a deep hard rock true triaxial tensile and compressive fixture. Using the fixture for experiments includes the following steps:

[0012] S1. Assemble the true triaxial tensile and compressive fixture and place the assembled true triaxial tensile and compressive fixture on the loading platform of the testing machine. Connect the push head of the true triaxial testing machine to the loading plate pad to ensure that there is no deviation of the fixture in the center of the testing machine, and adjust the true triaxial testing machine to make the fixture close and fastened.

[0013] S2. Using the true triaxial testing machine, uniformly transmit surface tensile / compressive forces to the six surfaces of the rock specimen from three directions of the rock specimen through the fixture to simulate the stress state existing in the deep underground hard rock unit. When applying tensile stress, apply high-strength glue between the end face of the rock specimen in the direction of the applied tensile force and the loading plate. The push head of the testing machine in the same direction and the corresponding loading plate pad are connected through the tension connection device. When applying compressive stress, there is no need to glue the rock specimen to the side loading plate. The push head of the testing machine pushes the corresponding side loading plate towards the center of the rock specimen through the loading plate pad to transmit the pressure to the rock specimen.

[0014] S3. After the loading test and data acquisition are completed, turn off the testing machine, remove the fixture and take out the rock specimen.

[0015] Further, in S1, the splicing method of the true triaxial compression and tension fixture includes the following steps:

[0016] Place the rock specimen in the upper right of the lower loading plate, then place the lower left of the upper loading plate on the rock specimen, place a side loading plate on the left side of the rock specimen, and align the lower end of the side loading plate with the left edge of the lower loading plate, the upper end with the left edge of the upper loading plate, and the upper end flush with the upper surface of the upper loading plate. Tighten the fixing bolt through the bolt hole of the end loading plate pad on the upper loading plate so that the U-bolt on the side loading plate pad of the side loading plate is clamped to complete the connection between the side loading plate and the upper loading plate. Similarly, connect and fix the side loading plate and the lower loading plate.

[0017] Then place another side loading plate in front of the rock specimen, align the lower end of the side loading plate with the front edge of the lower loading plate, the upper end of the side loading plate flush with the upper surface of the upper loading plate, the inner plate surface of the side loading plate fitting the end of the upper loading plate, and the upper and lower ends of the two installed side loading plates flush. Fix the side loading plate to the upper and lower loading plates through the U-bolt and the fixing bolt in the above manner.

[0018] Then place the third side loading plate on the right side of the rock specimen, the upper surface of the side loading plate fitting the lower surface of the upper loading plate, the lower surface flush with the lower surface of the lower loading plate. Fix the side loading plate to the upper and lower loading plates through the U-bolt and the fixing bolt in the above manner.

[0019] Then place the fourth side loading plate at the back of the rock specimen, the upper surface of the side loading plate fitting the lower surface of the upper loading plate, the lower surface flush with the lower surface of the lower loading plate. Fix the side loading plate to the upper and lower loading plates through the U-bolt and the fixing bolt, and the upper and lower ends of the third side loading plate and the fourth side loading plate are flush.

[0020] Further, in the four cases of the rock specimen in the true triaxial compression and tension test, the application methods of the tensile / compressive force are as follows:

[0021] When the rock specimen is under two-way compression and one-way tension: First, apply the maximum compressive stress and the intermediate compressive stress in two directions respectively so that the compressive stresses applied in the two directions reach the intermediate compressive stress simultaneously; Second, apply the tensile stress in the other direction; Finally, continuously apply the maximum compressive stress in the direction of applying the maximum compressive stress until the specimen fails;

[0022] Under the condition that the rock specimen is subjected to two-way tension and one-way compression: First, apply the maximum compressive stress in one direction; second, apply the intermediate tensile stress and the minimum tensile stress in the other two directions respectively, so that the two directions applying the tensile stress reach the minimum tensile stress simultaneously, and continue to apply the intermediate tensile stress in the direction applying the intermediate tensile stress; finally, continuously apply the maximum compressive stress in the direction applying the maximum compressive stress until the specimen fails;

[0023] Under the condition that the rock specimen is subjected to three-way tension: Simultaneously apply the maximum tensile stress, the intermediate tensile stress and the minimum tensile stress in three directions respectively, so that the three directions reach the minimum tensile stress simultaneously; continue to apply the intermediate tensile stress and the maximum tensile stress in the directions applying the intermediate tensile stress and the maximum tensile stress respectively, so that the two reach the intermediate tensile stress simultaneously; finally, continuously apply the maximum tensile stress in the direction applying the maximum tensile stress until the specimen fails;

[0024] Under the condition that the rock specimen is subjected to three-way compression: Simultaneously apply the maximum compressive stress, the intermediate compressive stress and the minimum compressive stress in three directions respectively, so that the three directions reach the minimum compressive stress simultaneously; continue to apply the intermediate compressive stress and the maximum compressive stress in the directions applying the intermediate compressive stress and the maximum compressive stress respectively, so that the two reach the intermediate compressive stress simultaneously; finally, continuously apply the maximum compressive stress in the direction applying the maximum compressive stress until the specimen fails.

[0025] Compared with the prior art, using the fixture of the present invention to carry out relevant experiments can accurately and truly reflect the deformation and failure conditions under the general tensile-compressive true triaxial stress conditions of actual deep hard rock, expand the deeper understanding of the true strength of deep hard rock, provide a theoretical basis and scientific basis for the subsequent establishment of a more perfect deep hard rock strength criterion, reveal the essential differences in the mechanical responses and disaster-causing mechanisms of the surrounding rocks of shallow rock engineering and deep rock engineering, clarify the reasons why the current shallow rock mechanics theory is difficult to fully apply to deep rock engineering, and reveal the disaster-causing mechanisms of special failure forms such as rock slab cracking and rockburst in the surrounding rocks of deep hard rock engineering. The specific beneficial effects of the present invention are:

[0026] 1. The present invention uses a rigid push head of a true triaxial testing machine to apply uniform surface tension / compression to six surfaces of a rock specimen in three directions through a fixture, so as to simulate the complex true triaxial stress state existing in deep hard rock, and can respectively conduct the following four types of hard rock deformation and failure tests under tensile and compressive true triaxial stress states: 1) True triaxial tensile stress state; 2) One direction is tensile stress, and the other two directions are compressive stress; 3) One direction is compressive stress, and the other two directions are tensile stress; 4) All three directions are compressive stress, truly reflecting the deformation and failure conditions of actual deep hard rock under general tensile and compressive true triaxial stress conditions. During the test, a cuboid-shaped space is enclosed by an upper loading plate, a lower loading plate, and multiple side loading plates, and a rock specimen is placed inside the cuboid-shaped space. The rock specimen is tightly wrapped by the cuboid-shaped space, effectively reducing the influence of corner effect and end effect on the accuracy of test data during the test of the rock specimen.

[0027] 2. The end faces of two adjacent side loading plates among the multiple side loading plates of the present invention are flush, and the end faces of the other two side loading plates are flush. When the two adjacent side loading plates are spliced with the other two side loading plates, the end faces stagger by a distance equal to the thickness of the upper loading plate. Each loading plate is combined together by staggering, so that the fixture completely wraps the rock specimen in an overlapping manner. Through the above splicing and installation method, the fixture completely wraps the rock specimen, solving the problem of corner effect commonly existing in previous rigid loading true triaxial experiments, further reducing the influence of corner effect and end effect on the accuracy of test data during the test of the rock specimen, and improving the accuracy of test data. Under such splicing conditions, due to the bolt hole connection method, the thread can move 1 mm - 2 mm, which is sufficient to adapt to the deformation required for rock failure.

[0028] 3. When applying tensile stress, the present invention ensures that the tensile stress is parallel to the corresponding direction of the rock specimen through the fixture connecting the tensile connection device and the bonding method, improving the accuracy of the test results and solving the problem that the specimen is easily damaged at the clamping part in previous tests, resulting in test failure.

[0029] 4. The fixture of the present invention has a simple structure and is convenient for disassembly and assembly, and can directly conduct tests on existing general true triaxial rock mechanics testing machines. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a perspective view of the structural schematic diagram of the present invention.

[0031] Figure 2 is a top view of the structural schematic diagram of the present invention.

[0032] Figure 3 is a front view of the structural schematic diagram of the present invention.

[0033] Figure 4It is a schematic structural diagram of the side loading plate, lower loading plate and loading plate spacer block of the present invention.

[0034] Figure 5 It is a schematic cross-sectional structure diagram of the present invention.

[0035] Figure 6 It is a schematic longitudinal cross-sectional structure diagram of the present invention.

[0036] Figure 7 It is a front view of the schematic structural diagram of the tensile connection device of the present invention.

[0037] Figure 8 It is a top view of the schematic structural diagram of the tensile connection device of the present invention.

[0038] Figure 9 It is a bottom view of the schematic structural diagram of the tensile connection device of the present invention.

[0039] Figure 10 It is a schematic diagram of the three-way compression force on the rock specimen of the present invention.

[0040] Figure 11 It is a schematic diagram of the three-way tension force on the rock specimen of the present invention.

[0041] Figure 12 It is a schematic diagram of the two-way compression and one-way tension force on the rock specimen of the present invention.

[0042] Figure 13 It is a schematic diagram of the two-way tension and one-way compression force on the rock specimen of the present invention.

[0043] Figure 14 It is the stress path of the true triaxial test of three-way compression of the present invention.

[0044] Figure 15 It is the stress path of the true triaxial test of three-way tension of the present invention.

[0045] Figure 16 It is the stress path of the true triaxial test of two-way compression and one-way tension of the present invention.

[0046] Figure 17 It is the stress path of the true triaxial test of two-way tension and one-way compression of the present invention.

[0047] Among them, 1. upper loading plate, 2. lower loading plate, 3. side loading plate, 4. end loading plate spacer block, 5. side loading plate spacer block, 6. U-bolt, 7. fixing bolt, 8. bolt through-hole, 9. short bolt, 10. pull rod, 11. connecting head, 12. long bolt. Detailed implementation mode

[0048] The following combines with the attached Figure 1 To the attached Figure 17, the specific embodiments of the present invention will be described in detail. In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0049] The terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features; in the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0050] Embodiment

[0051] Such as Figure 1As shown in the figure, a true triaxial fixture for deep hard rock tension and compression includes: four side loading plates 3, an upper loading plate 1, a lower loading plate 2, two end loading plate pads 4, and four side loading plate pads 5. The four side loading plates 3 are of the same size and are all rectangular plates. The four side loading plates 3 are vertically arranged, and the four side loading plates 3 are connected end to end to form a square tube space structure. Adjacent two side loading plates 3 are movably connected by a connecting piece. The side end face of the previous side loading plate is connected to the edge of the plate surface of the next side loading plate. Among the four side loading plates 3, taking two adjacent side loading plates 3 as a side loading plate group, and the other two adjacent side loading plates 3 as another side loading plate group. The upper end faces of the two side loading plates 3 in each side loading plate group are aligned, and the two side loading plate groups are arranged in a staggered manner in the height direction, so that there is a height distance between the upper end face and the lower end face of the two side loading plate groups, and the staggered height distance is the thickness of the upper loading plate 1. The upper loading plate 1 is hermetically connected to one end of the square tube space structure, located at the height distance where the upper end faces of the two side loading plate groups are staggered, and can move along the height direction of the square tube space structure. The lower loading plate 2 is the same size as the upper loading plate 1. The plate surface of the lower loading plate 2 is hermetically connected to the other end of the square tube space structure and can move along the height direction of the square tube space structure. The upper loading plate 1, the lower loading plate 2, and multiple side loading plates 3 enclose a cuboid space, and the inside of the cuboid space is used to place the rock specimen 13. The rock specimen 13 is a geometric structure matching the cuboid space structure, and the rock specimen 13 is wrapped by the cuboid space formed by the upper loading plate 1, the lower loading plate 2, and multiple side loading plates 3. Multiple loading plate pads include end loading plate pads 4 and side loading plate pads 5. The side loading plate pads 5 are correspondingly arranged on the plate surfaces of the respective side loading plates 3 away from the rock specimen 13, and the end loading plate pads 4 are correspondingly arranged on the plate surfaces of the upper loading plate 1 and the lower loading plate 2 away from the rock specimen 13. The loading plate pads are connected to the loading plates as a whole.

[0052] As Figure 5 shown, the end loading plate pads 4 and the side loading plate pads 5 are both arranged at the middle positions of the corresponding loading plates.

[0053] As Figure 4 , Figure 5 and Figure 6 shown, each outer side wall of the square tube space structure is composed of the splicing of the plate surfaces of two adjacent side loading plates 3, including the end face of one side loading plate 3 and the plate surface of the other side loading plate 3.

[0054] The top surface of the upper loading plate 1 is flush with the outer side wall of the square tube space structure, and the bottom surface of the lower loading plate 2 is flush with the outer side wall of the square tube space structure.

[0055] The end faces of two adjacent side loading plates 3 are flush with each other, and the end faces of the other two side loading plates 3 are also flush with each other. When the plates of two adjacent side loading plates 3 are spliced with those of the other two side loading plates 3, there is a distance staggered by the thickness of the upper loading plate 1 between the end faces. Each loading plate is combined together with others staggered to wrap the rock specimen to accommodate the movement caused by the deformation of the rock specimen 13.

[0056] In some embodiments, such as Figure 3 , Figure 4 , Figure 7 , Figure 8 , Figure 9 shown, bolt through holes 8 are provided at the center positions of the side faces of the end loading plate pads 4 and the side loading plate pads 5 away from the outer side walls of the cuboid-shaped space. The loading plate pads are connected to the tensile connection device through the bolt through holes 8, and the tensile connection device is used when the testing machine applies tensile force to the fixture; the tensile connection device includes: a short bolt 9, a pull rod 10 and a connection head 11. One end of the short bolt 9 is connected to the bolt through hole 8 on the loading plate pad; one end of the pull rod 10 is connected to the other end of the short bolt 9; the connection head 11 is connected to the other end of the pull rod 10, and a plurality of threaded holes are provided on the peripheral side of the connection head 11, and a long bolt 12 is arranged on each threaded hole. The push head of the testing machine is inserted into the connection head 11 and clamped and fixed by the long bolt 12.

[0057] Such as Figure 1 , Figure 2 , Figure 3 and Figure 6 shown, the connecting piece includes: a U-shaped bolt 6 and a fixing bolt 7. Bolt holes are provided on the peripheral side faces of the end loading plate pads 4 of the upper loading plate 1, and bolt holes are provided on one end face of the side loading plate pad 5. A U-shaped bolt 6 is provided on the other side face opposite to the side face of the side loading plate pad 5 where the bolt hole is provided. U-shaped bolts 6 are provided around the end loading plate pads 4 of the lower loading plate 2. The fixing bolt 7 is threadedly connected in the threaded hole, and the nut of the fixing bolt 7 abuts against the outer side face of the U-shaped bolt 6. Through the connecting piece with such a structure, not only can the upper loading plate 1, the lower loading plate 2 and the side loading plate 3 be quickly installed, but also the U-shaped bolt 6 can accommodate the movement of the fixing bolt 7 caused by the deformation of the rock specimen 13 after being stressed.

[0058] An experimental method for a deep hard rock true triaxial tensile and compressive fixture uses the above-mentioned deep hard rock true triaxial tensile and compressive fixture for experiments, including the following steps:

[0059] S1. Splice the true triaxial tensile and compressive fixture and place the spliced true triaxial tensile and compressive fixture on the loading platform of the testing machine. The push head of the true triaxial testing machine is connected to the loading plate pad to ensure that there is no deviation of the fixture in the center of the testing machine, and adjust the true triaxial testing machine to make the fixture close and fastened.

[0060] S2. Using a true triaxial testing machine, uniform planar tensile / compressive forces are transmitted to the six surfaces of the rock specimen 13 from three directions through fixtures. The six surfaces are the six faces of the rock, and the three directions are the x, y, and z directions, so as to simulate the stress state existing in deep underground hard rock units. When applying tensile stress, high-strength glue is applied between the end face of the rock specimen 13 in the tensile force application direction and the loading plate. The push head of the testing machine and the corresponding loading plate cushion block in the same direction are connected through a tensile connection device. When applying compressive stress, there is no need to glue the rock specimen 13 to the side loading plate 3. The push head of the testing machine pushes the corresponding side loading plate 3 towards the center of the rock specimen 13 through the loading plate cushion block, and transmits the pressure to the rock specimen 13.

[0061] S3. After data acquisition is completed, turn off the testing machine, remove the fixtures and take out the rock specimen.

[0062] In S1, the splicing method of the tensile-compressive true triaxial fixture includes the following steps:

[0063] Place the rock specimen 13 in the upper right of the lower loading plate 2, then place the lower left of the upper loading plate 1 on the rock specimen 13. Place a side loading plate 3 on the left side of the rock specimen 13, and align the lower end of the side loading plate 3 with the edge of the lower loading plate 2, and the upper end with the edge of the upper loading plate 1, and the upper end is flush with the upper surface of the upper loading plate 1. By tightening the fixing bolt 7 on the bolt hole of the end loading plate cushion block 4 on the upper loading plate 1, the U-shaped bolt 6 on the side loading plate cushion block 5 on the side loading plate 3 is clamped, completing the connection between the side loading plate 3 and the upper loading plate 1. Similarly, connect and fix the side loading plate 3 to the lower loading plate 2.

[0064] Then place a side loading plate 3 on the front of the rock specimen 13, align the lower end of the side loading plate 3 placed this time with the front edge of the lower loading plate 2, the upper end of the side loading plate 3 is flush with the upper surface of the upper loading plate 1, the inner plate surface of the side loading plate 3 fits against the end of the upper loading plate 1, and the upper and lower ends of the two installed side loading plates 3 are flush. In the above manner, fix the side loading plate 3 to the upper loading plate 1 and the lower loading plate 2 through the U-shaped bolt 6 and the fixing bolt 7.

[0065] Then place the third side loading plate 3 on the right side of the rock specimen 13, the upper surface of the third placed side loading plate 3 fits against the lower surface of the upper loading plate 1, and the lower surface is flush with the lower surface of the lower loading plate 2. In the above manner, fix the side loading plate 3 to the upper loading plate 1 and the lower loading plate 2 through the U-shaped bolt 6 and the fixing bolt 7.

[0066] Then, place the fourth side loading plate 3 at the rear side of the rock specimen 13. The upper end surface of the fourth placed side loading plate 3 is in contact with the lower surface of the upper loading plate 1, and the lower end surface is flush with the lower surface of the lower loading plate 2. Fix the side loading plate 3 to the upper loading plate 1 and the lower loading plate 2 through U-shaped bolts 6 and fixing bolts 7. The upper and lower ends of the third side loading plate 3 are flush with those of the fourth side loading plate 3.

[0067] Through the above splicing and installation method, the fixture completely wraps the rock specimen, solving the problem of corner effect that generally exists in the conventional rigid loading true triaxial experiment. Under such splicing conditions, due to the bolt hole connection method, the thread can move 1 mm - 2 mm, which is sufficient to adapt to the deformation required for rock failure.

[0068] In S2, when applying compressive stress to the rock specimen 13, the testing machine push head applies compressive stress at a loading rate of 0.5 MPa / s. When applying tensile stress to the rock specimen 13, the testing machine push head is controlled by adopting a displacement control method, and the testing machine push head is kept moving at a speed of 0.1 mm / min.

[0069] The mechanical properties of rocks are related to the loading rate. The mechanical properties under static load are studied in this embodiment. The above loading rate of 0.5 MPa / s is a commonly used rate for rock compression tests. However, the tensile stress of rocks is very low and cannot be applied at such a fast rate. A slower speed should be used. Moreover, compared with the load control method, the displacement control loading method will not generate impact near failure.

[0070] Such as Figures 10 - 13 , and Figures 14 - 17 As shown, in the four cases where the rock specimen 13 exists in the tensile-compression true triaxial test, the application methods for tensile / compressive stress are as follows:

[0071] When the rock specimen 13 is under two-way compression and one-way tension: First, apply the maximum compressive stress and the intermediate compressive stress in two directions respectively, so that the compressive stresses applied in the two directions reach the intermediate compressive stress simultaneously; secondly, apply tensile stress in the other direction; finally, continuously apply the maximum compressive stress in the direction where the maximum compressive stress is applied until the specimen fails;

[0072] When the rock specimen 13 is under two-way tension and one-way compression: First, apply the maximum compressive stress in one direction; secondly, apply the intermediate tensile stress and the minimum tensile stress in the other two directions respectively, so that the two directions where the tensile stress is applied reach the minimum tensile stress simultaneously, and continue to apply the intermediate tensile stress in the direction where the intermediate tensile stress is applied; finally, continuously apply the maximum compressive stress in the direction where the maximum compressive stress is applied until the specimen fails;

[0073] Under the condition of triaxial tension of the rock specimen 13: Apply the maximum tensile stress, the intermediate tensile stress, and the minimum tensile stress in three directions simultaneously, so that the minimum tensile stress is reached in all three directions at the same time; continue to apply the intermediate tensile stress and the maximum tensile stress in the directions where the intermediate tensile stress and the maximum tensile stress are applied, so that the two reach the intermediate tensile stress at the same time; finally, continuously apply the maximum tensile stress in the direction where the maximum tensile stress is applied until the specimen fails;

[0074] Under the condition of triaxial compression of the rock specimen 13: Apply the maximum compressive stress, the intermediate compressive stress, and the minimum compressive stress in three directions simultaneously, so that the minimum compressive stress is reached in all three directions at the same time; continue to apply the intermediate compressive stress and the maximum compressive stress in the directions where the intermediate compressive stress and the maximum compressive stress are applied, so that the two reach the intermediate compressive stress at the same time; finally, continuously apply the maximum compressive stress in the direction where the maximum compressive stress is applied until the specimen fails.

[0075] It should be noted that in the description of the stress magnitudes in the above three directions, "maximum", "intermediate", and "minimum" refer to the absolute values of the corresponding compressive stress or tensile stress.

[0076] Under the condition of triaxial compression of the rock specimen 13:

[0077] Such as Figure 14 The triaxial compression stress path shown is: ① Apply the three-direction compressive stresses σ1, σ2, σ3 to the specified minimum compressive stress σ 30 ; ② Apply the maximum and intermediate compressive stresses σ1, σ2 to the specified intermediate compressive stress σ 20 ; ③ Apply the maximum compressive stress σ1 until σ 1f fails.

[0078] Such as Figure 15 The triaxial tension stress path shown is: ① Apply the three-direction tensile stresses σ1, σ2, σ3 to the specified minimum tensile stress σ1; ② Apply the maximum and intermediate tensile stresses σ2, σ3 to the specified intermediate tensile stress σ2; ③ Apply the maximum tensile stress σ3 until σ 3f fails, where f represents the stress at the time of loading to failure.

[0079] Such as Figure 16 The two-way compression and one-way tension stress path shown is: ① Apply the maximum and intermediate compressive stresses σ1 and σ2 to the specified intermediate compressive stress σ2; ② Apply the tensile stress σ3 to σ 30 ; ③ Apply the maximum compressive stress σ1 until σ 1f fails.

[0080] Such as Figure 17 The two-way tension and one-way compression stress path shown is: ① Apply the maximum compressive stress σ1 to a certain σ 10 ; ② Apply the minimum tensile stress σ2 to σ 20 , and the intermediate tensile stress σ3 to σ 30; ③ Apply the maximum compressive stress σ1 until σ 1f failure occurs.

[0081] It should be noted that σ1, σ2, and σ3 are the stresses in three directions and are also used for general descriptions. Taking compressive stress as positive, the above are the maximum, intermediate, and minimum stresses respectively. σ 10 , σ 20 , σ 30 refer to the specific values of the stresses in the corresponding directions in the stress path under a specific situation, that is, the specific values applied in the test.

[0082] The above discloses only several preferred specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto, and any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. An experimental method for a deep hard rock true triaxial compression and tension fixture, characterized in that, Conduct tests using a deep hard rock true triaxial tensile-compressive fixture, and the deep hard rock true triaxial tensile-compressive fixture includes: Four side loading plates are connected end to end to form a square tube space structure. Adjacent side loading plates are movably connected through connecting pieces. The side end face of the previous side loading plate is connected to the edge of the plate surface of the next side loading plate. Among the four side loading plates, taking two adjacent side loading plates as one side loading plate group, and the other two adjacent side loading plates as another side loading plate group. And the upper end faces of the two side loading plates in each side loading plate group are aligned, and the two side loading plate groups are arranged with a dislocation in the height direction so that there is a height difference between the upper end faces and the lower end faces of the two side loading plate groups; An upper loading plate, the plate surface of which is hermetically connected to one end of the square tube space structure, is located at the height difference where the upper end faces of the two side loading plate groups are dislocated, and can move along the height direction of the square tube space structure; A lower loading plate, which has the same size as the upper loading plate, the plate surface of which is hermetically connected to the other end of the square tube space structure, is located at the height difference where the lower end faces of the two side loading plate groups are dislocated, and can move along the height direction of the square tube space structure. The upper loading plate, the lower loading plate and multiple side loading plates enclose a cuboid-shaped space for wrapping the rock specimen; Multiple loading plate pads, and the multiple loading plate pads include two end loading plate pads and multiple side loading plate pads. The multiple side loading plate pads are correspondingly arranged on the plate surfaces of the respective side loading plates away from the rock specimen, and the two end loading plate pads are correspondingly arranged on the plate surfaces of the upper loading plate and the lower loading plate away from the rock specimen; The connecting piece includes: a U-shaped bolt and a fixing bolt. Bolt holes are opened on the peripheral side surfaces of the end loading plate pads of the upper loading plate, and bolt holes are opened on one side end face of the side loading plate pad. A U-shaped bolt is provided on the other side surface opposite to the side end face where the bolt hole of the side loading plate pad is opened. U-shaped bolts are provided around the end loading plate pads of the lower loading plate. The fixing bolt is threadedly connected in the threaded hole, and the nut of the fixing bolt abuts against the outer side surface of the U-shaped bolt; The experimental method includes the following steps: S1. Assemble the true triaxial tensile-compressive fixture and place the assembled true triaxial tensile-compressive fixture on the loading platform of the testing machine. The push head of the true triaxial testing machine is connected to the loading plate pad to ensure that there is no deviation of the fixture in the center of the testing machine, and adjust the true triaxial testing machine to make the fixture close and fastened; S2. Using the true triaxial testing machine, transfer uniform surface tensile / compressive forces to the six surfaces of the rock specimen from three directions of the rock specimen through the fixture. When applying tensile stress, apply high-strength glue between the end face of the rock specimen in the direction of the applied tensile force and the loading plate. The push head of the testing machine in the same direction and the corresponding loading plate pad are connected through a tensile connecting device. When applying compressive stress, there is no need to glue the rock specimen to the side loading plate. The push head of the testing machine pushes the corresponding side loading plate towards the center of the rock specimen through the loading plate pad to transfer the pressure to the rock specimen; S3. After the loading test and data acquisition are completed, turn off the testing machine, remove the fixture and take out the rock specimen; In S2, when applying compressive stress to the rock specimen, the testing machine push head applies the compressive stress. When applying tensile stress to the rock specimen, the testing machine push head is controlled by adopting a displacement control method. In the true triaxial test of tension and compression, for the four cases existing in the rock specimen, the methods for applying tension / compression are as follows: When the rock specimen is compressed in two directions and tensioned in one direction: First, apply the maximum compressive stress and the intermediate compressive stress in two directions respectively, so that the compressive stresses applied in the two directions reach the intermediate compressive stress simultaneously; Second, apply tensile stress in the other direction; Finally, continuously apply the maximum compressive stress in the direction where the maximum compressive stress is applied until the specimen fails; When the rock specimen is tensioned in two directions and compressed in one direction: First, apply the maximum compressive stress in one direction; Second, apply the intermediate tensile stress and the minimum tensile stress in the other two directions respectively, so that the two directions where the tensile stress is applied reach the minimum tensile stress simultaneously, and continue to apply the intermediate tensile stress in the direction where the intermediate tensile stress is applied; Finally, continuously apply the maximum compressive stress in the direction where the maximum compressive stress is applied until the specimen fails; When the rock specimen is tensioned in three directions: Simultaneously apply the maximum tensile stress, the intermediate tensile stress and the minimum tensile stress in three directions respectively, so that the three directions reach the minimum tensile stress simultaneously; Continue to apply the intermediate tensile stress and the maximum tensile stress in the directions where the intermediate tensile stress and the maximum tensile stress are applied respectively, so that the two reach the intermediate tensile stress simultaneously; Finally, continuously apply the maximum tensile stress in the direction where the maximum tensile stress is applied until the specimen fails; When the rock specimen is compressed in three directions: Simultaneously apply the maximum compressive stress, the intermediate compressive stress and the minimum compressive stress in three directions respectively, so that the three directions reach the minimum compressive stress simultaneously; Continue to apply the intermediate compressive stress and the maximum compressive stress in the directions where the intermediate compressive stress and the maximum compressive stress are applied respectively, so that the two reach the intermediate compressive stress simultaneously; Finally, continuously apply the maximum compressive stress in the direction where the maximum compressive stress is applied until the specimen fails.

2. The experimental method of a deep hard rock true triaxial tensile-compressive fixture according to claim 1, characterized in that Both the end loading plate cushion block and the side loading plate cushion block are arranged at the middle positions of the corresponding loading plates.

3. The experimental method of a deep hard rock tensile-compressive true triaxial fixture according to claim 1, characterized in that, Both the end loading plate cushion block and the side loading plate cushion block are provided with bolt through holes at the central positions of the sides away from the outer side walls of the cuboid-shaped space, and are connected to the tensile connection device through the bolt through holes. The tensile connection device includes: A short bolt, with one end connected to the bolt through hole on the loading plate cushion block; A tie rod, with one end connected to the other end of the short bolt; A connector, connected to the other end of the tie rod. A plurality of threaded holes are provided on the peripheral side of the connector, and a long bolt is arranged on each threaded hole. The push head of the testing machine is inserted into the connector and clamped and fixed by the long bolt.

4. The experimental method of a deep hard rock tensile-compressive true triaxial fixture according to claim 1, characterized in that, The top surface of the upper loading plate is flush with the outer side wall of the square tube space structure, and the bottom surface of the lower loading plate is flush with the outer side wall of the square tube space structure.

5. The experimental method of a deep hard rock true triaxial tension-compression fixture according to claim 1, characterized in that In S1, the splicing method of the true triaxial tension and compression fixture includes the following steps: Place the rock sample on the upper right side of the lower loading plate, then place the lower left side of the upper loading plate on the rock sample, and place a side loading plate on the left side of the rock sample, with the lower end of the side loading plate aligned with the left edge of the lower loading plate, the upper end aligned with the left edge of the upper loading plate, and the upper end flush with the upper surface of the upper loading plate. Tighten the fixing bolts in the bolt holes of the end loading plate pads on the upper loading plate so that the U-bolts on the side loading plate pads on the side loading plate are clamped, completing the connection between the side loading plate and the upper loading plate. Similarly, connect and fix the side loading plate to the lower loading plate. Then, place a side loading plate on the front of the rock specimen, aligning the lower end of the side loading plate with the front edge of the lower loading plate, flushing the upper end of the side loading plate with the upper surface of the upper loading plate, and aligning the inner plate surface of the side loading plate with the end of the upper loading plate. The upper and lower ends of the two installed side loading plates are flush. In the same manner as described above, secure the side loading plate to the upper and lower loading plates using U-bolts and fixing bolts. Then, place the third side loading plate on the right side of the rock sample, with the upper end surface of the side loading plate in contact with the lower surface of the upper loading plate and the lower end surface flush with the lower surface of the lower loading plate. In the same manner as described above, secure the side loading plate to the upper and lower loading plates using U-bolts and fixing bolts. Then, place the fourth side loading plate on the rear side of the rock sample, with the upper end surface of the side loading plate in contact with the lower surface of the upper loading plate, and the lower end surface flush with the lower surface of the lower loading plate. The side loading plate is fixed to the upper loading plate and the lower loading plate by U-bolts and fixing bolts. The upper and lower ends of the third side loading plate are flush with the upper and lower ends of the fourth side loading plate.

Images