High ground temperature grouting tunnel stability FDEM analysis system

Abstract

The invention relates to the technical field of roadway grouting reinforcement, and discloses a high-ground-temperature grouting tunnel stability FDEM analysis system which comprises a heat transfer module, a diffusion module and a mechanical module. The heat transfer module comprises a three-dimensional crack heat conduction model constructed by a three-dimensional cohesive force unit and is used for acquiring the temperatures of all entity units and cohesive force units in the model under different boundary temperature conditions; the diffusion module respectively endows each cohesive force unit with a corresponding flow parameter according to the obtained temperature of the cohesive force unit; and the mechanical module is used for extracting a cohesive force unit set through which the slurry passes from the diffusion module. Through the heat conduction model constructed by the three-dimensional cohesive force unit, the influence of fracture opening change on heat conduction can be accurately captured, and refined prediction of the surrounding rock temperature field of the high-ground-temperature roadway is realized. And meanwhile, in combination with temperature sensitivity parameters of Bingham type grout, a diffusion path is dynamically adjusted, a high-temperature grout diffusion inhibition mechanism is disclosed, and the grouting design is optimized.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel grouting reinforcement, and in particular to a high ground temperature grouting tunnel stability FDEM analysis system. Background Art

[0002] Currently, grouting technology utilizes the fluidity of slurry to migrate into the internal cracks of the surrounding rock, filling the surrounding rock cracks after solidification. This allows the rock mass with developed cracks to be cemented into a surrounding rock structure with high strength, low permeability, and high stability. This significantly increases the bearing capacity of the surrounding rock and effectively improves the rock mass structure and physical and mechanical properties. Numerical simulation methods are widely used in the study of the support stability of broken rock masses in underground engineering due to their advantages in considering the nonlinearity, anisotropy, structural discontinuity, and multi-field coupling characteristics of the surrounding rock mass. However, there are currently few studies on the application of FDEM to the entire process of grouting diffusion and strength repair. There is also a lack of a systematic numerical simulation tool for predicting the grouting diffusion range in deep high-temperature tunnels. Summary of the Invention

[0003] In order to solve the technical problems raised in the background technology, the present invention provides a high ground temperature grouting tunnel stability FDEM analysis system.

[0004] The present invention is implemented by adopting the following technical solutions: a high ground temperature grouting tunnel stability FDEM analysis system, comprising: a heat transfer module, a diffusion module and a mechanics module.

[0005] The heat transfer module includes a three-dimensional fracture heat conduction model constructed with three-dimensional cohesion units to obtain the temperatures of all solid units and cohesion units in the model under different boundary temperature conditions.

[0006] The diffusion module assigns corresponding flow parameters to each cohesion unit according to the obtained temperature of the cohesion unit. The flow parameters include yield stress and plastic viscosity to accurately simulate the slurry diffusion range.

[0007] The mechanics module is used to extract the cohesion unit set through which the slurry passes from the diffusion module, identify the corresponding temperature values of the cohesion units in the set, and assign different shear mechanics parameters to each unit in the cohesion unit set according to the temperature-related shear mechanics parameter model to simulate the reinforcement effect.

[0008] Specifically, the three-dimensional cohesion unit temperature coupling model is to insert a three-dimensional cohesion unit into the crack to connect two adjacent solid units, and the thermal conductivity coefficient of the crack is calculated by the thermal conductivity coefficient k of the three-dimensional cohesion unit. cz To characterize it, it is assumed that no heat is generated inside the cohesion unit and only pure heat transfer function can be realized:

[0009] The relevant heat transfer equation is shown below:

[0010] Cohesion unit heat flux:

[0011] q cz = k cz δφ(ξ, η)

[0012] In the formula, δφ(ξ, η) represents the temperature jump of the reference surface and can be obtained by interpolation with the following formula:

[0013] δφ(ξ, η) = [H]{φ CZ}

[0014] In the formula,

[0015] [H] = [N1N2N3N4N5N6N7N8], N k = -N k+4 , k = 1, …, 4

[0016] And

[0017] {φ CZ} = {φ1φ2φ3φ4φ5φ6φ7φ8} T

[0018] In the formula, N i , i = 1, ···, 8 are interpolation shape functions, and φ i , i = 1, ···, 8 are the nodal temperatures of the cohesion unit;

[0019] Among them,

[0020]

[0021] The three-dimensional cohesion unit heat conduction model is implemented using an aperture-dependent heat conduction model, and the corresponding generated heat transfer stiffness matrix can be expressed by the following formula:

[0022]

[0023] In the formula, δ is the normal displacement between the upper and lower surfaces of the cohesion unit, δ c is the critical failure aperture of the cohesion unit, k0 is the initial heat conduction coefficient of the cohesion unit, and det[J] is the determinant of the Jacobian matrix;

[0024] Among them,

[0025]

[0026] Specifically, in step 2, the temperature in the diffusion module has an obvious inhibitory effect on the diffusion process of Bingham-type slurry. The higher the temperature, the poorer the connectivity of the fracture network; on the contrary, it is better, and it is beneficial to the formation of the grouting fracture network.

[0027] Specifically, the shear mechanical parameter model in step 3 is obtained by the following method:

[0028] Perform a slurry rheological shear test. The grouted rock mass used in the test is a grouting consolidation body formed by grouting under different temperature conditions. The test can obtain the shear strength of the grouting consolidation body under different grouting temperature conditions, and then the variation law of shear mechanical parameters (internal friction angle and cohesion) with temperature can be obtained, that is, the temperature-related shear mechanical parameter model.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] The present invention accurately simulates the grouting process under high-temperature environments; through the heat conduction model constructed by three-dimensional cohesive units, it can accurately capture the influence of crack aperture changes on heat conduction, and achieve refined prediction of the temperature field of the surrounding rock of high geothermal tunnels. At the same time, combined with the temperature sensitivity parameters (yield stress, plastic viscosity) of Bingham-type slurry, the diffusion path is dynamically adjusted to reveal the mechanism of high temperature inhibiting slurry diffusion and optimize the grouting design.

[0031] The present invention improves engineering reliability through multi-field coupling analysis. This solution integrates three major modules of heat transfer, diffusion, and mechanics to achieve multi-field coupling analysis of temperature-seepage-mechanics, and truly reflects the whole process of grouting reinforcement of deep high geothermal tunnels.

[0032] The present invention quantifies the influence of different grouting temperatures on the strength of the consolidation body through the temperature-related shear mechanical parameter model, providing a scientific basis for the evaluation of grouting effects under high-temperature environments. Its engineering application value is significant, solving the technical problems of predicting the grouting diffusion range and evaluating the reinforcement effect of deep high geothermal tunnels, reducing the cost of on-site tests, and reducing engineering risks.

[0033] The present invention can provide a systematic tool for roadway stability analysis, helping to optimize the construction plan and ensuring the safety and economy of deep underground engineering. Brief Description of the Drawings

[0034] Figure 1 It is the schematic diagram of the FDEM analysis method proposed by the present invention;

[0035] Figure 2 It is the schematic diagram of the aperture-related heat conduction model; where: Figure 2 (a) is the schematic diagram of transient heat conduction of fractured rock mass; Figure 2 (b) is the three-dimensional discrete numerical model diagram; Figure 2 (c) is the schematic diagram of three-dimensional eight-node cohesive heat transfer unit;

[0036] Figure 3 It is the heat conduction analysis diagram of a square plate with randomly inclined cracks under thermal load; Figure 3(a) Schematic diagram of the geometry and thermal load distribution of the heat conduction problem; Figure 3 (b) Schematic diagram of heat conduction of a continuous square plate under boundary thermal load; Figure 3 (c) Schematic diagram of heat conduction of a square plate with randomly inclined cracks under thermal load on the crack surface;

[0037] Figure 4 It is a comparison chart of the numerical solution and the steady-state analytical solution of the temperature field under different crack apertures;

[0038] Figure 5 It is a deep crack roadway model; Figure 5 (a) Geometric model and boundary conditions; Figure 5 (b) Numerical model;

[0039] Figure 6 It is the distribution of the roadway temperature field; Figure 6 (a) Temperature field distribution at 20 °C; Figure 6 (b) Temperature field distribution at 40 °C; Figure 6 (c) Temperature field distribution at 60 °C;

[0040] Figure 7 It is a roadway grouting model based on FDEM; Figure 7 (a) Geometric model; Figure 7 (b) Grouting settings; Figure 7 (c) Numerical model;

[0041] Figure 8 It is the inhibitory effect of pre-grouting on the process of large deformation of roadway rupture and swelling under different grouting temperatures;

[0042] Figure 9 It is the distribution of the roadway displacement field and rupture field; Figure 9 (a) Surrounding rock displacement; Figure 9 (b) Degree of rupture and maximum displacement;

[0043] Figure 10 It is a diagram of the evolution model of the shear mechanical parameters varying with temperature in the mechanical module proposed by the present invention. Detailed implementation manners

[0044] Next, in combination with the accompanying drawings and specific implementation manners, the present invention will be further described. It should be noted that, on the premise of no conflict, the following-described embodiments or technical features can be combined arbitrarily to form new embodiments.

[0045] Embodiment:

[0046] Referring to Figures 1 - 10 , a FDEM analysis method system for the stability of high geothermal grouting roadways proposed in this solution includes three major modules: a diffusion module, a heat transfer module, and a mechanical module.

[0047] It should be noted that in this solution, the heat transfer module provides the temperature field distribution for the diffusion module and the mechanical module. The seepage parameters of the Bingham-type slurry in the diffusion module are determined according to the unit temperature. The diffusion module provides the flow net for the mechanical module, and the grouting repair parameters of the units in the flow net are determined according to the unit temperature;

[0048] The following provides a more detailed description of each module proposed in this solution:

[0049] In this solution, the heat transfer module includes a three-dimensional fracture heat conduction model. Referring to Figure 2 , a three-dimensional cohesive element temperature coupling model is specifically proposed. As shown in parts (b) and (c), three-dimensional cohesive elements are inserted into the fractures to connect two adjacent solid elements. The heat conduction coefficient of the fracture is characterized by the heat conduction coefficient kcz of the cohesive element, and no heat is generated inside the cohesive element, and only pure heat transfer function can be achieved. Figure 2 (b) part and Figure 2 (c) part, three-dimensional cohesive elements are inserted into the fractures to connect two adjacent solid elements. The heat conduction coefficient of the fracture is characterized by the heat conduction coefficient kcz of the cohesive element, and no heat is generated inside the cohesive element, and only pure heat transfer function can be achieved.

[0050] The relevant heat transfer equation is as follows:

[0051] Heat flux of cohesive element:

[0052] q cz =k cz δφ(ξ,η)

[0053] In the formula, δφ(ξ,η) represents the temperature jump of the reference surface and can be obtained by interpolation with the following formula:

[0054] δφ(ξ,η)=[H]{φ CZ}

[0055] In the formula,

[0056] [H]=[N1N2N3N4N5N6N7N8],N k =-N k+4 ,k=1,…,4

[0057] And

[0058] {φ CZ}={φ1φ2φ3φ4φ5φ6φ7φ{8} T

[0059] In the formula, Ni, i = 1, ···, 8 are interpolation shape functions, and φi, i = 1, ···, 8 are the nodal temperatures of the cohesive element.

[0060] Among them,

[0061] The three-dimensional cohesive element heat conduction model proposed in this section adopts the aperture-dependent heat conduction model proposed by Benabou (as shown in Figure 7 - 2 ) to implement. The corresponding generated heat transfer stiffness matrix can be expressed by the following formula:

[0062]

[0063] In the formula, δ is the normal displacement between the upper and lower surfaces of the cohesive element, δc is the critical failure aperture of the cohesive element, k0 is the initial heat conduction coefficient of the cohesive element, and det[J] is the determinant of the Jacobian matrix.

[0064] Among them,

[0065]

[0066] This solution also verifies the algorithm for the temperature field prediction proposed above;

[0067] First, the transient heat conduction process of a single-fracture square plate with different thermal conductivities (different fracture apertures) is studied (as shown in Figure 3 ).

[0068] As shown in Figure 3 (a), the geometric size of the square plate is 0.4m×0.4m, and the half-length of an arbitrarily oriented fracture with different apertures located at the center of the plate is a = 0.06m.

[0069] By superimposing the temperature fields of the two problems in Figure 3 , the analytical solution of the problem is obtained: the first problem is a continuous plate under a uniform temperature load, as shown in Figure 3 (b); the second problem is a fractured square plate with an arbitrary inclination angle under a thermal load, as shown in Figure 3 (c). The exact solutions of the two problems are given as follows:

[0070]

[0071] In the formula and are the dimensionless temperatures of the problems shown in Figure 2 (b) and Figure 2 (c) respectively, k* is the thermal conductivity of the fracture, θ represents the fracture inclination angle shown in Figure 2 (a), δ is the fracture aperture, and is a dimensionless quantity that can be obtained from the following formula.

[0072]

[0073] In the formula, (x, y) and (s, r) are the Cartesian coordinate system and the local coordinate system respectively, and a represents the half-fracture length.

[0074] To further verify the proposed cohesive element heat conduction coupling model, a series of numerical simulation tests with different fracture apertures (δ = 0, 0.25e-7, 0.50e-7, 0.75e-7, 1.0e-7 m) were carried out on the problem shown in Figure 3 (a) using the established model.

[0075] The initial fracture heat conduction coefficient was k0 = 2000, and the critical fracture spacing was δ c = 1.0e-7 m. The thermal conductivity of the continuous region was k = 1, the mass density was ρ = 1, and the heat capacity was c = 1. The upper edge of the plate (T(0,t) = 1000) and the lower edge (T(1,t) = 0) were under constant temperature conditions; the initial temperature on the plane was set to zero.

[0076] Figure 3 The numerical results of the heat conduction problem shown in Figure 4 are shown as follows. It can be seen from the figure that the steady-state temperature field along the fracture surface calculated by the cohesive element heat conduction coupling model with different fracture apertures proposed in this scheme is in good agreement with the analytical solution given in Equation (1-3).

[0077] It can also be clearly seen from Figure 4 that as the normal fracture aperture increases, the temperature jump at the upper boundary of the fracture decreases. By specifying different thermal conductivities, the heat transfer properties of heat-conducting fractures (fracture aperture is zero) and adiabatic fractures (fracture aperture reaches the critical fracture aperture δ c = 1.0e-7 m) can be accurately simulated.

[0078] Thus, it can be seen that the proposed cohesive element heat conduction coupling model can better simulate the heat conduction process under different fracture apertures.

[0079] Regarding the diffusion module

[0080] This scheme simulated the roadway excavation and grouting reinforcement effects in deep fractured rock masses under different temperature conditions. The geometric model of the problem is shown in Figure 5 . The outer side length of the model is 60 m, and the diameter of the roadway is 5.93 m. The randomly distributed fracture network was generated by the Monte Carlo algorithm, with a total of 35 fractures. Any randomly distributed fracture network is defined by four parameters, namely the fracture center position (x o , y o ), fracture length (2a), fracture aperture δ, and fracture dip angle θ. The detailed parameters for generating randomly distributed fracture networks are shown in Table 1. A temperature load of 80 °C was uniformly applied to the outer boundary of the roadway numerical model, and temperature loads of 20 °C, 40 °C, and 60 °C were applied to the roadway perimeter and the initial temperature field of the model, respectively. The thermodynamic parameters are shown in Table 2 below. Correspondingly, Figure 6 the temperature field distribution characteristics of the roadway surrounding rock under different temperature conditions are given.

[0081] Table 1 - Generation Parameters of Randomly Distributed Fracture Networks

[0082]

[0083] Table 2 - Simulation Parameter Table of Roadway Temperature Field

[0084]

[0085] This scheme also simulated the grouting diffusion process of a roadway with a diameter of 5.93 m in anisotropic surrounding rock, as Figure 7 shown. To more precisely simulate the fluid - solid coupling mechanical response near the grouting holes, the grid near the grouting area was refined. The average diameter of the grid in the refined area was 0.05 m, and only cohesive elements were inserted for discretization in the refined area. A total of 64350 solid elements and 41990 cohesive elements were generated. The radius of the refined area was 20 m. The horizontal in - situ stress was taken as 17.7 MPa, and the vertical in - situ stress was 20 MPa. A temperature load of 80 °C was uniformly applied to the outer boundary of the roadway numerical model, and temperature loads of 20 °C, 40 °C, and 60 °C were respectively applied to the roadway perimeter and the initial temperature field of the model. The total calculation duration was set to 3600 s.

[0086] Table 3 - Meso - mechanical Parameters of Roadway Surrounding Rock

[0087]

[0088]

[0089] Continue to refer to Figure 8 , this scheme gives the migration and diffusion paths of Bingham - type slurry under three perimeter temperature conditions (20 °C, 40 °C, and 60 °C) when the calculation is completed. It can be clearly seen from the figure that temperature has an obvious inhibitory effect on the diffusion process of Bingham - type slurry. Under the condition of 60 °C, the fracture network has poor connectivity, and the number of deflected fractures is small; under the condition of 40 °C, the tip of the outermost - ring fracture deflects, and there are multiple obvious main fracture channels along the radial direction; under the condition of 20 °C, the fractures cross - penetrate significantly in the radial and circumferential directions, and the grouting fracture network has basically formed.

[0090] Based on the above results, the cohesive element numbers and the corresponding integration - point temperatures in the seepage network are extracted. In the subsequent grouting reinforcement simulation, for the proposed shear mechanical parameter model, the corresponding reinforcement mechanical parameters are respectively assigned.

[0091] And in the reinforcement module

[0092] It can be referred to Figure 8 , which gives the reinforcement effects of pre - grouting on the damage and fracture of fractured surrounding rock caused by unloading in deep - seated fractured roadways under different grouting temperatures.

[0093] It can be clearly seen from the figure that the higher the grouting temperature, the worse the repair effect of the grout on the surrounding rock of the roadway.

[0094] As Figure 8 (a) shows that when the grouting temperature is 20 °C, the grout has an obvious inhibitory effect on the damage and fracture of the surrounding rock of the roadway. The maximum damage and fracture area caused by the roadway unloading is mainly concentrated about 4.16 m above the tunnel roof, and the rest of the damage and fracture areas are mainly distributed within 2 m of the tunnel perimeter boundary, and are mainly shear cracks, accompanied by a small amount of tensile cracks at the tunnel perimeter boundary;

[0095] As Figure 8 (b) shows that when the grouting temperature is 40 °C, the shear cracks around the tunnel expand outward compared with those at 20 °C. Among them, the cracks at the top of the roadway expand to about 4.31 m, the cracks at the bottom expand to 2.24 m, and the cracks on the side of the roadway expand to about 3.05 m;

[0096] As Figure 8 (c) shows that when the grouting temperature is 60 °C, due to the inhibitory effect of high temperature on the diffusion ability of the grout, the grouting volume decreases, which in turn leads to a decrease in the shear strength of the bonding layer. The repair effect of the grout on the damage and fracture process of the surrounding rock of the roadway under higher temperature conditions is not obvious, and the damage and fracture area around the tunnel further expands outward. The cracks at the top expand to about 4 m, and the cracks at the bottom expand to 3.07 m.

[0097] Figure 9 The distribution characteristics of the roadway displacement field and fracture field are given, and the results fully reflect the weakening effect of high temperature conditions on the grouting repair effect of the roadway. It can be seen from the above research results that grouting reinforcement has a significant inhibitory effect on the expansion of the damaged area of fractured rock mass, and the repair effect on the mechanical strength of the surrounding rock depends on the temperature conditions during grouting. The higher the grouting temperature, the worse the reinforcement effect.

[0098] In this solution, the mechanical module introduces an experiment (grout rheological shear experiment) for three-dimensional cohesion units, and based on the temperature-related shear mechanical parameter model obtained from the experiment, it simulates the grouting reinforcement effect under different temperature conditions.

[0099] The above embodiments are only the preferred embodiments of the present invention, and the scope of protection of the present invention cannot be limited thereby. Any non-substantial changes and substitutions made by those skilled in the art on the basis of the present invention belong to the scope of protection required by the present invention.

Claims

1. A FDEM analysis system for the stability of a high geothermal grouting tunnel, characterized in that, Including: A heat transfer module, a diffusion module, and a mechanics module; The heat transfer module includes a three-dimensional fracture heat conduction model constructed by three-dimensional cohesive units for obtaining the temperatures of all solid units and cohesive units in the model under different boundary temperature conditions; The diffusion module assigns corresponding flow parameters to each cohesive unit according to the obtained temperature of the cohesive unit to accurately simulate the slurry diffusion range; the flow parameters include yield stress and plastic viscosity; The mechanics module is used to extract the set of cohesive units through which the slurry passes from the diffusion module, identify the corresponding self-temperature values of the cohesive units in the set, and assign different shear mechanical parameters to each unit in the set of cohesive units according to the shear mechanical parameter model related to temperature to simulate the reinforcement effect.

2. The FDEM analysis system for the stability of a high geothermal grouting tunnel according to claim 1, wherein The three-dimensional cohesion element temperature coupling model is to insert three-dimensional cohesion elements into the fissures to connect two adjacent solid elements, and the thermal conductivity of the fissures is characterized by the thermal conductivity k of the three-dimensional cohesion elements cz It is assumed that no heat is generated inside the cohesion element, and only pure heat transfer function can be realized: The relevant heat transfer equation is as follows: Cohesive unit heat flux: q cz = k cz δφ(ξ, η) In the formula, δφ(ξ,η) represents the temperature jump of the reference surface, which can be obtained by interpolation with the following formula: δφ(ξ,η) = [H]{φ CZ} In the formula, [H] = [N1 N2 N3 N4 N5 N6 N7 N8], N k = -N k+4 , k = 1, …, 4 And {φ CZ} = {φ1 φ2 φ3 φ4 φ5 φ6 φ7 φ8} T where N i , i = 1, ···, 8 are interpolation shape functions, and φ i , i = 1, ···, 8 are the nodal temperatures of the cohesion element; Where, The three-dimensional fracture heat conduction model is realized by using an aperture-related heat conduction model, and the generated heat transfer stiffness matrix can be expressed by the following formula: where δ is the normal displacement between the upper and lower surfaces of the cohesion element, δ c is the critical failure opening of the cohesion element, k0 is the initial thermal conductivity of the cohesion element, and det[J] is the determinant of the Jacobian matrix; Where, 3. The FDEM analysis system for the stability of a high geothermal grouting tunnel according to claim 1, characterized in that, In step 2, the temperature in the diffusion module has an obvious inhibitory effect on the Bingham slurry diffusion process. The higher the temperature, the worse the fracture network connectivity; on the contrary, it is better, and it is beneficial to the formation of the grouting fracture network.

4. The FDEM analysis system for the stability of a high geothermal grouting tunnel according to claim 1, wherein, The shear mechanical parameter model in step 3 is obtained by the following method: Perform a slurry rheological shear test, and the grouted rock mass used in the test is a grouted consolidated body formed by grouting under different temperature conditions. The test can obtain the shear strength of the grouted consolidated body under different grouting temperature conditions, and then the variation law of the shear mechanical parameters with temperature, that is, the shear mechanical parameter model related to temperature. The shear mechanical parameters include the internal friction angle and cohesion.

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