An experimental device and method for simulating excavation unloading under in-situ stress state

Abstract

The present invention provides an experimental device and method for simulating excavation unloading under an in-situ stress state. The experimental device of the present invention includes a dual-axis four-directional electromagnetic Hopkinson bar system, a pressure relief system, and a data monitoring and control system. The dual-axis four-directional electromagnetic Hopkinson bar system is used to load a static load on a sample or simulate the impact load disturbance during tunnel excavation, as well as load, maintain, unload, and dynamically adjust the loading and unloading rate; the pressure relief system is used to accurately simulate the process of asynchronous excavation unloading in the real unloading process by controlling the pressure relief rate and unloading start time at different positions of the simulated tunnel inside the rock sample; the data monitoring and control system is used to control the dual-axis four-directional electromagnetic Hopkinson bar system and the pressure relief system, and record and store test data. The present invention also provides a method for simulating excavation unloading when the rock is in an in-situ stress state. The present invention can accurately control the unloading rate and simulate the complex working conditions of dynamic and static combined loading.

Description

Technical Field

[0001] The invention relates to the technical field of rock unloading characteristic research, and in particular to an experimental device and method for simulating excavation unloading under an in-situ stress state. Background Art

[0002] With the rapid economic development of my country, shallow coal resources are gradually exhausted, and coal mining is gradually advancing into the deep. Under the conditions of deep coal mining, the role of the in-situ environment is becoming more and more obvious. Deep tunnels and mining areas are not only subject to high static stresses such as the deadweight of the overlying rock strata, tectonic stress, and mining stress, but may also be affected by external dynamic disturbances such as mine earthquakes, mining in adjacent mining areas, and mechanical vibration. Deep coal and rock mining faces extremely complex stress states, and the difficulty of mining increases. Deep coal and rock excavation will change the stress state of tunnels and mining areas, and transfer and release part of the energy stored in the surrounding rock, resulting in the weakening of the strength and bearing capacity of the near-field surrounding rock and the increase of unstable blocks, making deep mineral resource mining a very challenging world problem. In addition, in actual engineering, the support of the tunnel is installed after excavation and unloading. There is a vacuum period when the support installation is not completed after tunnel excavation, which greatly increases the risk of impact damage to the tunnel. Therefore, it is urgent to study the unloading characteristics of rocks caused by excavation under complex in-situ stress states.

[0003] Indoor testing is an important means to study the properties of deep rock mass. Many scholars have conducted extensive research on the unloading characteristics of rock. Currently, most of the research on the unloading characteristics of rock mass is based on uniaxial compression, triaxial compression and dynamic impact experiments, that is, loading the rock to the initial stress state and unloading the confining pressure at a certain rate; or, under uniaxial or biaxial compression conditions, real-time drilling of the rock is carried out to study its excavation unloading characteristics. There are many defects and shortcomings:

[0004] (1) It is impossible to accurately simulate the actual unloading condition.

[0005] In the actual excavation process, unloading is often asynchronous and may occur in different directions at different time periods. In the triaxial confining pressure unloading experiment, the confining pressure in three directions is usually unloaded at the same time, resulting in a mismatch between the unloading process and the actual excavation process; real-time drilling simulates the process of gradual unloading, which is suitable for studying slow unloading conditions, but difficult to simulate rapid unloading, such as the instantaneous unloading process caused by blasting excavation, mining tremors, etc. This makes this method limited in studying the mechanical behavior of rocks under high unloading rates, especially the inability to accurately simulate the stress response and failure mechanism under dynamic loads.

[0006] (2) It is impossible to simulate the unloading stress environment under the dynamic and static combined loading state.

[0007] During deep coal and rock mining, the mechanical behavior of coal and rock becomes complicated due to the combined effects of high static loads and external dynamic loads. The existing uniaxial, triaxial and drilling experiments are mainly used to simulate static or quasi-static stress states and unload the confining pressure or drilling at a certain rate. However, the shock wave caused by mine earthquakes or blasting has a high strain rate, and it is difficult for the experiment to accurately reflect the mechanical response of coal and rock under such a high strain rate. In dynamic impact experiments, the loading time of existing dynamic impact experiments (such as the split Hopkinson bar) is extremely short, and the main focus is on the impact response of coal and rock under instantaneous dynamic loads, without considering the stress accumulation and transfer process of dynamic and static combined loading.

[0008] (3) The unloading rate is difficult to control accurately.

[0009] When the unloading process of rock is simulated by real-time drilling under uniaxial or biaxial compression conditions, the unloading rate is directly related to the drilling speed, but in actual operation, the drilling speed is often difficult to achieve accurate and controllable requirements. The speed of the drilling rig will be affected by factors such as rock strength, drill bit wear, and operating errors, resulting in uneven and unpredictable unloading rates, and the repeatability of real-time drilling unloading experiments is poor. Summary of the invention

[0010] In order to solve the problems in the prior art, the present invention provides an experimental device for simulating excavation unloading under an in-situ stress state, and also provides a method for simulating excavation unloading of rock under an in-situ stress state based on the experimental device for simulating excavation unloading under an in-situ stress state, thereby realizing the simulation of asynchronous excavation unloading conditions and the simulation of deep in-situ stress states.

[0011] The experimental device for simulating excavation unloading under in-situ stress state of the present invention comprises a biaxial four-directional electromagnetic Hopkinson bar system, a pressure relief system, and a data monitoring and control system.

[0012] The dual-axis four-way electromagnetic Hopkinson bar system is used to load static loads on the specimen or simulate impact load disturbances during tunnel excavation, as well as load, maintain, unload, and dynamically adjust loading and unloading rates;

[0013] The pressure relief system is used to accurately simulate the process of asynchronous excavation and unloading in the real unloading process by controlling the pressure relief rate and unloading start time at different positions of the simulated tunnel inside the rock sample;

[0014] The data monitoring and control system is used to control the dual-axis four-way electromagnetic Hopkinson bar system and the pressure relief system, and record and store test data;

[0015] The pressure relief system includes a pressure relief cylinder, a pressure box, an oil pipeline and a pressure detection element, wherein the pressure box includes fixed brackets arranged at both ends, a frame arranged between the two fixed brackets and a pressurized film, the cross-section of the frame is circular or quasi-circular, and the frame is provided with n independent and uniform partition chambers through partitions along the length direction, and the pressurized film covers the outside of the frame, one of the fixed brackets is provided with n oil inlet interfaces connected to the partition chambers one by one, and the fixed bracket at the other end is provided with n oil return interfaces connected to the partition chambers one by one, one end of the pressure relief cylinder is connected to the n oil inlet interfaces respectively through the oil inlet pipe, and the other end of the pressure relief cylinder is connected to the n oil return interfaces respectively through the oil return pipe, and each oil inlet pipe is provided with a pressure detection element for monitoring the pressure in each partition chamber, and n is a positive integer greater than 1.

[0016] Furthermore, the dual-axis four-way electromagnetic Hopkinson bar system includes a loading frame system, a rod system, a fixture system, an electromagnetic pulse emission system, and a confining pressure servo control system, wherein:

[0017] The loading frame system includes a central cross support platform and a reference square box, wherein the reference square box is placed in the middle of the central cross support platform, and the four sides of the reference square box along the X-axis and Z-axis directions are provided with connecting holes corresponding to the rod system, and the two corresponding sides of the reference square box are completely connected through the connecting holes;

[0018] The rod system, as a carrier of stress wave propagation, includes a square rod and a square rod fixing support frame for fixing the square rod, the square rod fixing support frame is arranged on the central cross support platform, the number of the square rods is four, which are respectively arranged on both sides of the X-axis and Z-axis directions of the reference square box and aligned with the connecting holes on the corresponding sides of the reference square box;

[0019] The clamp system is used to fix the rock sample and the pressure box;

[0020] The electromagnetic pulse transmitting system comprises an electromagnetic pulse transmitting chamber, an electromagnetic pulse transmitting chamber support frame, an electromagnetic pulse buffer frame and a first boss, wherein the electromagnetic pulse transmitting chamber is arranged on the electromagnetic pulse transmitting chamber support frame, and the electromagnetic pulse transmitting chamber is directly connected to the square rod; the electromagnetic pulse buffer frame is arranged on the electromagnetic pulse transmitting chamber support frame, and a guide rail is arranged on the electromagnetic pulse transmitting chamber support frame for the electromagnetic pulse buffer frame to move; one side of the first boss is connected to the electromagnetic pulse buffer frame, and the other side is connected to one end of one of the square rods of the X-axis or Z-axis away from the reference square box;

[0021] The confining pressure servo control system comprises a confining pressure loading cylinder, a loading actuator, and a confining pressure loading fixed baffle. The confining pressure loading cylinder is fixed on the confining pressure loading fixed baffle and is used to drive the loading actuator.

[0022] Furthermore, the fixture system includes four loading plates and two fixing plates, wherein the four loading plates are respectively arranged on the matching surfaces with the square rod in the X-axis direction and the Z-axis direction for fixing the square rod, and the two fixing plates are respectively fixedly connected to the fixing brackets at both ends of the pressure box.

[0023] Furthermore, the loading plate and the fixing plate are made of non-magnetic titanium alloy.

[0024] Furthermore, the bottom structure of the loading plate in contact with the rock sample is a square structure matching the shape of the sample, the top structure of the loading plate is provided with a sleeve convex groove for fixing the square rod, and the side surface between the top structure and the bottom structure of the loading plate adopts a variable cross-section transition structure with a thickness and a gradually increasing area.

[0025] Furthermore, the bottom structure of the loading plate is a square base of 200mm×200mm×20mm, the top structure is a sleeve convex groove of 50mm×50mm×20mm, and the thickness of the variable cross-section transition structure is 20mm.

[0026] Furthermore, the data monitoring and control system includes a client, a control module, and a data acquisition and recording module, wherein the client is connected to the control module and the data acquisition and recording module respectively, and the data acquisition and recording module includes strain gauges arranged on each square rod.

[0027] The present invention also provides a method for simulating excavation unloading under an in-situ stress state of rock, which is implemented based on the experimental device for simulating excavation unloading under an in-situ stress state, and includes the following steps:

[0028] S1: Place a rock sample with simulated tunnel holes, place the rock sample in a reference square box of a dual-axis four-way electromagnetic Hopkinson bar system, install a pressure box in the hole of the rock sample, and then fix the pressure box on the reference square box, connect one end of the oil pipeline to the oil inlet interface and the oil return interface respectively, and connect the other end to the pressure relief cylinder, and install a pressure detection element on the oil inlet and oil pipeline;

[0029] S2: Calculate the in-situ stress state of the rock, then start the pressure relief system to make the rock sample reach the in-situ stress state of the deep in-situ tunnel without excavation;

[0030] S3: Apply a preset stress to the side wall of the rock sample at a certain rate to achieve static confining pressure loading, and maintain the load for a set time to make the internal stress of the rock sample reach a stable state;

[0031] S4: The pressure of each compartment in the pressure box is changed at a certain rate through the pressure relief system to simulate the unloading process of asynchronous excavation of the tunnel;

[0032] S5: The dual-axis four-way electromagnetic Hopkinson bar system emits stress waves to simulate the shock waves when the coal and rock mass are impacted, so as to simulate the impact load disturbance during the tunnel excavation process and study the mechanism of rock burst in the tunnel under the combined dynamic and static loading.

[0033] S6: Data monitoring and control system records and analyzes data.

[0034] Furthermore, in step S2, the deep ground stress environment is obtained according to the field measured data, the in-situ stress state of the rock is calculated, the pressure relief system is started, the pressure relief cylinder injects oil into each compartment, and the pressure detection element monitors the pressure in the compartment in real time, so that the inside of the coal rock sample reaches the in-situ stress state of the deep in-situ without excavation.

[0035] The calculation method for the in-situ stress state of the unexcavated tunnel of the rock sample is:

[0036] Number the n compartments 1-n respectively.

[0037] The calculation formula of compartment n stress is:

[0038]

[0039] in, are the stress in the X-axis direction and the stress in the Z-axis direction, is the shear stress on the two-dimensional XZ plane, is the radial coordinate, is the polar angle, are the stresses at the contact points between the two boundary corners of compartment n and the rock sample, are the radial coordinates of the two boundary corner points of compartment n, are the polar angles of the two boundary corners of compartment n, is the contact area between the pressure film of the compartment and the rock sample, is the hydraulic oil pressure inside compartment n.

[0040] Further, in step S3, the X-axis and Z-axis loading actuators are pushed forward by filling the confining pressure loading cylinder with oil, and contact the electromagnetic pulse buffer frame and push the electromagnetic pulse buffer frame forward. The electromagnetic pulse buffer frame contacts the first boss and pushes the square rod to act on the rock sample, so that the X-axis and Z-axis directions of the rock sample are subjected to static confining pressure, and the load is loaded at a constant rate so that the stress in the X-axis and Z-axis directions reaches , and keep the load for half a minute to allow the internal stress of the sample to reach a stable state.

[0041] In step S4, the pressure of each compartment in the pressure box is changed from the original stress state of the unexcavated tunnel to the stress state of the tunnel after excavation and unloading at a certain rate. At pressure relief rate Start to relieve pressure, so that the stress of coal rock sample changes from Drop to 0, simulating the asynchronous excavation and unloading process of the tunnel. During the unloading process, the unloading rate, unloading time point, and unloading degree of each compartment are fully autonomously controllable, realizing multi-rate asynchronous unloading;

[0042] In step S5, the electromagnetic pulse emission system of the dual-axis four-directional electromagnetic Hopkinson rod system is started, and the ideal stress wave characteristics are first debugged by changing the voltage and the discharge current, and then the electromagnetic pulse signal is released in the X-axis and Z-axis directions, and the single-axis unidirectional, single-axis bidirectional stress fluctuation load disturbance or the dual-axis bidirectional, dual-axis four-directional stress fluctuation load disturbance synchronous loading is performed in the tunnel excavation unloading process, so as to realize the simulation of impact load disturbance in the tunnel excavation process.

[0043] Compared with the prior art, the invention has the following beneficial effects: the invention can truly reflect the mechanical behavior of deep coal and rock under multiple stress conditions, and can accurately control the unloading rate through the dual-axis four-way electromagnetic Hopkinson bar system and the pressure relief system, and simulate the complex working conditions of dynamic and static combined loading, thereby solving the problem that traditional experiments cannot accurately simulate asynchronous unloading and dynamic and static load combinations, and improving the accuracy and repeatability of the experiment, which is of great significance to the research on deep coal mining. The specific advantages are as follows:

[0044] (1) Simulation of asynchronous excavation and unloading conditions.

[0045] The present invention can realize the simulation of asynchronous excavation and unloading conditions. By constructing a tunnel unloading model, under deep in-situ conditions, the servo hydraulic system in the data monitoring and control system is used to accurately simulate the excavation and unloading process of the tunnel. By controlling the pressure relief rate and unloading start time at different positions in the tunnel unloading model, the process of asynchronous excavation and unloading in the actual unloading process is accurately simulated.

[0046] (2) Simulation of deep in-situ stress state.

[0047] The present invention can realize dynamic and static combined loading and simulate the unloading condition under deep in-situ stress state. Compared with static loading or instantaneous dynamic loading, dynamic and static combined loading can more comprehensively study the unloading characteristics of coal and rock, thus helping to reveal the damage of coal and rock under different loading paths.

[0048] (3) Accurately control the unloading rate.

[0049] The present invention can realize accurate control of the unloading rate through the pressure relief system. By controlling the unloading rate in real time, the influence of the unloading rate on the mechanical behavior of coal and rock can be studied in depth. Especially under complex stress conditions, the change of the unloading rate may lead to different fracture modes and failure mechanisms. Accurate control of the unloading rate helps to simulate the actual excavation rate of tunnel excavation and drilling in actual engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the present invention or the solutions in the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0051] Figure 1 It is the structural block diagram of the experimental device of the present invention;

[0052] Figure 2 It is a schematic diagram of the structure of the dual-axis four-way electromagnetic Hopkinson rod system and the pressure relief system of the present invention;

[0053] Figure 3 This is a connection diagram of the pressure relief system of the present invention;

[0054] Figure 4 This is a schematic diagram of the installation of the pressure box of the present invention;

[0055] Figure 5 This is a schematic structural diagram of an embodiment of a pressure box of the present invention;

[0056] Figure 6 This is a schematic diagram of the internal structure of the pressure box of the present invention;

[0057] Figure 7 This is a schematic diagram of the structure of the pressure box fixing bracket of the present invention;

[0058] Figure 8 This is a flow chart of the method for simulating excavation unloading of the present invention;

[0059] Fig. 9 Schematic diagram of the in-situ stress state of the deep tunnel plane model.

[0060] Figure numerals: 1-loading frame system; 11-central cross support platform; 12-reference square box; 13-connecting support rod; 2-rod system; 21-square rod; 22-square rod fixed support frame; 3-clamp system; 31-loading plate; 32-fixed plate; 4-electromagnetic pulse launch system; 41-electromagnetic pulse launch chamber; 42-first boss; 43-electromagnetic pulse buffer frame; 5-confining pressure servo control system; 51-confining pressure loading cylinder; 52- Loading actuator; 53-confining pressure loading fixed baffle; 6-pressure relief system; 61-pressure relief cylinder; 62-oil inlet pipe; 63-oil return pipe; 64-pressure detection element; 65-pressure box; 651-fixed bracket; 652-bolt; 653-oil inlet interface; 654-bolt hole; 655-pressure box wall; 656-pressurized film; 657-thread; 658-compartment chamber; 7-rock sample; 8-data monitoring and control system. DETAILED DESCRIPTION

[0061] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs; the terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention; the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. The terms "first", "second", etc. in the specification and claims of the present invention or the above-mentioned drawings are used to distinguish different objects, not to describe a specific order.

[0062] Reference to "embodiments" in the present invention means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it mutually exclusive, independent, or alternative to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present invention may be combined with other embodiments.

[0063] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings.

[0064] like Figure 1 As shown, the experimental device for simulating excavation unloading under in-situ stress state of the present invention includes a biaxial four-directional electromagnetic Hopkinson bar system, a pressure relief system 6, and a data monitoring and control system 8, wherein the biaxial four-directional electromagnetic Hopkinson bar system is used to load static loads on the sample or simulate impact load disturbances during tunnel excavation, as well as load, maintain, unload, and dynamically adjust the loading and unloading rates, including a loading frame system 1, a rod system 2, a fixture system 3, an electromagnetic pulse emission system 4, and a confining pressure servo control system 5. The pressure relief system 6 is used to accurately simulate the process of asynchronous excavation unloading in the real unloading process by controlling the pressure relief rate and unloading start time at different positions of the simulated tunnel inside the rock sample 7; the data monitoring and control system 8 is used to control the biaxial four-directional electromagnetic Hopkinson bar system and the pressure relief system, and record and store test data.

[0065] like Figure 2 As shown, the structures of the various components of the dual-axis four-directional electromagnetic Hopkinson rod system of this example are described in detail as follows:

[0066] The loading frame system 1 of this example includes a central cross support platform 11 and a reference square box 12, wherein the reference square box 12 is placed in the middle of the central cross support platform 11, and the four sides of the reference square box 12 along the X-axis and Z-axis directions are provided with connecting holes corresponding to the rod system, and the two sides corresponding to the reference square box 12 are completely connected through the connecting holes. Preferably, the loading frame system 1 of this example also includes a connecting support rod 13, wherein the connecting support rod 13 connects the reference square box 12 and the confining pressure loading fixed baffle 53, so that the entire structure connection is more stable. The loading frame system 1 of this example is mainly used as a test platform and guides the centering of multi-axis and multi-directional rods.

[0067] The rod system 2 serves as a carrier for stress wave propagation, and includes a square rod 21 and a square rod fixing support frame 22 for fixing the square rod 21. The square rod fixing support frame 22 is arranged on the central cross support platform 11. There are four square rods 21, which are respectively arranged on both sides of the X-axis and Z-axis directions of the reference square box 12, and are aligned with the connecting holes on the corresponding sides of the reference square box 12.

[0068] The clamp system 3 is used to fix the rock sample 7 and the pressure box 65 of the pressure relief system 6 in the reference square box 12. The clamp system 3 includes four loading plates 31 and two fixing plates 32. The four loading plates 31 are respectively arranged on the matching surfaces with the four square rods 21 in the X-axis direction and the Z-axis direction, and are used to fix the square rods 21. The two fixing plates 32 are respectively used to fix the two side surfaces of the pressure box 65 in the Y-axis direction.

[0069] Preferably, the size of the rock sample 7 in this example is a cubic coal rock sample of 200mm×200mm×200mm. The bottom structure of the loading plate 31 in this example that contacts the rock sample is a square structure that matches the shape of the sample. The top structure of the loading plate is provided with a sleeve convex groove for fixing the square rod. The side surface between the top structure and the bottom structure of the loading plate adopts a variable cross-section transition structure with a thickness and a gradually increasing area, which is beneficial to reducing the dispersion of stress waves.

[0070] Preferably, the bottom structure of the loading plate is a 200mm×200mm×20mm square base, the top structure is a 50mm×50mm×20mm sleeve convex groove, and the thickness of the variable cross-section transition structure is 20mm. In this example, the loading plate 31 and the fixing plate 32 are made of metal, preferably non-magnetic titanium alloy.

[0071] In this example, a pair of electromagnetic pulse transmitting systems 4 and confining pressure servo control systems 5 are respectively arranged at the ends of the four square rods in the X-axis direction and the Z-axis direction. The confining pressure servo control system 5 is arranged at the rear end of the electromagnetic pulse transmitting system 4, and acts on the square rod 21 through the electromagnetic pulse transmitting system 4, and then acts on the rock sample.

[0072] The electromagnetic pulse transmitting system 4 of this example includes an electromagnetic pulse transmitting chamber 41, an electromagnetic pulse transmitting chamber support frame, an electromagnetic pulse buffer frame 43 and a first boss 42. The electromagnetic pulse transmitting chamber 41 is arranged on the electromagnetic pulse transmitting chamber support frame, and the electromagnetic pulse transmitting chamber 41 is directly connected to the square rod; the electromagnetic pulse buffer frame 43 is arranged on the electromagnetic pulse transmitting chamber support frame, and the electromagnetic pulse transmitting chamber support frame is provided with a guide rail for the electromagnetic pulse buffer frame 43 to move; one side of the first boss 42 is connected to the electromagnetic pulse buffer frame 43, and the other side is connected to one end of one of the square rods 21 of the X-axis or Z-axis away from the reference square box 12.

[0073] The confining pressure servo control system 5 of this example includes a confining pressure loading cylinder 51 , a loading actuator 52 , and a confining pressure loading fixed baffle 53 . The confining pressure loading cylinder 51 is fixed on the confining pressure loading fixed baffle 53 and is used to drive the loading actuator 52 .

[0074] like Figure 3-Figure 7 As shown, the pressure relief system 6 includes a pressure relief cylinder 61, a pressure box 65, an oil inlet pipeline 62, an oil return pipeline 63 and a pressure detection element 64, wherein the pressure box 65 includes fixed brackets 651 arranged at both ends, a frame arranged between the two fixed brackets 651 and a pressurized film 656, the cross section of the frame is circular or quasi-circular, and the frame is provided with n mutually independent and uniform compartments 658 through a partition along the length direction, and the pressurized film 656 covers the outside of the frame, one of which is fixed. The fixed bracket 651 is provided with n oil inlet interfaces 653 corresponding to the compartments 658, and the fixed bracket 651 at the other end is provided with n oil return interfaces corresponding to the compartments. One end of the pressure relief cylinder 61 is connected to the n oil inlet interfaces 653 through the oil inlet pipeline 62, and the other end of the pressure relief cylinder 61 is connected to the n oil return interfaces through the oil return pipeline 63. A pressure detection element is provided on each oil inlet pipeline to monitor the pressure in each compartment, and n is a positive integer greater than 1. The pressure detection element in this example can be a pressure sensor to monitor the pressure in each compartment 658. The frame is divided into n compartments with independent pressure control and independent oil circuit control by partitions and pressurized films, so as to realize multi-rate asynchronous unloading in the simulated tunnel inside the rock sample 7.

[0075] The fixing bracket 651 of this example is provided with four bolt holes 654, and is fixedly connected to the fixing plate 32 by bolts 652. Pressure box walls 655 are also provided at both ends of the frame of this example, and a mounting hole matching with the pressure box wall 655 is provided in the middle of the fixing bracket 651, and the end of the pressure box wall 655 and the mounting hole are both provided with mutually matching threads 657, so that the frame and the fixing bracket 651 are detachably fixedly connected by the threads 657, which facilitates the installation and replacement of the rock sample sleeved on the frame.

[0076] The data monitoring and control system of this example includes a client, a control module, and a data acquisition and recording module, wherein the client is connected to the control module and the data acquisition and recording module respectively, and the data acquisition and recording module includes strain gauges arranged on each square rod. As an embodiment of the present invention, the data acquisition and recording module of this example also includes a multi-channel high-speed synchronous recorder, a Wheatstone bridge, and a strain signal amplifier, wherein the input end of the Wheatstone bridge is connected to the output end of the strain gauge, the output end of the Wheatstone bridge is connected to the input end of the strain signal amplifier, and the output end of the strain signal amplifier is connected to the input end of the multi-channel high-speed synchronous recorder, thereby ensuring that the test data is recorded and stored completely and effectively. The stored data and the data collected by the pressure sensor can be viewed through the client.

[0077] like Figure 8 As shown, the present invention also provides a method for simulating excavation unloading of rocks under an in-situ stress state, which is implemented based on the experimental device for simulating excavation unloading under an in-situ stress state, and includes the following steps:

[0078] S1: Place a rock sample with simulated tunnel holes, place the rock sample in a reference square box of a dual-axis four-way electromagnetic Hopkinson bar system, install a pressure box in the hole of the rock sample, and then fix the pressure box on the reference square box, connect one end of the oil pipeline to the oil inlet interface and the oil return interface respectively, and connect the other end to the pressure relief cylinder, and install a pressure detection element on the oil inlet and oil pipeline;

[0079] S2: Calculate the in-situ stress state of the rock, then start the pressure relief system to make the rock sample reach the in-situ stress state of the deep in-situ tunnel without excavation;

[0080] S3: Apply a preset stress to the side wall of the rock sample at a certain rate to achieve static confining pressure loading, and maintain the load for a set time to make the internal stress of the rock sample reach a stable state;

[0081] S4: The pressure of each compartment in the pressure box is changed at a certain rate through the pressure relief system to simulate the unloading process of asynchronous excavation of the tunnel;

[0082] S5: The dual-axis four-way electromagnetic Hopkinson bar system emits stress waves to simulate the shock waves when the coal and rock mass are impacted, so as to simulate the impact load disturbance during the tunnel excavation process and study the mechanism of rock burst in the tunnel under the combined dynamic and static loading.

[0083] S6: Data monitoring and control system records and analyzes data.

[0084] Before executing the method of simulating excavation unloading when the rock is in an in-situ stress state of the present invention, it is necessary to quantitatively design and prepare the rock samples required for the test in advance. In this example, a coal rock sample (hereinafter referred to as the sample) is taken as an example. The preparation method of the coal rock sample is as follows: the coal rock is cut and polished into a 200mm×200mm×200mm cubic sample by on-site sampling, and a hole is drilled in the middle of one of the cross sections of the sample, and the drilling size is 50mm×50mm×200mm, so as to obtain a coal rock sample containing simulated tunnel holes.

[0085] In step S2, this example obtains the deep ground stress environment (vertical stress With horizontal stress , shear stress ), calculate the in-situ stress state of the rock, start the pressure relief system, and inject oil into each compartment. The pressure detection element monitors the pressure in the compartment in real time, so that the coal rock sample reaches the in-situ stress state in the deep in-situ without excavation, such as Fig. 9 The calculation method of the in-situ stress state of the unexcavated tunnel of the specimen is:

[0086] Number the n compartments 1-n respectively.

[0087] The calculation formula of compartment n stress is:

[0088]

[0089] in, are the stress in the X-axis direction and the stress in the Z-axis direction, is the shear stress on the two-dimensional XZ plane, is the radial coordinate, is the polar angle, are the stresses at the contact points between the two boundary corners of compartment n and the rock sample, are the radial coordinates of the two boundary corner points of compartment n, are the polar angles of the two boundary corners of compartment n, is the contact area between the pressure film of the compartment and the rock sample, is the hydraulic oil pressure inside compartment n.

[0090] Further, in step S3, the X-axis and Z-axis loading actuators are pushed forward by filling the confining pressure loading cylinder 51 with oil, and contact the electromagnetic pulse buffer frame and push the electromagnetic pulse buffer frame forward. The electromagnetic pulse buffer frame contacts the first boss and pushes the square rod to act on the rock sample, so that the X-axis and Z-axis directions of the sample are subjected to static confining pressure, and the load is loaded at a constant rate so that the stress in the X-axis and Z-axis directions reaches , and maintain the load for half a minute to allow the internal stress of the sample to reach a stable state.

[0091] In step S4, the pressure of each compartment in the pressure box is changed from the original stress state of the unexcavated tunnel to the stress state of the tunnel after excavation and unloading at a certain rate. At pressure relief rate Start to relieve pressure, so that the stress of coal rock sample changes from It drops to 0 to simulate the asynchronous excavation and unloading process of the tunnel. During the unloading process, the unloading rate, unloading time point and unloading degree of each compartment are fully autonomously controllable to achieve multi-rate asynchronous unloading.

[0092] In step S5, the electromagnetic pulse emission system of the dual-axis four-directional electromagnetic Hopkinson rod system is started, and the ideal stress wave characteristics are first debugged by changing the voltage and the discharge current, and then the electromagnetic pulse signal is released in the X-axis and Z-axis directions, and the single-axis unidirectional, single-axis bidirectional stress fluctuation load disturbance or the dual-axis bidirectional, dual-axis four-directional stress fluctuation load disturbance synchronous loading is performed in the tunnel excavation unloading process to simulate the impact load disturbance in the tunnel excavation process, and study the mechanism of tunnel impact ground pressure induced under dynamic and static combined loading.

[0093] In step S6, the data monitoring and control system records the pressure changes and stress changes of each compartment in real time; records the stress-strain changes of the sample, and draws a stress-strain curve.

[0094] Compared with the existing technology, the present invention can truly reflect the mechanical behavior of deep coal and rock under multiple stress conditions. Through the dual-axis four-directional electromagnetic Hopkinson bar system and the pressure relief system, it can accurately control the unloading rate and simulate the complex working conditions of dynamic and static combined loading. It solves the problem that traditional experiments cannot accurately simulate asynchronous unloading and dynamic and static load combinations, improves the accuracy and repeatability of the experiment, and is of great significance to the research on deep coal mining.

[0095] The innovative features of the present invention are as follows:

[0096] (1) Simulation of asynchronous excavation and unloading conditions.

[0097] The present invention can realize the simulation of asynchronous excavation and unloading conditions. By constructing a tunnel unloading model, under deep in-situ conditions, the servo hydraulic system in the data monitoring and control system is used to accurately simulate the excavation and unloading process of the tunnel. By controlling the pressure relief rate and unloading start time at different positions in the tunnel unloading model, the process of asynchronous excavation and unloading in the actual unloading process is accurately simulated.

[0098] (2) Simulation of deep in-situ stress state.

[0099] The present invention can realize dynamic and static combined loading and simulate the unloading condition under deep in-situ stress state. Compared with static loading or instantaneous dynamic loading, dynamic and static combined loading can more comprehensively study the unloading characteristics of coal and rock, thus helping to reveal the damage of coal and rock under different loading paths.

[0100] (3) Accurately control the unloading rate.

[0101] The present invention can realize accurate control of the unloading rate through the pressure relief system. By controlling the unloading rate in real time, the influence of the unloading rate on the mechanical behavior of coal and rock can be studied in depth. Especially under complex stress conditions, the change of the unloading rate may lead to different fracture modes and failure mechanisms. Accurate control of the unloading rate helps to simulate the actual excavation rate of tunnel excavation and drilling in actual engineering.

[0102] The specific implementation modes described above are preferred implementation modes of the present invention, and are not intended to limit the specific implementation scope of the present invention. The scope of the present invention includes but is not limited to the specific implementation modes, and all equivalent changes made according to the present invention are within the protection scope of the present invention.

Claims

1. An experimental device for simulating excavation unloading under in-situ stress state, characterized in that: Including dual-axis four-way electromagnetic Hopkinson rod system, pressure relief system, data monitoring and control system, The dual-axis four-way electromagnetic Hopkinson bar system is used to load static loads on the specimen or simulate impact load disturbances during tunnel excavation, as well as load, maintain, unload, and dynamically adjust loading and unloading rates; The pressure relief system is used to accurately simulate the process of asynchronous excavation and unloading in the real unloading process by controlling the pressure relief rate and unloading start time at different positions of the simulated tunnel inside the rock sample; The data monitoring and control system is used to control the dual-axis four-way electromagnetic Hopkinson bar system and the pressure relief system, and record and store test data; The pressure relief system includes a pressure relief cylinder, a pressure box, an oil pipeline and a pressure detection element, wherein the pressure box includes fixed brackets arranged at both ends, a frame arranged between the two fixed brackets and a pressurized film, the cross-section of the frame is circular or quasi-circular, and the frame is provided with n independent and uniform partition chambers through partitions along the length direction, and the pressurized film covers the outside of the frame, one of the fixed brackets is provided with n oil inlet interfaces connected to the partition chambers one by one, and the fixed bracket at the other end is provided with n oil return interfaces connected to the partition chambers one by one, one end of the pressure relief cylinder is connected to the n oil inlet interfaces respectively through the oil inlet pipe, and the other end of the pressure relief cylinder is connected to the n oil return interfaces respectively through the oil return pipe, and each oil inlet pipe is provided with a pressure detection element for monitoring the pressure in each partition chamber, and n is a positive integer greater than 1.

2. The experimental device for simulating excavation unloading under in-situ stress state according to claim 1, characterized in that: The dual-axis four-way electromagnetic Hopkinson bar system includes a loading frame system, a rod system, a fixture system, an electromagnetic pulse emission system, and a confining pressure servo control system, wherein: The loading frame system includes a central cross support platform and a reference square box, wherein the reference square box is placed in the middle of the central cross support platform, and the four sides of the reference square box along the X-axis and Z-axis directions are provided with connecting holes corresponding to the rod system, and the two corresponding sides of the reference square box are completely connected through the connecting holes; The rod system, as a carrier of stress wave propagation, includes a square rod and a square rod fixing support frame for fixing the square rod, the square rod fixing support frame is arranged on the central cross support platform, the number of the square rods is four, which are respectively arranged on both sides of the X-axis and Z-axis directions of the reference square box and aligned with the connecting holes on the corresponding sides of the reference square box; The clamp system is used to fix the rock sample and the pressure box; The electromagnetic pulse transmitting system comprises an electromagnetic pulse transmitting chamber, an electromagnetic pulse transmitting chamber support frame, an electromagnetic pulse buffer frame and a first boss, wherein the electromagnetic pulse transmitting chamber is arranged on the electromagnetic pulse transmitting chamber support frame, and the electromagnetic pulse transmitting chamber is directly connected to the square rod; a guide rail is arranged on the electromagnetic pulse transmitting chamber support frame for the electromagnetic pulse buffer frame to move; one side of the first boss is connected to the electromagnetic pulse buffer frame, and the other side is connected to one end of one of the square rods of the X-axis or Z-axis away from the reference square box; The confining pressure servo control system comprises a confining pressure loading cylinder, a loading actuator, and a confining pressure loading fixed baffle. The confining pressure loading cylinder is fixed on the confining pressure loading fixed baffle and is used to drive the loading actuator.

3. The experimental device for simulating excavation unloading under in-situ stress state according to claim 2, characterized in that: The fixture system includes four loading plates and two fixing plates, wherein the four loading plates are respectively arranged on the matching surfaces with the square rod in the X-axis direction and the Z-axis direction for fixing the square rod, and the two fixing plates are respectively fixedly connected to the fixing brackets at both ends of the pressure box.

4. The experimental device for simulating excavation unloading under in-situ stress state according to claim 3, characterized in that: The loading plate and the fixing plate are made of non-magnetic titanium alloy.

5. The experimental device for simulating excavation unloading under in-situ stress state according to claim 3, characterized in that: The bottom structure of the loading plate in contact with the rock sample is a square structure matching the shape of the sample, the top structure of the loading plate is provided with a sleeve convex groove for fixing the square rod, and the side surface between the top structure and the bottom structure of the loading plate adopts a variable cross-section transition structure with a gradually increasing thickness and area.

6. The experimental device for simulating excavation unloading under in-situ stress state according to claim 5, characterized in that: The bottom structure of the loading plate is a square base of 200mm×200mm×20mm, the top structure is a sleeve convex groove of 50mm×50mm×20mm, and the thickness of the variable cross-section transition structure is 20mm.

7. The experimental device for simulating excavation unloading under in-situ stress state according to any one of claims 1 to 6, characterized in that: The data monitoring and control system includes a client, a control module, and a data acquisition and recording module, wherein the client is connected to the control module and the data acquisition and recording module respectively, and the data acquisition and recording module includes strain gauges arranged on each square rod.

8. A method for simulating excavation unloading under in-situ stress state of rock, which is realized based on the experimental device for simulating excavation unloading under in-situ stress state according to any one of claims 1 to 7, characterized in that: The steps include: S1: Place a rock sample with simulated tunnel holes, place the rock sample in a reference square box of a dual-axis four-way electromagnetic Hopkinson bar system, install a pressure box in the hole of the rock sample, and then fix the pressure box on the reference square box, connect one end of the oil pipeline to the oil inlet interface and the oil return interface respectively, and connect the other end to the pressure relief cylinder, and install a pressure detection element on the oil inlet and oil pipeline; S2: Calculate the in-situ stress state of the rock, then start the pressure relief system to make the rock sample reach the in-situ stress state of the deep in-situ tunnel without excavation; S3: Apply a preset stress to the side wall of the rock sample at a certain rate to achieve static confining pressure loading, and maintain the load for a set time to make the internal stress of the rock sample reach a stable state; S4: The pressure of each compartment in the pressure box is changed at a certain rate through the pressure relief system to simulate the unloading process of asynchronous excavation of the tunnel; S5: The dual-axis four-way electromagnetic Hopkinson bar system emits stress waves to simulate the shock waves when the coal and rock mass are impacted, so as to simulate the impact load disturbance during the tunnel excavation process and study the mechanism of rock burst in the tunnel under the combined dynamic and static loading. S6: Data monitoring and control system records and analyzes data.

9. The method for simulating excavation unloading of rocks under in-situ stress state according to claim 8, characterized in that: In step S2, the deep ground stress environment is obtained according to the field measured data, the in-situ stress state of the rock is calculated, the pressure relief system is started, the pressure relief cylinder injects oil into each compartment, and the pressure detection element monitors the pressure in the compartment in real time, so that the inside of the coal rock sample reaches the deep in-situ stress state without excavation. The calculation method for the in-situ stress state of the unexcavated tunnel of the rock sample is: Number the n compartments 1-n respectively. The calculation formula of compartment n stress is: in, are the stress in the X-axis direction and the stress in the Z-axis direction, is the shear stress on the two-dimensional XZ plane, is the radial coordinate, is the polar angle, are the stresses at the contact points between the two boundary corners of compartment n and the rock sample, are the radial coordinates of the two boundary corner points of compartment n, are the polar angles of the two boundary corners of compartment n, is the contact area between the pressure film of the compartment and the rock sample, is the hydraulic oil pressure inside compartment n.

10. The method for simulating excavation unloading of rocks under in-situ stress state according to claim 9, characterized in that: In step S3, the X-axis and Z-axis loading actuators are pushed forward by filling the confining pressure loading cylinder with oil, and contact the electromagnetic pulse buffer frame and push the electromagnetic pulse buffer frame forward. The electromagnetic pulse buffer frame contacts the first boss and pushes the square rod to act on the rock sample, so that the X-axis and Z-axis directions of the rock sample are subjected to static confining pressure, and the load is loaded at a constant rate so that the stress in the X-axis and Z-axis directions reaches , and keep the load for half a minute to allow the internal stress of the sample to reach a stable state. In step S4, the pressure of each compartment in the pressure box is changed from the original stress state of the unexcavated tunnel to the stress state of the tunnel after excavation and unloading at a certain rate. At pressure relief rate Start to relieve pressure, so that the stress of coal rock sample changes from Drop to 0, simulating the asynchronous excavation and unloading process of the tunnel. During the unloading process, the unloading rate, unloading time point, and unloading degree of each compartment are fully autonomously controllable, realizing multi-rate asynchronous unloading; In step S5, the electromagnetic pulse emission system of the dual-axis four-directional electromagnetic Hopkinson rod system is started, and the ideal stress wave characteristics are first debugged by changing the voltage and the discharge current, and then the electromagnetic pulse signal is released in the X-axis and Z-axis directions, and the single-axis unidirectional, single-axis bidirectional stress fluctuation load disturbance or the dual-axis bidirectional, dual-axis four-directional stress fluctuation load disturbance synchronous loading is performed in the tunnel excavation unloading process, so as to realize the simulation of impact load disturbance in the tunnel excavation process.

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