Numerical simulation method of shield tunneling considering anisotropic stratum shear strength

Abstract

The present invention discloses a numerical simulation method for tunnel shield excavation considering the anisotropy of stratum shear strength, and relates to the technical field of numerical simulation of shield tunnel engineering. The size range of the three-dimensional finite element calculation model of the tunnel and the characteristics of the stratum material are determined; the detailed simulation process of the tunnel shield excavation is determined according to the structural size and operation mode of the shield machine, as well as the process of shield shell advancement, segment installation, and shield tail grouting; according to the anisotropic characteristics of the shear strength of the stratum material, the anisotropy of the shear strength of the stratum material is characterized by a microstructure tensor; using three-dimensional simulation calculation software, an analysis method for simulating the anisotropy of the shear strength of the stratum material is established, and numerical calculations of the tunnel shield excavation process are carried out to obtain the settlement value and plastic zone range of the shield excavation stratum, and analyze the degree of disturbance of the stratum by the shield excavation. The present invention can more accurately simulate the surface settlement and the generation of plastic zones during the shield excavation process, making up for the shortcomings of the previous incomplete shield excavation simulation.

Description

Technical Field

[0001] The invention relates to the technical field of numerical simulation of shield tunnel engineering, in particular to a numerical simulation method for shield tunneling considering anisotropic stratum shear strength. Background Art

[0002] Underground tunnel projects, such as subways, are rapidly developing, and shield excavation is often used for underground tunnels. Shield tunneling involves a shield machine, protected by a steel casing, using a cutterhead to excavate the rock and soil surrounding the tunnel along the designed tunnel excavation line. As the machine advances, a lining structure forms behind it, and the cutterhead pushes forward continuously.

[0003] The mechanical properties of tunnel surrounding rock have long been the foundation of engineering support design and safety assessment, and have long garnered significant attention from scholars both domestically and internationally. Currently, researchers typically study tunnel surrounding rock as an isotropic elastic material. However, in reality, tunnel surrounding rock exhibits anisotropic mechanical characteristics due to its varying structural properties, mechanical attributes, and stress-strain relationships in different directions. These anisotropic characteristics are primarily influenced by strength, structural characteristics, and loading direction.

[0004] Currently, most numerical simulation studies of shield tunneling are limited by modeling complexity and a lack of numerical simulation methods that properly account for anisotropy. Consequently, the surrounding strata are treated as isotropic during tunnel excavation, and initial models are often inadequately constructed. Because the surrounding rock mass of a tunnel is heterogeneous, nonlinear, and discontinuous, it is frequently subjected to loading and unloading during tunneling, while also experiencing complex boundary conditions. Numerical simulation methods that treat the strata being tunneled as isotropic in anisotropic geological environments fail to account for changes in the shear properties of the strata under the influence of excavation stresses. Summary of the Invention

[0005] In order to overcome the defects in the above-mentioned prior art, the present invention provides a numerical simulation method for tunnel shield excavation taking into account the anisotropic shear strength of the stratum. Taking into account the anisotropic factor of the shear strength of the stratum material can more accurately simulate the surface settlement and the formation of plastic zones during the shield excavation process, which makes up for the previous shortcomings of shield excavation simulation that only considered the isotropic influencing factors of the material.

[0006] To achieve the above object, the present invention adopts the following technical solutions, including:

[0007] The numerical simulation method of shield tunneling considering the anisotropy of stratum shear strength includes the following steps:

[0008] S1. Determine the size range and stratum material characteristics of the tunnel 3D finite element calculation model based on the tunnel site engineering geological conditions and tunnel size;

[0009] S2, based on the structural dimensions and operating mode of the shield machine, as well as the processes of shield advancement, segment installation, and shield tail grouting, sets the shield shell unit and segment unit in the tunnel 3D finite element calculation model, applies the tunnel face pressure and grouting pressure, and determines the tunnel shield excavation simulation process;

[0010] S3, according to the anisotropic characteristics of the shear strength of the formation material, the microstructure tensor is used to characterize the anisotropy of the shear strength of the formation material, and the anisotropic expression of the shear strength of the formation material is obtained;

[0011] S4, using three-dimensional simulation calculation software, established an analytical method for simulating the anisotropic shear strength of stratum materials, carried out numerical calculations of the tunnel shield excavation process, and obtained the settlement value and plastic zone range of the shield excavation stratum, which were used to analyze the degree of disturbance of the stratum by shield excavation.

[0012] Preferably, in step S1, a stratum geometric model is established using three-dimensional simulation calculation software based on the engineering geological conditions of the tunnel site and the size of the tunnel. In the stratum geometric model, an eight-node hexahedral unit is used, the X direction is the tunnel cross-section direction, the Y direction is the longitudinal excavation direction of the tunnel, and the Z direction is the vertical direction. The stratum geometric model is layered according to the different properties of the stratum material.

[0013] Preferably, in step S2, three-dimensional simulation calculation software is used to simulate the construction excavation process of the shield machine. According to the structural size and operation mode of the shield machine, the shield cycle excavation and segment assembly process are simulated in the three-dimensional simulation calculation software by changing the parameter properties of the units around the tunnel. During the shield cycle excavation, the grouting pressure of the shield tail is simulated by the equivalent layer units.

[0014] Preferably, the shield shell of the shield machine has an N-ring segment length. The N-ring segment length behind the tunnel face is used to simulate the activation of the shield shell unit, and the M-ring segment length is used to simulate the segment unit under the grouting pressure of the shield tail. The specific simulation steps of the construction excavation process of the shield machine are as follows:

[0015] S21, generating the initial stress field, i.e., activating all strata and enclosure structure units, selecting the gravity field as the stress field condition of the tunnel 3D finite element calculation model, calculating the initial stress of the tunnel 3D finite element calculation model, and then clearing the initial displacement and velocity;

[0016] S22, excavation of the first ring, passivation of the tunnel and segment units of the first ring, application of face pressure on the excavation face, activation of the equivalent layer units of the first ring as shield units;

[0017] S23, excavation of the second ring, passivation of the tunnel and segment elements of the second ring and the face pressure of the first ring, activation of the equivalent layer elements of the second ring as shield elements, and application of the face pressure on the excavation face;

[0018] S24, continuing shield tunneling in the manner of step S23 until the Nth ring is excavated and the shield shell is completely inside the tunnel, passivating the tunnel and segment units of the Nth ring and the face pressure of the N-1th ring, activating the equivalent layer units of the Nth ring as shield shell units, and applying the face pressure on the excavation face;

[0019] S25, excavation of the N+1 ring, passivation of the tunnel and segment units of the N+1 ring and the face pressure of the N ring, activation of the equivalent layer units of the N+1 ring as shield units, updating of the shield units of the 1st ring as equivalent layer units, application of grouting pressure to the equivalent layer units of the 1st ring, activation of the segment units of the 1st ring, and application of face pressure to the excavation face;

[0020] S26, continuing shield tunneling in the manner of step S25 until the N+Mth ring is excavated, passivating the tunnel and segment units of the N+Mth ring and the face pressure of the N+M-1th ring, activating the equivalent layer units of the N+Mth ring as shield shell units, updating the shield shell units of the Mth ring as equivalent layer units, applying grouting pressure to the equivalent layer units of the Mth ring, activating the segment units of the Mth ring, and applying face pressure to the excavation face;

[0021] S27, excavation of the N+M+1th ring, passivation of the tunnel and segment units of the N+M+1th ring and the face pressure of the N+Mth ring, activation of the equivalent layer units of the N+M+1th ring as shield units, update of the shield units of the M+1th ring as equivalent layer units, application of grouting pressure to the equivalent layer units of the M+1th ring, passivation of the grouting pressure in the equivalent layer units of the 1st ring, activation of the segment units of the M+1th ring, update of the equivalent layer units of the 1st ring as segment units, and application of face pressure to the excavation face;

[0022] S28, as the shield advances, the properties of the tunnel, segments, equivalent layers and face pressure at different locations are passivated or activated according to the method of step S27 until the excavation construction of all excavation sections is completed.

[0023] Preferably, in step S3, the shear strength of the formation material includes the internal friction angle and the cohesion, and the functional relationship between the internal friction angle and the microstructure tensor and the functional relationship between the cohesion and the microstructure tensor are obtained respectively, that is, the anisotropic expressions of the internal friction angle and the cohesion are obtained, as shown below:

[0024]

[0025]

[0026] Where c represents cohesion, c0 represents average cohesion; represents the internal friction angle, represents the average internal friction angle, A1 and A2 are parameters that characterize the degree of anisotropy of the rock mass, b1 and b2 are coefficients, and β is the inclination angle of the anisotropic structural plane of the layered stratum material.

[0027] Preferably, in step S3, the shear strength of the formation material includes the internal friction angle and the cohesion, and the functional relationship between the internal friction angle and the microstructure tensor and the functional relationship between the cohesion and the microstructure tensor are obtained respectively, that is, the anisotropic expressions of the internal friction angle and the cohesion are obtained, which specifically includes the following steps:

[0028] S31, the microstructure tensor is used to describe the yield criterion of anisotropic rock mass, and the expression is:

[0029] F=F(σ ij ,A ij )=F(trσ,trσ 2 ,trσ 3 ,η)=0;

[0030] Where F is stress, σ ij is the stress tensor, A ij is the deflection of the microstructure tensor, trσ, trσ 2 , trσ 3 are the three invariants of the stress tensor; i and j are the rows and columns of the tensor matrix respectively;

[0031] η is the anisotropy parameter, which represents the projection of the microstructure tensor on the loading direction l. The expression of η is:

[0032]

[0033] Where, a1 and a2 are coefficients;

[0034] l i 、l i are generalized loading directions, where l i The expression is:

[0035]

[0036] Where, the function tr(·) represents the sum of the diagonal elements of the corresponding tensor matrix; Represents the vector product of two vectors; N (i) (i=1,2,3) is a second-order tensor; e i (i=1,2,3) represents the main 3-valent basis of the microstructure tensor, which is a first-order tensor; σ 2=σ·σ represents the dot product of the stress tensor; l j The expression of l i same;

[0037] Assuming that the shear strength of formation materials is related to the formation structural surface, that is, the anisotropic structural surface, the functional relationship between cohesion and internal friction angle and the microstructure tensor is used to characterize the anisotropic characteristics of the shear strength of formation materials. Only considering the influence of the quadratic term of the microstructure tensor, the functional relationship between cohesion and internal friction angle and the microstructure tensor is obtained:

[0038]

[0039]

[0040] In the formula, c represents cohesion, c0 represents average cohesion, A ij is the deviator of the microstructure tensor, A1 and A2 are parameters that characterize the degree of anisotropy of the rock mass, and b1 and b2 are coefficients; represents the internal friction angle, represents the average internal friction angle;

[0041] S32, if the formation contains only one set of anisotropic structural surfaces, that is, layered formation material, then the functional relationships between cohesion and internal friction angle and microstructure tensor are:

[0042]

[0043]

[0044]

[0045] Where n is the unit normal vector of the anisotropic structural surface, σ 2 =σ·σ represents the dot product of two stress tensors;

[0046] S33, the shear strength of the formation material is obtained through triaxial compression test and uniaxial compression test. For layered formation materials, the functional relationship between cohesion and internal friction angle and microstructure tensor is as follows:

[0047] In the case of triaxial compression test, the confining pressure σ x =σ y ≠0, the functional relationships between cohesion and internal friction angle and microstructure tensor are:

[0048]

[0049]

[0050]

[0051] Where β is the inclination angle of the anisotropic structural surface of the layered stratum material, σ x , σ y , σ z represent the stress components in the x, y, and z directions, respectively;

[0052] In the case of uniaxial compression test of layered formation materials, the confining pressure σ x =σ y = 0, the functional relationships between cohesion and internal friction angle and microstructure tensor are:

[0053]

[0054]

[0055] Preferably, in step S4, FLAC is used 3D Software was used to establish an analytical method for simulating the anisotropic shear strength of strata materials. Numerical calculations were carried out during the tunnel shield excavation process to obtain the settlement value of the strata during shield excavation. This method was used to analyze the influence of the anisotropic shear strength of strata materials on surface settlement and the distribution range of the plastic zone during the tunnel shield excavation process, and to study the degree of disturbance of the strata caused by shield excavation. The details are as follows:

[0056] S41, use Import to import the 3D finite element calculation model of the tunnel, and assign various stratum material parameters, including cohesion, internal friction angle, elastic modulus, Poisson's ratio, bulk density, bulk modulus, and shear modulus, through custom functions;

[0057] S42, set the initial boundary conditions for the three-dimensional finite element calculation model of the tunnel in FLAC 3D Use the fix command to fix the tunnel boundary, perform initial stress calculation based on the actual situation of the tunnel shield project, and select the gravity field as the stress field condition of the model based on the characteristics of tunnel stress distribution.

[0058] S43, through the Fish language custom function, in FLAC 3D In each calculation step of the software, the stress tensor value of each unit is read through the loop command. According to the anisotropic expression of the shear strength of the formation material, the shear strength of each formation unit is updated in real time until the calculation is completed.

[0059] S44, based on the three-dimensional finite element calculation model of the tunnel, performs numerical calculation on the entire shield tunneling process, and reads FLAC 3D The calculation result file of the software is used to obtain the settlement value and plastic zone range of the shield tunneling stratum.

[0060] Preferably, the anisotropy of the shear strength of the formation material is affected by the microstructure tensor A related to the formation structure. ij and the stress tensor σ in the generalized loading direction, the shear strength of the formation material includes the cohesion c and the internal friction angle

[0061] The advantages of the present invention are:

[0062] (1) Since the tunnel surrounding rock is heterogeneous, nonlinear, and discontinuous, considering the anisotropy of the stratum material can more accurately simulate the surface settlement and the formation of plastic zones during shield tunneling, which makes up for the shortcomings of previous shield tunneling simulations that usually only consider the isotropy of the stratum.

[0063] (2) Considering the refined modeling of stratum anisotropy in the numerical simulation of shield tunneling in tunnel engineering will play an important role in optimizing the accuracy of numerical simulation of tunnel engineering and provide better guidance for engineering practice.

[0064] (3) The shield shell advancement, segment installation, shield tail grouting and other processes of shield tunneling are simulated in detail according to the steps of ring advancement, which can better reproduce the entire tunneling process and reveal the impact of the tunnel shield tunneling process on surface settlement. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 This is a flow chart of a numerical simulation method for shield tunneling that takes into account stratum anisotropy according to the present invention.

[0066] Figure 2 It is the three-dimensional finite element calculation model of the tunnel in the embodiment.

[0067] Figure 3 It is a schematic diagram of a refined simulation of the shield tunneling process of the cross-river tunnel in the embodiment.

[0068] Figure 4 This is the variation curve of shear strength (σ1-σ3) when the bedding angle changes under different confining pressure conditions based on the anisotropic shear strength model of formation materials based on microstructure tensor.

[0069] Figure 5 The YC20 monitoring section (location see Figure 2 ) surface subsidence curve.

[0070] Figure 6 The typical cross-section plastic zone distribution during shield tunneling considering the anisotropy of shear strength of stratum materials.

[0071] Figure 7 This is the typical cross-section plastic zone distribution during shield tunneling without considering the anisotropy of the shear strength of the stratum material. DETAILED DESCRIPTION

[0072] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0073] In this embodiment, a refined numerical simulation method for shield tunneling considering stratum anisotropy is used. The right tunnel of an actual large-diameter river crossing tunnel is selected and the finite element difference software FLAC is used to simulate the shield tunneling. 3D , and carry out detailed numerical simulation of shield tunneling considering the anisotropy of shear strength of stratum materials.

[0074] The main steps include:

[0075] S1. Determine the size range and stratum material characteristics of the tunnel 3D finite element calculation model based on the tunnel site engineering geological conditions and tunnel size.

[0076] According to the actual situation of the tunnel site, a three-dimensional finite element calculation model of the tunnel was established. The boundary size of the finite element calculation model is 62m (length) × 130m (width) × 78.2m (depth), the buried depth of the tunnel top is 11.25m, and the thickness of the corresponding rock and soil layers in the stratum (from top to bottom) are 1.8m, 6.7m, 20m, 16.5m, 3.2m, and 30m, respectively. According to the geological conditions of the stratum of the shield tunneling section of the subway tunnel under study, FLAC was used. 3D The software establishes a stratum geometric model. In this stratum geometric model, the X direction is the tunnel cross-section direction, the Y direction is the tunnel longitudinal excavation direction, and the Z direction is the vertical direction. The stratum model is layered according to the different properties of the stratum material. The three-dimensional finite element calculation model of the tunnel is shown in Figure 2 As shown, the stratigraphic unit uses an eight-node hexahedron, resulting in a total of 208,530 model units and 218,816 nodes. Zero-displacement normal constraints are applied to the bottom and both sides of the tunnel's three-dimensional finite element calculation model. Based on the tunnel's stress distribution characteristics, the gravity field is selected as the model's stress field condition.

[0077] S2, based on the structural dimensions and operation mode of the shield machine, the shield shell advancement, segment installation, and shield tail grouting processes are carefully considered. In the three-dimensional finite element calculation model of the tunnel, the shield shell unit and segment unit are accurately set, the face pressure and grouting pressure are applied, and the detailed simulation process of the tunnel shield excavation is determined, such as Figure 3 shown.

[0078] Select FLAC 3DFinite difference software is used to simulate the shield tunneling process. Based on the idea of ​​stiffness transfer method, FLAC 3D The software implements the shield tunneling process by continuously transforming unit parameter properties. During shield tunneling, equivalent layer units are used to simulate grouting pressure. Based on the actual shield construction process, the shield shell is assumed to have a length of seven segments. The seven segments behind the tunnel face are used to simulate the activation of the shell units, and the two segments are used to simulate the segment units subjected to grouting pressure at the shield tail.

[0079] The specific simulation steps of step S2 are as follows:

[0080] S21, generation of the initial stress field, that is, activating all strata and enclosure structure units, selecting the gravity field as the stress field condition of the tunnel 3D finite element calculation model, and after calculating the initial stress of the model, clearing the initial displacement and velocity to zero.

[0081] S22, excavation of the first ring, passivation of the tunnel and segment units of the first ring, application of a face pressure of 1.2 MPa on the excavation face, activation of the equivalent layer units of the first ring as shield units.

[0082] S23, excavation of the second ring, passivation of the tunnel and segment units of the second ring and the face pressure of the first ring to 1.2 MPa, activation of the equivalent layer units of the second ring as shield units, and application of the face pressure on the excavation face.

[0083] S24, continue shield tunneling in the manner of step S23 until the 7th ring is excavated, the shield shell completely enters the tunnel, passivates the tunnel and segment units of the 7th ring and the face pressure of the 6th ring, activates the equivalent layer units of the 7th ring as shield shell units, and applies a face pressure of 1.2 MPa on the excavation face.

[0084] S25, excavation of the 8th ring, passivation of the tunnel and segment units of the 8th ring and the face pressure of the 7th ring, activation of the equivalent layer units of the 8th ring as shield units, update of the shield units of the 1st ring as equivalent layer units, application of a grouting pressure of 0.2 MPa in the equivalent layer units of the 1st ring, activation of the segment units of the 1st ring, and application of a face pressure of 1.2 MPa on the excavation face.

[0085] S26, continue shield tunneling in the manner of step S25, excavate the 9th ring, passivate the tunnel and segment units of the 9th ring and the face pressure of the 8th ring, activate the equivalent layer units of the 9th ring as shield units, update the shield units of the 2nd ring as equivalent layer units, apply a grouting pressure of 0.2Mpa in the equivalent layer units of the 2nd ring, activate the segment units of the 2nd ring, and apply a face pressure of 1.2Mpa on the excavation face.

[0086] S27, excavation of the 10th ring, passivation of the tunnel and segment units of the 10th ring and the face pressure of the 9th ring, activation of the equivalent layer units of the 10th ring as shield units, update of the shield units of the 3rd ring as equivalent layer units, application of a grouting pressure of 0.2 MPa in the equivalent layer units of the 3rd ring, passivation of the grouting pressure in the equivalent layer units of the 1st ring, activation of the segment units of the 3rd ring, update of the equivalent layer units of the 1st ring as segment units, and application of a face pressure of 1.2 MPa on the excavation face.

[0087] S28, as the shield advances, the properties of the tunnel, segments, equivalent layers and face pressure at different locations are passivated or activated according to the method of step S27 until the excavation construction of all excavation sections is completed.

[0088] Among them, the tunnel face is the working surface that contacts the rock and soil in the forward direction of the shield machine, and the pressure applied on it is the tunnel face pressure; the shield shell is the outer hard shell of the shield machine, which protects the structural safety of the shield machine body during excavation; the segment is the annular segment automatically laid by the machine at the tail of the shield after the shield machine advances; grouting is the grouting material in the gap behind the segment wall to prevent the segment and soil from settling; the equal-generation layer unit is used to simulate the applied grouting pressure.

[0089] S3. Based on the anisotropic characteristics of the shear strength of formation materials, a microstructure tensor with a clear physical meaning is used to characterize the anisotropy of the shear strength of formation materials. Microstructure tensor theory is a rock mechanics method for studying the anisotropy of structural planes. Generally, the microstructure tensor contains multiple sets of anisotropic structural planes, which are controlled by the stress tensor. However, if the material contains only one set of anisotropic structural planes, the microstructure tensor is controlled by the inclination angle of the anisotropic structural plane. Anisotropy refers to the fact that the shear strength of formation materials varies with the different occurrences of the formation structural planes. Formation structural planes are also called anisotropic structural planes. The shear strength varies in different directions along the structural plane, exhibiting anisotropy. The shear strength of formation materials includes the internal friction angle and cohesion.

[0090] In step S3, based on the Mohr-Coulomb strength criterion, the functional relationships between the internal friction angle and the cohesion and the microstructure tensor are obtained, which specifically include the following:

[0091] S31. The anisotropy of the shear strength of strata depends on their internal structure, stress state, and direction of loading. As the loading direction and stress magnitude change, the anisotropy of the shear strength of strata exhibits different peak strengths, plastic deformations, and failure modes. A general expression describing the yield criterion of anisotropic rock masses using a physically well-defined microstructural tensor is:

[0092] F=F(σ ij ,A ij )=F(trσ,trσ 2 ,trσ3 ,η)=0 (1)

[0093] In formula (1), F is stress, σ ij is the stress tensor, A ij is the deflection of the microstructure tensor, trσ, trσ 2 , trσ 3 are the three invariants of the stress tensor;

[0094] η is the anisotropy parameter, which represents the projection of the microstructure tensor on the loading direction l. The general expression of η is:

[0095]

[0096] Where, a1 and a2 are coefficients;

[0097] l i 、l i are generalized loading directions, where l i The expression is:

[0098]

[0099] In formula (3), the function tr(·) represents the sum of the diagonal elements of the corresponding tensor matrix; Represents the vector product of two vectors; N (i) (i=1,2,3) is a second-order tensor; e (i) (i=1,2,3) represents the main 3-valent basis of the microstructure tensor, which is a first-order tensor; σ 2 =σ·σ represents the dot product of the stress tensor; l j The expression of l i same.

[0100] Assuming that the shear strength of formation materials is related to the internal anisotropic structural surface, the functional relationship between cohesion and internal friction angle and the microstructure tensor is used to characterize the anisotropic characteristics of the shear strength of formation materials. Only the influence of the quadratic term of the microstructure tensor is considered, and the functional relationship between cohesion and internal friction angle and the microstructure tensor is obtained as follows:

[0101]

[0102]

[0103] In formula (4), c represents cohesion, c0 represents average cohesion, A ij is the deviator of the microstructure tensor, A1 is the parameter representing the degree of anisotropy of the rock mass, and b1 is the coefficient; in formula (5), represents the internal friction angle, represents the average internal friction angle, A ij is the deviator of the microstructure tensor, A2 is the parameter that characterizes the degree of anisotropy of the rock mass, and b2 is the coefficient.

[0104] S32, by introducing the microstructure tensor to describe the anisotropic characteristics of the formation material. In actual engineering, there are a large number of rock and soil formations containing a set of anisotropic surfaces. This situation can be simplified. If the formation contains only one set of anisotropic structural surfaces, that is, layered formation materials, then the functional relationship between cohesion and internal friction angle and the microstructure tensor, that is, equations (4) and (5), can be simplified to:

[0105]

[0106]

[0107]

[0108] In formula (8), n is the unit normal vector of the anisotropic structural surface, σ 2 =σ·σ represents the dot product of the stress tensor.

[0109] S33, the shear strength of the formation material is obtained through triaxial compression test and uniaxial compression test. For layered formation materials, the functional relationship between cohesion and internal friction angle and microstructure tensor is as follows:

[0110] In the case of triaxial compression test, the confining pressure σ x =σ y ≠0, the functional relationships between cohesion and internal friction angle and microstructure tensor are:

[0111]

[0112]

[0113]

[0114] Where β is the inclination angle of the anisotropic structural surface of the layered stratum material, σ x , σ y , σ z represent the stress components in the x, y, and z directions, respectively;

[0115] In the case of uniaxial compression test of layered formation materials, the confining pressure σ x =σ y = 0, the functional relationships between cohesion and internal friction angle and microstructure tensor are:

[0116]

[0117]

[0118] In this embodiment, during the shield tunneling process of the right line of the river crossing tunnel, the stratum material is determined based on the results of on-site survey and indoor triaxial test. Figure 4 As shown, Figure 4 In order to simulate the shear strength (σ1-σ3) at different layer angles based on the anisotropic shear strength model of the material based on the microstructure tensor, the shear parameters of the formation material (cohesion c, internal friction angle ), and then according to the experimental values ​​of shear strength (σ1-σ3) with the change of layer angle β when the confining pressure is 0Mpa, 1Mpa, 3Mpa, and 5Mpa, they correspond to Figure 4 4a-4d in the equation, the relevant parameters in equations (6) and (7) are determined by theoretical formulas. Therefore, the cohesion c and internal friction angle of the tunnel stratum material are obtained when anisotropy is considered. The calculation expression is:

[0119]

[0120]

[0121] S4, by using FLAC 3D The software's built-in Fish language establishes an analytical method for simulating the anisotropic shear strength of stratum materials, and then carries out numerical calculations of the tunnel shield excavation process to obtain the settlement value and plastic zone range of the shield excavation stratum. This helps to understand the influence of the tunnel shield excavation process and the anisotropic shear strength of stratum materials on surface settlement, so as to provide guidance for the shield tunnel construction process.

[0122] FLAC 3D The Fish language in the software is an embedded programming language. The programs written in it can be embedded in the command stream file and can call all the built-in commands of the software, making up for the FLAC 3D The defects of the standard program code of the software make it convenient for users to use FLAC 3D Software usage. For FLAC 3D The software comes with the Mohr Coulomb criterion, the shear parameters of the formation material (cohesion c, internal friction angle ) is a fixed value, which cannot well reflect the anisotropic distribution characteristics of the shear parameters of the formation material. 3D The software's built-in Mohr-Coulomb model uses the built-in Fish language to convert the shear parameters of the formation material (cohesion c, internal friction angle ) is written into the command stream file to simulate and analyze the law of the shear parameters of the formation material changing with the layer angle. Specifically, it includes the following contents:

[0123] S41, use Import to import the three-dimensional finite element calculation model of the tunnel, and assign the parameters of each stratum material, including cohesion c, internal friction angle, etc., through custom functions. Elastic modulus, Poisson's ratio, bulk density, bulk modulus and shear modulus; details are shown in Table 1 below:

[0124] Table 1 Material parameters of each layer

[0125]

[0126]

[0127] S42, set the initial boundary conditions for the three-dimensional finite element calculation model of the tunnel in FLAC 3D The fix command is used in the software to fix the tunnel boundary; the initial stress calculation is performed based on the actual situation of the tunnel shield project, and the gravity field is selected as the stress field condition of the model based on the characteristics of the tunnel stress distribution.

[0128] S43, through the custom function of Fish language, to traverse each unit, according to the stress tensor σ and anisotropic structural surface inclination β of each unit, in FLAC 3D In each calculation step, the software uses the loop command to calculate the cohesion c and internal friction angle given by equations (13) and (14). The functional relationship between the loading stress tensor σ and the anisotropic structural surface inclination angle β is used to determine the cohesion c and internal friction angle of each unit. The parameters are updated in real time until the calculation is completed.

[0129] S44, apply face pressure through the apply command, take 0.12Mpa according to the actual project, and the null command means to passivate the excavation strata of the corresponding number of rings and advance the shield machine for the corresponding number of rings. Remove the originally applied face pressure through the remove command, and apply the face pressure at the new face through the apply command, passivate the next ring of strata, and move the shield machine forward one ring. The model is continuously excavated by continuously changing the face pressure and the passivated strata, and the model state when the corresponding number of rings are excavated is solved through the solve command until the shield machine leaves the excavation section. By reading FLAC 3D The calculation result file of the software is used to obtain the settlement value of the shield tunneling stratum and analyze the scope of the plastic zone and the degree of disturbance.

[0130] In this example, the entire excavation process of the ultra-large diameter river-crossing tunnel was numerically calculated through continuous and refined model calculations. The current construction data was compared with the simulation calculation results. The comparative analysis is as follows:

[0131] 1. Consider the influence of anisotropic factors on the settlement of the stratum during shield tunneling

[0132] Affected by geological action, the shear strength of stratum materials is usually anisotropic under natural conditions. In order to consider the influence of the anisotropic characteristics of stratum strength on the surface stratum settlement during shield tunneling, it is assumed that the shear strength of the stratum materials at the tunnel (cohesion c, internal friction angle ) is anisotropically distributed.

[0133] Considering that when the anisotropic structural surface has an inclination angle of 45°, the compressive strength of the stratum material is the lowest, the surface settlement value is the largest, and it is easy to form a large-scale shear failure. Taking the anisotropic structural surface with an inclination angle of 45° as an example, the settlement law of the surface stratum after the right line tunnel is excavated is compared and analyzed when the anisotropic shear strength anisotropy of the stratum material is considered and not considered. The calculation results are as follows: Figure 5 As shown, considering the cohesion c and the internal friction angle When anisotropy occurs, the cohesion c and the internal friction angle Calculate the values ​​according to formula (13) and (14) respectively. Without considering the anisotropy of the shear strength of the formation material, the cohesion c and the internal friction angle are Take fixed values ​​according to the parameter table. The surface settlement curves caused by tunnel shield excavation all show a parabolic distribution that first increases and then decreases, with the maximum settlement at the central section of the tunnel. The surface settlement caused by tunnel shield excavation is affected by the anisotropic characteristics of the shear strength of the stratum material. The surface settlement curve calculated when only the anisotropy of cohesion is considered is slightly different from that when the anisotropy of the shear strength of the stratum material is not considered. However, the surface settlement calculation results caused by tunnel excavation after considering the anisotropic distribution of the internal friction angle are significantly different from those in the isotropic case. When the anisotropic distribution of the internal friction angle is considered, the maximum settlement value at the tunnel centerline is 24.09mm, while the maximum settlement value is 38.00mm when the anisotropic distribution of cohesion and internal friction angle is considered at the same time, which exceeds the surface settlement range standard (+10 to -30mm). The above results show that the anisotropic shear strength characteristics of the stratum material have a significant impact on the surface settlement during shield tunneling. Using the calculation results when the shear strength of the stratum material is isotropic to guide actual construction will ignore the safety risks brought by the anisotropy of the material, which may lead to safety hazards in engineering construction. In practice, the influence of the anisotropy of the shear strength of the stratum material should be considered.

[0134] 2. Consider the influence of anisotropic factors on the plastic zone of the tunnel transverse section

[0135] In actual engineering, the degree of engineering disturbance and rock mass geological strength index have an impact on the shear strength of stratum materials (cohesion c and internal friction angle ) exists within a certain relationship. Using the effective internal friction angle and effective cohesion of the surrounding rock after disturbance, the actual displacement of the plastic zone of the surrounding rock at the construction site can be derived. This can guide construction technicians to appropriately consider a certain amount of overexcavation during construction, avoid repeated disturbances of the surrounding rock, and thus better ensure construction quality. By considering the impact of stratum strength anisotropy on the plastic zone, simulation calculations provide more precise and detailed guidance for on-site tunneling and excavation. Figure 6 In order to consider the anisotropy of shear strength of tunnel stratum materials caused by the anisotropic structural surface with an inclination angle of 45°, the tunnel was excavated to the YC20 monitoring section (location see Figure 2 ) is the plastic zone of a typical section, Figure 7 The calculation results do not consider the anisotropy effect. By comparison, it can be seen that the anisotropic characteristics of the shear strength of the stratum material intensify the disturbance effect of the stratum around the tunnel, making the range of its plastic zone larger than that of the homogeneous stratum.

[0136] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A numerical simulation method for shield tunneling considering anisotropic stratum shear strength, characterized by: The following steps are involved: S1. Determine the size range and stratum material characteristics of the tunnel 3D finite element calculation model based on the tunnel site engineering geological conditions and tunnel size; S2, based on the structural dimensions and operating mode of the shield machine, as well as the processes of shield advancement, segment installation, and shield tail grouting, sets the shield shell unit and segment unit in the tunnel 3D finite element calculation model, applies the tunnel face pressure and grouting pressure, and determines the tunnel shield excavation simulation process; S3, according to the anisotropic characteristics of the shear strength of the formation material, the microstructure tensor is used to characterize the anisotropy of the shear strength of the formation material, and the anisotropic expression of the shear strength of the formation material is obtained; S4, using 3D simulation software, establish an analytical method for simulating the anisotropic shear strength of strata materials, conduct numerical calculations of the tunnel shield excavation process, and obtain the settlement value and plastic zone range of the strata during shield excavation, which are used to analyze the degree of disturbance caused by shield excavation on the strata; In step S1, a stratum geometric model is established using three-dimensional simulation software based on the tunnel site engineering geological conditions and tunnel size. In the stratum geometric model, eight-node hexahedral elements are used, the X direction is the tunnel cross-section direction, the Y direction is the tunnel longitudinal excavation direction, and the Z direction is the vertical direction. The stratum geometric model is layered according to the different properties of the stratum materials; In step S2, a three-dimensional simulation software is used to simulate the construction excavation process of the shield machine. According to the structural dimensions and operation mode of the shield machine, the parameter attributes of the units surrounding the tunnel are changed in the three-dimensional simulation software to simulate the shield cyclic excavation and segment assembly process. During the shield cyclic excavation, the grouting pressure of the shield tail is simulated by the equivalent layer units. In step S3, the shear strength of the formation material includes the internal friction angle and the cohesion. The functional relationship between the internal friction angle and the microstructure tensor and the functional relationship between the cohesion and the microstructure tensor are obtained, that is, the anisotropic expressions of the internal friction angle and the cohesion are obtained, as shown below: c=c0[1+A1(1-3cos 2 b)+b1(A1(1-3cos 2 b)) 2 ]; Where c represents cohesion, c0 represents average cohesion; represents the internal friction angle, represents the average internal friction angle, A1 and A2 are parameters that characterize the degree of anisotropy of the rock mass, b1 and b2 are coefficients, and β is the inclination angle of the anisotropic structural plane of the layered stratum material.

2. The numerical simulation method for shield tunneling considering anisotropic stratum shear strength according to claim 1 is characterized in that: The shield shell of the TBM is composed of N ring segments. The N ring segment length behind the tunnel face is used to simulate the activation of the shield shell unit, and the M ring segment length is used to simulate the segment unit under the grouting pressure of the shield tail. The specific simulation steps of the construction excavation process of the shield machine are as follows: S21, generating the initial stress field, i.e., activating all strata and enclosure structure units, selecting the gravity field as the stress field condition of the tunnel 3D finite element calculation model, calculating the initial stress of the tunnel 3D finite element calculation model, and then clearing the initial displacement and velocity; S22, excavation of the first ring, passivation of the tunnel and segment units of the first ring, application of face pressure on the excavation face, activation of the equivalent layer units of the first ring as shield units; S23, excavation of the second ring, passivation of the tunnel and segment elements of the second ring and the face pressure of the first ring, activation of the equivalent layer elements of the second ring as shield elements, and application of the face pressure on the excavation face; S24, continuing shield tunneling in the manner of step S23 until the Nth ring is excavated and the shield shell is completely inside the tunnel, passivating the tunnel and segment units of the Nth ring and the face pressure of the N-1th ring, activating the equivalent layer units of the Nth ring as shield shell units, and applying the face pressure on the excavation face; S25, excavation of the N+1 ring, passivation of the tunnel and segment units of the N+1 ring and the face pressure of the N ring, activation of the equivalent layer units of the N+1 ring as shield units, updating of the shield units of the 1st ring as equivalent layer units, application of grouting pressure to the equivalent layer units of the 1st ring, activation of the segment units of the 1st ring, and application of face pressure to the excavation face; S26, continuing shield tunneling in the manner of step S25 until the N+Mth ring is excavated, passivating the tunnel and segment units of the N+Mth ring and the face pressure of the N+M-1th ring, activating the equivalent layer units of the N+Mth ring as shield shell units, updating the shield shell units of the Mth ring as equivalent layer units, applying grouting pressure to the equivalent layer units of the Mth ring, activating the segment units of the Mth ring, and applying face pressure to the excavation face; S27, excavation of the N+M+1th ring, passivation of the tunnel and segment units of the N+M+1th ring and the face pressure of the N+Mth ring, activation of the equivalent layer units of the N+M+1th ring as shield units, update of the shield units of the M+1th ring as equivalent layer units, application of grouting pressure to the equivalent layer units of the M+1th ring, passivation of the grouting pressure in the equivalent layer units of the 1st ring, activation of the segment units of the M+1th ring, update of the equivalent layer units of the 1st ring as segment units, and application of face pressure to the excavation face; S28, as the shield advances, the properties of the tunnel, segments, equivalent layers and face pressure at different locations are passivated or activated according to the method of step S27 until the excavation construction of all excavation sections is completed.

3. The numerical simulation method for shield tunneling considering anisotropic stratum shear strength according to claim 1 is characterized in that: In step S3, the shear strength of the formation material includes the internal friction angle and the cohesion. The functional relationship between the internal friction angle and the microstructure tensor and the functional relationship between the cohesion and the microstructure tensor are obtained, that is, the anisotropic expressions of the internal friction angle and the cohesion are obtained. The specific steps include: S31, the microstructure tensor is used to describe the yield criterion of anisotropic rock mass, and the expression is: F=F(σ ij ,A ij )=F(trσ,trσ 2 ,trσ 3 ,h)=0; Where F is stress, σ ij is the stress tensor, A ij is the deflection of the microstructure tensor, trσ, trσ 2 , trσ 3 are the three invariants of the stress tensor; i and j are the rows and columns of the tensor matrix respectively; η is the anisotropy parameter, which represents the projection of the microstructure tensor on the loading direction l. The expression of η is: Where, a1 and a2 are coefficients; l i 、l i are generalized loading directions, where l i The expression is: Where, the function tr(·) represents the sum of the diagonal elements of the corresponding tensor matrix; Represents the vector product of two vectors; N (i) (i=1,2,3) is a second-order tensor; e i (i=1,2,3) represents the main 3-valent basis of the microstructure tensor, which is a first-order tensor; σ 2 =σ·σ represents the dot product of the stress tensor; l j The expression of l i same; Assuming that the shear strength of formation materials is related to the formation structural surface, that is, the anisotropic structural surface, the functional relationship between cohesion and internal friction angle and the microstructure tensor is used to characterize the anisotropic characteristics of the shear strength of formation materials. Only considering the influence of the quadratic term of the microstructure tensor, the functional relationship between cohesion and internal friction angle and the microstructure tensor is obtained: c=c0[1+A ij l i l j +b1(A1A ij l i l j ) 2 +···]; In the formula, c represents cohesion, c0 represents average cohesion, A ij is the deviator of the microstructure tensor, A1 and A2 are parameters that characterize the degree of anisotropy of the rock mass, and b1 and b2 are coefficients; represents the internal friction angle, represents the average internal friction angle; S32, if the formation contains only one set of anisotropic structural surfaces, that is, layered formation material, then the functional relationships between cohesion and internal friction angle and microstructure tensor are: Where n is the unit normal vector of the anisotropic structural surface, σ 2 =σ·σ represents the dot product of two stress tensors; S33, the shear strength of the formation material is obtained through triaxial compression test and uniaxial compression test. For layered formation materials, the functional relationship between cohesion and internal friction angle and microstructure tensor is as follows: In the case of triaxial compression test, the confining pressure σ x =σ y ≠0, the functional relationships between cohesion and internal friction angle and microstructure tensor are: Where β is the inclination angle of the anisotropic structural surface of the layered stratum material, σ x , σ y , σ z represent the stress components in the x, y, and z directions, respectively; In the case of uniaxial compression test of layered formation materials, the confining pressure σ x =σ y = 0, the functional relationships between cohesion and internal friction angle and microstructure tensor are: c=c0[1+A1(1-3cos 2 b)+b1(A1(1-3cos 2 b)) 2 ]; 4. The numerical simulation method for shield tunneling considering anisotropic stratum shear strength according to claim 1 is characterized in that: In step S4, FLAC is used 3D Software was used to establish an analytical method for simulating the anisotropic shear strength of strata materials. Numerical calculations were carried out during the tunnel shield excavation process to obtain the settlement value of the strata during shield excavation. This method was used to analyze the influence of the anisotropic shear strength of strata materials on surface settlement and the distribution range of the plastic zone during the tunnel shield excavation process, and to study the degree of disturbance of the strata caused by shield excavation. The details are as follows: S41, use Import to import the 3D finite element calculation model of the tunnel, and assign various stratum material parameters, including cohesion, internal friction angle, elastic modulus, Poisson's ratio, bulk density, bulk modulus, and shear modulus, through custom functions; S42, set the initial boundary conditions for the three-dimensional finite element calculation model of the tunnel in FLAC 3D Use the fix command to fix the tunnel boundary, perform initial stress calculation based on the actual situation of the tunnel shield project, and select the gravity field as the stress field condition of the model based on the characteristics of tunnel stress distribution. S43, through the Fish language custom function, in FLAC 3D In each calculation step of the software, the stress tensor value of each unit is read through the loop command. According to the anisotropic expression of the shear strength of the formation material, the shear strength of each formation unit is updated in real time until the calculation is completed. S44, based on the three-dimensional finite element calculation model of the tunnel, performs numerical calculation on the entire shield tunneling process, and reads FLAC 3D The calculation result file of the software is used to obtain the settlement value and plastic zone range of the shield tunneling stratum.

5. The numerical simulation method for shield tunneling considering anisotropic stratum shear strength according to claim 4 is characterized in that: The anisotropy of the shear strength of the formation material is affected by the microstructure tensor A related to the formation structure. ij and the stress tensor σ in the generalized loading direction, the shear strength of the formation material includes the cohesion c and the internal friction angle

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