A simulation test method for studying different disturbance degrees of a working face rock burst

Abstract

The present application belongs to the field of rock mechanics and tunnel engineering, and discloses a method for simulating rock burst of a working face with different disturbance degrees, comprising the following steps: drilling a non-through circular hole in the center of an in-situ rock mass to obtain a rock sample with a simulated working face; performing dynamic impact treatment on the simulated working face of different rock samples, taking the P-wave velocity of the simulated working face as a quantitative index, and obtaining rock samples of simulated working faces with different disturbance degrees; supporting the non-through circular hole walls of the rock samples of simulated working faces with different disturbance degrees, and obtaining a plurality of simulated working face rock samples with support structures; and performing stress disturbance on the plurality of simulated working face rock samples with support structures to induce rock burst of the simulated working face. The present application can simulate the disturbance and damage effects of blasting excavation on the surrounding rock of the working face, and provides an effective simulation test method for the mechanism research and prevention of rock burst of the working face induced by blasting disturbance of deep hard rock underground caverns.

Description

Technical Field

[0001] This invention belongs to the fields of rock mechanics and tunnel engineering, and specifically relates to a method for simulating rockburst at the tunnel face to study different degrees of disturbance. Background Technology

[0002] With the continuous advancement of underground engineering, the construction scale of underground cavern projects in deep hard rock (such as highway tunnels, railway tunnels, and inter-basin water diversion tunnels) continues to expand. Rockburst disasters have become a core problem restricting the safe construction of these projects. In recent years, rockbursts have occurred not only at the tunnel walls in developed areas after excavation of underground caverns in deep hard rock, but also frequently at the working face. Compared with conventional tunnel wall rockbursts, rockbursts at the working face are more sudden and have a wider destructive range. They can directly damage tunneling equipment, threaten the lives of construction workers, and significantly delay the construction period. This is a key technical bottleneck that urgently needs to be solved in the construction of deep hard rock tunnels.

[0003] Currently, the mainstream excavation methods for deep hard rock tunnels are divided into two categories: mechanical excavation (using TBMs, cantilever tunneling machines, etc.) and drill-and-blast excavation. Among them, the drill-and-blast method, with its advantages of high rock breaking efficiency, strong geological adaptability, and low overall cost, is widely used in typical deep-buried hard rock projects such as the Jinping Hydropower Station water diversion tunnel, the Sangzhuling Tunnel, and the Ping'an Tunnel of the Chengdu-Lanzhou Railway. The blasting shock waves and stress waves generated by the drill-and-blast construction will continuously act on the surrounding rock at the tunnel face, causing the initiation, expansion, and connection of microcracks inside the rock mass. At the same time, the excavation unloads the rock mass into a three-dimensional high-stress state. The rapid transition to a two-dimensional stress state under open air, coupled with the dual effects, weakens the mechanical properties of the surrounding rock, forming an excavation damage zone. On-site acoustic monitoring data confirms that the P-wave velocity of the rock mass in the blasting disturbance area decreases significantly. On-site statistical data shows that the vast majority of strain-type rockbursts at the tunnel face occur within the surrounding rock damage zone formed by blasting excavation. The occurrence and development of rockbursts at the tunnel face are strongly coupled with the degree of excavation disturbance. Taking the Sangzhuling Tunnel as an example, rockbursts at the tunnel face account for as much as 40%, and 88.2% of the rockbursts at the tunnel face occur within a few hours after the blasting excavation exposure.

[0004] Currently, existing indoor rockburst simulation tests mostly use prefabricated through-hole or non-through-hole rock samples to simulate the tunnel space structure. These tests can only reproduce the stress failure process of the surrounding rock under conditions without excavation disturbance, and cannot reproduce the differentiated disturbance damage effects at the tunnel face caused by drilling and blasting operations. Specifically, different amounts of explosives and blasting depths will result in completely different degrees of surrounding rock disturbance damage. If indoor tests ignore the excavation disturbance variable, the test results will deviate significantly from the actual field engineering situation, making it difficult to accurately reveal the true disaster-causing mechanism of rockburst at the tunnel face. Therefore, it is urgent to develop an indoor simulation test method that can controllably prepare tunnel face samples with different degrees of excavation disturbance, simultaneously simulate tunnel wall support, and accurately induce rockbursts. This would compensate for the deficiencies of existing test technologies and provide complete and reliable indoor test technology support for the research on the mechanism of rockburst induced by disturbance at the tunnel face in deep hard rock tunnels and for disaster prevention and control. Summary of the Invention

[0005] To address the technical problems existing in the prior art, this invention provides a method for simulating rockburst at the working face under different disturbance levels, in order to solve the technical problem that existing indoor rockburst simulation tests can only reproduce the stress failure process of the surrounding rock under conditions without excavation disturbance, and cannot reproduce the differentiated disturbance damage effect at the working face caused by drilling and blasting operations.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for simulating rockburst at a working face under different disturbance levels, comprising: Non-penetrating circular holes were drilled in the center of the rock blocks at the site to simulate the working face structure after the excavation of the target underground cavern, and rock samples with simulated working faces were obtained. Dynamic impact treatment was applied to simulated working faces of different rock samples, and the P-wave velocity of the simulated working face was used as a quantitative index to obtain simulated working face rock samples with different degrees of disturbance. The walls of non-penetrating circular holes in simulated tunnel face rock samples with different degrees of disturbance were supported to simulate the tunnel wall support structure after the excavation of the target underground cavern, and several simulated tunnel face rock samples with support structures were obtained. Initial in-situ stress loading and stress disturbance were applied to several simulated working face rock samples with support structures to induce rockburst at the simulated working face.

[0007] Furthermore, the process of dynamically impacting the simulated tunnel face of different rock samples is as follows: First, place the non-penetrating circular hole of the rock sample with the opening facing upwards; then, place a metal shim and a rubber shim at the bottom of the non-penetrating circular hole of the rock sample in sequence; next, insert a circular tube of a preset size into the non-penetrating circular hole of the rock sample; then, use a cylindrical metal block to fall freely along the circular tube of a preset size to impact the bottom of the non-penetrating circular hole of the rock sample.

[0008] Furthermore, the degree of disturbance of the simulated face rock sample was characterized by the excavation disturbance factor; the excavation disturbance factor was calculated based on the P-wave velocity of the simulated face.

[0009] The calculation process for the excavation disturbance factor is as follows:

[0010] in, For excavation disturbance factors; The final P-wave velocity of the working face after dynamic impact; The initial P-wave velocity of the working face was simulated before dynamic impact.

[0011] Furthermore, epoxy resin reinforced with polypropylene fibers is used to support the walls of non-through circular holes.

[0012] Furthermore, the polypropylene fiber reinforced epoxy resin is made by mixing epoxy resin, curing agent and polypropylene fiber.

[0013] Furthermore, the initial in-situ stress loading process was carried out on several simulated tunnel face rock samples containing support structures, as follows: Based on the field stress test results or burial depth of the target underground cavern, determine the initial geostress conditions of the target underground cavern; Based on the initial geostress conditions of the target underground cavern, three-dimensional static loading is applied to the pre-acquired on-site rock blocks to bring the on-site rock blocks into the initial geostress state.

[0014] Furthermore, based on the predetermined stress path for inducing rockburst at the working face, stress disturbances were applied to several simulated rock samples with support structures at the working face to induce rockburst at the simulated working face; among them, the predetermined stress path for inducing rockburst at the working face included a unidirectional stress adjustment path strategy and a bidirectional stress adjustment path strategy.

[0015] Furthermore, the unidirectional stress adjustment path strategy is as follows: keep the horizontal lateral stress and horizontal axial stress constant, and monotonically increase the vertical stress.

[0016] Furthermore, the two-way stress adjustment path strategy is as follows: keep the horizontal axial stress constant, and monotonically increase the horizontal lateral stress and the vertical stress.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a simulation test method for studying rockburst at the tunnel face under different disturbance levels. This method can realistically simulate the disturbance and damage effects of blasting excavation on the surrounding rock at the tunnel face, providing an effective simulation test method for studying and preventing rockbursts induced by blasting disturbance in deep hard rock underground caverns. Specifically, by drilling non-penetrating circular holes in the center of the rock blocks at the actual tunnel face, the constraint morphology of the unexcavated rock mass is restored. Based on dynamic impact simulation of the damage effect of drilling and blasting stress waves on the surrounding rock, and by converting the excavation disturbance factor according to the P-wave velocity, the degree of disturbance can be quantitatively controlled. This method allows for the batch preparation of parallel samples with multi-gradient disturbance. Subsequently, a simulated support layer is applied to the inner wall of the hole to restore the constraint effect of on-site support on the surrounding rock, avoiding the problem of unsupported tunnels. The model exhibits distorted failure patterns. By applying initial ground stress and stress disturbance, the entire process of rockburst induced by stress redistribution in the surrounding rock under high ground stress is reproduced. This fully covers the influencing factors of the entire process, including ground stress occurrence, blasting disturbance, tunnel support, and stress-induced disaster. It can independently control the single variable of excavation disturbance to conduct comparative experiments, accurately quantifying the intrinsic relationship between the intensity of disturbance and the timing, scale of damage, and energy release characteristics of rockburst at the tunnel face. This fills the technical gap in existing indoor rockburst tests that cannot quantitatively simulate blasting excavation disturbance. The obtained experimental data is more consistent with actual on-site engineering conditions, providing repeatable and standardized indoor experimental support for the analysis of rockburst mechanisms at the tunnel face of deep-buried tunnels, the optimization design of support, and the development of rockburst prevention and control measures. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A flowchart of a method for simulating rockburst at a tunnel face under different disturbance levels, provided as an example; Figure 2 This is a schematic diagram illustrating the principle of dynamic impact treatment of a simulated working face of a rock sample in the embodiment. Figure 3 This is a flowchart illustrating how simulated face rock samples with different degrees of disturbance are obtained using the P-wave velocity of the simulated face as a quantitative indicator in an embodiment. Figure 4 This is a schematic diagram illustrating the principle of measuring the P-wave velocity at the working face in this embodiment. Figure 5 This is a flowchart illustrating the process of supporting the walls of non-penetrating circular holes in simulated rock samples at working faces with varying degrees of disturbance, as described in the embodiments. Figure 6 This is a schematic diagram illustrating the principle of the unidirectional stress adjustment path strategy in the embodiment; Figure 7 This is a schematic diagram illustrating the principle of the bidirectional stress adjustment path strategy in the embodiment. Detailed Implementation

[0020] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0021] This invention provides a method for simulating rockburst at a working face under different disturbance levels, comprising the following steps: Step 100: Drill a non-penetrating circular hole in the center of the rock block at the site to simulate the working face structure after the excavation of the target underground cavern, and obtain a rock sample with the simulated working face.

[0022] Step 200: Dynamic impact treatment is performed on the simulated working face of different rock samples, and the P-wave velocity of the simulated working face is used as a quantitative index to obtain simulated working face rock samples with different degrees of disturbance.

[0023] Step 300: Support the non-penetrating circular hole walls in simulated face rock samples with different degrees of disturbance to simulate the tunnel wall support structure after the excavation of the target underground cavern, and obtain several simulated face rock samples with support structures.

[0024] Step 400: Initial in-situ stress loading and stress disturbance are applied to several simulated working face rock samples with support structures to induce rockburst at the simulated working face.

[0025] The above embodiments can simulate the excavation disturbance caused to the surrounding rock at the tunnel face by blasting excavation in deep-buried hard rock tunnels, and fully consider the key influencing factors of rockburst induced by blasting excavation at the tunnel face. Specifically, by drilling non-penetrating circular holes in the center of the rock blocks on site, the geometric configuration of the non-penetrating circular holes is used to realistically reproduce the free mechanical state of the tunnel face after excavation, where three-dimensional stress is transformed into two-dimensional stress. Controllable dynamic impact treatment is applied to the simulated tunnel face, and the process of microcrack initiation and propagation caused by blasting shock waves and stress waves on the surrounding rock during drilling and blasting construction is directly reproduced by adjusting the impact energy. The P-wave velocity is used as a quantitative indicator to accurately calibrate different The degree of disturbance establishes a mapable correspondence between the experimental damage variables and on-site construction parameters such as blasting charge and advance. Supporting the borehole wall simulates the constraint effect of the on-site tunnel wall support structure on the surrounding rock deformation, ensuring that the stress field distribution inside the sample is consistent with the actual engineering situation. Rockburst is induced through initial ground stress loading and stress disturbance. Since the previous dynamic impact has already formed a real excavation damage zone in the tunnel face area, the rockburst initiation location, energy release scale, and failure mode are all directly controlled by the degree of disturbance. This provides an effective simulation test method for revealing the intrinsic connection and induction mechanism between rockburst at the tunnel face and the degree of excavation disturbance.

[0026] The following specific embodiments further explain the method for simulating rockburst at the working face under different disturbance levels provided by the present invention: Example This embodiment provides a method for simulating rockburst at the tunnel face under different disturbance levels. It addresses the technical shortcomings of existing indoor rockburst tests that cannot quantitatively simulate the differentiated disturbance damage to the surrounding rock at the tunnel face caused by drilling and blasting. It fully recreates the entire process of deep hard rock tunnels from the original high ground stress, blasting disturbance, tunnel wall support to stress disturbance-induced rockburst, and realizes the standardized preparation of samples with multiple levels of disturbance and control rockburst tests.

[0027] As attached Figure 1 As shown in Example 1, the method for simulating rockburst at the working face under different disturbance levels includes the following steps: Step 1: Drill a non-penetrating circular hole in the center of the rock block at the site to simulate the working face structure after the excavation of the target underground cavern, and obtain a rock sample with the simulated working face.

[0028] Explanatoryly, in step 1, a non-penetrating circular hole is drilled in the center of the rock block at the site to simulate the working face structure after the excavation of the target underground cavern. This constructs a physical test model that is consistent with the boundary conditions of the working face of the underground cavern at the site, solving the problem that conventional through-hole specimens cannot reproduce the constraint effect of the unexcavated rock mass in front of the working face.

[0029] The field rock block refers to a complete, representative surrounding rock block without primary fissures or weathering damage, collected from a deep hard rock engineering site with a tendency for rockbursts. The mechanical parameters and mineral composition of the rock block are completely consistent with the surrounding rock of the tunnel on site, which can eliminate the test error caused by the difference in sample materials. The non-penetrating circular hole refers to a circular hole that does not penetrate the entire cubic sample. The complete rock mass on the side where the hole is not penetrated is the simulated working face, and the hole space simulates the free face of the tunnel excavation.

[0030] It should be noted that, based on the geomechanical logic of deep tunnel engineering, there is always a certain thickness of undisturbed primary rock mass in front of the tunnel face during the excavation of the underground cavern. This rock mass forms a three-dimensional constraint on the surrounding rock of the free face. When a through-hole sample is used, both sides of the hole are free faces, and the constraint conditions of the rock mass in front of the tunnel face are completely missing. During the test, the stress evolution of the surrounding rock and the crack propagation path deviate fundamentally from the actual situation on site. Therefore, a non-through-hole structure is used in step 1.

[0031] For example, granite was selected as the test site rock in the engineering application. A standard cubic specimen was processed using a rock carving machine and a diamond drill. The specimen's dimensions were 100mm × 100mm × 100mm (length × width × height). All six surfaces of the cubic specimen were finely sanded to a smoothness that met the standards of the International Society for Rock Mechanics, eliminating local stress concentration caused by surface scratches. A circular hole was drilled vertically at the geometric center of a single face of the cubic specimen. The diamond drill bit diameter was 36mm, and the pre-drilling depth was 43mm. After drilling, the inner wall of the hole and the working face area at the bottom of the hole were finely sanded using a rock carving machine. The final hole depth was 45mm and the diameter was 38mm. The 45mm thick rock mass at the bottom of the hole served as the simulated working face, completely replicating the spatial geometry of the tunnel excavation face on site.

[0032] It should be noted that after processing, the samples are inspected. If the samples have defects such as chipped edges, internal original cracks, or uneven inner walls of holes, they are directly rejected. Only complete and undamaged samples are retained for subsequent testing procedures. This avoids the interference of sample defects on the quantification of rockburst test results.

[0033] Step 2: Dynamic impact treatment was performed on the simulated working face of different rock samples, and the P-wave velocity of the simulated working face was used as a quantitative index to obtain simulated working face rock samples with different degrees of disturbance.

[0034] Explanatoryly, in step 2, dynamic impact treatment is performed on the simulated working face of different rock samples to simulate the impact damage effect of blasting stress waves on the surrounding rock of the working face during drilling and blasting construction. At the same time, a unified and quantifiable evaluation standard for the degree of disturbance is established, and multiple sets of test samples with different disturbance gradients are prepared in batches to provide a sample basis for single-variable control rockburst tests.

[0035] Dynamic impact treatment refers to simulating the working face by impacting the bottom of a hole with a free-falling metal weight, creating controllable microcrack damage inside the rock mass, which is equivalent to simulating the impact load generated by on-site explosive blasting. P-wave velocity refers to the propagation speed of longitudinal sound waves inside the rock medium. The more microcracks and the higher the degree of damage inside the rock mass, the more severe the obstruction of the sound wave propagation path, and the lower the measured P-wave velocity value. Therefore, the change in P-wave velocity can intuitively reflect the degree of rock mass disturbance damage. Simulated working face rock samples with different degrees of disturbance refer to multiple sets of parallel samples with only differences in the degree of working face damage, while the other geometric dimensions, lithology, and integrity are completely consistent, ensuring that the subsequent rockburst test only has the single variable of excavation disturbance.

[0036] Based on the fundamental principle of sound wave propagation in rocks, the sound wave propagation speed inside a complete and dense rock mass is stable. When an external impact load induces a large number of microcracks inside the rock mass, the sound waves will be reflected, refracted, and scattered at the crack interface during propagation, increasing the sound wave propagation loss. The measured longitudinal wave velocity decreases significantly, and the wave velocity attenuation amplitude is monotonically positively correlated with the degree of rock mass disturbance damage. Therefore, selecting the P-wave velocity as a quantitative indicator of the degree of disturbance has sufficient physical basis. Compared with indirect indicators such as stress and deformation, sound wave testing has the advantages of being non-destructive, repeatable, and easy to operate, and will not cause secondary damage to the sample.

[0037] For example, before the test, the initial P-wave velocity of all unimpacted original samples is tested at the working face. Four sets of symmetrical measuring points are marked at the bottom of the working face area at the bottom of the hole, and Vaseline is applied to the measuring points to eliminate the air gap between the probe and the rock contact surface. The active pulse function of the acoustic emission monitoring system is used to measure the wave velocity in two directions respectively, and the average value is taken as the initial wave velocity of the sample. Then, each sample is subjected to dynamic impact alone. After a single impact, it is left to stand for 5 minutes to allow the stress inside the rock mass to be released. The P-wave velocity of the working face is measured again. The degree of disturbance is calculated by the change in wave velocity. If the preset disturbance gradient is not reached, the impact operation is repeated until the sample disturbance index meets the design requirements. By controlling the number of impacts and the drop height of the hammer, multiple sets of parallel samples with different disturbance gradients of low, medium and high can be prepared. At least 3 parallel samples are prepared for each disturbance gradient to reduce the random error of the test and ensure that the test data has statistical reference value.

[0038] In one possible implementation, as shown in the appendix Figure 2 As shown, the process of dynamic impact treatment on the simulated working face of different rock samples is as follows: First, the opening of the non-penetrating circular hole of the rock sample is placed upward; then, a metal shim and a rubber shim are placed at the bottom of the non-penetrating circular hole of the rock sample in sequence; next, a circular tube of a preset size is inserted into the non-penetrating circular hole of the rock sample; then, a cylindrical metal block is used to fall freely along the circular tube of a preset size to impact the bottom of the non-penetrating circular hole of the rock sample.

[0039] In this embodiment, the metal pad is a hard metal circular thin sheet, used to uniformly distribute the impact load of the falling hammer and avoid local brittle fracture of the working face caused by local point load; the rubber pad is a high-elasticity hard rubber circular thin sheet, used to buffer the instantaneous impact peak of the falling hammer and simulate the load characteristics of the on-site blasting stress wave being smoothly transmitted to the surrounding rock; the pre-sized circular tube is a PVC transparent hard circular tube, which serves as a falling hammer guide and constraint component, limiting the horizontal deviation of the falling hammer and ensuring that the impact load acts vertically on the center of the working face; the cylindrical metal block is an alloy steel solid falling hammer, which generates impact kinetic energy by falling freely under its own gravity, equivalently simulating the blasting shock wave load.

[0040] Explanatoryly, if a metal drop hammer is used to directly impact the rock at the bottom of the hole, the instantaneous concentrated impact load will cause the entire rock mass at the working face to collapse instantly, making it impossible to create uniform and controllable micro-crack damage and achieve low-gradient small-amplitude disturbance control; using rubber pads alone is not rigid enough, and the impact load energy is excessively lost, making it difficult to form effective damage cracks inside the rock mass; by setting a pre-sized circular tube, the trajectory of the cylindrical metal block can be constrained, preventing the cylindrical metal block from impacting the tube wall and generating lateral force, ensuring that all impact kinetic energy acts perpendicularly to the geometric center of the simulated working face, making the damage area of ​​the working face uniform and symmetrical, and ensuring a uniform distribution of disturbance damage for samples in the same batch.

[0041] For example, in actual operation, the metal gasket is 1.5mm thick and 37mm in diameter, and the rubber gasket is 2mm thick and 37mm in diameter. The diameters of the metal and rubber gaskets are smaller than the inner diameter of the non-through circular hole, allowing them to be placed stably at the bottom of the hole and fully fit the working face. The pre-sized circular tube is 2m long, 30mm in outer diameter, and 28mm in inner diameter, and is fully inserted into the circular hole and fixed vertically. The cylindrical metal block has a diameter of 22mm, a length of 200mm, and a total mass of 600g. During each impact operation, the center of gravity of the cylindrical metal block is released at the same level as the upper end of the circular tube to ensure a uniform drop height and reduce the difference in impact kinetic energy between parallel samples. If the gasket is deformed or damaged after multiple impacts, a brand new gasket is immediately replaced before continuing the impact operation to avoid uncontrolled disturbance caused by changes in buffer conditions.

[0042] In this embodiment, by using layered buffer pads in combination with a vertically guided drop hammer impact structure, controllable microcrack damage can be generated precisely and uniformly inside the simulated tunnel face, avoiding the overall destruction of the sample caused by single-point concentrated impact, achieving fine gradient control of the excavation disturbance degree, ensuring the consistency of disturbance damage distribution of multiple sets of parallel samples, and providing a standardized disturbance preparation method for subsequent quantitative comparison tests.

[0043] In one possible implementation, the degree of disturbance of the simulated face rock sample is characterized by an excavation disturbance factor; wherein the excavation disturbance factor is calculated based on the P-wave velocity of the simulated face.

[0044] Explanatoryly, the excavation disturbance factor is a dimensionless quantitative evaluation index, calculated based on the difference in measured P-wave velocity at the working face before and after impact disturbance, directly quantifying the degree of mechanical damage caused by the development of microcracks inside the rock mass; the P-wave velocity is the longitudinal wave propagation speed of sound waves, which is non-destructively measured by an active acoustic emission testing system, without causing secondary damage to the sample; by controlling the number of impacts to adjust the excavation disturbance factor to the preset target value, samples of different disturbance levels can be prepared in batches.

[0045] Specifically, the calculation process for the excavation disturbance factor is as follows:

[0046] in, For excavation disturbance factors; The final P-wave velocity of the working face after dynamic impact; The initial P-wave velocity of the working face was simulated before dynamic impact.

[0047] Explanatoryly, the propagation speed of sound waves in an elastic medium is proportional to the square root of the rock mass's elastic modulus. After the rock mass is disturbed and damaged, the elastic modulus decreases, and the wave velocity decreases synchronously. The excavation disturbance factor calculation formula uses the square term of the wave velocity ratio, which matches the attenuation law of the rock mass's elastic modulus. This can better fit the constitutive relationship of rock mechanical damage evolution, and is more sensitive to weak disturbance damage in the rock mass. It can accurately identify low-level small disturbance differences and is suitable for the preparation of refined gradient samples.

[0048] In one possible implementation, as shown in the appendix Figure 3 As shown, the process of obtaining simulated face rock samples with different degrees of disturbance, using the P-wave velocity of the simulated face as a quantitative index, is as follows: First, measure the initial P-wave velocity at the tunnel face. (See attached image) Figure 4 As shown, the specific implementation principle for measuring the initial P-wave velocity at the tunnel face is as follows: Mark the acoustic wave test positions on the sample. With the orifice of the sample containing the non-penetrating circular hole facing the tester, mark the position 5 mm away from the bottom of the non-penetrating circular hole using a marker pen. The marked positions are 50 mm away from the orifice of the sample (the pre-made circular hole depth is 45 mm, and there are 4 marks on the top, bottom, left and right of the sample). Next, apply Vaseline to the 4 marked positions 50 mm away from the orifice of the sample, and fix the acoustic emission probes at symmetrical positions in the top and bottom and left and right directions of the sample, with the top and bottom and left and right directions forming a group. Then, use the active excitation pulse function of the DS2-8B acoustic emission monitoring system to determine the P-wave velocity of the simulated working face before treatment. The average value (v0) of the two groups of test results (top and bottom and left and right) is used as the initial P-wave velocity of the working face of the sample.

[0049] Next, dynamic impact was used to treat the bottom of the non-penetrating circular granite hole to simulate the disturbance and damage effect of blasting on the surrounding rock at the working face.

[0050] Next, the wave velocity at the tunnel face after dynamic impact is measured. It should be noted that the principle for measuring the wave velocity at the tunnel face after dynamic impact is similar to the principle for measuring the initial P-wave velocity at the tunnel face. The specific implementation principle is as follows: After the impact ends, wait 5 minutes before measuring the wave velocity in both directions. The average of the up-down and left-right test results is then used. v d The final wave velocity of the test specimen face after dynamic impact is used as the final wave velocity. The excavation disturbance factor value of the test specimen face is calculated using the average wave velocity before and after dynamic impact. It is determined whether the calculated value of the excavation disturbance factor meets the requirements. If the excavation disturbance factor value does not reach the set value, the above impact operation is repeated. If the excavation disturbance factor value reaches the set value, the impact is stopped. Since it is difficult to accurately apply a fixed disturbance increment in dynamic impact, and there is a certain error in wave velocity measurement, if the deviation between the excavation disturbance factor value of the test specimen after impact and the set value does not exceed 0.02, it is considered to meet the requirements.

[0051] Step 3: Support the non-penetrating circular hole walls in simulated face rock samples with different degrees of disturbance to simulate the tunnel wall support structure after the excavation of the target underground cavern, and obtain several simulated face rock samples with support structures.

[0052] Explanatoryly, step 3 involves pouring a simulated support layer into the inner wall of the precast borehole to replicate the restraining effect of the sprayed fiber concrete support on the surrounding rock after the tunnel excavation is completed, thus solving the problem of the disconnect between the existing test model without support and the actual engineering conditions. Here, the non-through circular borehole wall refers to the entire inner rock surface of the precast circular borehole; the borehole wall support structure refers to the initial sprayed fiber concrete support applied in a timely manner after the deep tunnel excavation, used to limit the propagation of cracks in the surrounding rock and share the stress of the surrounding rock; the simulated tunnel face rock sample with support structure refers to a complete test sample with a pre-cast support layer on the inner wall of the borehole and the tunnel face having pre-set excavation disturbance damage.

[0053] In one possible implementation, polypropylene fiber-reinforced epoxy resin is used to support the walls of non-penetrating circular holes. Specifically, polypropylene fiber-reinforced epoxy resin is uniformly poured onto the entire inner wall of the non-penetrating circular holes, and after curing, a continuous and complete simulated initial support layer is formed. Polypropylene fiber-reinforced epoxy resin is selected as the simulated support material, taking into account the ease of molding, mechanical similarity, and bonding performance with the surrounding rock. This accurately reproduces the restraint and toughening effect of on-site fiber-reinforced shotcrete support, eliminates experimental deviations caused by missing support structures, and improves the similarity between indoor tests and on-site engineering conditions.

[0054] Optionally, the polypropylene fiber reinforced epoxy resin is composed of epoxy resin, curing agent and polypropylene fiber; wherein, the epoxy resin is a VG327 type two-component epoxy matrix material, which is the bonding substrate of the support composite material; the curing agent is a special curing agent for epoxy resin, which undergoes a cross-linking reaction after being mixed with epoxy resin to achieve room temperature curing; the polypropylene fiber is a short-cut artificial synthetic fiber with a length of 3mm, used to improve the tensile toughness and crack resistance of the composite material after curing.

[0055] Explanatoryly, pure epoxy resin is brittle after curing and is prone to penetrating cracks under the stress of surrounding rock, making it unable to simulate the toughening effect of in-situ fiber-reinforced concrete support. After adding polypropylene fibers with a fixed volume ratio, the fibers are randomly and interwoven inside the matrix, which can bridge microcracks inside the cured body, improve the ductility and anti-stripping ability of the support layer, and match the mechanical characteristics of in-situ fiber-reinforced shotcrete. Preferably, the volume ratio of epoxy resin to curing agent is 2:1, and polypropylene fibers are uniformly added to the mixing system at a volume ratio of 1.0%. First, the epoxy resin and curing agent are accurately measured with a measuring cup and a dropper and thoroughly stirred. Then, the short-cut polypropylene fibers are added and stirred for 10 minutes to ensure that the fibers are not agglomerated and are uniformly dispersed. After stirring, the mixture is allowed to stand at room temperature for 5 minutes to release the tiny air bubbles inside the mixture before the hole wall pouring operation is carried out to avoid the formation of pore defects inside the support layer.

[0056] For example, see attached Figure 5 As shown, the process of supporting the walls of non-penetrating circular holes in simulated rock samples of different disturbance levels is as follows: Before formally pouring the support material, the integrity of the samples after the disturbance and impact was checked, and samples with cracks or damage were directly discarded. A 0.5mm thick layer of paraffin wax was evenly applied to the bottom of the hole as a release agent to prevent the support material from sticking to the rock matrix after curing and making it impossible to demold. A silicone tube with an outer diameter of 31mm, an inner diameter of 25mm, and a length of 50mm was selected as the support molding mold. A 25mm diameter and 60mm long round wooden core was inserted into the silicone tube for support to ensure that the thickness of the support layer was uniform throughout the entire section after pouring. The prepared support composite material was slowly injected into the gap between the silicone tube and the rock hole wall through a dropper. After standing to remove the internal air bubbles, it was cured at a constant temperature. After curing, the silicone tube and wooden core were removed, and the excess support material overflowing from the hole opening was sanded with fine sandpaper. Finally, a uniform and continuous simulated support layer was formed, and a test sample with a complete support structure was obtained.

[0057] Step 4: Initial in-situ stress loading and stress disturbance are applied to several simulated working face rock samples with support structures to induce rockburst at the simulated working face.

[0058] Explanatoryly, stress disturbance refers to the process of continuously increasing the principal stress in a certain direction according to a preset stress path based on the three-dimensional static geostress of the sample, simulating the continuous intensification of stress concentration in the surrounding rock after on-site excavation; induced simulated rockburst at the working face refers to the process of increasing the energy storage of the surrounding rock through progressive loading. When the elastic strain energy of the rock mass exceeds the energy storage limit of the rock mass, the rock mass at the working face is instantly ejected and peeled off, forming a rockburst damage phenomenon that can be observed and recorded indoors.

[0059] It should be noted that, based on the theory of rockburst energy release, deep hard rock masses under high ground stress will store a large amount of elastic strain energy. After the tunnel excavation forms a free face, the stress of the surrounding rock continues to concentrate towards the tunnel face, and the elastic strain energy continues to accumulate. When the energy exceeds the rock mass strength threshold, the energy is released instantaneously in the form of rock mass bursting and ejection, which is the rockburst disaster. In this embodiment, the stress level of the surrounding rock is continuously increased through a controllable stress loading path, the timing of rockburst occurrence is precisely controlled, and experimental data such as rockburst failure mode, ejected block mass, and acoustic emission energy are recorded simultaneously. The differences in rockburst characteristics of samples with different degrees of disturbance are compared to achieve a quantitative study on the influence of excavation disturbance on rockburst.

[0060] In one possible implementation, the initial in-situ stress loading process is performed on several simulated tunnel face rock samples containing support structures, as follows: First, based on the on-site stress test results or burial depth of the target underground cavern, the initial geostress conditions of the target underground cavern are determined. Then, based on the initial geostress conditions of the target underground cavern, three-dimensional static loading is applied to the pre-acquired on-site rock blocks to bring the on-site rock blocks into the initial geostress state.

[0061] Interpretive terms include: initial geostress conditions, which refer to the naturally occurring three-dimensional principal stress values ​​of underground rock mass before excavation disturbance, including three sets of parameters: vertical principal stress, maximum horizontal principal stress, and minimum horizontal principal stress; field stress test results, which refer to the original geostress data of the tunnel surrounding rock obtained by in-situ testing methods such as in-situ hydraulic fracturing and stress relief methods; burial depth, which refers to the vertical depth of the tunnel face from the ground surface, and can be used to calculate approximate geostress values ​​using the formula for soil and rock self-weight stress; and three-dimensional static loading, which refers to the simultaneous application of constant compressive stress in three orthogonal directions to a cubic specimen using a true triaxial testing device to simulate the original three-dimensional stress constraint state of the underground rock mass.

[0062] For example, initial values ​​of the principal stresses in three directions (σ1>σ2>σ3) are set based on the results of the on-site ground stress test or the tunnel (cavity) burial depth (e.g., 500m or 1000m). For instance, when the initial ground stress is determined by the tunnel (cavity) burial depth, the initial stress of the test can be calculated by referring to the ground stress calculation expression to calculate the magnitude of the ground stress at the corresponding burial depth. Specifically, the ground stress calculation expression is as follows:

[0063] in, ρ is the vertical stress, MPa; h is the tunnel (cavity) burial depth; and These are the maximum and minimum horizontal principal stresses, respectively, in MPa.

[0064] The cured and demolded specimens with supports were placed inside a true triaxial rock mechanics loading test system. Three-dimensional synchronous loading was performed according to the preset initial geostress conditions, and the specimens were stabilized and static to eliminate instantaneous stress fluctuations during loading. Subsequently, stress disturbance was continuously applied according to the preset stress adjustment path. Throughout the process, an acoustic emission monitoring system, high-speed camera equipment, and stress-strain sensors were used to synchronously collect test data until typical rockburst failure phenomena such as rock mass ejection and spalling appeared at the working face. Loading was then stopped, and all test data for this specimen were completely recorded. The above loading test process was repeated for parallel specimens with each disturbance gradient. Multiple sets of parallel test data were combined to form a complete test dataset, which was used to analyze the correlation between the degree of excavation disturbance and various characteristic indicators of rockburst at the working face.

[0065] In one possible implementation, based on a predetermined stress path that induces rockburst at the working face, stress disturbances are applied to several simulated rock samples with support structures at the working face to induce rockburst at the simulated working face; wherein the predetermined stress path that induces rockburst at the working face includes a unidirectional stress adjustment path strategy and a bidirectional stress adjustment path strategy.

[0066] Specifically, before the experiment, two types of standardized stress loading paths were pre-selected based on the engineering geological structure characteristics. Stress disturbance loading was carried out for different structural stress conditions to gradually increase the energy storage capacity of the surrounding rock and induce rockburst at the working face. The unidirectional stress adjustment path strategy refers to a loading scheme in which the principal stress in only one direction is gradually increased while the other two principal stresses remain constant. The bidirectional stress adjustment path strategy refers to a loading scheme in which the two principal stresses are increased synchronously and monotonically while the remaining principal stress remains constant.

[0067] Explanatoryly, the distribution of structural stress fields varies significantly among different deep tunnel projects. In some tunnels, only vertical self-weight stress is continuously concentrated, while in others, vertical stress and horizontal structural stress increase simultaneously. A single loading path cannot cover all on-site conditions. By setting up two types of standardized stress adjustment paths, namely unidirectional and bidirectional, two typical structural stress disturbance conditions can be simulated respectively. This comprehensively analyzes the influence of the degree of excavation disturbance on rockburst at the tunnel face under different stress disturbance modes, and broadens the applicability of the test method.

[0068] In one possible implementation, as shown in the appendix Figure 6 As shown, the uniaxial stress adjustment path strategy is as follows: keep the horizontal lateral stress and horizontal axial stress constant, and monotonically increase the vertical stress.

[0069] Specifically, after the initial three-dimensional geostress synchronous loading is completed and stabilized, the two sets of parameters, horizontal lateral principal stress and horizontal axial principal stress, are locked and remain unchanged throughout the process. Only the vertical principal stress is continuously and monotonically increased in stages until rockburst failure occurs at the working face. It should be noted that the horizontal lateral stress refers to the horizontal principal stress in the Y direction of the sample, corresponding to the minimum horizontal tectonic stress in the field; the horizontal axial stress refers to the horizontal principal stress in the X direction of the sample, corresponding to the maximum horizontal tectonic stress in the field; the vertical stress refers to the vertical principal stress in the Z direction of the sample, corresponding to the self-weight stress of the rock mass in the field; monotonous increase means that there is no unloading or stress fluctuation during the loading process, and the stress value is continuously increased at a uniform rate in stages.

[0070] Interpretive, unidirectional stress adjustment path strategy is used to simulate deep tunnel conditions where burial depth continuously increases and self-weight stress concentration dominates. Horizontal structural stress remains stable with no significant change, while only vertical self-weight stress continuously accumulates towards the tunnel face as excavation progresses. This is the most common stress disturbance mode in deep-buried mountain tunnels in western my country. During the loading operation, the three principal stresses are first simultaneously loaded to the preset initial ground stress value, and the pressure is stabilized and left to stand for 30 minutes to ensure uniform stress distribution inside the sample. Then, the stress in the X and Y directions is kept constant, and the vertical stress in the Z direction is continuously increased at a fixed stress rate. Stress, strain, acoustic emission, and high-speed camera data are collected synchronously throughout the process to record the critical vertical stress and failure characteristics at the moment of rock burst occurrence.

[0071] In one possible implementation, as shown in the appendix Figure 7 As shown, the two-way stress adjustment path strategy is as follows: keep the horizontal axial stress constant, and monotonically increase the horizontal lateral stress and the vertical stress.

[0072] Specifically, after initial three-dimensional geostress stabilization, the horizontal axial principal stress is kept constant throughout the process. Simultaneously, the horizontal lateral principal stress and the vertical principal stress are monotonically increased at a uniform rate in stages, continuously applying stress disturbances until rockburst failure occurs at the simulated working face. In the glossary section, the horizontal axial stress is the maximum horizontal tectonic stress in the X direction of the sample, which remains constant throughout; the horizontal lateral stress is the minimum horizontal tectonic stress in the Y direction; and the vertical stress is the self-weight stress in the Z direction. Both stresses are simultaneously and monotonically increased.

[0073] Interpretive, bidirectional stress adjustment path strategy is used to simulate deep tunnel conditions in tectonically active areas. After excavation, the self-weight stress and lateral tectonic stress are simultaneously and continuously concentrated. The two sets of stresses jointly drive the accumulation of elastic strain energy in the surrounding rock. This is commonly seen in water diversion tunnels and deep-buried underground powerhouse projects in high tectonic stress areas. During the loading process, the three principal stresses are first loaded synchronously to the initial ground stress stabilization. The horizontal axial stress value in the X direction is fixed, and the horizontal lateral stress in the Y direction and the vertical stress in the Z direction are simultaneously increased at the same loading rate. There is no unloading or stress return throughout the process. Stress disturbance is continuously applied, and complete rockburst test characteristic data are recorded simultaneously.

[0074] The method described in this embodiment for simulating rockburst at the tunnel face under different disturbance levels solves the problem of preparing simulated rockburst samples with different excavation disturbance levels. It can effectively simulate the disturbance and damage effect of blasting excavation on the surrounding rock of the tunnel face, and provides an effective simulation test method for the study and prevention of rockburst induced by blasting disturbance in deep hard rock tunnels.

[0075] In this embodiment, a physical model of the tunnel face is constructed by machining non-penetrating circular holes inside a complete hard rock block at the site. This accurately restores the spatial constraint relationship between the unexcavated rock mass and the exposed tunnel face, eliminates abnormal stress concentration caused by defects in artificial machining, and ensures a high degree of matching between the test model and the geometric boundary conditions of the surrounding rock at the site. Pre-treatment of the tunnel face is carried out by a free-fall dynamic impact method with a drop hammer, which can simulate the damage and disturbance effect of the stress wave of the drill-and-blast method on the surrounding rock. The excavation disturbance factor is quantitatively calculated based on the P-wave velocity to achieve controllable and adjustable disturbance degree. Multiple sets of differentiated disturbance samples are prepared in batches to realize a control test of the single variable of excavation disturbance. The hole wall support layer is cast with polypropylene fiber reinforced epoxy resin, which fully simulates the toughening and constraint effect of the shotcrete fiber support at the site, eliminating the test distortion problem caused by the lack of support structure. By simulating different structural stress disturbance conditions at the site through unidirectional and bidirectional differentiated stress loading paths, the complete evolution process of rockburst at the tunnel face induced by stress redistribution after unloading of deep tunnel excavation can be fully reproduced.

[0076] The method for simulating rockbursts at tunnel face under different disturbance levels described in this invention can accurately quantify the influence of excavation disturbance on the timing of rockburst incubation, failure mode, and energy release characteristics. It provides a standardized and repeatable indoor testing method for analyzing the disaster mechanism of rockbursts at the tunnel face during drilling and blasting construction of deep-buried hard rock tunnels, developing support optimization schemes, and constructing rockburst early warning systems. It is widely applicable to indoor test research on rockbursts in hard rock of various deep highways, railways, and water diversion tunnels.

[0077] The above embodiments are merely one of the implementation methods for achieving the technical solution of the present invention. The scope of protection claimed by the present invention is not limited to this embodiment, but also includes any variations, substitutions and other implementation methods that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention.

Claims

1. A method for simulating rockburst at a working face under different disturbance degrees, characterized in that, include: Non-penetrating circular holes were drilled in the center of the rock blocks at the site to simulate the working face structure after the excavation of the target underground cavern, and rock samples with simulated working faces were obtained. Dynamic impact treatment was applied to simulated working faces of different rock samples, and the P-wave velocity of the simulated working face was used as a quantitative index to obtain simulated working face rock samples with different degrees of disturbance. The walls of non-penetrating circular holes in simulated tunnel face rock samples with different degrees of disturbance were supported to simulate the tunnel wall support structure after the excavation of the target underground cavern, and several simulated tunnel face rock samples with support structures were obtained. Initial in-situ stress loading and stress disturbance were applied to several simulated working face rock samples with support structures to induce rockburst at the simulated working face.

2. The method for simulating rockburst at a working face under different disturbance degrees as described in claim 1, characterized in that, The process of dynamically impacting the simulated tunnel face of different rock samples is as follows: First, place the non-penetrating circular hole of the rock sample with the opening facing upwards; then, place a metal shim and a rubber shim at the bottom of the non-penetrating circular hole of the rock sample in sequence; next, insert a circular tube of a preset size into the non-penetrating circular hole of the rock sample; then, use a cylindrical metal block to fall freely along the circular tube of a preset size to impact the bottom of the non-penetrating circular hole of the rock sample.

3. The method for simulating rockburst at a working face under different disturbance degrees as described in claim 1, characterized in that, The degree of disturbance of the simulated face rock sample was characterized by the excavation disturbance factor, which was calculated based on the P-wave velocity of the simulated face.

4. The method for simulating rockburst at a working face under different disturbance degrees according to claim 4, characterized in that, The calculation process for the excavation disturbance factor is as follows: in, For excavation disturbance factors; The final P-wave velocity of the working face after dynamic impact; The initial P-wave velocity of the working face was simulated before dynamic impact.

5. The method for simulating rockburst at a working face under different disturbance degrees as described in claim 1, characterized in that, Polypropylene fiber-reinforced epoxy resin is used to support the walls of non-through circular holes.

6. The method for simulating rockburst at a working face under different disturbance degrees according to claim 6, characterized in that, Polypropylene fiber reinforced epoxy resin is made by mixing epoxy resin, curing agent and polypropylene fiber.

7. The method for simulating rockburst at a working face under different disturbance degrees as described in claim 1, characterized in that, The process of applying initial in-situ stress to several simulated tunnel face rock samples with support structures is as follows: Based on the field stress test results or burial depth of the target underground cavern, determine the initial geostress conditions of the target underground cavern; Based on the initial geostress conditions of the target underground cavern, three-dimensional static loading is applied to the pre-acquired on-site rock blocks to bring the on-site rock blocks into the initial geostress state.

8. The method for simulating rockburst at a working face under different disturbance degrees as described in claim 1, characterized in that, Based on a predetermined stress path for inducing rockburst at the working face, stress disturbances were applied to several simulated rock samples with support structures at the working face to induce rockburst at the simulated working face. The predetermined stress path for inducing rockburst at the working face included a unidirectional stress adjustment path strategy and a bidirectional stress adjustment path strategy.

9. A method for simulating rockburst at a working face under different disturbance degrees, as described in claim 8, characterized in that, The uniaxial stress adjustment path strategy is as follows: keep the horizontal lateral stress and horizontal axial stress constant, and monotonically increase the vertical stress.

10. A method for simulating rockburst at a working face under different disturbance degrees, as described in claim 8, characterized in that, The two-way stress adjustment path strategy is as follows: keep the horizontal axial stress constant, and monotonically increase the horizontal lateral stress and the vertical stress.

Images