Soft and hard stratum shield tunnel segment damage analysis method under overload condition

Abstract

The invention relates to the technical field of shield tunnel engineering, and discloses a soft and hard stratum shield tunnel segment damage analysis method under an overload condition, which comprises the following steps: firstly, establishing a concrete plasticity-damage constitutive CDP model, paying attention to concrete tensile damage characteristics, determining stress-strain relations and other related formulas and a damage factor calculation method; then, a three-dimensional entity stratum-structure discontinuous contact model is constructed, ABAQUS simulation is adopted based on actual engineering, parameters of tunnel segments and soil bodies and a contact relation are set, material parameters and calculation working conditions are determined, finally, calculation results are analyzed, and the influence rule of lateral pressure coefficients on segment damage distribution, stress change, ovality and bolt stress is researched. The method not only considers the influence of the lateral pressure coefficient on the damage of the duct piece, but also analyzes the influence of different capping block positions on the damage distribution and stress value data of the duct piece, deeply studies the damage mechanism of the duct piece under the overload effect, and provides theoretical basis and technical support for the design, construction and maintenance of shield tunnel engineering.

Description

Technical Field

[0001] The present invention relates to the technical field of shield tunnel engineering, and particularly to an analysis method for damage and failure of segment lining in shield tunnels in hard and soft strata under overloading conditions. Background Art

[0002] The construction of shield tunnels is a commonly used method for underground engineering construction, which has the advantages of being fast, safe, and having little impact on surface traffic. In the construction of shield tunnels, segments, as the main components of tunnel linings, undertake the important tasks of supporting the tunnel structure and preventing groundwater and soil from invading the tunnel interior. Segments are usually made of reinforced concrete and have sufficient strength and stiffness to withstand the pressure of the surrounding soil and water pressure in the tunnel. In a shield tunnel, segments are connected into rings by bolts and then assembled into the overall tunnel structure ring by ring. Therefore, the performance and quality of segments are crucial for the overall stability and safety of the tunnel.

[0003] With the development of urban construction, shield tunnels are widely used, but the phenomenon of overloading in the upper part frequently occurs due to the increase in the buried depth of tunnels. The segment structure is prone to various diseases under overloading, which affects the safety of the tunnel. Current research methods have their own advantages and disadvantages, and existing research has deficiencies in the interaction between segments and soil and the connection between segment rings. Therefore, it is necessary to propose a new analysis method. Summary of the Invention

[0004] To solve the above problems, the present invention first establishes a concrete plasticity-damage constitutive CDP model, focuses on the tensile damage characteristics of concrete, and determines relevant formulas such as stress-strain relationships and calculation methods for damage factors. Then, a three-dimensional solid stratum-structure discontinuous contact model is constructed, and ABAQUS is used for simulation based on actual engineering. The parameters and contact relationships of tunnel segments and soil are set, material parameters and calculation conditions are determined, and the model is verified by comparing with the test model. Finally, the calculation results are analyzed to study the influence laws of the lateral pressure coefficient on the damage distribution, stress change, ovality, and bolt stress of segments. The present invention provides an analysis method for damage and failure of segment lining in shield tunnels in hard and soft strata under overloading conditions, which is characterized by the following specific steps:

[0005] S1. Construct a concrete plasticity-damage constitutive CDP model, and calculate the stress-strain relationship, compressive damage factor, and tensile damage factor in the concrete plasticity-damage constitutive CDP model;

[0006] S2. Construct a three-dimensional solid stratum-structure discontinuous contact model, use ABAQUS for simulation, set the parameters and contact relationships of tunnel segments and soil, construct a refined model of three rings using the stratum-structure method, calculate the vertical load, and simulate the soil load received by the tunnel;

[0007] S3. Construct a tunnel lining structure model, and set the material parameters and friction relationship of tunnel concrete segments and bolts;

[0008] S4. Set the material parameters and calculation conditions, determine the concrete strength grade of tunnel segments, the material parameters of concrete and bolts, adopt the Mohr-Coulomb constitutive model to simulate, determine the physical and mechanical parameters of the soil layer, and verify the model;

[0009] S5. Calculate and analyze the damage distribution and stress value data of shield tunnel segments under the influence of different lateral pressure coefficients from the variation laws of segment damage, stress, ovality and bolt stress;

[0010] S6. Calculate and analyze the damage distribution and stress value data of shield tunnels under the influence of different positions of the closure block from the variation laws of segment damage, stress, ovality and bolt stress.

[0011] Further, in the above S1, it specifically includes: when the load borne by the concrete exceeds the allowable value, the stress-strain relationship is:

[0012]

[0013] In the formula, represents the stiffness in the initial stage without damage; D el represents the damaged stiffness; d represents the damage factor, and its value range is (0, 1); ":" represents the second-order contracted product; ε represents the total strain tensor; ε pl represents the plastic strain tensor.

[0014] Further, the compression damage factor in the above S1 is:

[0015]

[0016] In the formula, σc is the effective stress under compression; E c is the elastic modulus; b c is a parameter; the tensile damage factor has the same form, and the parameter b c = 0.7.

[0017] Further, in the above S2, specifically, ABAQUS is used for numerical simulation modeling. The outer diameter of the tunnel segment is set to 6.8 m, the inner diameter is 6.1 m, the thickness is 0.35 m, the width is 1.2 m, and the segments are connected by M27 bolts. The stratum-structure method is adopted to construct a three-ring refined model, and the contact between the soil and the structure is regarded as a Coulomb friction interface to obtain the vertical load to simulate the soil load borne by the tunnel.

[0018] Further, in the above S3, the construction of the tunnel lining structure model specifically is:

[0019] The concrete segment is simulated by C3D8R solid elements, the bolt rod and nut are processed by B31 beam elements and S4R shell elements respectively, the non-bonding slip between the bolt and the concrete is simulated by the built-in contact method, the normal direction of the contact surface between segments adopts "hard contact", the tangential direction adopts Cloumb friction contact, the contact between the soil and the segment adopts the surface-to-surface contact method, and the tangential behavior is simulated by Cloumb friction based on the penalty function method. The friction coefficient between the tunnel and the soil is taken as 0.8.

[0020] Furthermore, the specific material parameters and calculation conditions set in S4 are as follows: the concrete strength grade of the tunnel segment is C50, the material parameters of the concrete and the bolt are determined, sandy silt and silty clay are selected as the soil layers where the tunnel is located, and the Mohr-Coulomb constitutive model is used for simulation.

[0021] Furthermore, S5 specifically includes: in the soft soil layer and the hard soil layer, as the lateral pressure coefficient increases, the damage distribution of the segment structure gradually decreases, and the damage value gradually decreases. The damage distribution range of the segment in the hard soil layer is smaller, and the maximum damage value is also smaller. The ellipticity of the tunnel in the soft soil layer is greater than that of the tunnel in the hard soil layer, and both gradually decrease as the lateral pressure coefficient increases. In the soft soil layer, when the lateral pressure coefficient is small, the bolt stress may reach the yield state; in the hard soil layer, the overall bolt stress value is low.

[0022] Furthermore, S6 specifically includes: at different positions of the crown block, the damage distribution of the segment structure is roughly the same, but the damage distribution range and the position where the initial damage appears are different. When the crown block is located at the bottom, the damage distribution range of the segment structure is the widest; when the crown block is located at the 90° of the arch waist, the damage distribution range is the smallest; when the crown block is located at the arch bottom, the ellipticity of the segment structure is the largest and the overall stiffness is the smallest; when the crown block is at the 90° of the left arch waist, the overall stiffness of the segment is the largest. In the soft soil layer, when the crown block is at the 90° of the arch waist, the process of bolt stress yield can be delayed; in the hard soil layer, the bolt stress gradually decreases at different positions of the crown block and does not reach the yield state.

[0023] The beneficial effects of the present invention are as follows:

[0024] By constructing the concrete plasticity-damage constitutive CDP model, the stress-strain relationship and damage evolution process of concrete under overload conditions can be more accurately simulated. By using the three-dimensional solid stratum-structure discontinuous contact model, the interaction relationship between the tunnel segment and the soil, as well as the stress state of the segment under complex stratum conditions, can be more realistically reflected.

[0025] This method not only considers the influence of the lateral pressure coefficient on the damage of the segment, but also analyzes the influence of different positions of the closure segment on the damage distribution and stress value data of the segment, so as to be able to more comprehensively evaluate the damage situation of the segment. Through calculation and analysis, the key parameters such as the damage distribution range, damage value and ovality of the segment under different working conditions can be obtained, providing an important basis for the safe design and maintenance of tunnel engineering.

[0026] According to the analysis results, the materials, dimensions, connection methods, etc. of the tunnel segments can be optimized to improve their bearing capacity and anti-damage ability. At the same time, the construction parameters of the tunnel, such as the grouting volume, tunneling speed, etc., can also be adjusted to reduce the damage risk of the segments during the construction process. This method can provide scientific guidance for the construction and maintenance of the tunnel. For example, during the construction process, the attitude and propulsion parameters of the shield machine can be adjusted according to the analysis results to avoid excessive deformation or damage of the segments. During the maintenance stage, corresponding maintenance plans can be formulated according to the damage situation of the segments, such as replacing damaged segments, strengthening bolts, etc., to ensure the safe operation of the tunnel. Through the application of this method, the overall quality and safety of tunnel engineering can be significantly improved. By accurately evaluating the damage situation of the segments, potential safety hazards can be discovered and dealt with in a timely manner, thus avoiding accidents.

[0027] Through the method of the present invention, the damage failure mechanism of the segments under overloading can be deeply studied, providing a theoretical basis and technical support for the design, construction and maintenance of shield tunnel engineering. Description of the Drawings

[0028] Figure 1 It is a schematic flow chart of a method for analyzing the damage and failure of segments of a shield tunnel in soft and hard strata under overloading;

[0029] Figure 2 It is the uniaxial tensile and compressive stress-strain curves of concrete:

[0030] (a) is the uniaxial tensile stress-strain relationship diagram, and (b) is the uniaxial compressive stress-strain relationship;

[0031] Figure 3 It is the lining structure of the shield tunnel;

[0032] Figure 4 It is the loading method and soil grid;

[0033] Figure 5 It is the distribution diagram of shield tunnel segments;

[0034] Figure 6 It is the stage diagram of the damage characteristics of segments under different lateral pressure coefficients in soft soil layers;

[0035] Figure 7 It is the stage diagram of the damage characteristics of segments under different lateral pressure coefficients in hard soil layers;

[0036] Figure 8 Time history diagrams of segment damage under different lateral pressure coefficients:

[0037] (a) is the time history diagram of soft soil damage, and (b) is the time history diagram of hard soil damage;

[0038] Figure 9 Maximum principal stress diagrams of segments under different lateral pressure coefficients in soft and hard soil layers;

[0039] Figure 10 Variation laws of ovality and bolt stress with lateral pressure coefficient:

[0040] (a) is the variation law of soft soil - ovality, (b) is the variation law of soft soil - bolt stress, (c) is the variation law of hard soil - ovality, and (d) is the variation law of hard soil - bolt stress;

[0041] Figure 11 Diagram of the change in the position of the closure segment;

[0042] Figure 12 Stage diagrams of segment damage characteristics under different positions of the closure segment in soft soil layers;

[0043] Figure 13 Stage diagrams of segment damage characteristics under different positions of the closure segment in hard soil layers;

[0044] Figure 14 Time history diagrams of segment damage under different positions of the closure segment:

[0045] (a) is the time history diagram of soft soil damage, and (b) is the time history diagram of hard soil damage;

[0046] Figure 15 Maximum principal stress diagrams of segments under different positions of the closure segment in soft and hard soil layers;

[0047] Figure 16 Variation laws of ovality and bolt stress with the position of the closure segment:

[0048] (a) is the variation law of soft soil - ovality, (b) is the variation law of soft soil - bolt stress, (c) is the variation law of hard soil - ovality, and (d) is the variation law of hard soil - bolt stress. Specific implementation manners

[0049] The following combines the attached Figure 1-16 A detailed description of the preferred embodiments of the present invention is given below, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making the protection scope of the present invention more clearly defined.

[0050] The present invention provides a method for analyzing segment damage and failure in shield tunnels in soft and hard strata under overloading conditions, specifically including the following steps:

[0051] S1. Construct the concrete plasticity-damage constitutive CDP model, and calculate the stress-strain relationship, the compressive damage factor, and the tensile damage factor in the concrete plasticity-damage constitutive CDP model;

[0052] S2. Construct a three-dimensional solid stratum-structure discontinuous contact model, simulate using ABAQUS, set the parameters of tunnel segments, soil, and the contact relationship, construct a refined three-ring model using the stratum-structure method, calculate the vertical load, and simulate the soil load on the tunnel;

[0053] S3. Construct a tunnel lining structure model, and set the material parameters and friction relationship of tunnel concrete segments and bolts;

[0054] S4. Set the material parameters and calculation conditions, determine the concrete strength grade of tunnel segments, the material parameters of concrete and bolts, simulate using the Mohr-Coulomb constitutive model, determine the physical and mechanical parameters of the layers, and verify the model;

[0055] S5. Calculate and analyze the data of the damage distribution and stress values of shield tunnel segments under the influence of different lateral pressure coefficients from the variation laws of segment damage, stress, ovality, and bolt stress;

[0056] S6. Calculate and analyze the data of the damage distribution and stress values of shield tunnels under the influence of different positions of the closure block from the variation laws of segment damage, stress, ovality, and bolt stress.

[0057] The concrete plasticity-damage constitutive (CDP) model is established. Concrete is a quasi-brittle material, and the present invention focuses on its tensile damage characteristics. When the load on the concrete exceeds the allowable value, its non-linear response is controlled by damage evolution and plastic slip. The stress-strain relationship in the CDP constitutive model is as follows:

[0058]

[0059]

[0060] In the formula, represents the stiffness at the initial stage without damage; D el represents the damaged stiffness; d represents the damage factor, and its value range is (0, 1); ":" represents the second-order contracted product; ε represents the total strain tensor; ε pl represents the plastic strain tensor; the Cauchy stress σ and the effective stress The functional relationship is:

[0061]

[0062] The stress-strain expression under uniaxial tension and compression is:

[0063]

[0064] In the formula, E0 represents the elastic modulus when there is no initial damage; and are the effective stresses in tension and compression respectively; d c is the uniaxial compression damage factor; d t is the uniaxial tension damage factor. The compression damage factor is obtained as follows:

[0065]

[0066] The tension damage factor has the same form, and the parameter b c = 0.7. The form of the tension damage factor is the same as that of the compression damage factor, and the damage evolution law is driven by strain.

[0067] Refer to Figures 2 to 5 , based on the concrete plasticity-damage model, combined with the actual subway shield tunnel project, numerical simulation modeling is carried out using ABAQUS. The outer diameter of the tunnel segment is set to 6.8 m, the inner diameter is 6.1 m, the thickness is 0.35 m, the width is 1.2 m, the ring is composed of a specific number and type of blocks, the rings are connected by M27 bolts, a refined model of three rings is constructed using the stratum-structure method, the influence of joints is considered and the calculation efficiency is taken into account, the influence of soil self-weight is not included, it is assumed that the soil is continuous, homogeneous and isotropic, the contact between the soil and the structure is regarded as a Coulomb friction interface, the vertical load is obtained through theoretical calculation to simulate the soil load on the tunnel, the thickness of the overlying soil layer above the tunnel is set to 30 m to simulate the overloading effect with reference to the relevant test loading method, the corresponding uniformly distributed vertical load value is 1.55 MPa, the horizontal load is obtained by multiplying the vertical load by the coefficient of lateral earth pressure, the concrete tunnel segment is simulated using C3D8R solid elements, the bolt rod and nut are simplified using B31 beam elements and S4R shell elements respectively, the non-bonding slip between the bolt and the concrete is simulated using the built-in contact method, the normal direction of the contact surface between segments adopts "hard contact", the tangential direction adopts Cloumb friction contact, the friction coefficient is set to 0.6, the contact between the soil and the segment adopts the surface-to-surface contact method, the tangential behavior is simulated based on the Cloumb friction of the penalty function method, and the friction coefficient between the tunnel and the soil is taken as 0.8.

[0068] Setting of material parameters and calculation conditions: The concrete strength grade of the tunnel segment is C50, the material parameters of the concrete and bolts are determined, sandy silt (soft soil) and silty clay (hard soil) are selected as the soil layers where the tunnel is located, and the Mohr-Coulomb constitutive model is used for simulation. The elastic moduli of the soft soil and hard soil are taken as 25 MPa and 75 MPa respectively, and other relevant mechanical parameters are determined, as shown in Table 1 and Table 2, where ρ, μ, E, c, are the soil density, Poisson's ratio, elastic modulus, cohesion and internal friction angle respectively.

[0069] Table 1 Physical and mechanical parameters of segments and bolts

[0070]

[0071] Table 2 Physical and Mechanical Parameters of Soil Layers

[0072]

[0073] Analysis of Extracted Calculation Results

[0074] 1) Analyze the influence of the lateral pressure coefficient. Calculate and analyze the data under different coefficients from the variation laws of segment damage, stress, ovality, and bolt stress.

[0075] Figure 6 For the damage distribution and evolution process of shield tunnel segments under different lateral pressure coefficients in soft soil layers, considering the actual situation of tunnel stress, the damage nephogram of the refined model of the middle ring is shown in the figure. It can be analyzed that the damage of the segment structure is mainly concentrated in the inner sides of the crown and invert of the ring, the outer sides of the left and right haunches, and the bolt connection parts. With the increase of the lateral pressure coefficient, the damage distribution of the segment structure gradually decreases, and the damage value also gradually decreases, indicating that the increase of the lateral pressure coefficient has a certain effect on improving the overall stiffness of the segment structure. The reason is that the increase of the lateral pressure coefficient makes the surface loads distributed in different directions of the soil body tend to be equal and the deformations caused to the soil body are also equal, making the stress of the segment structure gradually tend to be stable and reducing the risk of extremely large deformations.

[0076] Figure 7 For the damage distribution and evolution process of shield tunnel segments under different lateral pressure coefficients in hard soil layers, the damage distribution law of the segment structure is the same as that in soft soil layers. The damage areas are mainly concentrated in the inner sides of the top and bottom of the ring and the outer areas of the left and right haunches. And with the increase of the lateral pressure coefficient, the damage range of the segment structure gradually decreases. When the lateral pressure coefficient takes 0.7 and 0.8, there is almost no damage distribution at the crown of the segment structure. But by comparing with Figure 8 It can be known that the damage distribution range of the segments of the shield tunnel in the hard soil layer is smaller, and under the same load, the maximum damage value of the segments is smaller, indicating that the overall stability of the shield tunnel in the hard soil layer can be better guaranteed.

[0077] Figure 9 For the time history diagrams of segment structure damage under different lateral pressure coefficients in soft and hard soil layers, from Figure 8It can be seen from (a) and (b) in Figure 8 that the coefficient of lateral pressure is different, and the order of segment damage is also different. The greater the coefficient of lateral pressure, the later the maximum damage of the segment structure appears. The greater the coefficient of lateral pressure, the smaller the maximum damage value of the segment. The coefficient of lateral pressure is negatively correlated with both the maximum and minimum damage values of the segment structure and the timing of damage occurrence. When K0 = 0.5 in the hard soil layer, the maximum damage value of the segment structure is 0.994. When K0 = 0.5 in the soft soil layer, the maximum damage value of the segment structure is 0.983. The damage reduction rate of the segment structure in different soil layers is 1.1%. When K0 = 0.8 in the soft soil layer, the maximum damage value of the segment structure is 0.92. The damage reduction rate of the segment structure under different coefficients of lateral pressure is 7.4%. It can be concluded that the sensitivity of the coefficient of lateral pressure to the damage bearing capacity of the segment is greater than that of the soil layer hardness.

[0078] Figure 9 Figure 9 shows the maximum principal stress nephograms of the segment structure under different coefficients of lateral pressure in hard and soft soil layers. Through analysis, it can be seen that the inner edges of the crown and invert and the outer edges of the left and right haunches bear relatively large principal tensile stresses. As the coefficient of lateral pressure increases, the maximum value of the principal stress and its distribution area gradually decrease. The distribution law of the maximum principal stress and its variation law with the coefficient of lateral pressure are consistent with the segment damage law, further verifying that the damage of the segment is caused by relatively large tensile stresses. The ovality ‰D is selected to characterize the overall deformation degree of the tunnel. Figure 10 Figure 10 shows the curves of the ovality of the segment and the bolt stress varying with the coefficient of lateral pressure in hard and soft soil layers. Through analysis, it can be seen that as the load increases, the lateral deformation of the tunnel gradually increases, and then the increasing rate of the tunnel deformation begins to decrease. Under the action of the same load, the ovality of the tunnel in the soft soil layer is greater than that in the hard soil layer, and both gradually decrease as the coefficient of lateral pressure increases. The main reason for this phenomenon is that the increase in load enhances the compactness of the soil layer near the outer wall of the tunnel, improves the lateral resistance of the tunnel, and slows down the further development of the lateral deformation of the tunnel. The greater the coefficient of lateral pressure, the stronger the lateral resistance, and the loads acting on the periphery of the tunnel structure tend to be similar, so the lateral deformation of the tunnel gradually decreases. Since the compactness of the hard soil layer is higher than that of the soft soil layer, the overall ovality of the tunnel in the hard soil layer is lower than that in the soft soil layer. The change in the coefficient of lateral pressure also has a certain impact on the bolt stress. In the soft soil layer, when K0 < 0.8, the bolt stress reaches 400 MPa and is in a yield state. When K0 = 0.8, the bolt stress does not reach the yield state, and as the coefficient of lateral pressure increases, the bolt stress shows a gradually decreasing trend. In the hard soil layer, the overall bolt stress value is lower than that in the soft soil layer. When K0 = 0.5, the bolt yields, and as the coefficient of lateral pressure increases to 0.7 and 0.8, the bolt stress is linearly correlated with the load value.

[0079] 2) Analyze the influence of the position of the closure block. Calculate and analyze the data under different coefficients from the variation laws of segment damage, stress, ovality, and bolt stress.

[0080] When the tunnel is assembled with staggered joints, different assembly angles will cause the position of the closure segment to change accordingly, which will in turn cause certain changes in the overall stress state of the segment. Therefore, it is also equally important to analyze the influence of the change in the position of the closure segment on the stress and damage distribution law of the segment structure under the action of external overload, such as Figure 11 As shown, four working conditions of the closure segment position at the crown, invert, 90° of the arch waist, and 22.5° of the arch shoulder are selected for analysis.

[0081] Figure 12 It is the stage diagram of the segment damage characteristics at different closure segment positions in the soft soil layer. From Figure 12 it can be seen that the damage distribution of the segment structure is roughly the same at different closure segment positions, mainly concentrated on the inner sides of the top and bottom of the segment ring, the outer sides of the left and right arch waists, and the bolt connection points. However, at different closure segment positions, the damage distribution range of the segment structure under the same load is different. When the closure segment is at the bottom, the damage distribution range of the segment structure is the widest, and when the closure segment is at 90° of the arch waist, the damage distribution range is the smallest; the initial damage occurrence positions of the segments at different closure segment positions are different. When the closure segment is at the top, the initial damage appears on the inner side of the invert; when the closure segment is at the bottom, the initial damage appears on the inner side of the crown; when the closure segment is at 90° of the left waist, the initial damage appears on the outer side of the 90° of the right waist of the segment; when the closure segment is at 22.5° of the arch shoulder, the initial damage appears on the outer side of the 90° of the left waist of the segment. It can be seen from this that the different positions of the closure segment have a great influence on the damage distribution of the segment structure.

[0082] Figure 13 It is the stage diagram of the segment damage characteristics at different closure segment positions in the hard soil layer. From Figure 13 it can be seen that when the tunnel is in the hard soil layer with a relatively large elastic modulus, the damage distribution positions and the initial damage occurrence positions of the segments at different closure segment positions are the same as those of the segment damage distribution under the change of the closure segment position in the soft soil layer. The difference is that the damage distribution range and damage value of the segments at different closure segment positions tend to decrease, indicating that when the tunnel segment is in the soft soil layer with a relatively small elastic modulus, the possibility of segment damage and failure is greater. With the increase of the operation time, effective reinforcement measures need to be taken to enhance the bearing capacity of the segment and ensure its operation safety. Figure 12 It is the damage time history diagram of the segments at different closure segment positions. From

[0083] Figure 14 it can be seen that the order of damage occurrence at different closure segment positions is the invert, crown, 22.5° of the arch shoulder, and 90° of the left waist positions, indicating that when the closure segment is at the invert, the bearing capacity of the segment structure is the lowest, and the damage appears earliest under the same loading mode. Moreover, when the closure segment is at the invert, the damage distribution of the segment is the largest, and the corresponding damage value is also the largest. Figure 14 it can be seen that the order of damage occurrence at different closure segment positions is the invert, crown, 22.5° of the arch shoulder, and 90° of the left waist positions, indicating that when the closure segment is at the invert, the bearing capacity of the segment structure is the lowest, and the damage appears earliest under the same loading mode. And when the closure segment is at the invert, the damage distribution of the segment is the largest, and the corresponding damage value is also the largest.

[0084] Figure 15It is the diagram of the maximum principal stress of the segment under different positions of the closure block in soft and hard soil layers. It can be seen from Figure 15 that the stress of the segment in the soft soil layer is greater than that in the hard soil layer, indicating that the surrounding rock pressure borne by the segment in the hard soil layer is smaller. The maximum stress of the segment appears in the inner side of the crown and invert of the segment structure and the outer side of the left and right springlines, which is the same as the damage distribution area, and the maximum stress of the segment in the hard soil layer is lower than that in the soft soil layer.

[0085] Figure 16 The variation laws of ovality and bolt stress with the position of the closure block. It can be seen from Figure 16 (a) that when the closure block is located at the invert, crown, 22.5° of the springing and 90° of the springline, the ovalities of the segment structure are 30‰D, 23.5‰D, 14.8‰D, and 12.1‰D respectively. The ovality of the segment gradually decreases. The ovality of the segment structure is the largest when the closure block is at the bottom, and the smallest when the closure block is at 90° of the springline, indicating that the overall stiffness of the segment structure is the smallest when the closure block is at the invert, and the overall stiffness of the segment is the largest when the closure block is at 90° of the left springline. It can be seen from Figure 16 (b) that when the closure block is at the crown, invert, 22.5° of the springing and 90° of the springline, the bolt stresses all reach the yield state, and the load magnitudes corresponding to the bolts reaching yield are different. The bolt stress reaches yield first when the closure block is at the invert, followed by when the closure is at the crown, and the bolt reaches yield last when the closure block is at 90° of the springline, indicating that when the closure block is at 90° of the springline in the soft soil layer, the yield process of the bolt stress can be delayed. It can be seen from Figure 16 (c) that in the hard soil layer with an elastic modulus of 75 MPa, when the closure block is located at the invert, crown, 22.5° of the springing and 90° of the springline, the ovalities of the segment structure are 13‰D, 8‰D, 7‰D, and 4‰D respectively, and the ovality of the segment gradually decreases; Figure 16 (b) shows that the bolt stress at the positions of the invert, crown, 22.5° of the springing and 90° of the left springline of the closure block decreases in turn and the bolts do not reach yield, which is different from the bolt stress law in the soft soil layer. The reason is that the hard soil layer with a larger elastic modulus has a stronger resistance to the load. The same load action may have reached the ultimate load for the soft soil layer, but it has not reached the ultimate load that the soil can bear for the hard soil layer. Therefore, the bolt stress gradually decreases at different positions of the closure block in the hard soil layer.

[0086] Influence of the lateral pressure coefficient:

[0087] Segment damage: In the soft soil layer and the hard soil layer, with the increase of the lateral pressure coefficient, the damage distribution of the segment structure gradually decreases and the damage value gradually decreases.

[0088] The damage distribution range of the segment in the hard soil layer is smaller, and the maximum damage value is also smaller.

[0089] Maximum principal stress: The inner edges of the crown and invert and the outer edges of the left and right springlines bear relatively large principal tensile stresses.

[0090] As the lateral pressure coefficient increases, the maximum value of the principal stress and its distribution area gradually decrease.

[0091] Ellipticity and bolt stress: As the load increases, the lateral deformation of the tunnel gradually increases and then the deformation rate decreases.

[0092] The ellipticity of the tunnel in soft soil layer is greater than that in hard soil layer, and both gradually decrease with the increase of the lateral pressure coefficient.

[0093] In soft soil layer, when the lateral pressure coefficient is small, the bolt stress may reach the yield state; in hard soil layer, the overall bolt stress value is low.

[0094] Influence of the closure segment position:

[0095] Segment damage: At different closure segment positions, the distribution of segment structure damage is roughly the same, but the distribution range of damage and the position where initial damage appears are different.

[0096] When the closure segment is at the bottom, the distribution range of segment structure damage is the widest; when the closure segment is at 90° of the springline, the distribution range of damage is the smallest.

[0097] Maximum principal stress: The stress of the segment in soft soil layer is greater than that in hard soil layer, and the maximum stress appears in the areas of the inner sides of the crown and invert and the outer sides of the left and right springlines.

[0098] Ellipticity and bolt stress: When the closure segment is at the invert, the ellipticity of the segment structure is the largest and the overall stiffness is the smallest; when the closure segment is at 90° of the left springline, the overall stiffness of the segment is the largest.

[0099] In soft soil layer, when the closure segment is at 90° of the springline, it can delay the process of bolt stress yield; in hard soil layer, the bolt stress gradually decreases at different closure segment positions and does not reach the yield.

[0100] The increase of the lateral pressure coefficient has a certain effect on improving the overall stiffness of the segment structure, and can reduce segment damage and ellipticity.

[0101] The overall stability of the tunnel in hard soil layer can be better guaranteed, and the segment damage and stress value are small.

[0102] The closure segment position has a great influence on the damage distribution, stress and ellipticity of the segment structure, and optimization design should be carried out according to specific conditions.

[0103] During the design and construction process, the influence of factors such as soil layer conditions, lateral pressure coefficient and closure segment position on the tunnel structure should be fully considered to ensure the safety and stability of the tunnel.

[0104] By constructing the concrete plasticity-damage constitutive CDP model, the stress-strain relationship and damage evolution process of concrete under overload conditions can be more accurately simulated. Using the three-dimensional solid stratum-structure discontinuous contact model can more realistically reflect the interaction relationship between tunnel segments and soil mass, as well as the stress state of segments under complex stratum conditions.

[0105] This method not only considers the influence of the lateral pressure coefficient on the damage of segments, but also analyzes the influence of different positions of the closure block on the damage distribution and stress value data of segments, so as to be able to more comprehensively evaluate the damage situation of segments. Through calculation and analysis, the key parameters such as the damage distribution range, damage value and ovality of segments under different working conditions can be obtained, providing an important basis for the safety design and maintenance of tunnel engineering.

[0106] Any example of the present invention can be used as an independent technical solution or combined with other examples. All patents and publications mentioned in the specification of the present invention indicate that these are public technologies in the field and can be used by the present invention. All patents and publications cited herein are equally listed in the references, just as each publication is specifically referenced individually. The present invention can be implemented in the absence of any one or more elements, one or more limitations, and such limitations are not specifically described here. The terms and expressions used herein are for descriptive purposes and are not limited by them, and there is no intention to indicate that the terms and explanations described in this book exclude any equivalent features, but it can be known that any appropriate changes or modifications can be made within the scope of the present invention and the claims. It can be understood that the embodiments 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 according to 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 dependent claims.

Claims

1. A method for analyzing the damage and failure of shield tunnel segments in soft and hard strata under overload conditions, characterized in that: The specific steps include: S1. Construct a concrete plasticity-damage constitutive CDP model, and calculate the stress-strain relationship and compressive damage factor and tensile damage factor in the concrete plasticity-damage constitutive CDP model; S2. Construct a three-dimensional solid stratum-structure discontinuous contact model, use ABAQUS simulation, set the tunnel segment, soil parameters and contact relationship, use the stratum-structure method to construct a three-ring refined model, calculate the vertical load, and simulate the soil load on the tunnel; S3, construct the tunnel lining structure model, set the tunnel concrete segments, bolt material parameters and friction relationship; S4. Set material parameters and calculation conditions, determine the concrete strength grade of the tunnel segment, concrete and bolt material parameters, use Mohr-Coulomb constitutive simulation to determine the physical and mechanical parameters of the layer, and verify the model; S5. Calculate and analyze the shield tunnel segment damage distribution and stress value data under the influence of different lateral pressure coefficients based on segment damage, stress, ovality and bolt stress variation rules; S6. Calculate and analyze the shield tunnel damage distribution and stress value data under the influence of different capping block positions based on the variation rules of segment damage, stress, ovality and bolt stress.

2. The method for analyzing the damage and failure of shield tunnel segments in soft and hard strata under overload conditions according to claim 1 is characterized in that: S1 specifically includes: when the concrete is subjected to a load exceeding the allowable value, the stress-strain relationship is: In the formula, Indicates the stiffness at the initial stage without damage; D el represents lossy stiffness; d represents damage factor, which ranges from (0,1); ":" represents the second-order contraction product; ε represents the total strain tensor; ε pl represents the plastic strain tensor.

3. The method for analyzing damage and failure of shield tunnel segments in soft and hard strata under overload conditions according to claim 1 is characterized in that: The compressive damage factor in S1 is: Where, σc is the effective stress during compression; E c is the elastic modulus; b c is a parameter; the tensile damage factor has the same form as that of the parameter b c =0.

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4. The method for analyzing damage and failure of shield tunnel segments in soft and hard strata under overload conditions according to claim 1 is characterized in that: Specifically, S2 uses ABAQUS for numerical simulation modeling, setting the outer diameter of the tunnel segment to 6.8m, the inner diameter to 6.1m, the thickness to 0.35m, and the width to 1.2m. The rings are connected with M27 bolts, and a three-ring refined model is constructed using the stratum-structure method. The contact between the soil and the structure is regarded as a Coulomb friction interface, and the vertical load is obtained to simulate the soil load on the tunnel.

5. The method for analyzing the damage and failure of shield tunnel segments in soft and hard strata under overload conditions according to claim 1 is characterized in that: The tunnel lining structure model constructed in S3 is specifically as follows: The concrete segments are simulated using C3D8R solid elements, the bolt rods and nuts are processed using B31 beam elements and S4R shell elements respectively, and the built-in contact method is used to simulate the unbonded sliding between the bolts and concrete. The normal contact surface between the segments adopts "hard contact", the tangential contact adopts Cloumb friction contact, the contact between the soil and the segments adopts surface-to-surface contact, and the tangential behavior is simulated based on the Cloumb friction simulation of the penalty function method. The friction coefficient between the tunnel and the soil is 0.

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6. The method for analyzing damage and failure of shield tunnel segments in soft and hard strata under overload conditions according to claim 1 is characterized in that: The material parameters and calculation conditions set in S4 are specifically as follows: the concrete strength grade of the tunnel segment is C50, the material parameters of concrete and bolts are determined, sandy silt and silty clay are selected as the soil layer where the tunnel is located, and the Mohr-Coulomb constitutive simulation is used.

7. The method for analyzing the damage and failure of shield tunnel segments in soft and hard strata under overload conditions according to claim 1 is characterized in that: The S5 specifically includes: in the soft soil layer and the hard soil layer, as the lateral pressure coefficient increases, the damage distribution of the segment structure gradually decreases, and the damage value gradually decreases; the damage distribution range of the segment in the hard soil layer is smaller, and the maximum damage value is also smaller; the ellipticity of the soft soil layer tunnel is greater than that of the hard soil layer tunnel, and both gradually decrease with the increase of the lateral pressure coefficient; in the soft soil layer, when the lateral pressure coefficient is small, the bolt stress may reach the yield state; in the hard soil layer, the overall bolt stress value is low.

8. The method for analyzing the damage and failure of shield tunnel segments in soft and hard strata under overload conditions according to claim 1 is characterized in that: The S6 specifically includes: at different capping block positions, the damage distribution of the segment structure is roughly the same, but the damage distribution range and the position of initial damage are different; when the capping block is at the bottom, the damage distribution range of the segment structure is the widest; when the capping block is at 90° at the arch waist, the damage distribution range is the smallest; when the capping block is at the arch bottom, the ellipticity of the segment structure is the largest and the overall stiffness is the smallest; when the capping block is at 90° at the left arch waist, the overall stiffness of the segment is the largest; in the soft soil layer, the capping block position at 90° at the arch waist can delay the bolt stress yield process; in the hard soil layer, the bolt stress at different capping block positions gradually decreases and does not reach yield.

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