A tunnel on-site monitoring optimization design method

Abstract

The present invention discloses a tunnel field monitoring optimization design method, comprising the following steps: step 1: determine the intended monitoring area during tunnel construction; step 2: obtain rock samples in the intended monitoring area to obtain the macroscopic physical and mechanical parameters of the rock; step 3: calibrate the obtained macroscopic physical and mechanical parameters of the rock, and determine the boundary conditions of the model at the same time; step 4: correct the numerical simulation parameters to obtain parameters that can be used for subsequent numerical simulations; step 5: respectively carry out steel arch strain FEM-DEM coupling simulation and initial support contact stress CFD-DEM coupling simulation to determine the layout positions of steel arch strain monitoring points and initial support contact stress monitoring points; step 6: lay out steel arch strain gauges and earth pressure gauges, and carry out real-time monitoring. Through the present invention, the layout positions of monitoring points in the tunnel monitoring area can be scientifically and reasonably determined, and "key parts priority" can be achieved while considering the overall area, reducing the loss of monitoring instruments and monitoring costs.

Description

Technical Field

[0001] The invention belongs to the field of tunnel engineering construction, relates to tunnel monitoring technology, and in particular to a tunnel on-site monitoring optimization design method. Background Art

[0002] At present, as tunnel and underground engineering construction develops towards plateau mountainous areas with more complex geology and deep underground space, engineering construction faces extreme working conditions such as high altitude, high ground stress, and super-hard rock. Disasters such as tunnel water and mud bursts, surrounding rock collapse, large deformation, and rock bursts frequently occur. In this context, monitoring, measurement, and early warning technologies have gradually developed and have become an important support for the safety risk control of tunnels and underground engineering.

[0003] Different projects have different geological conditions, hydrological conditions and construction methods. In the existing monitoring technical specifications, only specific requirements for monitoring items and monitoring section spacing are given, but the specific layout location and monitoring frequency of monitoring points are not targeted, and it is impossible to provide complete and reliable information for tunnels and underground projects. In addition, the existing monitoring projects are mainly manual, with high monitoring frequency, large workload and measurement difficulty, and extremely high costs for carrying out monitoring work in the entire project area. Therefore, for different projects, it is an important part of tunnel and underground project monitoring to design a scientific and reasonable monitoring point layout plan in a targeted manner.

[0004] With the development of computer technology and the improvement of numerical theory, numerical simulation technology has become one of the mainstream means of studying underground engineering problems. Based on numerical calculation, the evolution process of rock damage disasters can be analyzed theoretically, and on this basis, the development of tunnel damage zone can be analyzed and predicted, and the numerical simulation safety factor of tunnel construction can be given. In actual engineering, the monitoring plan is dynamically adjusted according to the numerical simulation prediction results, and the scientific and reasonable monitoring points and section spacing are determined. The dynamic data of physical information of key parts in the tunnel is obtained in real time, which can provide a basis for real-time early warning of disasters such as sudden water and mud and surrounding rock collapse that may be encountered during construction, and realize active prevention and control of tunnels and underground projects. However, there are still few studies in this area. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a tunnel field monitoring optimization design method, which is particularly based on numerical calculation. According to the numerical simulation results, the layout positions of monitoring points in the tunnel monitoring area can be scientifically and reasonably determined, while considering the overall area, achieving "key parts priority" and reducing the loss of monitoring instruments and monitoring costs.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] The present invention provides a tunnel on-site monitoring optimization design method, which comprises the following steps:

[0008] (1) Based on the geological data and construction conditions obtained in the early stage, determine the areas where monitoring projects should be implemented during the tunnel construction process;

[0009] (2) Obtain rock samples from the planned monitoring area and conduct indoor rock mechanics experiments, such as uniaxial compression test, Brazilian splitting test, biaxial compression test, stacking angle test, particle screening test, etc., to obtain the particle grading curve of the rock sample, as well as the sample's uniaxial compressive strength, triaxial strength, tensile strength, elastic modulus, Poisson's ratio, friction angle, cohesion, friction coefficient and other macroscopic mechanical parameters, to provide basis parameters for subsequent discrete element numerical calculation;

[0010] (3) In the discrete element DEM software, the “trial and error method” is used to carry out parameter calibration based on the macroscopic physical and mechanical parameters of the rock obtained above, so that the strength index of the generated rock model is consistent with the obtained rock sample, and the three-dimensional calculation model of the monitoring area is established. Secondly, based on the previous geological data, the boundary conditions and other parameters of the calculation model are determined;

[0011] (4) Based on geological data, a typical pile number is selected in the monitoring area to carry out preliminary numerical simulation and monitoring for the correction of numerical calculation parameters. If the numerical calculation result at the pile number is the same as the monitoring result, the parameter is determined as the parameter used for subsequent calculations. If they are different, the parameter is further corrected;

[0012] (5) Based on the modified model parameters and boundary conditions, the FEM-DEM coupled simulation of the steel arch strain and the CFD-DEM coupled simulation of the initial support contact stress were carried out to determine the most likely deformation point of the steel arch and the maximum contact stress point of the initial support, so as to determine the layout locations of the steel arch strain monitoring points and the initial support contact stress monitoring points;

[0013] Specifically, the FEM-DEM coupled simulation of steel arch strain includes the following steps:

[0014] 1) Steel arch model settings:

[0015] Based on the on-site design data, obtain the layout of the steel arch frame used on the tunnel project site;

[0016] According to the layout of the steel arch frame used in the tunnel engineering site, the three-dimensional steel arch frame model is established in the solidworks software, and the grid is divided in the pre-processing software and imported into the DEM software. Then the steel arch frame model is imported into the DEM software to wait for coupling calculation;

[0017] 2) Particle model establishment:

[0018] According to the model parameters and boundary conditions corrected in step 4, and in accordance with geological data and construction conditions, the three-dimensional particle model is established in the DEM software, mainly including setting the particle radius to r, the particle density to ρ_p, the particle Poisson's ratio to γ_p, the particle-particle static friction system to μ_r1, the particle-arch static friction system to μ_r2, the particle-particle static friction coefficient to μ_s1, the particle-particle rolling friction coefficient to μ_s2, the particle recovery coefficient to μ_j, the Hertz-Mindlin Bonding model is selected as the particle contact model, the normal stiffness k_n of the bond between particles, the tangential strength k_s of the bond, the normal tensile strength δ_n of the bond, the shear strength δ_s of the bond, the radius r_b of the bond are set, and the contact torque is set to be fed back to the particles in the contact model to complete the establishment of the three-dimensional particle model, as shown in the attached figure. Figure 2 As shown;

[0019] 3) FEM-DEM coupling calculation:

[0020] In the DEM software, the time step is set to In order to ensure the stability of discrete element calculation, the time step should be set to 20% of the Rayleigh time step, the discrete element contact search grid size should be set to 2.5 times the minimum particle size, the total simulation time should be set to T, and the discrete element calculation should be stopped when the calculation time t>T.

[0021] Then, the FEM-DEM coupling interface is opened, and the particle load in the DEM is imported into the FEM software, so that the particle load is distributed on the surface of the steel arch frame. According to the actual situation on site, the stiffness of the arch frame is set to K_g, the tensile yield strength of the arch frame is δ_g, and the tensile ultimate strength is δ_t, and the stress and deformation of the steel arch frame are analyzed;

[0022] 4) Determination of steel arch strain monitoring points:

[0023] In the FEM software, the stiffness K_g, tensile yield strength δ_g, and tensile ultimate strength δ_t of the arch frame are gradually reduced, the DEM particle parameters and boundary conditions remain unchanged, and multi-condition simulation is carried out to analyze the deformation and stress of the steel arch frame under different yield strengths;

[0024] The position of the arch frame with large strain is obtained according to the simulation results. Specifically, the strain threshold of the steel arch frame is set to ε1. The strain size under the steel arch frame at different strengths is obtained through the post-processing function of the FEM software. The points where the strain exceeds the threshold ε1 are marked and numbered as x1, x2, x3, x4, ..., which are the actual layout points of the subsequent arch frame strain monitoring work.

[0025] Specifically, the CFD-DEM simulation of initial support contact stress includes the following steps:

[0026] 1) Particle model settings:

[0027] According to the model parameters and boundary conditions corrected in step 4, and in accordance with geological data and construction conditions, the three-dimensional particle model is established in the DEM software, mainly including setting the particle radius to r, the particle density to ρ_p, the particle Poisson's ratio to γ_p, the particle-particle static friction system to μ_r1, the particle-arch static friction system to μ_r2, the particle-particle static friction coefficient to μ_s1, the particle-particle rolling friction coefficient to μ_s2, the particle recovery coefficient to μ_j, the Hertz-Mindlin Bonding model is selected as the particle contact model, the normal stiffness k_n of the bond between particles, the tangential strength k_s of the bond, the normal tensile strength δ_n of the bond, the shear strength δ_s of the bond, the radius r_b of the bond, and setting the contact torque to be fed back to the particles in the contact model to complete the establishment of the three-dimensional particle model; as shown in the attached figure, Figure 3 As shown;

[0028] 2) Fluid domain generation:

[0029] Obtain the groundwater distribution in the monitoring area based on geological data;

[0030] Divide the 3D groundwater model at the corresponding spatial position in the numerical model, and divide the 3D groundwater model into appropriate fluid calculation grids in the pre-processing software, ensuring that the grid size is larger than the particle size, which is used to simulate the flow of groundwater in the surrounding rock, set the fluid inlet and outlet conditions, and wait for the coupled calculation;

[0031] 3) Initial support setting:

[0032] Through the API secondary development function of the discrete element software, the particles within a certain range of the tunnel excavation circle are retrieved and grouped, and the bonding parameters of this group of particles are reassigned, mainly including improving the bonding strength δ_n and δ_s between particles, thereby improving the overall strength of the surrounding rock, to simulate the process of initial support and reinforcement of the surrounding rock by shotcrete;

[0033] 4) CFD-DEM coupling calculation:

[0034] In the CFD software, the fluid time step is set to , the DEM time step is set to , and Set to The simulation time step is set to s_0, the CFD-DEM coupling interface is turned on, the incomplete solution strategy is adopted, the Di Felice drag model is selected to simulate the interaction between groundwater and rock, and the groundwater pressure is set to P_w according to the geological data. If the current calculation time step s_t>s_0, the CFD-DEM coupling calculation is stopped to analyze the stress condition of the initial support;

[0035] 5) Determination of initial support contact stress monitoring point:

[0036] In the CFD software, the groundwater pressure is gradually increased to P_w, and multiple working condition simulations are carried out according to the same DEM particle parameters to analyze the deformation and stress of the initial support under different water pressures P_w;

[0037] The initial support contact stress is obtained according to the simulation results. Specifically, the initial support strain threshold is set to ε2. The particle stress of the initial support under different water pressures is obtained through the post-processing function of the DEM software. The points where the particle stress exceeds the threshold ε2 are marked and numbered as y1, y2, y3, y4, ..., which are the actual layout points for subsequent initial support stress monitoring work.

[0038] (6) The arch frame strain monitoring points and initial contact stress monitoring points obtained by the above numerical simulation are the actual monitoring points. Steel frame strain gauges are arranged at the arch frame x1, x2, x3, x4, etc. for subsequent monitoring of the arch frame strain information. The bottom surfaces of the bases at the left and right ends of the strain gauges should fit tightly with the surface of the steel arch frame and be welded to the side of the steel frame; earth pressure gauges are arranged at the initial support y1, y2, y3, y4, etc. for subsequent monitoring of the initial support contact stress. The pressure-bearing surface of the earth pressure gauge should face the surrounding rock surface. The pressure-bearing surface should be selected as close to the surrounding rock as possible at a relatively flat place, and the bracket should be welded to the steel arch frame. The tail of the bracket that exceeds the steel frame needs to be cut to prevent the tail from being too long and causing construction damage.

[0039] (7) The steel arch strain gauges and earth pressure gauges installed above are connected to wireless spread spectrum monitoring instruments for real-time acquisition of monitoring information. If the monitoring value exceeds the set threshold and the structure shows obvious deformation and displacement, an early warning is issued and corresponding disposal measures are taken according to the on-site emergency plan.

[0040] Beneficial effects: Compared with the prior art, the present invention has at least the following advantages: 1. The method of the present invention is based on numerical calculations, and can optimize the point distribution mode and layout location of existing tunnel monitoring projects based on the results of three-dimensional numerical calculations, while considering the overall area to achieve "priority for key areas", reducing the loss of monitoring instruments and monitoring costs. 2. The method of the present invention dynamically adjusts the monitoring scheme based on the numerical simulation prediction results, and obtains dynamic data of physical information of key parts in the tunnel in real time, which can provide a basis for real-time early warning of disasters such as sudden water and mud and surrounding rock collapse that may be encountered during construction, and take corresponding disposal measures according to the on-site emergency plan, thereby improving the ability to respond to and resolve emergencies.

[0041] It should be understood that the implementation of any embodiment of the present invention does not mean that multiple or all of the above-mentioned beneficial effects must be possessed or achieved at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0043] The structures, proportions, sizes, etc. illustrated in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantial technical significance. Any structural modification, change in proportion or adjustment in size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0044] Figure 1 A flow chart of the on-site monitoring optimization design method according to an embodiment of the present invention;

[0045] Figure 2 Schematic diagram of FEM-DEM coupled simulation of steel arch strain in an embodiment of the present invention, wherein 1 is a particle model and 2 is a laid steel arch;

[0046] Figure 3 Schematic diagram of CFD-DEM coupled simulation of initial support contact stress in an embodiment of the present invention, wherein 1 is the flow field inlet, 2 is the flow field outlet, and 3 is the tunnel face position.

[0047] In the various drawings, the same or corresponding reference numerals represent the same or corresponding parts. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in conjunction with the embodiments and drawings. Here, the illustrative embodiments of the present invention and their description are used to explain the present invention, but are not intended to limit the present invention.

[0049] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0050] It should be understood that the terms "include / comprise", "consist of..." or any other variations are intended to cover non-exclusive inclusion, so that a product, device, process or method that includes a series of elements includes not only those elements, but also may include other elements not explicitly listed when necessary, or also includes elements inherent to such product, device, process or method. In the absence of more restrictions, the elements defined by the sentence "include / comprise...", "consist of..." do not exclude the presence of other identical elements in the product, device, process or method that includes the elements.

[0051] It is also necessary to understand that terms such as "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside" and "outside" to indicate directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device, component or structure must have a specific direction, be constructed or operate in a specific direction, and should not be understood as a limitation on the present invention.

[0052] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0053] Numerical simulation technology has become one of the mainstream means of studying underground engineering problems. In actual projects, the monitoring plan is dynamically adjusted based on the numerical simulation prediction results, and scientific and reasonable monitoring points and section spacing are determined. The dynamic data of physical information of key parts in the tunnel is obtained in real time, which reduces the loss and monitoring cost of monitoring instruments, provides a basis for real-time early warning of disasters such as sudden water and mud and surrounding rock collapse that may be encountered during construction, and realizes active prevention and control of tunnels and underground projects.

[0054] Based on this, the present invention provides a tunnel on-site monitoring optimization design method, which includes the following steps: Step 1: Based on the acquired geological data and construction conditions, determine the area to be monitored during the tunnel construction process; Step 2: Obtain rock samples in the area to be monitored, carry out rock mechanics tests and obtain the macroscopic physical and mechanical parameters of the rock; Step 3: calibrate the obtained macroscopic physical and mechanical parameters of the rock, and establish a three-dimensional calculation model of the area to be monitored, and determine the boundary conditions of the model; Step 4: Based on the geological data, select typical pile numbers in the monitoring area to carry out preliminary numerical simulation and monitoring, and then The parameters of numerical simulation are corrected to obtain the parameters that can be used for subsequent numerical simulation; Step 5: Based on the corrected model parameters and boundary conditions, the FEM-DEM coupling simulation of steel arch strain and the CFD-DEM coupling simulation of initial support contact stress are respectively carried out to determine the most likely deformation point of the steel arch and the maximum contact stress of the initial support, so as to determine the layout positions of the steel arch strain monitoring points and the initial support contact stress monitoring points; Step 6: The steel arch strain gauge is laid out at the steel arch strain monitoring point for monitoring the steel arch strain information; the soil pressure gauge is laid out at the initial support contact stress monitoring point for monitoring the initial support contact stress. Through the method of the present invention, the layout mode, layout position, etc. of the tunnel monitoring project can be optimized, and "key parts priority" can be achieved while considering the overall area, and the dynamic data of the physical information of the key parts in the tunnel can be obtained in real time, reducing the loss of monitoring instruments and monitoring costs.

[0055] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0056] The present invention provides a tunnel on-site monitoring optimization design method, combined with Figure 1 The flowchart shown is used to describe the embodiment of the present invention in detail.

[0057] Step 1: Based on the geological data and construction conditions obtained in the early stage, determine the area to be monitored during the tunnel construction process, that is, the area where the monitoring project will be implemented.

[0058] Step 2: Obtain rock samples in the planned monitoring area and further obtain the macroscopic physical and mechanical parameters of the rock; the macroscopic physical and mechanical parameters include uniaxial compressive strength, tensile strength, etc.;

[0059] The specific steps include:

[0060] Step 2.1: Drill a set of rock samples using a tunnel borehole and transport them to the laboratory for indoor rock mechanics experiments;

[0061] Step 2.2: Carry out indoor rock mechanics experiments on the obtained rock samples. First, a screening experiment is carried out to obtain the particle grading curve of the rock. Then the rock samples are made into standard samples of 50mm*100mm. Uniaxial compression test, Brazilian splitting test, biaxial compression test and stacking angle test are carried out to obtain the macroscopic physical and mechanical parameters of the rock, including Poisson's ratio ε, uniaxial compressive strength UCS, elastic modulus E, tensile strength ten, friction angle φ and friction coefficient υ.

[0062] Step 3: Calibrate the obtained macroscopic physical and mechanical parameters of the rock, establish a three-dimensional calculation model of the planned monitoring area, and determine the boundary conditions of the model;

[0063] The specific steps include:

[0064] Step 3.1: According to the rock macroscopic physical and mechanical parameters such as Poisson's ratio ε, uniaxial compressive strength UCS, elastic modulus E, tensile strength ten, friction angle φ, friction coefficient υ obtained in step 2, the discrete element parameter calibration is carried out by the "trial and error method" to obtain the parameters of the Hertz-Mindlin Bonding model, including: bond normal stiffness k_n, bond tangential strength k_s, bond normal tensile strength δ_n, bond shear strength δ_s, bond radius r_b, so that the strength index of the generated rock calculation model is consistent with the obtained rock sample;

[0065] Step 3.2: Based on the previous geological data, determine the boundary conditions of the three-dimensional numerical model, including horizontal stress δ_h and deadweight δ_g.

[0066] Step 4: Based on geological data, select typical pile numbers in the monitoring area to carry out preliminary numerical simulation and monitoring, and modify the numerical simulation parameters to obtain parameters that can be used for subsequent numerical simulations;

[0067] The specific steps include:

[0068] Step 4.1: Based on the geological data, select the IV-V level surrounding rock in the monitoring area, assuming that the pile number is K_1;

[0069] Step 4.2: Carry out preliminary numerical simulation based on the parameters and boundary conditions calibrated in step 3, and gradually install sensors at K_1 to compare the stress and strain data obtained by numerical calculation and monitoring;

[0070] Step 4.3: If the stress-strain data obtained by numerical calculation and monitoring are the same or approximately the same, then the simulation parameters and boundary conditions at this time are determined to be consistent with the actual situation. If the results are different, change the parameters and boundary conditions and conduct the simulation again until the stress-strain results are the same, thus completing the parameter correction.

[0071] By initially comparing the on-site sensor monitoring data with the numerical simulation data, and continuously correcting the model's boundary conditions to make the simulation data consistent with the historical monitoring data, the correct boundary conditions can be determined. Compared with the traditional method of setting boundary conditions based only on the results of previous geological surveys, this method is more accurate.

[0072] Step 5: Based on the modified model parameters and boundary conditions, carry out FEM-DEM coupling simulation of steel arch strain and CFD-DEM coupling simulation of initial support contact stress respectively, determine the most likely deformation point of the steel arch and the maximum contact stress point of the initial support, and determine the layout positions of the steel arch strain monitoring points and the initial support contact stress monitoring points;

[0073] Among them, the FEM-DEM coupling simulation of steel arch strain specifically includes the following steps:

[0074] Step 5.11: Based on the on-site design data, obtain the layout of the steel arch frame used on the tunnel engineering site;

[0075] Step 5.12: Complete the establishment of the three-dimensional steel arch model in the solidworks software, complete the mesh division in the pre-processing software and import it into the DEM software, and then import the steel arch model into the DEM software to wait for coupling calculation;

[0076] Step 5.13: Based on the model parameters and boundary conditions modified in step 4, and in accordance with geological data and construction conditions, the three-dimensional particle model is established in the DEM software, mainly including setting the particle radius to r, the particle density to ρ_p, the particle Poisson's ratio to γ_p, the particle-particle static friction system to μ_r1, the particle-arch static friction system to μ_r2, the particle-particle static friction coefficient to μ_s1, the particle-particle rolling friction coefficient to μ_s2, the particle recovery coefficient to μ_j, the Hertz-Mindlin Bonding model is selected as the particle contact model, the normal stiffness k_n of the bond between particles, the tangential strength k_s of the bond, the normal tensile strength δ_n of the bond, the shear strength δ_s of the bond, the radius r_b of the bond, and setting the contact torque to be fed back to the particles in the contact model to complete the establishment of the three-dimensional particle model, as shown in the attached figure. Figure 2 As shown;

[0077] Step 5.14: Set the time step in the DEM software to In order to ensure the stability of discrete element calculation, the time step should be set to 20% of the Rayleigh time step, the discrete element contact search grid size should be set to 2.5 times the minimum particle size, the total simulation time should be set to T, and the discrete element calculation should be stopped when the calculation time t>T.

[0078] Step 5.15: After the DEM calculation is completed, the FEM-DEM coupling interface is opened, and the particle load in the DEM is imported into the FEM software to distribute the particle load on the surface of the steel arch. According to the actual situation on site, the stiffness of the arch is set to K_g, the tensile yield strength of the arch is δ_g, and the tensile ultimate strength is δ_t, and the stress and deformation of the steel arch are analyzed;

[0079] Step 5.16: In the FEM software, the stiffness K_g, tensile yield strength δ_g, and tensile ultimate strength δ_t of the arch frame are gradually reduced, the DEM particle parameters and boundary conditions remain unchanged, and multi-condition simulation is carried out to analyze the deformation and stress of the steel arch frame under different yield strengths;

[0080] Step 5.17: Set the strain threshold of the steel arch frame to ε1. Through the post-processing function of the FEM software, obtain the strain size under the steel arch frame at different strengths. Mark the points where the strain exceeds the threshold ε1 and number them as x1, x2, x3, x4, ..., which are the actual layout points for subsequent arch frame strain monitoring work.

[0081] When encountering weak rock formations during tunnel construction, steel arch support must be carried out to improve the stability of the surrounding rock. However, traditional tunnel discrete element simulation only considers the deformation of the surrounding rock and cannot simulate the mechanical behavior of the steel arch. This step uses the FEM-DEM method to simulate the strain of the tunnel steel arch based on the previously modified numerical model and boundary conditions, that is, the DEM is used to establish the tunnel surrounding rock model, and the FEM method is used to establish the steel arch model. The stress mapping of the surrounding rock particles can be transferred to the FEM grid through the coupling interface to simulate the mechanical behavior of the steel arch. Compared with the traditional discrete element tunnel simulation, it can analyze the stability of the surrounding rock more scientifically.

[0082] The CFD-DEM simulation of the initial support contact stress includes the following steps:

[0083] Step 5.21: Based on the model parameters and boundary conditions modified in step 4, and in accordance with geological data and construction conditions, the three-dimensional particle model is established in the DEM software, mainly including setting the particle radius to r, the particle density to ρ_p, the particle Poisson's ratio to γ_p, the particle-particle static friction system to μ_r1, the particle-arch static friction system to μ_r2, the particle-particle static friction coefficient to μ_s1, the particle-particle rolling friction coefficient to μ_s2, the particle recovery coefficient to μ_j, the Hertz-Mindlin Bonding model is selected as the particle contact model, the normal stiffness k_n of the bond between particles, the tangential strength k_s of the bond, the normal tensile strength δ_n of the bond, the shear strength δ_s of the bond, the radius r_b of the bond, and setting the contact torque to be fed back to the particles in the contact model to complete the establishment of the three-dimensional particle model, as shown in the attached figure. Figure 3As shown;

[0084] Step 5.22: Based on geological data, obtain the groundwater distribution in the monitoring area;

[0085] Step 5.23: Divide the 3D groundwater model at the corresponding spatial position in the 3D particle model, and divide the 3D groundwater model into appropriate fluid calculation grids in the pre-processing software, ensure that the grid size is larger than the particle size, set the fluid inlet and outlet conditions, and wait for the coupled calculation;

[0086] Step 5.24: Through the API secondary development function of discrete element software (such as EDEM, PFC), the particles within a certain range of the tunnel excavation circle are retrieved and grouped, and the bonding parameters of this group of particles are reassigned, mainly including improving the bonding strength δ_n and δ_s between particles, thereby improving the overall strength of the surrounding rock, to simulate the process of initial support and reinforcement of the surrounding rock by shotcrete;

[0087] When grouting reinforcement is carried out on the tunnel site, the thickness of the grouting reinforcement ring has a great influence on the mechanical behavior of the surrounding rock. This step uses API secondary development to reassign the particle strength at the corresponding position in the model according to the actual grouting reinforcement thickness on site.

[0088] Step 5.25: Set the fluid time step in the CFD software to , the DEM time step is set to , and Set to The simulation time step is set to s_0, the CFD-DEM coupling interface is turned on, the incomplete solution strategy is adopted, the Di Felice drag model is selected to simulate the interaction between groundwater and rock, and the groundwater pressure is set to P_w according to the geological data. If the current calculation time step s_t>s_0, the CFD-DEM coupling calculation is stopped to analyze the stress condition of the initial support;

[0089] Step 5.26: In the CFD software, gradually increase the groundwater pressure to P_w, carry out multi-condition simulation according to the same DEM particle parameters, and analyze the deformation and stress of the initial support under different water pressures P_w;

[0090] Step 5.27: Set the initial support strain threshold to ε2, and obtain the particle stress of the initial support under different water pressures through the post-processing function of the DEM software. Mark the points where the particle stress exceeds the threshold ε2 and number them as y1, y2, y3, y4, ..., which are the actual layout points for subsequent initial support stress monitoring work. These points are arranged on the initial support.

[0091] This step takes into account the influence of pressurized water on the mechanical properties of rock mass and the stability of tunnel excavation. The fluid-solid coupling (CFD-DEM) method is used to establish a tunnel excavation coupling calculation model. The changing laws of the mechanical properties of rock mass and the stability of tunnel excavation under different water pressures are studied, and the mechanical behavior of the support under water pressure can be obtained.

[0092] Step 6: Arrange steel arch strain gauges at the steel arch strain monitoring points obtained in step 5.17 to monitor the steel arch strain information; arrange soil pressure gauges at the initial support contact stress monitoring points obtained in step 5.27 to monitor the initial support contact stress.

[0093] Step 6.1: At the steel arch positions x1, x2, x3, x4, etc., steel frame strain gauges are arranged for subsequent monitoring of the arch strain information. The bottom surfaces of the bases at the left and right ends of the strain gauges should fit closely with the surface of the steel arch and be welded to the side of the steel frame;

[0094] Step 6.2: At the large strain positions of the arch frame, such as y1, y2, y3, and y4, earth pressure gauges are laid out for subsequent monitoring of the initial support contact stress. The pressure-bearing side of the earth pressure gauge should face the surrounding rock surface, and the pressure-bearing surface should be selected as close to the surrounding rock as possible at a relatively flat part of the surrounding rock. The bracket is welded to the steel arch frame, and the tail of the bracket that extends beyond the steel frame needs to be cut to prevent the tail from being too long and causing construction damage.

[0095] Step 7: Finally, connect the steel arch frame strain gauge and earth pressure gauge to the wireless spread spectrum monitor to obtain real-time monitoring information of the steel arch frame strain and initial support contact stress. If the monitoring value exceeds the set threshold and the structure shows obvious deformation and displacement, an early warning will be issued and corresponding disposal measures will be taken according to the on-site emergency plan.

[0096] Although several specific implementation details are included in the above discussion, these should not be construed as limiting the scope of the present invention. Certain features described in the context of separate embodiments may also be implemented in a single implementation in combination. On the contrary, the various features described in the context of a single implementation may also be implemented in multiple implementations individually or in any suitable sub-combination.

Claims

1. A tunnel on-site monitoring optimization design method, characterized in that: The steps include: Step 1: Based on the acquired geological data and construction conditions, determine the area to be monitored during tunnel construction; Step 2: Obtain rock samples in the planned monitoring area, conduct rock mechanics tests and obtain the macroscopic physical and mechanical parameters of the rock; Step 3: Calibrate the obtained macroscopic physical and mechanical parameters of the rock, establish a three-dimensional calculation model of the planned monitoring area, and determine the boundary conditions of the model; Step 4: Based on geological data, select typical pile numbers in the monitoring area to carry out preliminary numerical simulation and monitoring, and modify the numerical simulation parameters to obtain parameters that can be used for subsequent numerical simulations; Step 5: Based on the modified model parameters and boundary conditions, carry out FEM-DEM coupling simulation of steel arch strain and CFD-DEM coupling simulation of initial support contact stress respectively, determine the most likely deformation point of the steel arch and the maximum contact stress point of the initial support, and determine the layout positions of the steel arch strain monitoring points and the initial support contact stress monitoring points; Step 6: Arrange steel arch strain gauges at the steel arch strain monitoring points to monitor the steel arch strain information; arrange earth pressure gauges at the initial support contact stress monitoring points to monitor the initial support contact stress; and In step 5, the FEM-DEM coupled simulation of the steel arch strain includes: Step 5.11: Based on the on-site design data, obtain the layout of the steel arch frame used on the tunnel engineering site; Step 5.12: Establish a three-dimensional steel arch model, complete the mesh division in the pre-processing software and import it into the DEM software, and then import the steel arch model into the DEM software to wait for coupling calculation; Step 5.13: Based on the revised model parameters and boundary conditions, according to the geological data and construction conditions, a three-dimensional particle model is established in the DEM software; Step 5.14: Set the time step in the DEM software to , perform discrete element calculation, set the total simulation time to T, and stop discrete element calculation when the calculation time t>T; Step 5.15: After the DEM calculation is completed, the FEM-DEM coupling interface is opened, and the particle load in the DEM is imported into the FEM software to distribute the particle load on the surface of the steel arch. According to the actual situation on site, the stiffness of the steel arch is set to K_g, the tensile yield strength is set to δ_g, and the tensile ultimate strength is set to δ_t, and the stress and deformation of the steel arch are analyzed; Step 5.16: In the FEM software, the stiffness K_g, tensile yield strength δ_g, and tensile ultimate strength δ_t of the steel arch frame are gradually reduced, the DEM particle parameters and boundary conditions remain unchanged, and multi-condition simulation is carried out to analyze the deformation and stress of the steel arch frame under different yield strengths; Step 5.17: Set the strain threshold of the steel arch frame to ε1, obtain the strain size of the steel arch frame under different strengths through the post-processing function of the FEM software, mark the points where the strain exceeds the threshold ε1, and number them as x1, x2, x3, x4, ..., which are the layout points for subsequent steel arch frame strain monitoring; In step 5, the initial support contact stress CFD-DEM coupled simulation is carried out including: Step 5.21: Based on the revised model parameters and boundary conditions, according to the geological data and construction conditions, a three-dimensional particle model is established in the DEM software; Step 5.22: Based on geological data, obtain the groundwater distribution in the monitoring area; Step 5.23: Divide the 3D groundwater model at the corresponding spatial position in the 3D particle model, and divide the 3D groundwater model into appropriate fluid calculation grids in the pre-processing software, ensure that the grid size is larger than the particle size, set the fluid inlet and outlet conditions, and wait for the coupled calculation; Step 5.24: Use discrete element software to simulate the process of initial support and reinforcement of surrounding rock by shotcrete; Step 5.25: Set the fluid time step in the CFD software to , the DEM time step is set to , and Set to The simulation time step is set to s_0, the CFD-DEM coupling interface is turned on, the incomplete solution strategy is adopted, the Di Felice drag model is selected to simulate the interaction between groundwater and rock, and the groundwater pressure is set to P_w according to the geological data. If the current calculation time step s_t>s_0, the CFD-DEM coupling calculation is stopped to analyze the stress condition of the initial support; Step 5.26: In the CFD software, gradually increase the groundwater pressure to P_w, carry out multi-condition simulation according to the same DEM particle parameters, and analyze the deformation and stress of the initial support under different water pressures P_w; Step 5.27: Set the initial support strain threshold to ε2, and obtain the particle stress of the initial support under different water pressures through the post-processing function of the DEM software. Mark the points where the particle stress exceeds the threshold ε2 and number them as y1, y2, y3, y4, ..., which are the layout points for subsequent initial support contact stress monitoring.

2. The method according to claim 1, characterized in that: The step 2 comprises: Step 2.1: Drilling a set of rock samples using a tunnel bore; Step 2.2: Carry out indoor rock mechanics experiments on the obtained rock samples to obtain the particle grading curve of the rock and obtain the macroscopic physical and mechanical parameters of the rock, including Poisson's ratio ε, uniaxial compressive strength UCS, elastic modulus E, tensile strength ten, friction angle φ, and friction coefficient υ.

3. The method according to claim 1, characterized in that The step 3 comprises: Step 3.1: According to the obtained macroscopic physical and mechanical parameters of the rock, the discrete element parameter calibration is carried out by the "trial and error method" to obtain the parameters of the Hertz-Mindlin Bonding model, including: bond normal stiffness k_n, bond tangential strength k_s, bond normal tensile strength δ_n, bond shear strength δ_s, bond radius r_b, so that the strength index of the generated rock calculation model is consistent with the obtained rock sample; Step 3.2: Based on the previous geological data, determine the boundary conditions of the three-dimensional numerical model, including horizontal stress δ_h and deadweight δ_g.

4. The method according to claim 1, characterized in that: The step 4 comprises: Step 4.1: Based on the geological data, select the IV-V level surrounding rock in the monitoring area, assuming that the pile number is K_1; Step 4.2: Carry out preliminary numerical simulation based on the calibrated parameters and boundary conditions, and gradually install sensors at K_1 to compare the stress and strain data obtained by numerical calculation and monitoring; Step 4.3: If the stress-strain data obtained by numerical calculation and monitoring are the same or approximately the same, then the simulation parameters and boundary conditions at this time are determined to be consistent with the actual situation. If the results are different, change the parameters and boundary conditions and conduct the simulation again until the stress-strain results are the same, thus completing the parameter correction.

5. The method according to claim 1, characterized in that: In step 5.24, the process of simulating the initial support and reinforcement of the surrounding rock by shotcrete is specifically as follows: through the API secondary development function of the discrete element software, the particles within a certain range of the tunnel excavation circle are retrieved and grouped, and the bonding parameters of this group of particles are reassigned, mainly including improving the bonding strength of the bonding bonds between the particles to enhance the overall strength of the surrounding rock, to simulate the process of initial support and reinforcement of the surrounding rock by shotcrete.

6. The method according to claim 1, characterized in that The establishment of the three-dimensional particle model mainly includes: Set the particle radius to r, the particle density to ρ_p, the particle Poisson's ratio to γ_p, the particle-particle static friction system to μ_r1, the particle-arch static friction system to μ_r2, the particle-particle static friction coefficient to μ_s1, the particle-particle rolling friction coefficient to μ_s2, the particle restitution coefficient to μ_j, select the Hertz-Mindlin Bonding model as the inter-particle contact model, set the inter-particle bond normal stiffness k_n, the bond tangential strength k_s, the bond normal tensile strength δ_n, the bond shear strength δ_s, the bond radius r_b, and set the contact torque to be fed back to the particle in the contact model to complete the establishment of the three-dimensional particle model.

7. The method according to claim 1, characterized in that The step 6 comprises: Step 6.1: At the x1, x2, x3, and x4 positions of the steel arch frame, steel frame strain gauges are arranged for subsequent monitoring of the steel arch frame strain information. The bottom surfaces of the bases at the left and right ends of the strain gauges are tightly fitted to the surface of the steel arch frame and welded to the side of the steel frame; Step 6.2: At the positions of large strain y1, y2, y3, and y4 of the initial support, earth pressure gauges are arranged for subsequent monitoring of the initial support contact stress. The pressure-bearing surface of the earth pressure gauge faces the surrounding rock surface, and the earth pressure gauge bracket is welded to the steel arch frame.

8. The method according to claim 1, characterized in that Also includes: Step 7: Connect the steel arch strain gauge and soil pressure gauge to the wireless spread spectrum monitor to obtain real-time monitoring information on the steel arch strain and initial support contact stress. If the monitoring value exceeds the set threshold and the structure shows obvious deformation and displacement, an early warning will be issued and corresponding disposal measures will be taken according to the on-site emergency plan.

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