Deep hard rock tension and compression true triaxial clamp and experimental method

Abstract

The invention discloses a deep hard rock tension and compression true triaxial clamp and an experiment method.The clamp comprises an upper loading plate, a lower loading plate, side loading plates, end loading plate cushion blocks and side loading plate cushion blocks, the multiple side loading plates are connected and enclosed into a whole, and a cuboid-shaped space used for containing a rock sample is formed; according to the invention, a true triaxial testing machine is utilized to apply uniform pressure or tensile force to six surfaces of the rock sample from three directions of the rock sample through a clamp, and the pressure is applied by pushing the loading plates in the corresponding directions to move towards the center of the rock sample by an oil cylinder; and pulling force is applied by pulling a loading plate bonded with the rock sample by an oil cylinder to move in a direction far away from the center of the rock sample, so that the indoor simulation test of the tension-compression true triaxial stress state of the deep hard rock is realized.

Description

Technical Field

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

[0002] The stress state of rock in actual engineering is very complex, and is generally in a state of unequal stress in three directions. Most previous studies have focused on rock compression. However, after entering the deep, the rock that was originally under high stress will produce unloading stress waves and tensile stress due to the unloading effect of excavation after excavation. In particular, when excavating by blasting, tensile stress will be generated in the rock mass due to the propagation and refraction of stress waves. In addition, for general rock engineering, since the ground stress is not a uniform hydrostatic pressure, there will be concentrated areas of compressive stress and tensile stress. In short, in actual in-situ engineering, the rock is in a true triaxial stress state, and tensile stress exists in it.

[0003] Rock, especially hard rock, is a typical hard and brittle geological material. Its notable feature is that its compressive strength is much higher than its tensile strength, and the compressive strength of hard rock is dependent on confining pressure. That is to say, under true triaxial conditions, confining pressure (if the intermediate and minimum compressive stresses are equal, it is usually called conventional triaxial) has a significant enhancing effect on the strength of rock, but the effects of intermediate stress and minimum stress are different. The minimum stress has the strongest effect on the strength of rock, which is why most rock strength criteria currently only consider the influence of minimum stress. Intermediate stress has an enhancing effect on the strength of rock, but the effect is limited and not as good as the minimum stress. When the intermediate stress exceeds a certain limit, the strength is reduced. The above studies all assume that the rock is under true triaxial compression. It can be seen that when the minimum stress is pressure, it is most beneficial to improve the strength of the rock. From the above analysis, it can be seen that it is a favorable condition for the minimum and intermediate stresses to be pressure. On the contrary, if the minimum stress is tensile stress, the rock will be more easily damaged and its strength will be lower. According to the idea that tensile stress is an unfavorable factor, there are four situations under true triaxial stress conditions: 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.

[0004] At present, most of the fixtures of experimental devices for studying deep hard rock only focus on the true triaxial compressive stress state of hard rock, and it is difficult to carry out experimental research on the other existing tensile and compressive true triaxial stress states mentioned above. Moreover, when designing the experimental fixtures that focus on the true triaxial compressive stress state of hard rock, the plate surface of the loading plate and the surface of the rock sample are designed to be the same size, resulting in deformation of the rock sample when the compressive stress is loaded on the rock sample. At this time, the size of the rock surface changes, resulting in a certain gap deviation between the loading plate and the edge of the rock sample, thereby causing a corner effect, resulting in significant stress concentration at the gap during the pressurization process, and the rock is damaged here, thereby changing the failure mode of the rock specimen, affecting the shear band distribution inside the specimen, lateral deformation characteristics and other properties, and affecting the accuracy of rock strength measurement. Summary of the invention

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

[0006] The technical solution of the present invention is: A deep hard rock tension and compression true triaxial fixture comprises: four side loading plates, which are of the same size and are all vertically arranged rectangular plates, 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 surface of the front side loading plate is connected to the edge of the plate surface of the rear side loading plate, among the four side loading plates, two adjacent side loading plates are one side loading plate group, and the other two adjacent side loading plates are another side loading plate group, and the upper end surfaces of the two side loading plates in each side loading plate group are aligned, and the two side loading plate groups are staggered in the height direction so that the two side loading plate groups are between the upper end surface and the lower end surface They are all staggered by a height distance; the staggered height distance is the thickness of the upper loading plate; the upper loading plate, the plate surface is closed and connected to one end of the square tube space structure, located at the height distance staggered between the upper end surfaces of the two side loading plate groups, and can move along the height direction of the square tube space structure; the lower loading plate, which is the same size as the upper loading plate, has a plate surface closed and connected to the other end of the square tube space structure, located at the height distance staggered between the lower end surfaces of the two side loading plate groups, 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 surround a rectangular space, the interior of the rectangular space is used to place rock samples and wrap the rock samples.

[0007] Furthermore, the end loading plate pad and the side loading plate pad are provided with bolt through holes at the center positions of the sides of the outer walls away from the rectangular space, and the loading plate pad is connected to the stretching connection device through the bolt through holes, and the stretching connection device is used when the testing machine applies tension to the clamp; the stretching 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 connecting head, which is connected to the other end of the pull rod, and a plurality of threaded holes are provided on the circumference of the connecting head, each of the threaded holes is provided with a long bolt, and the push head of the testing machine is inserted into the connecting head and clamped and fixed by the long bolt.

[0008] Furthermore, the connecting parts include: U-shaped bolts and fixing bolts. Bolt holes are opened on the side surfaces around the loading plate pad at the end of the upper loading plate, and bolt holes are opened on one end surface of the side loading plate pad. A U-shaped bolt is provided on the other side surface opposite to the end surface of the side loading plate pad where the bolt hole is opened. U-shaped bolts are provided around the loading plate pad at the end of the lower loading plate. The fixing bolts are threadedly connected in the threaded holes, and the nuts of the fixing bolts abut against the outer surfaces of the U-shaped bolts. The U-shaped bolts are mainly used to meet the movement of the fixing bolts caused by the deformation of the rock sample after being subjected to force.

[0009] Furthermore, 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.

[0010] An experimental method for a deep hard rock tension and compression true triaxial fixture, using the fixture to conduct an experiment, includes the following steps: S1. Splice the tension and compression true triaxial fixture, and place the spliced ​​tension and compression true triaxial fixture on the loading platform of the testing machine. Connect the push head of the true triaxial testing machine with the loading plate pad to ensure that the fixture has no deviation in the center of the testing machine. Adjust the true triaxial testing machine to make the fixture close and tight.

[0011] S2. Use a true triaxial testing machine to transfer uniform surface tension / pressure to the six surfaces of the rock sample from three directions through a fixture to simulate the stress state of hard rock units deep underground. When applying tensile stress, high-strength glue is applied between the end face of the rock sample in the direction of tensile force and the loading plate. The push head of the testing machine and the corresponding loading plate pad in the same direction are connected by a tensile connection device. When applying compressive stress, there is no need to glue the rock sample to the side loading plate. The push head of the testing machine pushes the corresponding side loading plate toward the center of the rock sample through the loading plate pad to transfer the pressure to the rock sample.

[0012] S3. After the loading test and data collection are completed, turn off the testing machine, remove the fixture and take out the rock sample.

[0013] Further, in S1, the method for splicing the tension and compression true triaxial fixture includes the following steps: Place the rock sample on the upper right side of the lower loading plate, and then place the lower left side of the upper loading plate on the rock sample, place a side loading plate on the left side of the rock sample, and align the lower end of the side loading plate with the left edge of the lower loading plate, align the upper end with the left edge of the upper loading plate, and the upper end is flush with the upper surface of the upper loading plate, and tighten the fixing bolts on 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.

[0014] Then place a side loading plate on the front of the rock sample, align the lower end of the side loading plate with the front edge of the lower loading plate, flush the upper end of the side loading plate with the upper surface of the upper loading plate, and the inner plate surface of the side loading plate fits the end of the upper loading plate. The upper and lower ends of the two installed side loading plates are flush. In the above manner, the side loading plate is fixed to the upper loading plate and the lower loading plate by U-bolts and fixing bolts.

[0015] 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 above manner, the side loading plate is fixed to the upper loading plate and the lower loading plate by U-bolts and fixing bolts.

[0016] 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, and the upper and lower ends of the third side loading plate are flush with those of the fourth side loading plate.

[0017] Furthermore, in the four cases where the rock specimens exist in the true triaxial test, the methods for applying tension / compression are: When the rock specimen is under compression in two directions and tension in one direction: firstly, apply the maximum compressive stress and the intermediate compressive stress in two directions respectively, so that the compressive stress applied in the two directions reaches the intermediate compressive stress at the same time; secondly, apply tensile stress in the other direction; finally, continue to load the maximum compressive stress in the direction where the maximum compressive stress is applied until the specimen is destroyed; When the rock specimen is subjected to tension in two directions and compression in one direction: first apply the maximum compressive stress in one direction; then 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 at the same time, and continue to apply the intermediate tensile stress in the direction where the intermediate tensile stress is applied; finally, continue to load the maximum compressive stress in the direction where the maximum compressive stress is applied until the specimen is destroyed; When the rock sample is subjected to three-way tension: the maximum tensile stress, the intermediate tensile stress and the minimum tensile stress are applied in the three directions at the same time, so that the minimum tensile stress is reached in the three directions at the same time; the intermediate tensile stress and the maximum tensile stress are continued to be applied in the direction 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, the maximum tensile stress is continuously applied in the direction where the maximum tensile stress is applied until the sample is destroyed; When the rock specimen is subjected to three-way compression: the maximum compressive stress, the intermediate compressive stress and the minimum compressive stress are applied in the three directions respectively at the same time, so that the minimum compressive stress is reached in the three directions at the same time; the intermediate compressive stress and the maximum compressive stress are continued to be applied in the direction 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, the maximum compressive stress is continued to be applied in the direction where the maximum compressive stress is applied until the specimen is destroyed.

[0018] Compared with the prior art, the relevant experiments carried out using the fixture of the present invention can accurately and truly reflect the deformation and failure of actual deep hard rock under generalized tension and compression true triaxial stress conditions, 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 complete deep hard rock strength criterion, reveal the essential differences in the mechanical response and disaster-pregnancy mechanism of the surrounding rock of shallow rock engineering and deep rock engineering, explain why the current shallow rock mechanics theory is difficult to fully apply to deep rock engineering, and reveal the disaster mechanism of special damage forms such as slab cracking and rock burst in the surrounding rock of deep hard rock engineering. The specific beneficial effects of the present invention are: 1. The present invention utilizes a rigid push head of a true triaxial testing machine to apply uniform surface tension / pressure to six surfaces of a rock sample in three directions through a fixture to simulate the complex true triaxial stress state of deep hard rock, and can respectively carry out the following four hard rock deformation and failure tests under true triaxial stress states of tension and compression: 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, which truly reflects the deformation and failure of actual deep hard rock under generalized true triaxial stress conditions of tension and compression. In the test process, a rectangular space is enclosed by an upper loading plate, a lower loading plate and a plurality of side loading plates, and a rock sample is placed inside the rectangular space. Each surface of the rock sample is tightly wrapped by the rectangular space, which effectively reduces the influence of corner effect and end effect on the accuracy of test data during rock sample testing.

[0019] 2. The end faces of two adjacent side loading plates of the present invention are flush, and the end faces of the other two side loading plates are flush, and when the two adjacent side loading plates are spliced ​​with the plate surfaces of the other two side loading plates, the end faces are staggered by a distance of the thickness of the upper loading plate, and the loading plates are staggered and combined together so that the clamp completely wraps the rock sample in a mutually overlapping manner. Through the above-mentioned splicing and installation method, the clamp completely wraps the rock sample, solving the corner effect problem commonly existing in the previous rigid loading true triaxial test, further reducing the influence of the corner effect and the end effect on the accuracy of the test data during the rock sample test, and improving the accuracy of the test data. Under such splicing conditions, due to the bolt hole connection method, the thread can move 1mm-2mm, which is sufficient to adapt to the deformation required for rock failure.

[0020] 3. When applying tensile stress, the present invention ensures that the tensile stress is parallel to the corresponding direction of the rock sample by connecting the tensile connection device with a clamp and the bonding method, thereby improving the accuracy of the test results and solving the problem of test failure caused by the easy damage of the test piece at the clamping position in previous tests.

[0021] 4. The fixture of the present invention has a simple structure and is easy to assemble and disassemble, and can be directly used to carry out tests on an existing universal true triaxial rock mechanics testing machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a stereogram of the structural schematic diagram of the present invention.

[0023] Figure 2 It is a top view of the structural schematic diagram of the present invention.

[0024] Figure 3 It is a front view of the structural schematic diagram of the present invention.

[0025] Figure 4 It is a schematic diagram of the structure of the side loading plate, the lower loading plate and the loading plate pad block of the present invention.

[0026] Figure 5 It is a schematic diagram of the transverse section structure of the present invention.

[0027] Figure 6 It is a schematic diagram of the longitudinal section structure of the present invention.

[0028] Figure 7 It is a front view of the structural schematic diagram of the stretching connection device of the present invention.

[0029] Figure 8 It is a top view of the structural schematic diagram of the stretching connection device of the present invention.

[0030] Fig. 9 It is a bottom view of the structural schematic diagram of the stretching connection device of the present invention.

[0031] Fig.10 It is a schematic diagram of the three-dimensional compressive force of the rock sample of the present invention.

[0032] Fig.11 It is a schematic diagram of the three-way tensile force of the rock sample of the present invention.

[0033] Fig.12 It is a schematic diagram of the rock sample of the present invention being subjected to compression in two directions and tension in one direction.

[0034] Fig.13 It is a schematic diagram of the rock sample of the present invention being subjected to tension in two directions and compression in one direction.

[0035] Fig.14 This is the stress path of the true triaxial test under three-way compression of the present invention.

[0036] Fig.15 This is the stress path of the true triaxial test under three-way tension of the present invention.

[0037] Fig.16 This is the true triaxial test stress path of the present invention under two-way compression and one-way tension.

[0038] Fig.17 This is the true triaxial test stress path of the present invention under two-way tension and one-way compression.

[0039] Among them, 1. upper loading plate, 2. lower loading plate, 3. side loading plate, 4. end loading plate pad, 5. side loading plate pad, 6. U-bolt, 7. fixing bolt, 8. bolt through hole, 9. short bolt, 10. pull rod, 11. connecting head, 12. long bolt. DETAILED DESCRIPTION

[0040] The following is combined with Figure 1 To the attached Fig.17 , the specific implementation methods of the present invention are described in detail. In the description of the present invention, it should be understood that the terms "center", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are 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 and be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0041] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features; in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0042] Example like Figure 1 As shown, a deep hard rock tension and compression true triaxial fixture comprises: 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 have 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. Two adjacent side loading plates 3 are movably connected through connecting pieces. The side end surface of the front side loading plate is connected to the edge of the plate surface of the rear side loading plate. Among the four side loading plates 3, two adjacent side loading plates 3 are one side loading plate group, and the other two adjacent side loading plates 3 are another side loading plate group. The upper end surfaces of the two side loading plates 3 in each side loading plate group are aligned. The two side loading plate groups are staggered in the height direction so that the two side loading plate groups are staggered by a height distance between the upper end surface and the lower end surface, and the staggered height distance is the thickness of the upper loading plate 1; the plate surface of the upper loading plate 1 is closed and connected to one side of the square tube space structure. The lower end of the square tube space structure is located at a 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, and the plate surface of the lower loading plate 2 is closed and 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 a plurality of side loading plates 3 surround a rectangular space, and the interior of the rectangular space is used to place a rock sample 13, and the rock sample 13 is a geometric structure matching the rectangular space structure, and the rock sample 13 is wrapped by the rectangular space surrounded by the upper loading plate 1, the lower loading plate 2 and a plurality of side loading plates 3; the plurality of loading plate pads include an end loading plate pad 4 and a side loading plate pad 5, and the side loading plate pad 5 is correspondingly arranged on the plate surface of each side loading plate 3 away from the rock sample 13, and the end loading plate pad 4 is correspondingly arranged on the plate surface of the upper loading plate 1 and the lower loading plate 2 away from the rock sample 13, and the loading plate pad is connected to the loading plate as a whole.

[0043] like Figure 5 As shown, the end loading plate pad 4 and the side loading plate pad 5 are both arranged at the middle position of the corresponding loading plate.

[0044] like Figure 4 , Figure 5 and Figure 6 As shown, each outer side wall of the square tube space structure is formed by splicing the plate surfaces of two adjacent side loading plates 3 , including the end surface of one side loading plate 3 and the plate surface of the other side loading plate 3 .

[0045] 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.

[0046] The end faces of two adjacent side loading plates 3 are flush, and the end faces of the other two side loading plates 3 are flush, and when the two adjacent side loading plates 3 are spliced ​​with the plate surfaces of the other two side loading plates 3, the end faces are staggered by a distance equal to the thickness of the upper loading plate 1. The loading plates are staggered and combined to wrap the rock sample, so as to meet the movement caused by the deformation of the rock sample 13.

[0047] In some embodiments, Figure 3 , Figure 4 , Figure 7 , Figure 8 , Fig. 9 As shown, a bolt through hole 8 is provided at the center position of the side surface of the outer wall of the rectangular space away from the end loading plate pad 4 and the side loading plate pad 5. The loading plate pad is connected to the stretching connection device through the bolt through hole 8. The stretching connection device is used when the testing machine applies tension to the fixture; the stretching connection device includes: a short bolt 9, a pull rod 10 and a connecting 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 connecting head 11 is connected to the other end of the pull rod 10, and a plurality of threaded holes are provided on the circumference of the connecting head 11, each threaded hole is provided with a long bolt 12, and the push head of the testing machine is inserted into the connecting head 11 and is clamped and fixed by the long bolt 12.

[0048] like Figure 1 , Figure 2 , Figure 3 as well as Figure 6 As shown, the connecting piece includes: U-shaped bolts 6 and fixing bolts 7. Bolt holes are opened on the sides of the loading plate pad 4 at the end of the upper loading plate 1, and bolt holes are opened on one end face of the side loading plate pad 5. The U-shaped bolts 6 are arranged on the other side opposite to the end face of the side loading plate pad 5 with the bolt holes. The loading plate pad 4 at the end of the lower loading plate 2 is provided with U-shaped bolts 6 around it. The fixing bolts 7 are threadedly connected in the threaded holes, and the nuts of the fixing bolts 7 abut against the outer sides of the U-shaped bolts 6. Through the connecting piece of this structure, not only the upper loading plate 1, the lower loading plate 2 and the side loading plate 3 can be quickly installed, but the U-shaped bolts 6 can also meet the movement of the fixing bolts 7 caused by the deformation of the rock sample 13 after being stressed.

[0049] An experimental method of a deep hard rock tension and compression true triaxial fixture is provided, wherein the experiment is conducted using the deep hard rock tension and compression true triaxial fixture, and the method comprises the following steps: S1. Splice the tension and compression true triaxial fixture, and place the spliced ​​tension and compression true triaxial fixture on the loading platform of the testing machine. Connect the push head of the true triaxial testing machine with the loading plate pad to ensure that the fixture has no deviation in the center of the testing machine. Adjust the true triaxial testing machine to make the fixture close and tight.

[0050] S2. Use a true triaxial testing machine to transfer uniform surface tension / pressure to the six surfaces of the rock sample 13 from three directions through a fixture. The six surfaces are the six faces of the rock, and the three directions are the xyz directions, so as to simulate the stress state of the hard rock unit deep underground. When applying tensile stress, high-strength glue is applied between the end face of the rock sample 13 in the direction of tensile force and the loading plate. The push head of the testing machine and the corresponding loading plate pad in the same direction are connected by a tensile connection device. When applying compressive stress, there is no need to glue the rock sample 13 to the side loading plate 3. The push head of the testing machine pushes the corresponding side loading plate 3 toward the center of the rock sample 13 through the loading plate pad to transfer the pressure to the rock sample 13.

[0051] S3. After data collection is completed, turn off the testing machine, remove the fixture and take out the rock sample.

[0052] In S1, the splicing method of the tension and compression true triaxial fixture includes the following steps: Place the rock sample 13 on the upper right side of the lower loading plate 2, and then place the lower left side of the upper loading plate 1 on the rock sample 13, and place a side loading plate 3 on the left side of the rock sample 13, and align the lower end of the side loading plate 3 with the edge of the lower loading plate 2, align 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, and tighten the fixing bolts 7 on the bolt holes of the end loading plate pads 4 on the upper loading plate 1 so that the U-bolts 6 on the side loading plate pads 5 on the side loading plate 3 are clamped, thereby completing the connection between the side loading plate 3 and the upper loading plate 1. Similarly, the side loading plate 3 is connected and fixed to the lower loading plate 2.

[0053] A side loading plate 3 is then placed on the front side of the rock sample 13, so that the lower end of the side loading plate 3 is aligned 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 is in contact with 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, the side loading plate 3 is fixed to the upper loading plate 1 and the lower loading plate 2 by the U-bolt 6 and the fixing bolt 7.

[0054] Then place the third side loading plate 3 on the right side of the rock sample 13, with the upper end surface of the third side loading plate 3 in contact with the lower surface of the upper loading plate 1, and the lower end surface flush with the lower surface of the lower loading plate 2. In the above manner, the side loading plate 3 is fixed to the upper loading plate 1 and the lower loading plate 2 by the U-bolt 6 and the fixing bolt 7.

[0055] Then, the fourth side loading plate 3 is placed on the rear side of the rock sample 13, the upper end surface of the fourth 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. The side loading plate 3 is fixed to the upper loading plate 1 and the lower loading plate 2 by U-bolts 6 and fixing bolts 7, and the upper and lower ends of the third side loading plate 3 are flush with the fourth side loading plate 3.

[0056] Through the above-mentioned splicing installation method, the fixture completely wraps the rock sample, solving the corner effect problem that is common in previous rigid loading true triaxial tests. Under such splicing conditions, due to the bolt hole connection method, the thread can move 1mm-2mm, which is enough to adapt to the deformation required for rock failure.

[0057] In S2, when compressive stress is applied to the rock sample 13, the push head of the testing machine applies compressive stress at a loading rate of 0.5 MPa / s. When tensile stress is applied to the rock sample 13, the push head of the testing machine is controlled by displacement control to keep the push head of the testing machine displacing at a speed of 0.1 mm / min.

[0058] The mechanical properties of rock are related to the loading rate. This embodiment studies the mechanical properties under static load. The above-mentioned loading rate of 0.5 MPa / s is a commonly used rate for rock compression tests. However, the tensile stress of rock is very low and cannot be applied at such a fast rate. It must be applied at a slower speed. Moreover, compared with the load control method, the displacement-controlled loading method will not produce impact when it is close to failure.

[0059] like Figure 10-13 ,as well as Figure 14-17 As shown in the figure, in the four cases where the rock sample 13 exists in the tension and compression true triaxial test, the methods for applying tension / compression are: When the rock sample 13 is under compression in two directions and tension in one direction: firstly, the maximum compressive stress and the intermediate compressive stress are applied in two directions respectively, so that the compressive stress applied in the two directions reaches the intermediate compressive stress at the same time; secondly, tensile stress is applied in the other direction; finally, the maximum compressive stress is continuously applied in the direction where the maximum compressive stress is applied until the sample is destroyed; When the rock sample 13 is subjected to tension in two directions and compression in one direction: first, the maximum compressive stress is applied in one direction; second, the intermediate tensile stress and the minimum tensile stress are applied in the other two directions respectively, so that the two directions where the tensile stress is applied reach the minimum tensile stress at the same time, and the intermediate tensile stress is continued to be applied in the direction where the intermediate tensile stress is applied; finally, the maximum compressive stress is continuously applied in the direction where the maximum compressive stress is applied until the sample is destroyed; When the rock sample 13 is subjected to three-dimensional tension: the maximum tensile stress, the intermediate tensile stress and the minimum tensile stress are applied in the three directions at the same time, so that the minimum tensile stress is reached in the three directions at the same time; the intermediate tensile stress and the maximum tensile stress are applied in the direction where the intermediate tensile stress and the maximum tensile stress are applied, so that the intermediate tensile stress is reached in the direction where the intermediate tensile stress and the maximum tensile stress are applied at the same time; finally, the maximum tensile stress is applied in the direction where the maximum tensile stress is applied until the sample is destroyed; When the rock sample 13 is subjected to three-way compression: the maximum compressive stress, the intermediate compressive stress and the minimum compressive stress are applied in the three directions respectively at the same time, so that the minimum compressive stress is reached in the three directions at the same time; the intermediate compressive stress and the maximum compressive stress are continued to be applied in the direction 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, the maximum compressive stress is continued to be applied in the direction where the maximum compressive stress is applied until the sample is destroyed.

[0060] It is worth noting that in the description of stress magnitude in the above three directions, "maximum", "middle" and "minimum" refer to the absolute values ​​of the corresponding compressive stress or tensile stress.

[0061] Rock sample 13 under three-dimensional compression: like Fig.14 The three-dimensional compressive stress path shown is: ① Apply three-dimensional compressive stress σ1, σ2, σ3 to the specified minimum compressive stress σ 30 ;② Apply maximum and intermediate compressive stresses σ1, σ2 to the specified intermediate compressive stress σ 20 ;③ Apply maximum compressive stress σ1 until σ 1f destroy.

[0062] like Fig.15 The three-dimensional tensile stress path shown is: ① Apply three-dimensional tensile stress σ1, σ2, σ3 to the specified minimum tensile stress σ1; ② Apply maximum and intermediate tensile stresses σ2, σ3 to the specified intermediate tensile stress σ2; ​​③ Apply maximum tensile stress σ3 until σ 3f Failure, f represents the stress when loaded to failure.

[0063] like Fig.16 The stress path shown in the figure 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 maximum compressive stress σ1 until σ 1f destroy.

[0064] like Fig.17 The stress path shown in the figure is: ① Apply the maximum compressive stress σ1 to a certain σ 10 ;②Apply minimum tensile stress σ2 to σ 20 , intermediate tensile stress σ3 to σ 30 ; ③ Apply maximum compressive stress σ1 until σ 1fdestroy.

[0065] It is worth noting that σ1, σ2, and σ3 are stresses in three directions, which are also used for general descriptions. Compressive stress is positive, and the above are the maximum, middle, and minimum stresses, respectively. 10 , σ 20 , σ 30 It refers to the specific value of stress in the corresponding direction in the stress path under a specific situation, and the specific value applied in the test.

[0066] The above disclosures are only several preferred specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A deep hard rock tension and compression true triaxial fixture, characterized in that: include: Four side loading plates are connected end to end to form a square tube space structure. Adjacent side loading plates are movably connected by connecting pieces. The side end surface of a preceding side loading plate is connected to the edge of the plate surface of a succeeding side loading plate. Among the four side loading plates, two adjacent side loading plates form a side loading plate group, and the other two adjacent side loading plates form another side loading plate group. The upper end surfaces of the two side loading plates in each side loading plate group are aligned. The two side loading plate groups are staggered in the height direction so that the upper end surfaces and the lower end surfaces of the two side loading plate groups are staggered by a height distance. An upper loading plate, the plate surface of which is closed and connected to one end of the square tube space structure, is located at a height distance staggered between the upper end surfaces of the two side loading plate groups, and can move along the height direction of the square tube space structure; The lower loading plate has the same size as the upper loading plate, and the plate surface is closed and connected to the other end of the square tube space structure. It is located at a height distance staggered between the lower end surfaces of the two side loading plate groups, 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 rectangular space for wrapping rock samples.

2. A deep hard rock tension and compression true triaxial fixture according to claim 1, characterized in that: Also includes: Multiple loading plate pads, including two end loading plate pads and multiple side loading plate pads, the multiple side loading plate pads are correspondingly arranged on the plate surface of each side loading plate away from the rock sample, and the two end loading plate pads are correspondingly arranged on the plate surface of the upper loading plate and the lower loading plate away from the rock sample.

3. A deep hard rock tension and compression true triaxial fixture according to claim 2, characterized in that: The end loading plate pad and the side loading plate pad are both arranged at the middle position of the corresponding loading plate.

4. A deep hard rock tension and compression true triaxial fixture according to claim 3, characterized in that: The end loading plate pad and the side loading plate pad are provided with bolt through holes at the center of the side away from the outer wall of the rectangular space, and are connected to the tension connection device through the bolt through holes. The tension connection device includes: A short bolt, one end of which is connected to a bolt through hole on the loading plate pad; A tie rod, one end of which is connected to the other end of the short bolt; A connecting head is connected to the other end of the pull rod. A plurality of threaded holes are arranged on the peripheral side of the connecting head. Each of the threaded holes is provided with a long bolt. The push head of the testing machine is inserted into the connecting head and is clamped and fixed by the long bolt.

5. The deep hard rock tension and compression true triaxial fixture according to claim 2 is characterized in that: Connectors include: U-shaped bolts and fixing bolts, bolt holes are opened on the sides around the loading plate pad at the end of the upper loading plate, bolt holes are opened on one end face of the side loading plate pad, U-shaped bolts are arranged on the other side opposite to the end face of the side loading plate pad with the bolt holes, U-shaped bolts are arranged around the loading plate pad at the end of the lower loading plate, the fixing bolts are threadedly connected in the threaded holes, and the nuts of the fixing bolts abut against the outer sides of the U-shaped bolts.

6. A deep hard rock tension and compression 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.

7. An experimental method for a deep hard rock tension and compression true triaxial fixture, characterized in that: The experiment is carried out using the fixture described in any one of claims 1 to 6, comprising the following steps: S1. Splice the tension and compression true triaxial fixture, and place the spliced ​​tension and compression true triaxial fixture on the loading platform of the testing machine. Connect the push head of the true triaxial testing machine with the loading plate pad to ensure that the fixture has no deviation in the center of the testing machine. Adjust the true triaxial testing machine to make the fixture close and tight. S2. Use a true triaxial testing machine to transmit uniform surface tension / pressure to the six surfaces of the rock sample from three directions through a fixture. When applying tensile stress, apply high-strength glue between the end face of the rock sample in the direction of tensile force and the loading plate. The push head of the testing machine and the corresponding loading plate pad in the same direction are connected by a tensile connection device. When applying compressive stress, there is no need to glue the rock sample to the side loading plate. The push head of the testing machine pushes the corresponding side loading plate toward the center of the rock sample through the loading plate pad to transmit the pressure to the rock sample. S3. After the loading test and data collection are completed, turn off the testing machine, remove the fixture and take out the rock sample.

8. The deep hard rock tension and compression true triaxial fixture experimental method according to claim 7 is characterized in that: In S1, the splicing method of the tension and compression true triaxial fixture includes the following steps: Place the rock sample on the upper right of the lower loading plate, and then place the lower left of the upper loading plate on the rock sample, place a side loading plate on the left side of the rock sample, and align the lower end of the side loading plate with the left edge of the lower loading plate, align the upper end with the left edge of the upper loading plate, and the upper end is flush with the upper surface of the upper loading plate, and tighten the fixing bolts on 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, and 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 sample, align the lower end of the side loading plate with the front edge of the lower loading plate, flush the upper end of the side loading plate with the upper surface of the upper loading plate, and make the inner plate surface of the side loading plate fit the end of the upper loading plate. The upper and lower ends of the two installed side loading plates are flush. In the above manner, fix the side loading plate to the upper loading plate and the lower loading plate by 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 above manner, the side loading plate is fixed to the upper loading plate and the lower loading plate by means of 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, and the upper and lower ends of the third side loading plate are flush with those of the fourth side loading plate.

9. The deep hard rock tension and compression true triaxial fixture experimental method according to claim 7 is characterized in that: In S2, when compressive stress is applied to the rock sample, the test machine pusher applies compressive stress. When tensile stress is applied to the rock sample, the test machine pusher is controlled by displacement control. In the tensile-compression true triaxial test, the rock sample has four conditions, and the methods for applying tension / pressure are as follows: When the rock specimen is under compression in two directions and tension in one direction: firstly, apply the maximum compressive stress and the intermediate compressive stress in two directions respectively, so that the compressive stress applied in the two directions reaches the intermediate compressive stress at the same time; secondly, apply tensile stress in the other direction; finally, continue to load the maximum compressive stress in the direction where the maximum compressive stress is applied until the specimen is destroyed; When the rock specimen is subjected to tension in two directions and compression in one direction: first apply the maximum compressive stress in one direction; Secondly, apply intermediate tensile stress and minimum tensile stress in the other two directions respectively, so that the two directions where tensile stress is applied reach the minimum tensile stress at the same time, and continue to apply intermediate tensile stress in the direction where intermediate tensile stress is applied; finally, continue to load the maximum compressive stress in the direction where maximum compressive stress is applied until the sample is destroyed; When the rock sample is subjected to three-way tension: the maximum tensile stress, the intermediate tensile stress and the minimum tensile stress are applied in the three directions at the same time, so that the minimum tensile stress is reached in the three directions at the same time; the intermediate tensile stress and the maximum tensile stress are continued to be applied in the direction 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, the maximum tensile stress is continuously applied in the direction where the maximum tensile stress is applied until the sample is destroyed; When the rock specimen is subjected to three-way compression: the maximum compressive stress, intermediate compressive stress and minimum compressive stress are applied in three directions at the same time, so that the minimum compressive stress is reached in the three directions at the same time; the intermediate compressive stress and the maximum compressive stress are continued to be applied in the direction 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, the maximum compressive stress is continued to be applied in the direction where the maximum compressive stress is applied until the specimen is destroyed.

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