Construction method for preventing tunnel rockburst

Abstract

This application relates to the technical field of tunnel construction, and this application provides a construction method for preventing tunnel rock bursts. The construction method for preventing tunnel rock bursts includes the following steps: obtaining the characteristic information of the surrounding rock in the target rock burst section; wherein, the characteristic information includes: in-situ stress characteristics and integrity characteristics; obtaining the secondary stress distribution of the surrounding rock in the target rock burst section during the tunnel excavation process according to the in-situ stress characteristics; judging the rock burst grade according to the secondary stress distribution of the surrounding rock in the target rock burst section; combining the rock burst grade with the distribution characteristics of microcracks to determine the on-site construction measures for preventing rock bursts. The solution provided by this application can specifically provide corresponding on-site construction measures for preventing rock bursts.

Description

Technical Field

[0001] This application relates to the technical field of tunnel construction. Specifically, this application relates to a construction method for preventing rock bursts in tunnels. Background Art

[0002] For dealing with rock bursts, the current technical level generally adopts the conventional bench cut method for excavation for safety reasons, gradually releases the stress, and strengthens the protection intensity of bolts and wire meshes. Although the possibility of stress concentration and explosion is greatly reduced to improve the safety of tunnel construction, most of them are treated according to the intensity of the rock burst after the rock burst occurs.

[0003] Therefore, the prediction of rock bursts is particularly important. Due to the complexity of the problem, the current method system for rock burst prediction is still imperfect. The current methods for rock burst prediction are classified into three categories: the first category is various rock burst criteria established based on the occurrence mechanism of rock bursts; the second category is the rock burst prediction method based on on-site monitoring data; the third category is the rock burst prediction method considering the comprehensive influence of various factors established by referring to methods and tools in related disciplinary fields such as mathematics and systems engineering. However, the currently provided methods are difficult to well prevent the occurrence of rock bursts. Summary of the Invention

[0004] In view of the technical problem in the prior art that the occurrence of rock bursts cannot be accurately predicted, this application provides a construction method for preventing rock bursts in tunnels.

[0005] This application provides a construction method for preventing rock bursts in tunnels, including the following steps:

[0006] Obtain the characteristic information of the surrounding rock in the target rock burst section; wherein, the characteristic information includes: in-situ stress characteristics and integrity characteristics;

[0007] According to the in-situ stress characteristics, obtain the secondary stress distribution of the surrounding rock in the target rock burst section during the tunnel excavation process;

[0008] According to the secondary stress distribution of the surrounding rock in the target rock burst section, determine the rock burst grade;

[0009] Combine the rock burst grade with the distribution characteristics of microcracks to determine the on-site construction measures for preventing rock bursts.

[0010] In an optional embodiment of one aspect, when the characteristic information is the in-situ stress characteristics, the obtaining of the characteristic information of the surrounding rock in the rock burst section includes:

[0011] According to the drilling depth of the surrounding rock in the target rock burst section, obtain the maximum principal stress value in the plane, the minimum principal stress value in the plane, and the direction of the maximum principal stress in the plane, and obtain the maximum horizontal in-situ stress value, the minimum horizontal principal stress value, and the vertical principal stress value at the maximum buried depth of the surrounding rock in the target rock burst section.

[0012] In an alternative embodiment of one aspect, obtaining the secondary stress distribution of the surrounding rock in the target rockburst section during tunnel excavation according to the in-situ stress characteristics includes:

[0013] Establish a calculation model in a finite element program, place the roadway section of the tunnel in the calculation model, and preset a shape for the roadway section; wherein, the roadway section includes corresponding observation points established at the top, side walls, bottom, right side inside the rock mass, and top inside the rock mass.

[0014] According to the maximum horizontal in-situ stress value, minimum horizontal principal stress value, and vertical principal stress value at the maximum buried depth of the surrounding rock in the target rockburst section, obtain the secondary stress distribution model of each observation point of each roadway section.

[0015] In an alternative embodiment of one aspect, obtaining the secondary stress distribution model of each observation point of each roadway section includes:

[0016] Determine a starting roadway section on the tunnel, take the starting roadway section as the starting point, obtain the stress values of all observation points of each roadway section at an equidistant excavation length, and obtain the secondary stress distribution information of the stress values of the observation points corresponding to the excavation depth.

[0017] In an alternative embodiment of one aspect, the characteristic information includes rock mass strength.

[0018] Judging the rockburst grade according to the secondary stress distribution of the surrounding rock in the target rockburst section includes:

[0019] According to the secondary stress distribution information and the rock mass strength of the surrounding rock in the target rockburst section, obtain the corresponding rockburst grade.

[0020] In an alternative embodiment of one aspect, when the characteristic information is the integrity characteristic, obtaining the characteristic information of the surrounding rock in the rockburst section includes:

[0021] According to the rock type of the surrounding rock in the target rockburst section and the physical state of the specimen, obtain the corresponding saturated uniaxial compressive strength and dry compressive strength, and obtain the overall integrity characteristic of the tunnel excavation position of the surrounding rock in the target rockburst section.

[0022] In an alternative embodiment of one aspect, combining the distribution characteristics of microcracks to determine the construction measures for preventing rockburst on site includes:

[0023] According to the integrity characteristic, apply the secondary stress to the corresponding tunnel excavation model containing a fracture network to obtain the distribution characteristics of microcracks in the surrounding rock during excavation unloading.

[0024] Predict the degree of surrounding rock damage caused by excavation according to the distribution characteristics of the microcracks, and determine the construction measures for on-site prevention of rockburst.

[0025] In an alternative embodiment of one aspect, the construction method for preventing tunnel rockburst further includes:

[0026] Predict the degree of surrounding rock damage caused by excavation according to the distribution characteristics of the microcracks, and calculate the quantitative effect of reducing microcracks in the surrounding rock of the micro-rocks during the excavation of the upper and lower benches according to the degree of surrounding rock damage.

[0027] In an alternative embodiment of one aspect, the construction method for preventing tunnel rockburst further includes:

[0028] Obtain the microseismic signal of the tunnel face, identify the corresponding rockburst level, and correct the construction measures for on-site prevention of rockburst.

[0029] In an alternative embodiment of one aspect, compare the rockburst levels obtained by identifying through microseismic signals with the rockburst levels obtained by identifying through the secondary stress distribution of the surrounding rock in the target rockburst section, and use the higher rockburst level as the currently predicted rockburst level of the surrounding rock in the target rockburst section.

[0030] The beneficial effects of the construction method for preventing tunnel rockburst provided by this application are as follows:

[0031] Based on the construction method for preventing tunnel rockburst provided by this application, select the surrounding rock in the target rockburst section as the prediction and evaluation object for rockburst prediction, obtain its characteristic information such as in-situ stress characteristics and integrity characteristics, and based on the in-situ stress characteristics among them, obtain the secondary stress distribution of the surrounding rock in the target rockburst section during the tunnel excavation process, so as to judge the corresponding rockburst level. Moreover, according to the distribution characteristics of the microcracks in the surrounding rock of the target rockburst section, predict the degree of surrounding rock damage caused by excavation, and thus determine the construction measures for on-site prevention of rockburst. Based on this tunnel rockburst prevention construction plan, it is possible to overcome the technical problem in the prior art that the occurrence of rockburst cannot be predicted very accurately, and thus realize the combination of the secondary stress distribution obtained by combining the characteristic information of the surrounding rock in the target rockburst section with the distribution characteristics of the microcracks, which can more comprehensively predict the tunnel rockburst and obtain the corresponding preventive construction measures, so as to accurately prevent the occurrence of rockburst and provide the corresponding on-site construction measures for preventing rockburst. Compared with the bench cut method, accurate geological forecasting of rock parameters can reduce the material consumption of the advanced support, shorten the construction time of the advanced support, and since the optimized surrounding rock parameters are used, the construction time of installing rigid supports is reduced, improving the construction progress.

[0032] The additional aspects and advantages of this application will be partially given in the following description, and these will become obvious from the following description or be understood through practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above and / or additional aspects and advantages will become apparent and readily understood from the following description of embodiments in conjunction with the accompanying drawings, where:

[0034] Figure 1 is a schematic flow chart of a construction method for preventing tunnel rockburst provided by an embodiment of the present application;

[0035] Figure 2 is a three-dimensional schematic diagram of a calculation model provided by an embodiment of the present application;

[0036] Figure 3 is a schematic diagram of in-situ stress at different observation points of the same cross-section of a calculation model provided by an embodiment of the present application;

[0037] Figure 4a is a three-dimensional stress schematic diagram of the top surrounding rock D of a cross-section of a calculation model provided by an embodiment of the present application;

[0038] Figure 4b is a three-dimensional stress schematic diagram of the side-wall surrounding rock E of a cross-section of a calculation model provided by an embodiment of the present application;

[0039] Figure 4c is a three-dimensional stress schematic diagram of the top unit A of a cross-section of a calculation model provided by an embodiment of the present application;

[0040] Figure 4d is a three-dimensional stress schematic diagram of the side-wall unit B of a cross-section of a calculation model provided by an embodiment of the present application;

[0041] Figure 4e is a three-dimensional stress schematic diagram of the bottom unit C of a cross-section of a calculation model provided by an embodiment of the present application;

[0042] Figure 5 is a three-dimensional stress schematic diagram of the difference between the vertical stress and the horizontal stress of the top unit A, the side-wall unit B, and the bottom unit C of a cross-section of a calculation model provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] The present application will be further described below in conjunction with the accompanying drawings and exemplary embodiments, where the same reference numerals in the drawings all refer to the same components. In addition, if a detailed description of the known technology is unnecessary for showing the features of the present application, it will be omitted.

[0044] Refer to Figure 1 , Figure 1 is a schematic flow chart of a construction method for preventing tunnel rockburst provided by an embodiment of the present application.

[0045] The present application provides a construction method for preventing tunnel rock bursts, which can solve the technical problem in the prior art that the occurrence of rock bursts cannot be accurately prevented.

[0046] The construction method for preventing tunnel rock bursts includes the following steps:

[0047] S110. Obtain the characteristic information of the surrounding rock in the target rock burst section; wherein, the characteristic information includes: in-situ stress characteristics and integrity characteristics;

[0048] S120. Obtain the secondary stress distribution of the surrounding rock in the target rock burst section during the tunnel excavation process according to the in-situ stress characteristics;

[0049] S130. Judge the rock burst grade according to the secondary stress distribution of the surrounding rock in the target rock burst section;

[0050] S140. Determine the on-site construction measures for preventing rock bursts in combination with the distribution characteristics of microcracks.

[0051] During the process of the above steps S110 to S140, according to the data of the preliminary exploration, the in-situ stress test data for each rock burst section in the tunnel area are obtained. For a better and clear description of the implementation plan, in the subsequent embodiments provided, the rock burst prediction method for the surrounding rock of a target rock burst section is described in detail.

[0052] Before step S110, the surrounding rock of the target rock burst section is explored, drilled, and measured to obtain the characteristic information of the surrounding rock of the target rock burst section. In this embodiment, the characteristic information of the surrounding rock of the target rock burst section includes: in-situ stress characteristics and integrity characteristics.

[0053] Among them, the in-situ stress characteristic is to measure the in-situ stress effect of the surrounding rock in the target rock burst section. During the tunnel excavation process, the in-situ stress characteristic may include secondary stress. The secondary stress refers to the normal stress or shear stress required to meet the external constraint conditions or the continuous deformation conditions of the structure itself.

[0054] The integrity characteristic is used to measure the development degree of various geological interfaces mainly composed of fissures in the rock mass. Less fissures mean good rock mass integrity, and more fissures mean poor rock mass integrity.

[0055] During the tunnel excavation process, in order to more comprehensively evaluate the situation of the surrounding rock in the target rock burst section, in this embodiment, for the surrounding rock in the target rock burst section, especially in the area of the tunnel to be excavated, multiple observation points are set in different areas. During the process of obtaining the characteristic information of the surrounding rock in the target rock burst section, it may include obtaining the in-situ stress characteristics of each observation point. And according to the in-situ stress characteristics of each observation point, the secondary stress distribution of the surrounding rock in the target rock burst section during the tunnel excavation process is obtained.

[0056] Based on the secondary stress distribution obtained above, the rockburst level of the surrounding rock of the target rockburst section is assessed to obtain the corresponding rockburst grade. Furthermore, based on the distribution characteristics of microcracks in the surrounding rock of the target rockburst section, the degree of surrounding rock damage caused by excavation is predicted, thereby determining on-site construction measures to prevent rockbursts.

[0057] Based on the construction method for preventing tunnel rock bursts provided by the present application, the target rock burst section surrounding rock is selected as the prediction and evaluation object for rock burst prediction, and characteristic information such as its ground stress characteristics and integrity characteristics is obtained. According to the ground stress characteristics, the secondary stress distribution of the surrounding rock of the target rock burst section during tunnel excavation is obtained, thereby judging the corresponding rock burst level. In addition, according to the distribution characteristics of the microcracks in the surrounding rock of the target rock burst section, the degree of surrounding rock damage caused by excavation is predicted, thereby determining the on-site construction measures for preventing rock bursts. Based on this tunnel rock burst prevention construction scheme, it is possible to overcome the technical problem of the inability to accurately predict the occurrence of rock bursts in the existing technology, thereby realizing the combination of the secondary stress distribution obtained by combining the characteristic information of the surrounding rock of the target rock burst section with the distribution characteristics of the microcracks, so as to more comprehensively predict the tunnel rock burst and determine the corresponding preventive construction measures, thereby accurately preventing the occurrence of rock bursts so as to provide corresponding on-site construction measures for preventing rock bursts in a targeted manner. Compared with the bench excavation method, the accurate geological prediction of rock parameters can reduce the material consumption of advance support and shorten the construction time of advance support. In addition, due to the use of optimized surrounding rock parameters, the construction time of installing rigid support is reduced, which improves the construction progress.

[0058] When the characteristic information provided in the above embodiment is a geostress characteristic, step S110 includes:

[0059] According to the drilling depth of the surrounding rock of the target rockburst section, the plane maximum principal stress value, the plane minimum principal stress value and the plane maximum principal stress direction are obtained, and the maximum horizontal ground stress value, the minimum horizontal principal stress value and the vertical principal stress value at the maximum burial depth of the surrounding rock of the target rockburst section are obtained.

[0060] The target rockburst section surrounding rock is explored and drilled, and then measured to obtain characteristic information of the target rockburst section surrounding rock. In this embodiment, the characteristic information of the target rockburst section surrounding rock includes: ground stress characteristics and integrity characteristics.

[0061] Based on the above embodiment, the target rock burst section surrounding rock is explored and drilled, the hole depth of the target rock burst section surrounding rock is determined, and the corresponding ground stress data is measured on the drill hole.

[0062] In this embodiment, a drilling data involved in a tunnel excavation project is used as characteristic information corresponding to the surrounding rock of the target rockburst section and data involved in the construction method for description and explanation.

[0063] The depth of this borehole ranges from 445.5 m to 473.4 m. For the convenience of subsequent data processing, the depth of this borehole is fixed at 450 m. For the surrounding rock of the target rockburst section, the measured data obtained include: the maximum principal stress in the plane ranges between 8.24 MPa and 12.15 MPa, the minimum principal stress in the plane ranges between 6.41 and 8.95, the direction of the maximum principal stress in the plane is 115° to 118°, and the maximum principal stress is the self-weight stress (the unit weight is taken as 2,660 kg / m³). The maximum buried depth of the tunnel where the surrounding rock of the target rockburst section is located reaches 650 m.

[0064] Since the position of this borehole is not at the maximum buried depth, but for safety considerations, the in-situ stress of the tunnel at the maximum buried depth is determined by extrapolation based on the buried depth. The in-situ stress of the tunnel at the maximum buried depth includes:

[0065] The maximum horizontal in-situ stress at the maximum buried depth: 11.45 * 650 / 450 = 16.53 Mpa

[0066] The minimum horizontal principal stress is: 8.85 * 650 / 450 = 12.78 Mpa

[0067] The vertical principal stress: 650 * 2.66 = 17.29 Mpa

[0068] For the above-mentioned secondary stress distribution of the surrounding rock of the target rockburst section during the tunnel excavation obtained according to the in-situ stress characteristics, it may further include:

[0069] Establish a calculation model in the finite element program, place the roadway section of the tunnel in the calculation model, and preset the shape for the roadway section; wherein, the roadway section includes corresponding observation points established at the top, side walls, bottom, the right side inside the rock mass, and the top inside the rock mass.

[0070] According to the maximum horizontal in-situ stress value, the minimum horizontal principal stress value, and the vertical principal stress value at the maximum buried depth of the surrounding rock of the target rockburst section, obtain the secondary stress distribution models of each roadway section for each observation point.

[0071] Reference Figures 2-3 , Figure 2 is a three-dimensional schematic diagram of the calculation model provided by an embodiment of the present application, Figure 3 is a schematic diagram of the in-situ stress of different observation points of the same section of the calculation model provided by an embodiment of the present application.

[0072] In this embodiment, the finite element program is the FLAC3D finite element program, and a calculation model with dimensions of 50m×50m×30m is established within the FLAC3D finite element program. The roadway section of the tunnel is placed at the center of the calculation model, and the roadway section is set as a horseshoe shape. The bottom boundary of the calculation model is subjected to fixed displacement constraints, and certain surface pressure loads are applied to the left and right sides, front and back sides, and the upper surface. The magnitude of the load depends on the actual in-situ stress level. The maximum horizontal stress is set perpendicular to the tunnel axis.

[0073] Reference Figure 3 As shown, taking the top unit A, sidewall unit B, bottom unit C, right-side unit E inside the rock mass, and top unit D of the roadway section of the tunnel as observation points, the changes in horizontal stress, tunnel axial stress, and vertical stress with the advancement of the excavation face are extracted respectively. The force schematic diagrams of each observation point refer to Figures 4a-4d . Among them, in this embodiment, each excavation length is 3m. In this embodiment, the starting roadway section is determined on the tunnel, and taking the starting roadway section as the starting point, the stress values of all observation points of each roadway section at equal-distance excavation lengths are obtained.

[0074] Figure 4a It is a three-dimensional stress schematic diagram of the top surrounding rock D of a cross-section of the calculation model provided by an embodiment of the present application. Figure 4b It is a three-dimensional stress schematic diagram of the sidewall surrounding rock E of a cross-section of the calculation model provided by an embodiment of the present application. Figure 4c It is a three-dimensional stress schematic diagram of the top unit A of a cross-section of the calculation model provided by an embodiment of the present application. Figure 4d It is a three-dimensional stress schematic diagram of the sidewall unit B of a cross-section of the calculation model provided by an embodiment of the present application. Figure 4e It is a three-dimensional stress schematic diagram of the bottom unit C of a cross-section of the calculation model provided by an embodiment of the present application.

[0075] As Figures 4a-4b shown, when the excavation face is far from the observation point, the stress in the three directions of the rock mass near the top or side of the tunnel is less affected by the excavation and is basically in the initial in-situ stress state.

[0076] For Figures 4c-4eFor comparison, when the excavation face is far from the observation point, the rock mass near the observation surface is in the initial in-situ stress state. As the excavation face continues to advance forward, when the distance in front of the excavation face is about 3 meters from the observation surface, the stress states of each observation point begin to change. The tangential stress of the rock mass at the top and bottom of the tunnel gradually increases, the radial stress gradually decreases to 0, and the axial stress shows a certain fluctuation under the action of excavation unloading and finally remains basically unchanged. The three-dimensional stresses of the rock mass on the side walls of the roadway all decrease to varying degrees, and the decrease amplitude of the radial stress is much greater than that of the tangential stress. When the distance behind the excavation face exceeds 3 - 5 meters from the observation surface, the stress state of the surrounding rock of the roadway tends to be stable again after adjustment.

[0077] Reference Figure 5 , Figure 5 is a stress three-dimensional schematic diagram of the difference between the vertical stress and the horizontal stress of the top unit A, the side wall unit B, and the bottom unit C of a cross-section of the calculation model provided by an embodiment of the present application.

[0078] The Figure 5 stress change trend in Figures 4c-4e is obtained by respectively obtaining the representations of the vertical stress and the horizontal stress of the corresponding top unit A, side wall unit B, and bottom unit C, and getting the trend of the difference between the vertical stress and the horizontal stress changing with excavation.

[0079] In Figure 5 , as the excavation face advances forward, the stress difference between the top unit and the bottom unit of the tunnel at the observation surface gradually increases significantly, while the stress difference of the tunnel side wall unit gradually decreases. It shows that under this in-situ stress state of the roadway cross-section, the tangential stress of the surrounding rock at the top and bottom of the roadway before and after excavation is loaded to a relatively high level, and the radial stress is unloaded to zero, and its surrounding rock gradually differentiates and evolves from a relatively uniform three-dimensional stress state to a two-dimensional stress state; while the surrounding rock of the roadway side wall is in the stress unloading area after excavation, and the stress concentration degree is weak.

[0080] Input the obtained stress values into the calculation model established in the FLAC3D finite element program to form a secondary stress distribution model of the stress value of the observation point and the corresponding excavation depth. From this secondary stress distribution model, the stress generated by tunnel excavation unloading in the surrounding rock is obtained. This stress includes:

[0081] Maximum principal stress: σ max = 37.22 MPa

[0082] Maximum tangential stress: σ θ = 27.73 MPa

[0083] Maximum axial stress: σ L = 11.41 MPa

[0084] In the above embodiments, the characteristic information further includes: rock mass strength. On this basis, step S130 may further include:

[0085] Obtain the corresponding rockburst grade according to the secondary stress distribution information and the rock mass strength of the surrounding rock in the target rockburst section.

[0086] Wherein, the rock mass strength includes the uniaxial compressive strength Rc of the rock.

[0087] According to the stress criterion for rockburst prediction, obtain the rockburst grades corresponding to each stress criterion, as shown in Table 1.

[0088] Table 1 Stress criterion for rockburst prediction

[0089]

[0090] Note: R c is the uniaxial compressive strength of the rock, σ max is the maximum principal stress, σ θ is the maximum tangential stress, σ L is the axial stress.

[0091] For the surrounding rock in the target rockburst section, obtain the uniaxial compressive strength Rc of the rock according to the sample depth, physical state and rock type of the surrounding rock.

[0092] In this embodiment, the sample depth is the drilling depth, that is, the sample depth is 450 m, the rock type is granite, and the physical state of the sample is saturated. Therefore, the corresponding uniaxial compressive strength Rc of the rock = 50 Mpa.

[0093] According to Table 1, from the numerical calculation results, only the Tao Zhenyu criterion determines that the section at the maximum tunnel depth (650 m) of the surrounding rock in the target rockburst section has a weak rockburst risk.

[0094] When the characteristic information is the integrity characteristic, the obtaining of the characteristic information of the surrounding rock in the rockburst section includes:

[0095] Obtain the corresponding saturated uniaxial compressive strength and dry compressive strength according to the rock type of the surrounding rock in the target rockburst section and the physical state of the sample, and obtain the overall integrity characteristic of the tunnel excavation position of the surrounding rock in the target rockburst section.

[0096] According to the sample depth, physical state and rock type of the surrounding rock, the dry compressive strength is also obtained as 130 Mpa, and the corresponding integrity characteristic is between 0.25 and 0.6, that is, the integrity is poor.

[0097] In this example, the secondary stress distribution information of the tunnel surrounding rock obtained in the previous example was loaded into a tunnel excavation model containing a fracture network, built using discrete element software. The distribution characteristics of microcracks in the surrounding rock during excavation unloading were obtained. The degree of surrounding rock damage caused by excavation was predicted based on these microcrack distribution characteristics. The quantitative effect of reducing microcracks within the surrounding rock using the upper and lower bench excavation method was calculated based on this damage level. Combined with the rockburst severity, on-site construction measures for preventing rockbursts were determined.

[0098] Determine on-site construction measures to prevent rock bursts. In this embodiment, the discrete element software is PFC2D.

[0099] After step S140, the present application may further include:

[0100] Obtain microseismic signals from the tunnel face and determine the corresponding rockburst level;

[0101] According to the rock burst level and the rock burst grade, corresponding on-site construction measures for preventing rock burst are determined.

[0102] Sensors for the microseismic monitoring system are installed at the tunnel face. These sensors can be installed in a borehole 2.5m deep, 40mm in diameter, and 1.5m above ground level. One row of sensors is installed approximately 70m from the tunnel face, with two rows spaced 30m apart. The last row of sensors is moved forward every 30m as excavation progresses. This allows the monitoring equipment to track the tunnel face's progress, enabling 24-hour monitoring of microseismic events caused by rock fractures near the tunnel face during tunnel construction.

[0103] In this embodiment, the energy criterion of microseismic signals is used to identify rockbursts. In principle, the number of valid microseismic events within 24 hours should reach 20. When the number of microseismic events within each energy level exceeds 3, it is considered that a rockburst of this level will occur. The energy criterion for identifying rockbursts with microseismic signals is shown in Table 2:

[0104] Table 2 Stress criteria for rockburst prediction

[0105]

[0106] During the excavation process, the tunnel face position on the first day was set as the initial position, and the tunnel face position on the 12th day was set as the final position. Because microfractures are rare when the rock mass is in a state of triaxial stress equilibrium, as blasting and excavation disrupt the initial stress field, stresses begin to shift and adjust, leading to a large number of microcracks and microseismic signals. The locations of concentrated microseismic signals generally exhibit a pattern of continuous advancement along the tunnel axis as the tunnel face advances. Once stress reaches secondary equilibrium, microfractures in the rock mass decrease, resulting in the phenomenon of microseismic signals continuously advancing as the tunnel face advances.

[0107] Compare the judgment conclusion of the energy criterion for discriminating rock bursts from microseismic signals with the actual rock burst situation. If the time length of the actual rock burst is less than the judgment conclusion, and the rock burst intensity is also less than or equal to the rock burst intensity of the judgment conclusion, the predicted rock burst level corresponding to it is lower than the rock burst level corresponding to the judgment conclusion; if the time length and / or rock burst intensity of the actual rock burst situation is equal to or higher than the judgment conclusion, then the predicted rock burst level corresponding to it is higher than the rock burst level corresponding to the judgment conclusion.

[0108] Compare the rock burst levels obtained by discriminating microseismic signals with those obtained by discriminating the secondary stress distribution of the surrounding rock in the target rock burst section, and use the higher rock burst level as the currently predicted rock burst level of the surrounding rock in the target rock burst section, so as to ensure that the corresponding on-site construction measures for preventing rock bursts can maximize the strengthening of the construction measures for preventing rock bursts.

[0109] For the corresponding construction measures for preventing rock bursts, according to the characteristics and related properties of rock bursts, rock bursts can be divided into 3 levels: weak rock burst, medium rock burst, and strong rock burst. Among the 3 levels, weak rock bursts have minimal impact on construction and basically pose no threat to personnel and machinery, so basically no special measures need to be taken during actual construction; medium rock bursts last for a long time and have a serious impact on the safety and psychology of machinery and construction personnel. Based on the idea of strengthening the surrounding rock, currently, the overall support method of steel support and shotcrete-anchor-mesh (steel mesh) is often used to support the medium rock burst section of the tunnel, and passive temporary support measures such as protective nets may also be adopted according to the actual situation during construction; strong rock bursts are extremely dangerous, and while strengthening the support, various auxiliary measures (such as advance stress construction release holes, etc.) are also required to weaken the surrounding rock and reduce the frequency and energy of rock bursts.

[0110] It should be understood that although the steps in the flowchart of the accompanying drawings are shown in sequence according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless there is a clear indication in this article, there is no strict order restriction for the execution of these steps, and they can be executed in other orders. Moreover, at least a part of the steps in the flowchart of the accompanying drawings may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be executed alternately or in turn with at least a part of other steps or sub-steps or stages of other steps.

[0111] The above description is only a preferred embodiment of the present application and an explanation of the technical principles applied. Those skilled in the art should understand that the scope of disclosure involved in the present application is not limited to the technical solutions formed by the specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the above disclosure concept. For example, the technical solutions formed by mutually replacing the above features with the technical features (but not limited to) disclosed in the present application that have similar functions.

Claims

1. A construction method for preventing tunnel rock bursts, characterized in that, It includes the following steps: Obtain the characteristic information of the surrounding rock in the target rockburst section; wherein, the characteristic information includes: in-situ stress characteristics and integrity characteristics; when the characteristic information is integrity characteristics, obtaining the characteristic information of the surrounding rock in the target rockburst section includes: according to the rock type of the surrounding rock in the target rockburst section and the physical state of the specimen, obtain the corresponding saturated uniaxial compressive strength and dry compressive strength, and obtain the overall integrity characteristics of the tunnel excavation location of the surrounding rock in the target rockburst section; According to the in-situ stress characteristics, obtain the secondary stress distribution of the surrounding rock in the target rockburst section during the tunnel excavation process; According to the secondary stress distribution of the surrounding rock in the target rockburst section, determine the rockburst grade through a stress criterion; Combine the rockburst grade with the distribution characteristics of microcracks to determine the on-site construction measures for preventing rockburst, including: according to the integrity characteristics, apply the secondary stress to the corresponding tunnel excavation model containing a fracture network to obtain the distribution characteristics of microcracks in the surrounding rock during excavation unloading; predict the damage degree of the surrounding rock caused by excavation according to the distribution characteristics of microcracks, and determine the on-site construction measures for preventing rockburst; according to the distribution characteristics of microcracks, predict the damage degree of the surrounding rock caused by excavation, and calculate the quantitative effect of reducing microcracks in the surrounding rock by using the top-down bench excavation according to the damage degree of the surrounding rock; Obtain the microseismic signal of the tunnel face, and determine the corresponding rockburst grade; compare the rockburst grade obtained by discriminating through the microseismic signal with the rockburst grade obtained by discriminating through the secondary stress distribution of the surrounding rock in the target rockburst section, and use the higher rockburst grade as the currently predicted rockburst grade of the surrounding rock in the target rockburst section to correct the on-site construction measures for preventing rockburst.

2. The construction method for preventing tunnel rockburst according to claim 1, wherein When the characteristic information is in-situ stress characteristics, obtaining the characteristic information of the surrounding rock in the target rockburst section includes: According to the drilling depth of the surrounding rock in the target rockburst section, obtain the plane maximum principal stress value, plane minimum principal stress value and plane maximum principal stress direction, and obtain the maximum horizontal in-situ stress value, minimum horizontal principal stress value and vertical principal stress value at the deepest buried part of the surrounding rock in the target rockburst section.

3. The construction method for preventing tunnel rockburst according to claim 2, wherein The obtaining of the secondary stress distribution of the surrounding rock in the target rockburst section during the tunnel excavation process according to the in-situ stress characteristics includes: Establish a calculation model in a finite element program, place the roadway section of the tunnel in the calculation model, and preset a shape for the roadway section; wherein, the roadway section includes corresponding observation points established at the top, side walls, bottom, right side inside the rock mass and top inside the rock mass; According to the maximum horizontal in-situ stress value, minimum horizontal principal stress value and vertical principal stress value at the deepest buried part of the surrounding rock in the target rockburst section, obtain the secondary stress distribution model of each observation point of each roadway section.

4. The construction method for preventing tunnel rockburst according to claim 3, wherein The obtaining of the secondary stress distribution model of each observation point of each roadway section includes: Determine the starting roadway section on the tunnel. Taking the starting roadway section as the starting point, obtain the stress values of all the observation points of each roadway section at the equidistant excavation length, and obtain the secondary stress distribution information of the stress values of the observation points corresponding to the excavation depth.

5. The construction method for preventing rock bursts in tunnels according to claim 4, wherein the characteristic information includes the rock mass strength; the judging of the rock burst grade according to the secondary stress distribution of the surrounding rock in the target rock burst section includes: obtaining the corresponding rock burst grade according to the secondary stress distribution information and the rock mass strength of the surrounding rock in the target rock burst section.

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