Shield tunnel segment failure mechanism test method considering assembly effect

Abstract

The invention relates to the technical field of tunnel segment engineering, and discloses a shield tunnel segment failure mechanism test method considering an assembly effect, which adopts a three-ring staggered joint assembly tunnel segment calculation scheme, and adopts a Taisha foundation loose soil pressure formula to calculate vertical and horizontal soil pressure. 24 loading points are arranged to simulate loads such as stratum resistance, soil pressure and upper pile unloading borne by an actual shield. According to the method, DIANA finite element software is used for building a numerical model of refined three-ring staggered joint assembly, mechanical response of the shield tunnel segments under the top overload condition is analyzed, material and contact nonlinearity are considered, the segments are connected through solid bolts, the deformation characteristics and the cracking damage state of the overall structure of the shield tunnel can be accurately obtained, and the construction efficiency is improved. And introducing a tensile damage factor to predict a segment crack distribution area. The safety of the tunnel structure is improved, the assembly effect and the stress state of the shield tunnel segments are accurately simulated through the finite element model, and the overall safety and stability of the tunnel structure can be evaluated more accurately.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel segment engineering, and particularly to a test method for the failure mechanism of shield tunnel segments considering the assembly effect. Background Art

[0002] The shield tunneling method is a modern construction technology widely used in urban tunnel construction, which has the advantages of fast tunneling speed, high automation degree, safety and reliability, and little disturbance to the surrounding soil mass, and can effectively avoid interfering with surrounding buildings and traffic. During the construction process, the shield machine tunnels under the support and protection of the shield shell, and at the same time, precast lining segments are assembled synchronously. The segments are spliced by connecting bolts and waterproof gaskets to form the overall structure of the tunnel. However, due to the large size of the tunnel, there are a large number of longitudinal and circumferential joints between the segments and between the rings, and these joints have a weakening effect on the overall stiffness of the tunnel, which may affect the long-term stability of the tunnel. Therefore, studying the assembly effect and failure mechanism of shield tunnel segment joints is of great significance for tunnel design, construction and operation. By deeply analyzing the mechanical behavior, deformation characteristics and durability of the joints, it can provide theoretical support and practical guidance for optimizing the design scheme, improving construction safety and ensuring the long-term stability of the tunnel.

[0003] The research methods for shield tunnel structures mainly include three means: in-situ tests, numerical simulations, and simplified mechanical models. Each has its unique advantages and disadvantages and is suitable for different research needs. In practical engineering applications, the selection of an appropriate research method depends on the specific requirements of the project and the available resources. As the most intuitive research method, in-situ tests can truly reproduce the stress behavior of tunnel linings through full-scale or reduced-scale experiments and reveal the structural deformation and failure modes. However, in-situ tests usually face problems such as high costs, long cycles, strict requirements for experimental sites and equipment, and due to the limitations of the experimental scale, it is difficult to comprehensively cover complex working conditions and long-term effects, so it can only provide data support for local or short-term effects. Numerical simulations rely on the powerful computing power of computers and use numerical methods such as finite element analysis to virtually simulate tunnel structures, with advantages such as high efficiency and easy operation. It can quickly evaluate the structural response under complex working conditions and is especially suitable for predicting the behavior of tunnels under variable environments. However, current numerical models are still insufficient in considering factors such as segment cracking and the nonlinear characteristics of joints. Convergence difficulties are prone to occur during refined calculations, and the calculation time is relatively long. Simplified mechanical models simplify some complex factors through relatively idealized assumptions. The stratum structure method can better consider the interaction between the soil layer and the tunnel structure but ignores the weakening effect of joints and is difficult to accurately reflect the behavior of the entire tunnel system; the load structure method can accurately simulate the nonlinear characteristics of joints, but its calculation efficiency is low, and it is too dependent on the assumption of constant stiffness, which may lead to certain result deviations. To overcome these limitations, scholars have begun to attempt to combine the stratum structure method with the load structure method and use a composite model to fully utilize the advantages of both, thereby improving the accuracy and practicality of tunnel structure analysis. This improved model is closer to the actual engineering needs, can comprehensively consider the nonlinear characteristics of soil layers, joints, and the discreteness of linings, and thus provides more accurate and reliable theoretical support and practical guidance for the design, construction, and operation of shield tunnels. With the progress of technology and the continuous improvement of models, future research is expected to provide more comprehensive solutions and promote the safety, economy, and sustainable development of shield tunnel projects. In summary, although a large amount of research has been done on the failure mechanism of shield tunnel segments at home and abroad, there are still many deficiencies. There is a problem that the existing technology cannot accurately obtain the deformation characteristics and cracking damage states of the overall structure of shield tunnels. Summary of the Invention

[0004] To solve the above problems, the present invention adopts the method of numerical simulation. Starting from the integral structure of the shield tunnel, a three-ring full-scale shield tunnel model is established based on the segment parameters of a severely damaged section of a certain urban subway. Considering the segment staggered joint assembly effect and the structural nonlinear characteristics, research is carried out on aspects such as the overall convergence deformation of the structure, joint opening, segment cracks, bolt stress, etc., to obtain the mechanical response mechanism of the overall structure of the shield tunnel after top overload. To solve the problem that the prior art cannot accurately obtain the deformation characteristics and cracking damage state of the overall structure of the shield tunnel, and introduce a tensile damage factor to predict the crack distribution area of the segments. The present invention provides a test method for the failure mechanism of shield tunnel segments considering the assembly effect, which specifically includes the following steps:

[0005] S1. Construct a shield tunnel model for the simulation test, and determine the assembly method and basic parameters of the segments of the shield tunnel model for the simulation test;

[0006] S2. Construct the geological conditions for the simulation test;

[0007] S3. Arrange 24 loading points to simulate the formation resistance, earth pressure, and upper loading and unloading loads on the actual shield tunnel;

[0008] S4. Select the DIANA finite element software to establish a full-scale three-ring staggered joint assembly shield tunnel model, including: calibrating the parameter values of the shield tunnel model, and the parameters include concrete parameters and steel parameters;

[0009] S5. Set the interaction between each component in the final shield tunnel model. The interaction between concrete segments and segments, and between bolts and concrete is simulated by interface elements that are only compressed and not tensioned;

[0010] S6. Set the boundary conditions of the shield tunnel model. Use the horizontal loading method to apply a Z-direction displacement constraint to the bottom of the lower ring segment to ensure that the direction of the jacking force is always perpendicular to the outer surface of the segment, and apply one-way constraints to the inside of the segment respectively;

[0011] S7. Determine the vertical and lateral earth pressures of the shield tunnel. For strata with arching effect, the Terzaghi relaxation earth pressure formula is used to calculate the vertical earth pressure. For medium-consolidated clay and soft clay, the full-overburden earth pressure calculation method is used. For sandy soil layers, the method of separate calculation of water and soil is used to calculate the vertical and lateral forces on the tunnel, and the vertical earth pressure at the top of the tunnel is calculated by the combination of Terzaghi loose earth pressure and water pressure;

[0012] S8. Conduct load case design, simulate the vertical soil pressure on the tunnel top, the foundation reaction force on the tunnel bottom, the lateral pressure on the tunnel, the pressure on the tunnel transition section, simulate the loading process of the overloading failure load, and introduce a tensile damage factor as the cracking risk coefficient for judging concrete elements. When its value reaches 1, it indicates that the segment has a cracking risk.

[0013] Further, in S1, it specifically includes: The tunnel is assembled with a universal ring in a staggered joint pattern. The universal ring segment is divided into 6 pieces, including 1 crown block at 15°, 2 adjacent blocks at 64.5°, and 3 standard blocks at 72°. The segment ring width is 1.2 m, the inner diameter of the segment is 5.4 m, the outer diameter is 6 m, and the segment thickness is 300 mm. The concrete strength grade is C50, the impermeability grade is P10, and the steel bars adopt HPB300 grade and HRB400 grade steel. The single-ring segments are connected by 12 M27 bent bolts, and the adjacent pipe rings are connected by 10 M27 bent bolts of grade 5.8.

[0014] Further, in S2, it specifically includes geological boreholes corresponding to the strata in the severely damaged tunnel section. From top to bottom, it is successively divided into plain fill, silty clay, silty sand, fine sand, medium sand, coarse sand, gravel sand, and moderately weathered argillaceous siltstone.

[0015] Further, in S4, it specifically includes: The concrete parameters are taken as follows: Select the total strain rotating crack model as the constitutive model of the concrete material. The constitutive equation of the concrete material constitutive model is:

[0016] D = T T D secant T

[0017]

[0018] In the formula are respectively defined as follows:

[0019]

[0020] In the formula, σ 1 , σ 2 , σ 3 are respectively the three principal stresses;

[0021] ε 1 , ε 2 , ε 3 are respectively the principal strains corresponding to the three principal stress directions;

[0022] T is the strain transformation matrix of the total strain rotating crack model after rotation;

[0023] The concrete strength grade of the segment in the shield tunnel is C50. The tensile curve of the concrete adopts an exponential type, and the compressive curve adopts a parabolic type. The Young's modulus E = 3.45×10 4 MPa, the Poisson's ratio ν = 0.2, the compressive strength f c = 43.5 MPa, and the tensile strength f t = 2.64 MPa.

[0024] Furthermore, the steel parameters in the S4 are as follows:

[0025] The Von Mises elastoplastic model is selected as the steel, including the constitutive models of bolts and steel bars. The segments are connected by solid bent bolts, and the bolt grade is 5.8; the steel bars adopt embedded elements, and the steel bar grade is HRB400 steel; the steel bar diameter = 18 mm, the Young's modulus E = 2.0×105 MPa, the yield strength = 370 MPa, and the ultimate strength = 400 MPa; the bolt diameter = 27 mm, the Young's modulus E = 2.1×105 MPa, the yield strength = 4000 MPa, and the ultimate strength = 500 MPa.

[0026] Furthermore, the S5 also includes: The interactions between the concrete segments and between the bolts and the concrete are all simulated by interface elements that are only compressed and not tensioned. This interface element can realize the real physical behavior of the tension side opening and the compression side squeezing each other at the joint under the coupled action of tension and compression;

[0027] The tensile opening behavior is determined by the interface opening strength. To achieve the free opening of the joint, the interface opening strength is taken as 0 N / m2. The damage behavior after the two squeeze each other is determined by the interface normal stiffness. The interface normal stiffness is taken as 1.0×1012 N / m3, and the interface friction angle is taken as 30° to simulate the mutual friction between the segments.

[0028] Furthermore, the S6 also includes: Setting the boundary conditions for the final geometric model, including:

[0029] In the numerical simulation, referring to the full-scale test loading method, the horizontal loading method is used to apply a Z-direction displacement constraint to the bottom of the lower ring segment to simulate the effect of the lower support bearing;

[0030] In the test, under the combined action of the overall reaction frame and the jack ear seat, it is ensured that the direction of the jacking force is always perpendicular to the outer surface of the segment, eliminating the tangential force effect caused by the tangential deformation of the segment;

[0031] Due to the uneven loads around the segment, in order to prevent the three-ring segment from rotating under the action of surrounding loads in numerical simulation, one-way constraints are applied to the inner part of the segment. Specifically, X-direction constraints are applied to the upper and lower parts of the pipe ring to avoid lateral displacement during vertical convergence deformation; Y-direction constraints are applied to the left and right parts of the pipe ring to avoid vertical displacement during horizontal convergence deformation.

[0032] Furthermore, in S7, it also includes: for medium-consolidated clay, specifically 4 ≤ N < 8, or for soft clay 2 ≤ N < 4, where N is the standard penetration blow count, the total overburden earth pressure calculation method is adopted, and the earth pressure is calculated by the following formula:

[0033]

[0034] In the formula: P 0 is the overlying load; B 1 is half of the influence width of tunnel excavation (m); H is the overburden depth (m); is the internal friction angle of the soil; P ν is the Terzaghi vertical loose earth pressure (kN / m 2 ); K 0 is the ratio of horizontal earth pressure to vertical earth pressure; c is the cohesion of the soil (kPa); R 0 is the outer radius of the segment (m).

[0035] Furthermore, in S7, it also includes: the main strata in the interval are mainly sandy soil layers, so the method of separate calculation of water and soil is adopted to calculate the vertical and lateral forces on the tunnel, and the lateral earth pressure is calculated:

[0036]

[0037] In the formula: P a is the lateral earth pressure value at the top of the tunnel; P b is the lateral earth pressure value at the bottom of the tunnel; h i , γ i ′ is the thickness and unit weight of the corresponding i-th soil layer; h a , h b are the distances from the top and bottom of the tunnel to the water surface; γ D is the unit weight of the soil within the tunnel range; D is the outer diameter of the tunnel.

[0038] Furthermore, in S8, it also includes: P 1 simulates the vertical earth pressure on the top of the tunnel and the foundation reaction force on the bottom of the tunnel; P 2 simulates the lateral pressure on the tunnel, and the value is the product of P 1 and the lateral pressure coefficient; P 3 simulates the pressure at the transition section of the tunnel, and the value is the average of P 1 and P 2 ;

[0039] P 1 For the determination of 1 :

[0040]

[0041]

[0042] The loading process of the overloading failure load is as follows:

[0043] P 1 is gradually loaded from 0 kN to P 1 designed, P 1 The load increment for each level is P 1 0.1 times of the designed P 2 The load increment for each level is P 2 0.1 times of the designed P 3 P = (P 1 + P 2 ) / 2;

[0044] Maintain P 2 unchanged, and load P 1 and P 3 until the ultimate state, and maintain P 3 = (P 1 + P 2 ) / 2, P 1 The load increment for each level is P 1 0.05 times of the designed one;

[0045] The tensile damage factor F tu based on the linear elastic theory is defined by the following formula:

[0046]

[0047] Where: f t is the tensile strength of concrete; σ 1 is the maximum principal stress of the current element.

[0048] The beneficial effects of the present invention are as follows:

[0049] First, it improves the safety of the tunnel structure. By accurately simulating the assembly effect and stress state of the shield tunnel segments through the finite element model, the overall safety and stability of the tunnel structure can be evaluated more accurately. The research method can reveal the failure mechanism of the segments under complex loads, so as to take preventive measures in advance to avoid the failure of the tunnel structure.

[0050] II. Optimize tunnel design. Based on the research results, the design parameters of shield tunnels can be optimized, such as segment size, material selection, assembly method, etc., to improve the overall performance of the tunnel. By optimizing the design parameters, unnecessary material consumption and construction difficulty can be reduced, thereby lowering the project cost.

[0051] III. Improve construction efficiency and quality. The research method can provide scientific guidance for the construction of shield tunnels, ensuring safety and quality during the construction process. By understanding in advance the failure mechanism and stress state of segments, potential risks and problems that may occur during construction can be predicted, and corresponding countermeasures can be taken. By enhancing the safety and stability of the tunnel structure and reducing risks and problems during construction, significant economic and social benefits can be achieved. Description of the Drawings

[0052] Figure 1 It is a schematic flow chart of a test method for the failure mechanism of shield tunnel segments considering the assembly effect;

[0053] Figure 2 It is a segment assembly drawing and bolt connection drawing;

[0054] Figure 3 It is a drawing of a three-ring segment model;

[0055] Figure 4 It is a drawing of the upper, middle and lower models of the three-ring segments;

[0056] Figure 5 It is a reaction frame for shield tunnel structure tests;

[0057] Figure 6 It is a schematic diagram of numerical model constraints;

[0058] Figure 7 It is a schematic diagram of loading points;

[0059] Figure 8 It is a schematic diagram of the equivalence between actual load and simplified load;

[0060] Figure 9 It is a curve of the load loading process;

[0061] Figure 10 It is a horizontal convergence curve of the shield tunnel;

[0062] Figure 11 It is a drawing of segment deformation;

[0063] Figure 12 It is a drawing of crack width in the elastic stage;

[0064] Figure 13 It is a drawing of crack width in the plastic stage;

[0065] Figure 14It is the segment crack distribution diagram;

[0066] Figure 15 It is the opening amount of the pipe ring;

[0067] Figure 16 It is the offset amount of the pipe ring;

[0068] Figure 17 It is the opening amount of the segment;

[0069] Figure 18 It is the offset amount of the segment;

[0070] Figure 19 It is the opening curve of the middle-ring segment;

[0071] Figure 20 It is the offset curve of the middle-ring segment;

[0072] Figure 21 It is the bolt stress in the plastic stage;

[0073] Figure 22 It is the tensile damage factor. Specific implementation mode

[0074] The following combines the attached Figures 1 - 22 The preferred embodiments of the present invention are elaborated in detail so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0075] The embodiment of the present invention proposes a research method for the failure mechanism of shield tunnel segments considering the assembly effect. Based on the measured data of a certain urban subway, the disease conditions and crack distribution characteristics of the subway line and the overall typical section in this area are statistically analyzed. On this basis, a numerical model of three-ring staggered joint assembly is established according to the tunnel segment parameters of the disease typical section, and the cracking and damage mechanism of shield tunnel segments under top overload is analyzed. As Figure 1 shown, it specifically includes the following steps:

[0076] S1. Construct a shield tunnel model for the simulation test, and determine the assembly method and basic parameters of the segments of the shield tunnel model for the simulation test;

[0077] The tunnel adopts the general ring staggered joint assembly. The general ring segments are divided into 6 pieces (including 1 crown block of 15°, 2 adjacent blocks of 64.5°, and 3 standard blocks of 72°); the segment ring width is 1.2 m, the inner diameter of the segment is 5.4 m, the outer diameter is 6 m, and the segment thickness is 300 mm; the concrete strength grade is C50, the impermeability grade is P10, and the steel bars adopt HPB300 grade and HRB400 grade steel; 12 M27 bent bolts are used to connect between single-ring segments, and 10 M27 bent bolts of grade 5.8 are used to connect between adjacent pipe rings;

[0078] S2. Construct the geological conditions for the simulation test;

[0079] For the geological boreholes corresponding to the strata in the severely damaged section of the tunnel, from top to bottom, they are divided into plain fill, silty clay, silty sand, fine sand, medium sand, coarse sand, gravel sand, and moderately weathered argillaceous siltstone in sequence;

[0080] S3. Arrange 24 loading points to simulate the formation resistance, earth pressure, and loads such as upper pile loading and unloading on the actual shield tunnel;

[0081] To simulate the actual loading and deformation of the shield tunnel and considering the operability of the test, it is proposed to arrange 24 loading points to simulate the formation resistance, earth pressure, and loads such as upper pile loading and unloading on the actual shield;

[0082] Through this, the free combination of forces is carried out to simulate the most unfavorable load conditions of the actual formation on the segment, so as to obtain the internal force characteristics and deformation characteristics of the segment structure, and the full-process loading of the shield lining structure until ultimate failure can be realized.

[0083] S4. Select DIANA finite element software to establish a full-scale shield tunnel model with three-ring staggered joints, including: calibrating the parameter values of the shield tunnel model, and the parameters include concrete parameters and steel parameters;

[0084] Calibrate the parameter values of the shield segment model, the parameters include concrete parameters and steel parameters, set the interaction between components in the final model, the boundary conditions of the model, earth pressure calculation, and load case design;

[0085] The concrete parameter values are as follows: Select the total strain rotating crack model as the constitutive model of concrete materials, and the constitutive equation of the material constitutive model is:

[0086] D = T T D secant T

[0087]

[0088] In the formula They are respectively defined as follows:

[0089]

[0090] In the formula, σ 1 , σ 2 , σ 3 Are respectively the three principal stresses;

[0091] ε 1 , ε 2 , ε 3 Are respectively the principal strains corresponding to the three principal stress directions;

[0092] T is the strain transformation matrix of the total strain crack model after rotation;

[0093] The concrete strength grade of the segment in the shield tunnel is C50. The tensile curve of the concrete adopts an exponential type, and the compressive curve adopts a parabolic type. The Young's modulus E = 3.45×10 4 MPa, the Poisson's ratio ν = 0.2, the compressive strength f c = 43.5 MPa, and the tensile strength f t = 2.64 MPa.

[0094] The Von Mises elastoplastic model is selected as the constitutive model of the steel materials (bolts, steel bars). Solid bent bolts are used to connect the segments, and the bolt grade is 5.8. Embedded elements are used for the steel bars, and the steel bar grade is HRB400 steel. The steel bar diameter = 18 mm, the Young's modulus E = 2.0×10 5 MPa, the yield strength σ s = 370 MPa, and the ultimate strength σ b = 400 MPa; the bolt diameter = 27 mm, the Young's modulus E = 2.1×10 5 MPa, the yield strength σ s = 4000 MPa, and the ultimate strength σ b = 500 MPa.

[0095] S5. Set the interactions between the contacts of each component in the final shield tunnel model. The interactions between the concrete segments and between the bolts and the concrete are simulated using interface elements that are only compressed and not tensioned;

[0096] The interactions between the concrete segments and between the bolts and the concrete are both simulated using interface elements that are only compressed and not tensioned. This interface element can realize the real physical behavior of the tensile side opening and the compressive side squeezing each other at the joint under the coupled action of tension and compression;

[0097] The tensile opening behavior is determined by the interface opening strength. To achieve the free opening of the joint, the interface opening strength is taken as 0 N / m2. The damage behavior after the mutual extrusion of the two is determined by the interface normal stiffness, and the interface normal stiffness is taken as 1.0×10 12 N / m3. The interface friction angle is taken as 30° to simulate the mutual friction between the segments.

[0098] S6. Set the boundary conditions of the shield tunnel model. Use the horizontal loading method to apply a Z-direction displacement constraint to the bottom of the lower ring segment to ensure that the direction of the jacking force is always perpendicular to the outer surface of the segment, and apply one-way constraints to the inside of the segment respectively;

[0099] In numerical simulation, referring to the loading method of full-scale test, the horizontal loading method is used to apply Z-direction displacement constraints to the bottom of the lower ring segment to simulate the effect of the lower support bearing;

[0100] In the test, under the combined action of the overall reaction frame and the jack ear seat, it is ensured that the direction of the jacking force is always perpendicular to the outer surface of the segment, eliminating the tangential force caused by the tangential deformation of the segment;

[0101] Since the loads around the segment are different in magnitude, in order to avoid the rotation of the three-ring segment under the action of the surrounding loads in numerical simulation, one-way constraints are applied to the inside of the segment respectively: X-direction constraints are applied to the upper and lower parts of the pipe ring to avoid lateral displacement during vertical convergence deformation; Y-direction constraints are applied to the left and right parts of the pipe ring to avoid vertical displacement during horizontal convergence deformation.

[0102] S7. Determine the vertical and lateral earth pressures of the shield tunnel. For the formation with arching effect, the Terzaghi relaxation earth pressure formula is used to calculate the vertical earth pressure. For medium-consolidated clay and soft clay, the full-overburden earth pressure calculation method is adopted. For sandy soil layers, the method of separate calculation of water and soil is used to calculate the vertical and lateral forces acting on the tunnel. The vertical earth pressure at the top of the tunnel is calculated by combining the Terzaghi loosening earth pressure and water pressure;

[0103] For the formation with arching effect, the vertical earth pressure can be calculated according to the Terzaghi relaxation earth pressure formula;

[0104] For medium-consolidated clay (4 ≤ N < 8, N is the standard penetration blow count) or soft clay (2 ≤ N < 4), the full-overburden earth pressure calculation method is usually adopted. The Terzaghi principle relaxation earth pressure is calculated as follows:

[0105]

[0106] When the earth pressure is calculated by the following formula:

[0107]

[0108] In the formula: P 0 is the overlying load; B 1 is half of the influence width of tunnel excavation (m); H is the overburden depth (m); is the internal friction angle of the soil; P ν is the Terzaghi vertical loosening earth pressure (kN / m 2 ); K 0 is the ratio of horizontal earth pressure to vertical earth pressure; c is the cohesion of the soil (kPa); R 0 is the outer radius of the segment (m);

[0109] Since the main strata in the interval are mainly sandy soil layers, the vertical and lateral forces on the tunnel are calculated by separating the soil and water pressures, and the buoyant unit weight of the soil is used for all the above calculations. The water pressure calculation formula is:

[0110] P w1 =γ w h w

[0111] The vertical soil pressure at the top of the shield tunnel is calculated by combining the Terzaghi loose soil pressure and the water pressure:

[0112] P’ v =P v +P w1

[0113] The soil and water pressures in the sandy soil are calculated by separating the soil and water pressures, and the lateral soil pressure is calculated in combination with relevant regulations:

[0114]

[0115] In the formula: P a is the value of the lateral soil pressure at the top of the tunnel; P b is the value of the lateral soil pressure at the bottom of the tunnel; h i , γ i ′ are the thickness and unit weight of the corresponding i-th soil layer; h a , h b are the distances from the top and bottom of the tunnel to the water surface; γ D is the unit weight of the soil within the tunnel range; D is the outer diameter of the tunnel.

[0116] S8. Conduct a load case design to simulate the vertical soil pressure on the top of the tunnel and the foundation reaction force on the bottom of the tunnel, simulate the lateral pressure on the tunnel, simulate the pressure in the transition section of the tunnel, simulate the loading process of the overload failure load, and introduce a tensile damage factor as the cracking risk coefficient for judging the concrete element. When its value reaches 1, it indicates that the segment has a cracking risk.

[0117] P 1 Simulate the vertical soil pressure on the top of the tunnel and the foundation reaction force on the bottom of the tunnel; P 2 Simulate the lateral pressure on the tunnel, and the value is the product of P 1 and the lateral pressure coefficient; P 3 Simulate the pressure in the transition section of the tunnel, and the value is the average of P 1 and P 2 ;

[0118] P 1 is determined by equivalently applying the vertical load on the top of the tunnel as a single-point applied P 1

[0119] According to the force balance relationship, it can be obtained that:

[0120]

[0121] P 2 Determination of:

[0122]

[0123] P 3 Determination of:

[0124]

[0125] Using the above Terzaghi's relaxed earth pressure formula for calculation, the tunnel segment P with a buried depth of 10m is obtained 1 Design = 206 kN, P 2 Design = 170 kN, P 3 Design = 133 kN. To study the problems of deformation, cracks, damage, and bolt forces of shield tunnel segments under overloading conditions.

[0126] The loading process of the overloading failure load is as follows:

[0127] (1) P 1 Is incrementally loaded from 0 kN to P 1 Design, P 1 The load increment for each level is 0.1 times of P 1 Design, P 2 The load increment for each level is 0.1 times of P 2 Design, P 3 =(P 1 +P 2 ) / 2;

[0128] (2) Keep P 2 Unchanged, load P 1 And P 3 Until the ultimate state, during which keep P 3 =(P 1 +P 2 ) / 2, P 1 The load increment for each level is 0.05 times of P 1 Design.

[0129] Please refer to Figure 2, First of all, the tunnel is assembled by the general ring with staggered joints. The general ring segment is divided into 6 pieces (including 1 crown block of 15°, 2 adjacent blocks of 64.5°, and 3 standard blocks of 72°). The segment ring width is 1.2 m, the inner diameter of the segment is 5.4 m, the outer diameter is 6 m, and the segment thickness is 300 mm. The concrete strength grade is C50, the impermeability grade is P10, and the steel bars adopt HPB300 grade and HRB400 grade steel. The single-ring segments are connected by 12 M27 bent bolts, and the adjacent pipe rings are connected by 10 M27 bent bolts of grade 5.8.

[0130] For the geological boreholes corresponding to the strata in the severely damaged section of the tunnel, from top to bottom, they are successively divided into plain fill, silty clay, silty sand, fine sand, medium sand, coarse sand, gravel sand, and moderately weathered argillaceous siltstone; the stratum distribution and physical and mechanical properties are shown in Table 1:

[0131] Table 1 Stratum Distribution

[0132]

[0133] Please refer to Figures 3 to 9 , select the DIANA finite element software to establish a full-scale three-ring staggered joint assembled shield segment model, calibrate the parameter values of the shield segment model, and the parameters include concrete parameters, steel parameters, set the interaction between the contacts of each component in the final model, the boundary conditions of the model, earth pressure calculation, and load case design;

[0134] The concrete strength grade of the shield tunnel segment is C50, and the total strain rotating crack model is adopted for the concrete constitutive in the numerical simulation. The exponential curve is adopted for the concrete tensile curve, and the parabolic curve is adopted for the compressive curve. The material parameters are shown in Table 2:

[0135] Table 2 C50 Concrete Parameters

[0136]

[0137] The segments are connected by solid bent bolts, and the bolt grade is 5.8. The steel bars adopt embedded units, and the steel bar grade is HRB400 grade steel. The steel materials (bolts, steel bars) all adopt the Von Mises elastoplastic model, and the material parameters are shown in Table 3:

[0138] Table 3 Steel Parameters

[0139]

[0140] The interaction between concrete segments and between bolts and concrete is simulated using interface elements that are only compressed and not tensioned. This interface element can realize the real physical behavior of the tensile side opening and the compressive side squeezing at the joint under the combined action of tension and compression. The tensile opening behavior is determined by the interface opening strength. To achieve free opening of the joint, the interface opening strength is taken as 0 N / m 2 The damage behavior after the mutual extrusion of the two is determined by the interface normal stiffness, and the interface normal stiffness is taken as 1.0×10 12 N / m 3 The interface friction angle is taken as 30° to simulate the mutual friction between segments. The contact element parameters are shown in Table 4:

[0141]

[0142] In the numerical simulation, the full-scale test loading method is borrowed, and the horizontal loading method is used. A Z-direction displacement constraint is applied to the bottom of the lower ring segment to simulate the effect of the lower support bearing. In the test, under the combined action of the overall reaction frame and the jack ear seat, it is ensured that the direction of the jacking force is always perpendicular to the outer surface of the segment, eliminating the tangential force caused by the tangential deformation of the segment. Since the loads around the segment are different, to avoid the rotation of the three-ring segments under the action of the surrounding loads in the numerical simulation, one-way constraints are applied to the inside of the segments respectively: X-direction constraints are applied to the upper and lower parts of the pipe ring to avoid lateral displacement during vertical convergence deformation; Y-direction constraints are applied to the left and right parts of the pipe ring to avoid vertical displacement during horizontal convergence deformation.

[0143] In the numerical model, the same as the test device, 24 circumferentially distributed elastic cushions are arranged on the outside of the segment to disperse the load. The flexible contact with the segment can more realistically simulate the actual stress state of the segment in the stratum and avoid local damage of the concrete on the outer surface of the segment caused by concentrated loads. The 24 load points are applied on the elastic cushions to simulate the stratum forces and water pressures suffered by the segment in the actual process respectively. The most unfavorable load conditions of the actual stratum on the segment are simulated by the free combination of forces, so as to obtain the internal force characteristics and deformation characteristics of the segment structure, and the full-process loading of the shield lining structure until ultimate failure can be realized. Among them, P1 simulates the vertical soil pressure on the top of the tunnel and the foundation reaction force on the bottom of the tunnel; P2 simulates the lateral pressure on the tunnel, and its value is the product of P1 and the lateral pressure coefficient; P3 simulates the pressure in the tunnel transition section, and its value is the average of P1 and P2.

[0144] P 1 is determined by equivalently converting the vertical load on the top of the tunnel into a single-point applied P 1 ,

[0145] According to the force balance relationship, it can be obtained that:

[0146]

[0147] P 2 Determination:

[0148]

[0149] P 3 Determination

[0150]

[0151] Using the above Terzaghi's relaxed earth pressure formula for calculation, the segment P of the tunnel with a buried depth of 10 m is obtained 1 Design = 206 kN, P 2 Design = 170 kN, P 3 Design = 133 kN. To study the problems of deformation, cracks, damage, and bolt forces of shield tunnel segments under overloading conditions. The loading process of the overloading failure load is as follows:

[0152] (1) P 1 Is loaded in increments from 0 kN to P 1 Design, P 1 The load increment for each level is 0.1 times of P 1 Design, P 2 The load increment for each level is 0.1 times of P 2 Design, P 3 =(P 1 +P 2 ) / 2.

[0153] (2) Keep P 2 Unchanged, load P 1 And P 3 Until the ultimate state. During the process, keep P 3 =(P 1 +P 2 ) / 2, P 1 The load increment for each level is 0.05 times of P 1 Design.

[0154] Please refer to Figure 10 And Figure 11 By analyzing the horizontal convergence value curve of the shield tunnel, it is found that with the application of the proportional load, there are three stages in the horizontal convergence change of the shield tunnel. After reaching each performance point, the horizontal convergence trend changes significantly. The specific change process is as follows: Figure 10 Phase A is the linear elastic phase: The tunnel convergence value is approximately linearly related to the load. The segment structure reaches the elastic limit performance point, corresponding to the load P1 = 206 kN, and the horizontal convergence deformation reaches 18 mm.

[0155]

[0156] ​Stage B is the plastic stage: In this stage, the horizontal deformation increases significantly. The segment structure reaches the elastic-plastic deformation limit performance point and undergoes plastic deformation at this time. The horizontal convergence deformation reaches the specified control value of 16 - 42 mm (3 - 5‰ of the segment diameter), corresponding to the load P1 = 236 kN.

[0157] Stage C is the yield failure stage: The convergence value of the shield segment increases rapidly, and the segment structure enters large deformation instability failure. The convergence deformation exceeds the specification limit, and there are potential safety hazards in the structure.

[0158] The overall deformation of the lining segment ring under the ultimate state is as Figure 11 shown. With the application of the load, the convergence value of the tunnel diameter increases and develops faster and faster. The deformation trend of the tunnel segment structure is that the waist deforms outward, and the top and bottom deform inward, showing an "oblique egg" shape.

[0159] Please refer to Figures 12 to 14 , when the load reaches the design load in the normal operation stage, that is, P 1 = 206 kN, there are a small number of micro-cracks in the tunnel segments. The cracks are mainly of two types: tensile cracks on the surface of the concrete segments and local crushing cracks at the bolt holes. The width of the cracks on the surface of the concrete segments is in the range of 0.05 - 0.1 mm, meeting the design requirement that the crack width is less than 0.2 mm. The cracks are distributed in small amounts on the inner arc surfaces of the crown and invert and the outer arc surface of the arch waist. The cracks only exist on the surface of the concrete segments, as Figure 12 shown.

[0160] When the load increases to P 1 = 236 kN and the tunnel structure enters the plastic stage, the crack width on the inner arc surfaces of the crown and invert reaches 0.2 - 0.28 mm, as Figure 13 shown. The distribution range of the cracks on the surface of the concrete segments expands, and micro-cracks also appear at the joint end faces.

[0161] The crack distribution pattern after the segment structure is completely damaged is as Figure 14 shown. The positions of the upper and lower ring segments are the same, so the crack distributions are similar. The cracks are mainly distributed in: the inner arc surface of the B1 segment at the crown, the inner arc surface of the B3 segment at the invert, and the outer arc surface of the B2 segment at the arch waist. The outer arc surface of the joint part of the B1 - L1 segment at the crown is compressed and cracked, and transverse expansion cracks appear at the joint end face. Similarly, transverse cracks also appear at the B3 - L2 joint at the invert. The crack distribution of the middle ring segments is: the inner arc surface of the B3 segment at the crown, the inner arc surface of the B1 segment at the invert, and the outer arc surface of the B2 segment at the arch waist. The outer arc surface of the joint part of the B3 - L2 segment at the crown is compressed, and transverse expansion cracks appear at the joint end face. Similarly, transverse cracks also appear at the B1 - L1 joint at the invert.

[0162] Please refer to Figures 15 to 20 , when the segments reach the plastic stage, the opening amount between the segment rings is asFigure 15 As shown. Since the same load is adopted in the tunnel radial direction in this section and the uneven radial load of the tunnel is not considered, the opening amount of the joints between rings is very small. The stagger amount between the pipe rings is as Figure 16 shown. The maximum stagger deformation between the rings is 2.69 mm, and its position mainly exists in the joint parts near the crown and the invert, and the stagger amount in other positions is small. It can be seen from this that attention should be paid to the local stagger deformation of the pipe ring joints near the crown and the invert in actual projects.

[0163] In each single ring, the opening deformation and stagger deformation between the segments are as Figure 17 and Figure 18 shown. The opening positions of the segments are mainly located at the joints on both sides of the crown, the invert and the closure blocks at the springline. The maximum opening amount reaches 1.42 mm. The stagger positions of the segments are mainly located at the joints of the crown and the invert, and the maximum stagger amount reaches 5.13 mm. Combining the stagger deformation and the opening deformation between the segments, it can be seen that the joints near the crown and the invert simultaneously have opening and stagger deformations, and the stagger deformation is significantly greater than the opening deformation. The joints on both sides of the closure blocks at the springline show pure opening deformation.

[0164] Combined with Figure 19 and Figure 20 it can be seen that both the opening curve and the stagger curve change in three stages: elastic stage, plastic stage, and yield stage, which is the same as the overall structural convergence deformation stage in the previous text. During the loading process, the stagger amount of most joints is greater than the opening amount at the corresponding position, indicating that the joints are more prone to stagger deformation. It can be seen from this that the control of the stagger deformation of the joint parts should be strengthened in actual projects. The deformation of the joints near the crown and the invert is mainly stagger deformation supplemented by opening deformation; the deformation of the joints at 53° and 127° shows single stagger deformation, and the joints at this position are shear damaged; the deformation of the joints on both sides of the closure blocks at the springline shows single opening deformation.

[0165] Taking the middle ring segments as an example, when the tunnel structure is in the plastic stage, the stress distribution of the bolts between the middle ring segments is as Figure 21 shown. In order to facilitate the observation of the morphological changes of the bolts, the bolt deformation has been magnified. Through Figure 21 it can be seen that in the plastic stage, there is local stress concentration in the bolts near the crown and the invert. The maximum stress of the bolts reaches the yield strength of 400 MPa, and the bolts have yield failure. The stress of the bolts at other joint positions is smaller and in a safe state. Through the deformation of the bolts, it can be seen that the shear deformation of the bolts near the invert and the crown is larger. Therefore, the yield failure of the bolts is shear failure. Combining the stagger amount of the joints above, it can be seen that the larger stagger deformation of the joints near the invert and the crown is caused by the shear failure of the bolts. Therefore, the shear resistance of the joints should be strengthened in actual projects.

[0166] Please refer to Figure 22 , due to non-linear numerical calculations, the calculation is difficult and the calculation of large concrete structures takes a long time. In order to more simply and quickly predict the distribution range of concrete cracks, a tensile damage factor F based on linear elastic theory is introduced tu , and its definition is given by the following formula:

[0167]

[0168] In the formula: f t is the tensile strength of concrete;

[0169] σ 1 is the maximum principal stress of the current element.

[0170] The tensile damage factor can be regarded as the cracking risk coefficient of the concrete element. When its value reaches 1, it indicates that the segment may crack. The cloud diagrams of the tensile damage factors of the middle ring segments in the elastic stage and the plastic stage are as Figure 22 shown. The blue area is the "safe area", indicating that the principal stress of the concrete in the current area is small. The red area is the "dangerous area" where cracks are about to occur, and the maximum principal stress of the concrete in this area reaches the tensile strength of the concrete. From Figure 21 the tensile damage factor in the elastic stage on the left, it can be predicted that cracks will first occur on the surface of the segments at the crown, invert and haunch (bricks in B2 section). From the cloud diagram of the tensile damage factor in the plastic stage on the right, it can be predicted that if the top load is continuously applied, cracking damage will also occur on the outer arc surfaces of the F closure block and the adjacent blocks on both sides. The damage depth of the inner arc surfaces of the crown, invert and the outer arc surface of the right haunch along the thickness direction of the segment, and the cracks will penetrate into the interior of the segment, and the local concrete at the bolt holes will be crushed.

[0171] The present invention can improve the safety of the tunnel structure. By accurately simulating the assembly effect and stress state of the shield tunnel segments through a finite element model, the overall safety and stability of the tunnel structure can be more accurately evaluated. The research method can reveal the failure mechanism of the segments under complex loads, so as to take preventive measures in advance to avoid the failure of the tunnel structure.

[0172] Any example of the present invention can be used as an independent technical solution or can be combined with other examples. All patents and publications mentioned in the specification of the present invention indicate that these are publicly known technologies in the art and can be used in the present invention. All patents and publications cited herein are equally listed in the references, just as each publication is specifically individually referenced. The present invention herein can be implemented in the absence of any one or more elements, one or more limitations, where such limitations are not specifically stated. The terms and expressions used herein are for the purpose of description and are not limiting, and there is no intention herein to indicate that the terms and interpretations described in this book exclude any equivalent features, but it can be understood that any suitable changes or modifications can be made within the scope of the present invention and the claims. It is understood that the examples described in the present invention are examples and features in some embodiments, and any person of ordinary skill in the art can make some changes and variations based on the essence described in the present invention, and these changes and variations are also considered to be within the scope of the present invention and the scope limited by the independent claims and the dependent claims.

Claims

1. A test method for the failure mechanism of shield tunnel segments taking into account the assembly effect, characterized in that: The specific steps include: S1. Construct a shield tunnel model for simulation test and determine the assembly method and basic parameters of the segments of the shield tunnel model for simulation test; S2. Construct geological conditions for simulation experiments; S3, 24 loading points are arranged to simulate the actual shield tunnel loads such as stratum resistance, earth pressure and upper pile unloading; S4. Select DIANA finite element software to establish a full-scale three-ring staggered assembly shield tunnel model, including: calibrating parameter values ​​of the shield tunnel model, the parameters include concrete parameters and steel parameters; S5. Set the interaction between the contacts of the components in the final shield tunnel model. The interaction between concrete segments and between bolts and concrete is simulated by using interface units that are only subjected to compression but not tension. S6. Set the boundary conditions of the shield tunnel model. Use the horizontal loading method to apply Z-direction displacement constraints to the bottom of the lower ring segment to ensure that the direction of the jack force is always perpendicular to the outer surface of the segment, and apply unidirectional constraints to the inside of the segment. S7. Determine the vertical and lateral earth pressures of the shield tunnel. For strata with arching effect, the vertical earth pressure is calculated using the Terzaghi relaxed earth pressure formula. For medium-consolidated clay and soft clay, the full overburden earth pressure calculation method is used. For sandy soil layers, the vertical force and lateral force on the tunnel are calculated by separate calculation of water and soil. The vertical earth pressure on the top of the tunnel is calculated by combining Terzaghi's loose earth pressure and water pressure. S8. Carry out load condition design, simulate the vertical soil pressure on the top of the tunnel and the foundation reaction force on the bottom of the tunnel, simulate the lateral pressure on the tunnel, simulate the pressure in the transition section of the tunnel, simulate the overload load loading process, and introduce the tensile damage factor as the crack risk coefficient for judging the concrete unit. When the value reaches 1, it indicates that the segment is in danger of cracking.

2. A shield tunnel segment failure mechanism test method considering assembly effect according to claim 1, characterized in that: The S1 specifically includes: the tunnel is assembled with universal rings and staggered seams, and the universal ring segments are divided into 6 blocks, including 1 capping block with an angle of 15°, 2 adjacent blocks with an angle of 64.5°, and 3 standard blocks with an angle of 72°; the segment ring width is 1.2m, the segment inner diameter is 5.4m, the outer diameter is 6m, and the segment thickness is 300mm; the concrete strength grade is C50, the water-resistance grade is P10, and the steel bars are HPB300 grade and HRB400 grade steel; the single-ring segment blocks are connected with 12 M27 bent bolts, and the adjacent rings are connected with 10 M27 bent bolts with a grade of 5.

8.

3. The shield tunnel segment failure mechanism test method considering the assembly effect according to claim 1 is characterized in that: The S2 specifically includes geological drill holes corresponding to the strata at the locations of the tunnel disease-severe intervals, which are divided into plain fill, silty clay, silt sand, fine sand, medium sand, coarse sand, gravel sand, and moderately weathered mud siltstone from top to bottom.

4. The method for testing the failure mechanism of shield tunnel segments taking into account the assembly effect according to claim 1 is characterized in that: The S4 specifically includes: the concrete parameter values ​​are as follows: the total strain rotation crack model is selected as the concrete material constitutive model, and the constitutive equation of the concrete material constitutive model is: D=T T D secant T In the formula They are defined as follows: Where σ1, σ2, and σ3 are the three principal stresses respectively; ε1, ε2, and ε3 are the principal strains corresponding to the three principal stress directions; T is the strain transformation matrix of the total strain crack model after rotation; The concrete strength grade of shield tunnel segments is C50. The concrete tensile curve is exponential, the compressive curve is parabolic, and the Young's modulus E=3.45×10 4 MPa, Poisson's ratio ν=0.2, compressive strength f c =43.5MPa, tensile strength f t =2.64MPa.

5. The method for testing the failure mechanism of shield tunnel segments taking into account the assembly effect according to claim 1 is characterized in that: The S4 also includes the following steel material parameters: The Von Mises elastoplastic model is selected as the steel material, including the constitutive model of bolts and steel bars. The segments are connected by solid bent bolts with a bolt grade of 5.

8. The steel bars use embedded units with a steel grade of HRB400. The steel bar diameter is 18 mm, the Young's modulus is E=2.0×105 MPa, the yield strength is 370 MPa, and the ultimate strength is 400 MPa. The bolt diameter is 27 mm, the Young's modulus is E=2.1×105 MPa, the yield strength is 4000 MPa, and the ultimate strength is 500 MPa.

6. The shield tunnel segment failure mechanism test method considering the assembly effect according to claim 1 is characterized in that: The S5 also includes: the interactions between concrete segments and between bolts and concrete are simulated by using interface units that are only compressed but not tensile, and the interface units can realize the real physical behavior of the tension side of the joint opening and the compression side squeezing each other under the tension-compression coupling; The tensile opening behavior is determined by the interface opening strength. In order to achieve free opening of the joint, the interface opening strength is taken as 0N / m2. The damage behavior after mutual extrusion between the two is determined by the interface normal stiffness. The interface normal stiffness is taken as 1.0×1012N / m3. The interface friction angle is 30° to simulate the mutual friction between the segments.

7. The method for testing the failure mechanism of shield tunnel segments taking into account the assembly effect according to claim 1 is characterized in that: The step S6 also includes: setting the boundary conditions of the final geometric model, including: In the numerical simulation, the full-scale test loading method is used to simulate the effect of the lower support bearing by applying Z-direction displacement constraint to the bottom of the lower ring segment using the horizontal loading method. In the test, the reaction frame and the jack lugs work together to ensure that the direction of the jack force is always perpendicular to the outer surface of the segment, eliminating the tangential force caused by the tangential deformation of the segment. Since the loads around the segments are of different sizes, in order to prevent the three-ring segments from rotating under the surrounding loads in the numerical simulation, unidirectional constraints are applied to the inside of the segments. Specifically, X-direction constraints are applied to the upper and lower parts of the ring to avoid lateral displacement during vertical convergence deformation; Y-direction constraints are applied to the left and right parts of the ring to avoid vertical displacement during horizontal convergence deformation.

8. The method for testing the failure mechanism of shield tunnel segments taking into account the assembly effect according to claim 1 is characterized in that: The step S7 also includes: for medium consolidated clay, specifically 4≤N<8, or soft clay 2≤N<4, N is the standard penetration hammer number, the full cover soil pressure calculation method is adopted, and the soil pressure is calculated by the following formula: Where: P0 is the overburden load; B1 is half of the tunnel excavation width (m); H is the overburden depth (m); is the internal friction angle of soil; P ν is Terzaghi vertical loose soil pressure kN / m 2 ; K0 is the ratio of horizontal soil pressure to vertical soil pressure; c is the cohesion of soil in kPa; R0 is the outer radius of the segment in m.

9. The method for testing the failure mechanism of shield tunnel segments taking into account the assembly effect according to claim 1 is characterized in that: The S7 also includes: the main stratum in the section is mainly sandy soil layer, so the vertical force and lateral force of the tunnel are calculated by separate calculation of water and soil, and the lateral earth pressure is calculated: Where: P a is the lateral earth pressure value at the top of the tunnel; P b Lateral earth pressure value at the bottom of the tunnel; h i , γ i ′ is the thickness and weight of the corresponding i-th soil layer; h a ,h b is the distance between the top and bottom of the tunnel and the top surface of the water; γ D is the weight of soil within the tunnel; D is the outer diameter of the tunnel.

10. The method for testing the failure mechanism of shield tunnel segments taking into account the assembly effect according to claim 1 is characterized in that: The S8 also includes: P1 simulates the vertical soil pressure on the top of the tunnel and the foundation reaction force on the bottom of the tunnel; P2 simulates the lateral pressure on the tunnel, and its value is the product of P1 and the lateral pressure coefficient; P3 simulates the pressure of the transition section of the tunnel, and its value is the average of P1 and P2; Determination of P1: The vertical load on the tunnel top is equivalent to P1 applied at a single point: The overload failure load loading process is: P1 is loaded from 0kN to P1 design in stages. The load increment of each stage of P1 is 0.1 times of P1 design. The load increment of each stage of P2 is 0.1 times of P2 design. P3 = (P1 + P2) / 2. Keep P2 unchanged, load P1 and P3 until the limit state, maintain P3 = (P1 + P2) / 2 during the process, and the load increment of each level of P1 is 0.05 times the design of P1; Tensile damage factor F based on linear elastic theory tu , which is defined by the following formula: Where: f t is the tensile strength of concrete; σ1 is the current maximum principal stress of the unit.

Images