Deep tunnel surrounding rock pressure arch range determination method based on energy density theory

Abstract

The invention discloses a deep tunnel surrounding rock pressure arch range determination method based on an energy density theory. The method comprises the following steps: establishing a tunnel calculation model; setting an energy density calculation formula; setting a model excavation process and excavation unbalanced force precision; exporting a detailed. Dat file after calculation to Tecplot software, and visualizing energy density calculation results before and after excavation of the model tunnel; and determining a pressure arch range according to the inner and outer boundary curves. According to the method, the inner boundary and the outer boundary of the surrounding rock pressure arch are determined according to the energy density change disturbance range, the situation that pressure arch definition and boundary determination methods at the present stage depend on the magnitude and the direction of surrounding rock stress is avoided, and meanwhile the problem of judgment dispute of the deflection degree of a principal stress vector can be solved; by means of the method, the inner boundary range and the outer boundary range of the surrounding rock pressure arch can be rapidly and effectively obtained, and the evolution rule of the three-dimensional pressure arch along with tunnel excavation can be observed.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel pressure arch calculation, and in particular relates to a method for determining the range of a deep-buried tunnel surrounding rock pressure arch based on energy density theory. Background Art

[0002] After the excavation of the rough tunnel, the overlying strata will undergo a deformation-loosening and collapse process, and terminate within a relatively stable range below the surface. This phenomenon is called stratum arching. Due to the existence of the surrounding rock pressure arch, the mechanical action range of the rough tunnel excavation on the surrounding rock is limited. The rock and soil within the pressure arch bears its own and the stratum load above it, ensuring that the stratum above it will not continue to collapse. Therefore, the study of the surrounding rock pressure arch theory has very important practical significance for guiding the support design and construction of the rough tunnel tunnel, especially the study of the surrounding rock pressure arch range.

[0003] At present, the definition and boundary determination methods of pressure arch rely on the magnitude and direction of surrounding rock stress, but rarely consider the deformation of surrounding rock. However, from the perspective of the formation of pressure arch, pressure arch is a self-regulating phenomenon of surrounding rock subjected to uneven deformation. The pressure arch determination index obtained only based on the redistribution of surrounding rock stress after tunnel excavation is difficult to reflect the essence of pressure arch formation. Although pressure arch is derived from the perspective of stress field, stress is often not intuitive enough in judging the macroscopic state of rock mass, and it is even more difficult to quantify the relationship with pressure arch area.

[0004] Literature such as Wang Chengbing's research on the progressive failure mechanism of weak and broken tunnel surrounding rock and Qu Shiwei's research on the influence of deep-buried urban subway tunnels on stratum deformation and the formation law of pressure arches proposed that the shape of pressure arches is a closed ring. However, research has shown that pressure arches are only generated in the tunnel vault part and the inverted arch surrounding rock, and the arch waist surrounding rock is only the "arch foot" and "arch seat" of the pressure arch. The arch waist surrounding rock bears the surrounding rock pressure transmitted by the pressure arch and forms a pressure concentration. Therefore, whether the arch waist is stable determines the stability of the entire cavern.

[0005] Liang Xiaodan's paper on determination of pressure arch body and analysis of arch formation in underground engineering proposed that no matter whether the surrounding rock is damaged or not, the maximum principal stress is the largest on the inner boundary of the pressure arch. Based on this feature, the inner boundary of the pressure arch can be identified, but this identification method is imperfect. This method is feasible in the vertical stress increase area, but not in the horizontal stress increase area. Z Huang et al.'s paper on Cavern roof stability-mechanism of arching and stabilization by rockbolting proposed the concept of "inverted principal stress cone" to determine the position and thickness of the pressure arch. The inverted principal stress cone is defined as the maximum and minimum principal stresses in the cone and only in the vertical and horizontal directions. The position and thickness of the arch directly below the top of the cone are determined accordingly. Obviously, the inverted principal stress cone can only determine the outer boundary point of the pressure arch. Summary of the invention

[0006] In view of the fact that the definition and boundary determination methods of pressure arch in the prior art all rely on the size and direction of surrounding rock stress, which are difficult to reflect the essence of pressure arch formation and difficult to quantify the relationship between stress and pressure arch area, the present invention proposes a method for determining the range of pressure arch in the surrounding rock of deep buried tunnels based on energy density theory.

[0007] In order to solve the above technical problems, the present invention adopts the following technical means:

[0008] The method for determining the range of the surrounding rock pressure arch of a deep buried tunnel based on the energy density theory includes the following steps:

[0009] Step 1: Establish a tunnel calculation model based on the geographical data of the tunnel location;

[0010] Step 2: Set the energy density calculation formula, and define "extra3" as the energy density value inside the surrounding rock before excavation, "extra2" as the energy density value inside the surrounding rock after excavation, and "extra1" as the energy density difference before and after excavation, and extra1 = extra2-extra3;

[0011] This step uses the fish language to write the energy density calculation formula.

[0012] Step 3: Set the model excavation process to full-section excavation or step-by-step excavation, and set the excavation unbalanced force accuracy. When the cyclic calculation unbalanced force accuracy is less than the set accuracy, the program cyclic calculation is terminated and the corresponding data is saved.

[0013] This step uses the fish language to write a program in the GUI interface.

[0014] Step 4: Write the data export code, reopen the stored model through the interface file, and export the calculated detailed .dat file;

[0015] Step 5, import the obtained .dat file into Tecplot software to visualize the energy density calculation results before and after the model tunnel excavation;

[0016] Step 6: The inner and outer boundary curves determine the range of the pressure arch.

[0017] Furthermore, the specific method of step 1 is: determine the specific buried depth of the tunnel and the corresponding geological parameters, and import the model into Flac3D after modeling through Flac3D or other modeling software according to the above data, and pay attention to the grid error problem and model grouping problem during import. Determining the specific buried depth and the corresponding geological parameters and the modeling method are all prior art.

[0018] Furthermore, when the corresponding energy density calculation formula is incorporated into step 2, the user can define the calculation content according to his / her needs. For example, when the constitutive model is Mohr-Coulomb, the energy density "extra3" inside the rock mass before tunnel excavation is the elastic energy density, and the calculation formula is:

[0019]

[0020] The energy density "extra2" inside the rock mass after tunnel excavation consists of two parts: the plastic energy density inside the rock mass that has undergone plastic failure and the elastic energy density inside the rock mass that has undergone elastic failure.

[0021] If the rock mass undergoes elastic failure, the elastic energy density calculation formula is:

[0022]

[0023] If the rock mass undergoes plastic failure, the calculation formula for plastic energy density is:

[0024] v d =[(1+μ) / 6E]|(σ1-σ2) 2 +(σ2-σ3) 2 +(σ3-σ1) 2 ] (3)

[0025] The Moore-Coulomb failure criterion is used to determine whether the surrounding rock has been damaged:

[0026]

[0027] In the formula, σ1, σ2, and σ3 are three principal stresses, μ is Poisson's ratio, E is the elastic modulus, P0 is the far-zone vertical stress, L is the excavation distance along the direction of the working face, and r is the vertical distance from the top of the tunnel. is the internal friction angle, c is the cohesion, υ ε represents the elastic energy density, v dIndicates the plastic energy density. The energy density difference "extra1" before and after tunnel surrounding rock excavation is: extra1 = extra2-extra3.

[0028] Furthermore, in step 3, fish can autonomously control the excavation process to achieve various tunnel excavation methods, such as step excavation, segmented excavation, and full-section excavation, etc. The tunnel excavation process is controlled to better meet the actual situation.

[0029] Furthermore, the step 4 requires writing a data export interface file, and the data export content should include the following parts: model node data, grid data, model X, Y, Z data and user required data. The user required data includes additional definition options Extra, horizontal stress Sxx, horizontal stress Syy, vertical stress Szz, pore water pressure Pore Pressure, soil displacement Displacement, etc.

[0030] Furthermore, the step 5 imports the result exported in the step 4 into Tecplot, and when an error is reported, the interface file or the model grid needs to be modified according to the error.

[0031] Furthermore, in step 6, the energy density difference EDD of the surrounding rock before and after excavation is calculated, and the corresponding EDD contour map is drawn. The contour line with EDD of 0 is defined as the inner boundary of the pressure arch, and the contour line with EDD of 10% is defined as the outer boundary of the pressure arch, that is, the difference between the energy density value after excavation and 90% of the energy density value before excavation is made to obtain the result of the outer boundary.

[0032] When determining the outer boundary of the pressure arch, if only the energy density before and after the model excavation is used for difference, the outer boundary of the pressure arch will be slightly smaller than the actual situation. In the calculation formula of extra1=extra2-extra3, a coefficient is constantly multiplied to extra3 to make the calculated value of extra1 close to the actual situation. After many model calculations, the final conclusion is that when this coefficient is 90%, the outer boundary of the model pressure arch calculated by the software is closest to the actual situation.

[0033] When determining the inner boundary of the pressure arch, the energy density difference before and after the excavation of the model is just consistent with the actual situation, so there is no need to add an additional multiplication coefficient to determine the inner boundary as the contour point where EDD is 0.

[0034] The beneficial effects of the present invention are:

[0035] The present invention determines the range of the pressure arch of the surrounding rock of a deep-buried tunnel based on the energy density theory. The energy density inside the tunnel surrounding rock before excavation and the energy density inside the tunnel surrounding rock after excavation are calculated, and then the difference between the two is made to obtain the difference in the energy density inside the tunnel surrounding rock before and after excavation. The inner and outer boundaries of the pressure arch of the surrounding rock are determined according to the disturbance range of the energy density change, thereby avoiding the current definition of the pressure arch and the boundary determination method, which are both dependent on the magnitude and direction of the surrounding rock stress. At the same time, the method can eliminate the controversial problem of determining the degree of deflection of the principal stress vector. The method of the present invention can be used to quickly and effectively obtain the inner and outer boundary ranges of the pressure arch of the surrounding rock, which is simple to implement and can also observe the evolution law of the three-dimensional pressure arch with tunnel excavation.

[0036] The present invention has proved through examples that the method reveals the range and shape of the pressure arch of the surrounding rock of the deep-buried tunnel with higher accuracy. Through the analysis of energy density, the influence of geological conditions on pressure distribution can be understood more comprehensively and accurately, thereby revealing the changes in arch shape under complex geological background. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a flow chart of the present method;

[0038] Figure 2 is a schematic diagram of a deep buried tunnel model in an example of the present invention;

[0039] Figure 3 The energy density calculation result of the deep tunnel and the boundary range and verification of the pressure arch in Example 1 of the present invention;

[0040] Figure 4 is a schematic diagram of a deep buried segmented tunnel excavation model in Example 2 of the present invention;

[0041] Figure 5 It is a schematic diagram of the range of surrounding rock pressure arch and energy density difference after excavation in the example of the present invention, in which ZoneTensor Stress is three principal stress vectors;

[0042] Figure 6 It is the inner and outer boundary range of the pressure arch under different excavation working faces in the examples of the present invention;

[0043] Figure 7 It is a schematic diagram of the pressure arch range and energy density difference of the surrounding rock longitudinal section in the example of the present invention, in which ZoneTensor Stress is three principal stress vectors;

[0044] Figure 8 It is a schematic diagram of the energy density variation trend of the monitoring line at different angles in the example of the present invention;

[0045] Fig. 9 It is a schematic diagram of the three-dimensional shape of the surrounding rock pressure arch after excavation in an example of the present invention. DETAILED DESCRIPTION

[0046] The technical solution of the present invention is further described below in conjunction with the accompanying drawings:

[0047] A method for determining the range of pressure arch in surrounding rock of deep buried tunnel based on energy density theory, such as Figure 1 As shown, the specific steps include:

[0048] Step 1: Establish tunnel numerical model:

[0049] According to the detailed geographic data of the simulated tunnel, the fixed points, loading points, monitoring points and other information of the calculation model are set. According to the basic information of the surrounding rock of the simulated tunnel, the relevant parameters of the rock mass are determined, including the gravity γ, elastic modulus E, shear modulus G, Poisson's ratio μ, cohesion c, lateral stress coefficient λ and internal friction angle. Carry out modeling calculations, and model through Flac3D or other modeling software according to the above data. After modeling, import it into Flac3D. Pay attention to the grid error problem and model grouping problem during import. The modeling method is the existing technology, such as the reference: Zhao Wen et al. Research on complex three-dimensional geological modeling of FLAC3D based on Matlab and Surfer platform.

[0050] In this embodiment, Rhino modeling and Flac3D are used for modeling calculation and analysis. The three-dimensional finite difference program uses explicit or implicit finite differences, which can effectively simulate the three-dimensional structural stress characteristics of soil, rock and other materials. All constitutive models in Flac3D are provided to users in the form of dynamic link library files (dll files), and the dll files of the constitutive models specified by the user will be called autonomously during the calculation process. The software allows users to compile custom constitutive models into dynamic link library dll files in the C++ environment, which are called and executed by the main program to achieve secondary development.

[0051] After creating a "new project" and a "new data file", the user imports the model created in Rhino through "Grid" → "import from flac3d". After confirming that the grouping information is correct, the calculation information is entered in the GUI interface, including information such as each group of fixed points, loading points, monitoring points, and ground stress parameters.

[0052] Step 2. After the model information is input, continue to write the energy density calculation formula on the GUI, including the elastic energy density calculation formula and the plastic energy density calculation formula, and use fish to write the storage path.

[0053] For example, when the constitutive model is Mohr-Coulomb, before tunnel excavation, under the triaxial stress state, the rock mass strain energy and the work done by the external force are numerically equal, and only depend on the final value of the external force and deformation, and have nothing to do with the force application process. Under the condition of linear elasticity, each principal stress and the corresponding principal strain maintain a linear relationship. Under the triaxial stress state, "extra3" can be defined as the elastic energy density inside the rock mass before tunnel excavation, and the calculation formula is:

[0054]

[0055] “Extra2” can be defined as the energy density inside the rock mass after tunnel excavation;

[0056] The energy density "extra2" inside the rock mass after tunnel excavation consists of two parts: the plastic energy density inside the rock mass that has undergone plastic failure and the elastic energy density inside the rock mass that has undergone elastic failure;

[0057] If the rock mass undergoes elastic failure, the elastic energy density calculation formula is:

[0058]

[0059] If the rock mass undergoes plastic failure, the calculation formula for plastic energy density is:

[0060] v d =[(1+μ) / 6E]|(σ1-σ2) 2 +(σ2-σ3) 2 +(σ3-σ1) 2 ] (3)

[0061] The Moore-Coulomb failure criterion is used to determine whether the surrounding rock has been damaged:

[0062]

[0063] In the above formula, σ1, σ2, and σ3 are three principal stresses, μ is Poisson's ratio, E is the elastic modulus, P0 is the far-field vertical stress, L is the excavation distance along the working face, and r is the vertical distance from the tunnel top. is the internal friction angle, υ ε represents the elastic energy density, v d It represents the plastic energy density. "Extra1" is further defined as the energy density difference (EDD) before and after tunnel surrounding rock excavation: extra1 = extra2 - extra3.

[0064] Step 3. Continue to write the model excavation process in the GUI interface, such as full-section excavation or step-by-step excavation, and set the excavation unbalanced force accuracy; the excavation unbalanced force refers to the number of decimal places to which the model calculation formula is accurate. For example, in the following embodiment, 1*e-5 is set, which means that the calculation stops when the number of decimal places is reached. When the cyclic calculation unbalanced force accuracy is not less than the set accuracy, the calculation will continue until the cyclic calculation unbalanced force accuracy is less than the set accuracy, save the corresponding data, and execute step 4;

[0065] Step 4. Write data export code in an additional .dat file, reopen the stored calculation result model through the interface file, and export the detailed data calculated by the software. The exported data includes tunnel model node information, overall displacement deformation, displacement in the xyz direction, pore water pressure, energy density extra, three principal stresses, etc., where extra can be defined by the user, such as defined as energy density or pressure, etc., as long as it can be calculated and expressed by code in the software. In this application, extra is defined as energy density.

[0066] Step 5, inner and outer boundary curves determine the range of the pressure arch: Import the obtained .dat file into Tecplot software, and draw the corresponding EDD contour map by calculating the energy density difference (EDD) of the surrounding rock before and after excavation. The contour line with EDD of 0 is defined as the inner boundary of the pressure arch, and the contour line with EDD of 10% of the original rock energy density is defined as the outer boundary of the pressure arch.

[0067] Tecplot is a numerical simulation and CFD visualization software that combines critical engineering drawing with advanced data visualization functions. It can directly read .cas and .dat files, analyze complex data, and make various layout arrangements, so that data can be analyzed and compared faster. After importing the .dat file, select the model section that the user wants in "Details" in "Slices", and select the desired model contour boundary type in "Contour" - "contour type".

[0068] In order to verify the effect of the method of the present invention, two specific embodiments are given below:

[0069] Embodiment 1:

[0070] A full-section deep-buried tunnel is excavated. The tunnel is buried 150m deep and has a radius of 5m. Considering the spatial effect during construction, according to theoretical estimation and model test results, Figure 2As shown, the final calculation model takes the rock mass of 100m in height × 5m in thickness × 100m in width as the investigation scope, with a total of 24,000 units. The strata are simulated using solid units, which conforms to the Moore-Coulomb criterion; the main basis for the value of the model height and width is the excavation disturbance range caused by the tunnel radius. The geological conditions in the study area are simple and can be simplified to homogeneous rock formations. The excavation of the cavern is achieved by deleting the excavation block at one time. The horizontal movement is restricted on the left and right sides of the model, and the bottom of the model is fixedly constrained. The steps for calculating the range of the surrounding rock pressure arch using the method of the present invention are as follows:

[0071] Step 1: Based on the tunnel radius and actual geological parameters, the model is modeled using the command stream modeling method of Flac3D. The tunnel adopts the full-section excavation mode. For the convenience of calculation, the model thickness is taken as 5m; the parameter information is set as follows: gravity γ = 26kN / m 3 , elastic modulus E = 5.0 GPa, Poisson's ratio μ = 0.25, cohesion c = 0.85 MPa, lateral stress coefficient λ = 0.5, internal friction angle Shear modulus G = 2.0 Gpa.

[0072] Assume that the initial geostress is uniformly distributed in the calculation area, and the two principal stress components act in the x and y directions respectively. The initial geostress value is applied in a linearly increasing manner with the burial depth, and the horizontal geostress is proportional to the vertical geostress. The ratio is the geostress lateral pressure coefficient. In this embodiment, the geostress lateral pressure coefficient is 0.5. The depth of the overburden from the surface to the cave roof is H = 150m. A thickness of H is required to be applied on the upper surface of the model. d = 150-(50-5) = 105m uniformly distributed load of rock weight. The depth of overburden from the ground surface to the cave roof is the tunnel burial depth, which is the distance from the model surface to the cave roof plus the distance from the ground surface to the model surface. The overburden load from the ground surface to the model surface is equivalent to the vertical load acting on the model surface.

[0073] Step 2: Write the energy density calculation formula and define the storage path. The internal energy density calculation formula before rock mass excavation is:

[0074]

[0075] If the rock mass undergoes elastic failure, the energy density inside the rock mass after tunnel excavation is calculated as:

[0076]

[0077] If the rock mass undergoes plastic failure, the calculation formula for the internal energy density of the rock mass after tunnel excavation is:

[0078] v d =[(1+μ) / 6E][(σ1-σ2) 2 +(σ2-σ3)2 +(σ3-σ1) 2 ] (3)

[0079] The Moore-Coulomb failure criterion is used to determine whether the surrounding rock has been damaged:

[0080]

[0081] Where σ1, σ2, and σ3 are the three principal stresses, μ is Poisson's ratio, E is the elastic modulus, P0 is the far-field vertical stress, L is the excavation distance along the working face, and r is the vertical distance from the tunnel top. is the internal friction angle.

[0082] The energy density calculation results before excavation are stored in "extra3", and the energy density calculation results after excavation are stored in "extra2". The values ​​of elastic energy density and plastic energy density are saved in "extra2" respectively, and the energy density difference of the tunnel surrounding rock before and after excavation is stored in "extra1".

[0083] Step 3: Write the tunnel excavation process. Restore the node initial displacement and initial velocity to 0, set the tunnel part to "null", and use the command "zone cmodel assign null range group'tunnel'union". This means that the tunnel named "tunnel" is excavated, and the unbalanced force accuracy is set to 1*10 before excavation. -5 When the accuracy of the cyclic calculation of unbalanced force is less than the set accuracy, the program cycle calculation is terminated and the corresponding data is saved.

[0084] Step 4. After the above modeling and excavation command flow settings are completed, the excavation calculation of the tunnel model can be started. Click the "Execute" button, and the program will automatically calculate the model. After the model calculation is less than the unbalanced force accuracy, the calculation ends and the model file is saved. Create a new interface file, import the saved model file, read the user-defined parameters (including user-defined Extra-energy density information, Sxx, Syy, Szz, Pore Pressure, Displacement, etc.), to facilitate the study and draw conclusions.

[0085] Step 5. Open Tecplot software, read the text data .dat file exported through the interface file, and import it through the LoadData File(s) command. After importing the .dat file, select the model section the user wants in "Details" in "Slices", and select the desired EDD contour boundary type in "contour type". Generally, "Lines and flood" is selected to facilitate the observation of contour lines.

[0086] The contour line with EDD of 0 is defined as the inner boundary of the pressure arch, and the contour line with EDD of 10% of the original rock energy density is defined as the outer boundary of the pressure arch. The calculated heights of the inner and outer boundaries of the tunnel roof and the pressure arch are 1.43m and 7.9m respectively.

[0087] In order to verify the accuracy of the results, the method is compared with the existing method for determining the inner and outer boundaries of the pressure arch. The existing method takes the area where the surrounding rock tangential stress increases after tunnel excavation as the range of the surrounding rock pressure arch, that is, the point where the near-field surrounding rock tangential stress is equal to the original rock stress is taken as the inner boundary of the pressure arch, and the point where the far-field surrounding rock tangential stress recovers to 90% of the original rock stress is taken as the outer boundary of the pressure arch. According to the measured data, the heights of the inner and outer boundaries of the pressure arch are 1.3m and 7.6m, respectively. Under the same working conditions, according to the definition of the existing method (reference: Fu Helin et al. Study on the range of the surrounding rock pressure arch of a deep-buried circular rough tunnel [J]. Journal of Hunan University: Natural Science Edition, 2018, 45(7)), the heights of the inner and outer boundaries of the tunnel roof pressure arch are 1.5m and 8.8m, respectively. Compared with the actual project, the inner and outer boundary errors of the existing method are 15.38% and 15.79%, respectively; compared with the actual project, the inner and outer boundary errors of this method are 10% and 3.94%, respectively. Figure 3 ,In general, the inner and outer boundary range of the tunnel surrounding rock ,pressure arch calculated based on these two methods is closer to the actual ,data.

[0088] Embodiment 2:

[0089] A segmented deep tunnel excavation, such as Figure 4 As shown in the figure, the tunnel is buried 100m deep and has a radius of 5m. Considering the spatial effect during construction, according to theoretical estimation and model test results, the final calculation model takes a rock mass of 100m×60m×100m as the investigation range, with a total of 48279 units. The geological conditions in the study area are simple and can be simplified to homogeneous rock layers with a specific gravity of γ=20kN / m 3 , elastic modulus E = 1.3Gpa, Poisson's ratio μ = 0.3, cohesion c = 0.2MPa, lateral stress coefficient λ = 0.5, internal friction angle is also 30°, and tunnel depth is 50m. The excavation of the cavern is achieved by deleting the excavation block at one time, the horizontal movement of the left and right sides of the model is restricted, and the bottom of the model is fixedly constrained. The steps for calculating the range of the surrounding rock pressure arch using the method of the present invention are as follows:

[0090] Step 1: Based on the tunnel radius and actual geological parameters, the model is built using the command stream modeling method of Flac3D, and the tunnel adopts the full-section excavation mode.

[0091] Step 2: Write the energy density calculation formula and define the storage path.

[0092] The calculation formula of internal energy density of rock mass before excavation is:

[0093]

[0094] If the rock mass undergoes elastic failure, the energy density inside the rock mass after tunnel excavation is calculated as:

[0095]

[0096] If the rock mass undergoes plastic failure, the calculation formula for the internal energy density of the rock mass after tunnel excavation is:

[0097] v d =[(1+μ) / 6E][(σ1-σ2) 2 +(σ2-σ3) 2 +(σ3-σ1) 2 ] (3)

[0098] The Moore-Coulomb failure criterion is used to determine whether the surrounding rock has been damaged:

[0099]

[0100] The energy density calculation results before excavation are stored in "extra3", and the energy density calculation results after excavation are stored in "extra2". The energy density difference of the tunnel surrounding rock before and after excavation is defined as extra1 = extra2 – extra3.

[0101] Step 3: Write the excavation process. Since it is a segmented excavation, it is necessary to excavate according to the tunnel grouping. It is necessary to define "fish define" to control the tunnel excavation process. Before calculating the excavation, the unbalanced force accuracy needs to be set to 1*10 -5 When the accuracy of the cyclic calculation of unbalanced force is less than the set accuracy, the program cycle calculation is terminated and the corresponding data is saved.

[0102] Step 4. After the above modeling and excavation command flow settings are completed, the excavation calculation of the tunnel model can be started. Click the "Execute" button to perform the model calculation. After the model calculates the unbalanced force accuracy, the calculation ends and the model file is saved. Create a new interface file, import the saved model file, and read the user-defined parameters.

[0103] Step 5. Open Tecplot software and import the entire .dat file through the Load Data File(s) command. After importing the .dat file, select the model section you want in "Details" in "Slices" and select the desired model contour boundary type in "contour type". Generally, "Lines and flood" is selected to facilitate the observation of contour lines.

[0104] The contour line with EDD of 0 is defined as the inner boundary of the pressure arch, and the contour line with EDD of 10% of the original rock energy density is defined as the outer boundary of the pressure arch, such as Figure 5 The inner and outer boundary heights of the tunnel pressure arch at different excavation depths, such as Figure 6 As shown. Among them, when the excavation is 10m, the inner and outer boundaries of the pressure arch are 1.53m and 6.68m respectively; when the excavation is 40m, the inner and outer boundaries of the pressure arch are 2.13m and 9.92m respectively. According to the measured data, when the excavation is 10m, the inner and outer boundary heights of the tunnel pressure arch are 1.6m and 6.4m respectively, while when the excavation is 40m, the inner and outer boundary heights of the tunnel pressure arch are 2.3m and 9.4m respectively. Under the same working conditions, according to the definition of the existing method (Fu Helin et al. Study on the range of the surrounding rock pressure arch of deep-buried circular rough tunnel [J]. Journal of Hunan University: Natural Science Edition, 2018, 45(7):8.), when the excavation is 10m, the inner and outer boundary heights of the tunnel pressure arch are 1.4m and 7.1m respectively, while when the excavation is 40m, the inner and outer boundary heights of the tunnel pressure arch are 1.96m and 10.5m respectively.

[0105] Compared with the actual project, the existing method in this embodiment has an inner and outer boundary error of 12.5% ​​and 10.94% when excavating 10m, and an inner and outer boundary error of 14.78% and 11.7% when excavating 40m. Compared with the actual project, the inner and outer boundary errors of the pressure arch when excavating 10m are 4.38% and 4.38% when excavating 10m, and an inner and outer boundary error of 7.39% and 5.53% when excavating 40m. In general, the inner and outer boundary ranges of the tunnel surrounding rock pressure arch calculated by the two methods are closer to the actual data.

[0106] Figure 7 This is the change in energy density of the side profile after tunnel excavation. It can be seen that the energy density is mainly concentrated on both sides of the arch waist. Figure 8 The energy density changes at different monitoring angles. Fig. 9 It is the actual three-dimensional situation of the pressure arch shell after excavation, and can intuitively reflect the scope and shape of the pressure arch.

[0107] This method is applicable in composite rock formations or other complex rock formation conditions; this method can take into account heterogeneity and nonlinear effects by setting different constitutive models and capture the complex deformation behavior of the rock mass. The time required for calculating the pressure arch range by this method is very short, and the simple model only needs a few minutes to obtain the pressure arch range. Therefore, this method can consider the diversity of geological conditions with higher accuracy, effectively deal with heterogeneity and nonlinear effects, and reduce costs and time consumption by simplifying the calculation process, providing more reliable, economical and practical design support for deep buried tunnel projects.

[0108] The above mentioned is only an example of the advantages of this invention. It should be emphasized that for technical experts in this technical field, without departing from the technical basis of this invention, various technical improvements and variations can be made, which should be regarded as the protection object of this invention.

Claims

1. A method for determining the range of surrounding rock pressure arch of a deep buried tunnel based on energy density theory, characterized in that: The steps include: Step 1: Establish a tunnel calculation model based on the geographical data of the tunnel location; Step 2: Set the energy density calculation formula, and define "extra3" as the energy density value inside the surrounding rock before excavation, "extra2" as the energy density value inside the surrounding rock after excavation, "extra1" as the energy density difference before and after excavation, and extra1 = extra2-extra3; Step 3: Set the model excavation process to full-section excavation or step-by-step excavation, and set the excavation unbalanced force accuracy. When the cyclic calculation unbalanced force accuracy is less than the set accuracy, the program cyclic calculation is terminated and the corresponding data is saved. Step 4: Write the data export code, reopen the stored model through the interface file, and export the calculated detailed .dat file; Step 5, import the obtained .dat file into Tecplot software to visualize the energy density calculation results before and after the model tunnel excavation; Step 6: The inner and outer boundary curves determine the range of the pressure arch.

2. The method for determining the range of the surrounding rock pressure arch of a deep buried tunnel based on the energy density theory according to claim 1 is characterized in that: In step 1, the model is built using Flac3D, or it is built using other modeling software and then imported into Flac3D.

3. The method for determining the range of the surrounding rock pressure arch of a deep buried tunnel based on the energy density theory according to claim 1 is characterized in that: When the constitutive model is Mohr-Coulomb, the energy density calculation formula is set as follows in step 2: The calculation formula of the elastic energy density inside the rock mass before tunnel excavation is: If the rock mass undergoes elastic failure, the calculation formula for the elastic energy density inside the rock mass after tunnel excavation is: If the rock mass undergoes plastic failure, the calculation formula for the plastic energy density inside the rock mass after tunnel excavation is: v d =[(1+μ) / 6E][(σ1-σ2) 2 +(σ2-σ3) 2 +(σ3-σ1) 2 ](3) The Moore-Coulomb failure criterion is used to determine whether the surrounding rock has been damaged: Where σ1, σ2, and σ3 are the three principal stresses, μ is Poisson's ratio, E is the elastic modulus, P0 is the far-field vertical stress, L is the excavation distance along the working face, and r is the vertical distance from the tunnel top. is the internal friction angle, c is the cohesion, v ε represents the elastic energy density, v d represents the plastic energy density.

4. The method for determining the range of the surrounding rock pressure arch of a deep buried tunnel based on the energy density theory according to claim 1 is characterized in that: The exported data in step 4 include: model node data, grid data, model X, Y, Z data and user required data. The user required data include Extra, Sxx, Syy, Szz, Pore Pressure and Displacement.

5. The method for determining the range of the surrounding rock pressure arch of a deep buried tunnel based on the energy density theory according to claim 1 is characterized in that: In step 6, the contour line where the surrounding rock energy density changes to 0 is defined as the inner boundary of the pressure arch, and the contour line where the surrounding rock energy density changes to 10% is defined as the outer boundary of the pressure arch.

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