Soft soil stratum shield tunnel tough structure design method

Abstract

The invention discloses a soft soil stratum shield tunnel tough structure design method which specifically comprises the following steps: A, establishing a refined numerical model containing a whole-ring shield tunnel, and calculating a reasonable thickness-diameter ratio of the shield tunnel adapted to soft soil stratum environment change characteristics; b, a three-dimensional refined nonlinear finite element model of the shield tunnel joint is established, and shield tunnel joint optimization construction under the full-life-cycle service condition is carried out; c, providing a joint rigidity internal force-deformation cross iteration method, calculating shield bearing deformation, and analyzing shield tunnel deformation resistance under different design conditions; and D, carrying out a field experiment, proposing a double-control principle of construction performance and waterproof performance of the rubber sealing gasket, and carrying out optimal design of the tunnel waterproof sealing gasket. Compared with a conventional staggered joint assembly shield tunnel, the tough main body structure of the staggered joint assembly shield tunnel has the advantages that the allowable limit convergence deformation and the unloading amount of the tunnel under the lateral unloading damage working condition are improved by 37% and 141% respectively.

Description

Technical Field

[0001] This invention belongs to the field of tunnel engineering technology, specifically relating to a method for designing a tough structure for shield tunnels in soft soil strata. Background Art

[0002] Subway construction has greatly promoted urban development. However, if subway shield tunnels experience significant deformation during construction and operation, or if deformation places the tunnel in a poor stress state, it will negatively impact their long-term service performance and restrict the freedom of surrounding development. This is a problem concerning not only the safety and long-term serviceability of the subway itself, but also the harmonious coexistence of subway construction and urban development. Currently, the design of subway shield tunnels does not adequately consider these issues, has not received sufficient attention, and lacks effective control. This is also the reason why some subway lines have experienced significant deformation in recent years, affecting operation and requiring substantial investment in corrective measures, as well as impacting the development of surrounding land. This necessitates a systematic consideration of subway and urban development, and a more comprehensive study of the subway's performance throughout its entire life cycle.

[0003] In the eastern coastal areas, subway shield tunnels are mostly located in deep soft soil, facing numerous challenges: Shield tunnels are prefabricated, modular structures, and in soft soil layers, the soil's resistance is insufficient. Experience shows that shield tunnels in soft soil layers suffer from significant defects, sometimes even affecting normal subway operations. In deep soft soil layers, urban development causes greater and deeper disturbances to the soil, posing a significant threat to subway shield tunnels. Therefore, shield tunnels in soft soil layers must have large safety protection zones, which to some extent restricts the freedom of urban development. The operation and maintenance costs of shield tunnels in soft soil areas are enormous throughout their entire life cycle. Experience in the UK and Japan shows that maintenance costs are 2 to 6 times the construction costs. In some soft soil areas in China, excessive deformation of shield tunnels has led to a significant increase in operation and maintenance costs. From the perspective of comprehensive life-cycle benefits, rationally strengthening the shield structure and balancing the construction and maintenance costs of subway shield tunnels are important challenges and opportunities for new rail transit cities. Summary of the Invention

[0004] To address the technical problem that existing tunnel structures cannot meet the requirements for high-quality tunnel construction, this invention provides a method for designing a resilient structure for shield tunnels in soft soil strata.

[0005] The technical solution adopted in the present invention is:

[0006] A method for designing the resilient structure of a shield tunnel in soft soil strata, characterized by the following steps:

[0007] A. Establish a refined numerical model including a full-ring shield tunnel and calculate the reasonable thickness-to-diameter ratio of the shield tunnel to adapt to the environmental changes of soft soil strata;

[0008] B. Establish a three-dimensional refined nonlinear finite element model of the shield tunnel joint and carry out optimized construction of the shield tunnel joint under the conditions of the entire service life;

[0009] C. A cross-iteration method of joint stiffness internal force-deformation is proposed to calculate the shield bearing deformation and analyze the shield tunnel's deformation resistance under different design conditions;

[0010] D. Conduct on-site experiments, propose the principle of dual control of the construction performance and waterproof performance of rubber sealing gaskets, and optimize the design of tunnel waterproof sealing gaskets.

[0011] Furthermore, step A specifically includes the following steps:

[0012] A1. Establish a refined numerical model of the whole-ring shield tunnel and study the cross-sectional deformation characteristics of the shield tunnel under different thickness-to-diameter ratio designs.

[0013] A2. Analyze the impact of foundation pit excavation on the deformation of shield tunnel structure, and obtain the deformation resistance of shield tunnel segments with different thickness-to-diameter ratios;

[0014] A3. Calculate the appropriate thickness-to-diameter ratio of shield tunnels to adapt to the environmental changes of soft soil strata, and enhance the deformation resistance of subway shield tunnel structures.

[0015] Furthermore, step B specifically includes the following steps:

[0016] B1. Establish a three-dimensional refined nonlinear finite element model of a shield tunnel joint, including concrete segments, reinforcing bars, bolts, handholes, tenons and mortises, and trench details on both sides of the joint; B2. Study the influence of the tenon and mortise construction on the overall structural deformation and the opening and misalignment of the joint.

[0017] B3. Based on the failure characteristics and critical conditions of the joint throughout its entire life cycle, optimize the joint parameters of the tongue and groove joints in shield tunnels in soft soil areas, including length, depth, and inclination angle, to improve the damage resistance of the segment structure.

[0018] Furthermore, step C specifically includes the following steps:

[0019] C1. Establish a library of bending and shear stiffness for circumferential and longitudinal joints of shield tunnels, and propose a cross-iteration method for joint stiffness internal force-deformation.

[0020] C2. Construct a shell-spring model of staggered shield tunnel structure based on joint stiffness library to improve the calculation efficiency of shield tunnel bearing deformation, and analyze the full-stage deformation resistance of shield tunnel under different design conditions.

[0021] Furthermore, the cross-iteration method for joint stiffness internal force-deformation in step C1 specifically includes the following steps:

[0022] C11. Based on the given tunnel convergence deformation D v Assume the neutral axis function of the joint is:

[0023]

[0024] In the formula, y n The corresponding convergent deformation D at the joint v The position of the neutral axis at time A, y0 and t are unknown coefficients, which can be solved by iterative methods;

[0025] C12. According to the continuous rotation method, it is assumed that only the overall displacement of the tunnel and the rotation of the tunnel segments will occur, thus based on the convergence deformation D v Determine the joint rotation angles θ1, θ2, and θ3, as well as the joint opening amounts x1 and x2;

[0026] C13. Based on the joint deformation, a mechanical analysis model is established, assuming that the joint rotation deformation is small relative to the segment and that the contact and separation surfaces of the segment after loading are both planes. The stress state of the joint under this convergent deformation condition is obtained, and a new neutral axis function is derived.

[0027] C14. Determine whether the derived joint neutral axis function is consistent with the assumed joint neutral axis function:

[0028] If there is a discrepancy, the parameters need to be adjusted and the iteration needs to be repeated.

[0029] If they match, the mechanical parameters of the joint, namely axial force N, bending moment M, and rotation angle θ, can be obtained by combining the stress state of the joint. The bending stiffness k of the joint can then be obtained by tangent slope analysis of the bending moment-rotation angle curve. θ That is, when the tunnel exhibits convergent deformation, the convergent deformation D v The bending stiffness value of the lower shield joint is k θ When the convergence deformation D v When k changes θ It will also change accordingly.

[0030] Furthermore, step D specifically includes the following steps:

[0031] D1. The principle of dual control of construction performance and waterproof performance of rubber sealing gaskets is proposed. The waterproof performance, material hardness and closing compression performance of the sealing gasket are comprehensively considered. Field tests are carried out to optimize the design of tunnel waterproof sealing gaskets and ensure the waterproof effect of shield tunnel joints.

[0032] D2. Based on the above analysis steps, the final design is a resilient main structure for staggered-joint shield tunnels that adapts to the environmental changes in soft soil areas.

[0033] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0034] 1. This invention optimizes the structural design of subway shield tunnels, including inner diameter, thickness, and joints, through numerical simulation and theoretical analysis. Compared with conventional staggered-joint shield tunnels, the designed staggered-joint shield tunnel has 37% and 141% higher allowable limit convergence deformation and unloading amount under lateral unloading failure conditions, respectively, which greatly enhances the deformation resistance of subway shield tunnel structures in the context of surrounding development.

[0035] 2. Conventional finite element models involve a large number of contact problems, resulting in high computational costs. Especially in the high-load and severely nonlinear bearing stages that are close to structural failure, the results are even difficult to converge. The cross-iteration method of joint stiffness internal force-deformation proposed in this invention greatly improves the computational efficiency of shield tunnel bearing deformation. Attached Figure Description

[0036] Figure 1 This is a flowchart illustrating the overall implementation process of this invention;

[0037] Figure 2a This is a schematic diagram of the refined numerical model of the shield tunnel in this invention. Figure 1 ;

[0038] Figure 2b This is a schematic diagram of the refined numerical model of the shield tunnel in this invention;

[0039] Figure 3a These are the curves showing the variation of the lateral earth pressure coefficient and system stiffness under different segment inner diameters and thicknesses in this invention.

[0040] Figure 3b These are the curves showing the changes in vertical load and lateral convergent deformation under different segment thicknesses in this invention.

[0041] Figure 4a This is a schematic diagram of the stress distribution in the longitudinal joint of the tunnel in this invention;

[0042] Figure 4b This is a schematic diagram of the stress distribution of the circumferential joint in this invention;

[0043] Figure 5a This is a curve showing the variation of the offset of the segment structure and the shear force under the condition of no tongue and groove in this invention;

[0044] Figure 5b This is the second curve showing the variation of the offset and shear force of the segment structure under different tenon and mortise lengths in this invention;

[0045] Figure 5c This is the third curve showing the variation of the offset and shear force of the segment structure under different bevel angles of the tenon and mortise in this invention;

[0046] Figure 6This is the main process of the cross-iteration method of joint stiffness internal force-deformation in this invention;

[0047] Figure 7 This is a schematic diagram of the shield tunnel shell-spring model in this invention;

[0048] Figure 8a This is the first sealing gasket design scheme in this invention;

[0049] Figure 8b This is the second sealing gasket design scheme in this invention;

[0050] Figure 8c This is the third sealing gasket design in this invention;

[0051] Figure 9 This is a diagram showing the design results of the shield tunnel toughness structure in this invention. Detailed Implementation

[0052] The specific embodiments of the present invention are further described below with reference to the accompanying drawings.

[0053] refer to Figure 1 The present invention provides a method for designing a resilient structure for a shield tunnel in soft soil strata, comprising the following steps:

[0054] A. Establish a refined numerical model including a full-ring shield tunnel and calculate the reasonable thickness-to-diameter ratio of the shield tunnel to adapt to the environmental changes of soft soil strata;

[0055] B. Establish a three-dimensional refined nonlinear finite element model of the shield tunnel joint and carry out optimized construction of the shield tunnel joint under the conditions of the entire service life;

[0056] C. A cross-iteration method of joint stiffness internal force-deformation is proposed to calculate the shield bearing deformation and analyze the shield tunnel's deformation resistance under different design conditions;

[0057] D. Conduct on-site experiments, propose the principle of dual control of the construction performance and waterproof performance of rubber sealing gaskets, and optimize the design of tunnel waterproof sealing gaskets.

[0058] Specifically, step A includes the following steps:

[0059] As shown in Figure 2, a refined numerical model of the entire ring shield tunnel is established to study the cross-sectional deformation characteristics of the shield tunnel under different thickness-to-diameter ratio designs; the influence of foundation pit excavation on the structural deformation of the shield tunnel is analyzed to obtain the deformation resistance of shield tunnel segments with different thickness-to-diameter ratios; and a reasonable thickness-to-diameter ratio for shield tunnels that adapt to the environmental changes of soft soil strata is calculated to enhance the deformation resistance of subway shield tunnel structures.

[0060] like Figure 3aAs shown, the mechanical properties of the tunnel segment structure are demonstrated under different inner diameters and thicknesses. Compared to conventional tunnel segments with an inner diameter of 5.5m and a thickness of 350mm, the stiffness of the tunnel-soil system decreases significantly when the thickness of the toughening tunnel segment structure remains constant and the inner diameter is increased to 5.9m. To improve the system's toughness, the structural design needs to further optimize the thickness and diameter. When the segment thickness increases from 350mm to 400mm, the tunnel system stiffness is restored and even exceeds the original design level to some extent. When the segment thickness increases to 450mm, the tunnel-soil system stiffness is still significantly improved. However, increasing the segment thickness greatly increases the internal forces in the tunnel, increasing the risk of segment cracking. On the other hand, the weakest point in the tunnel structure is always at the joints, and simply reinforcing the segments themselves may further amplify the weakness of the joints.

[0061] Therefore, the ultimate bearing capacity of tunnel deformation under different segment thicknesses was tested, such as... Figure 3b As shown, when the tunnel reaches critical instability, the critical convergence deformation of the 350mm segment is 158.1mm; for the 400mm segment, the critical convergence deformation increases to 182.1mm, representing a 15.2% improvement in the tunnel's deformation resistance. However, the improvement is only 4.3% compared to the 400mm segment. This indicates that the 400mm segment can significantly improve the tunnel's deformation resistance; however, since the weakest point in the tunnel is at the joint, further increasing the segment thickness beyond 400mm is not very meaningful. Therefore, for a ductile segment structure with a diameter of 5.9m, a reasonable thickness is 400mm.

[0062] Specifically, step B includes the following steps:

[0063] A refined three-dimensional nonlinear finite element model of a shield tunnel joint was established, incorporating detailed structural elements such as concrete segments on both sides of the joint, reinforcing bars, bolts, manholes, tenons and grooves, etc. Figure 4a and Figure 4b The figures show the stress distribution diagrams of the longitudinal and circumferential joints of the tunnel, respectively. The study investigates the influence of the tenon and mortise joint structure on the overall deformation of the structure and the opening and misalignment of the joints. Based on the failure characteristics and critical conditions of the joint throughout its entire life cycle, the study optimizes the joint parameters such as the length and inclination angle of the tenon and mortise joints in shield tunnels in soft soil areas to improve the damage resistance of the segment structure.

[0064] Figure 5a , Figure 5b and Figure 5cThe curves showing the variation of segment offset and shear force under different tenon / concave joint configurations are presented. The tenon / concave joint lengths are 135mm, 165mm, and 195mm, and the bevel angles are 33°, 53°, and 73°, respectively. The conclusions are as follows: Compared to joints without tenons / concave joints, joints with tenons / concave joints can effectively increase the shear strength of the joint by approximately 5 to 10 times. The tenon / concave joint length has a relatively small impact on the shear capacity of the joint; when the bevel angle increases, the force on the tenon / concave joint is more even, which can prevent the tenon / concave joint from failing. Changing the tenon / concave joint dimensions did not significantly affect the segment structure under normal loads. However, under overload conditions, increasing or decreasing the tenon / concave joint length and angle based on the original design will increase the convergence deformation, misalignment, and opening of the structure. The changes caused by decreasing the length and angle are greater than those caused by increasing them. Therefore, based on the existing design, the tenon / concave joint length can be kept constant, while the bevel angle of the tenon / concave joint can be appropriately reduced.

[0065] Specifically, step C includes the following steps:

[0066] A library of bending stiffness values ​​for circumferential and longitudinal joints in shield tunnels is established, and a cross-iteration method for joint stiffness internal force-deformation is proposed, such as... Figure 6 As shown, the main process of this method is as follows: based on the given tunnel convergence deformation D... v Assume the joint neutral axis function:

[0067]

[0068] In the formula, y n The corresponding convergent deformation D at the joint v The position of the neutral axis at time A, y0 and t are unknown coefficients, which can be solved by iterative methods;

[0069] Subsequently, based on the continuous rotation method, it is assumed that only the overall displacement of the tunnel and the rotation of the segments will occur, and thus the convergence deformation D is used as a basis. v Determine the joint rotation angles θ1, θ2, and θ3, as well as the joint opening amounts x1 and x2;

[0070] A mechanical analysis model is established based on the joint deformation. It is assumed that the joint rotation deformation is small relative to the segment, and that the contact and separation surfaces of the segment after loading are both planes. The stress state of the joint under this convergent deformation condition is obtained, and a new neutral axis function is derived.

[0071] If the derived joint neutral axis function is inconsistent with the assumed function, parameter adjustment and re-iteration are required. If they are consistent, the joint mechanical parameters axial force N, bending moment M, and rotation angle θ can be obtained by combining the stress state of the joint. The bending stiffness k of the joint can be obtained by performing tangent slope analysis on the bending moment-rotation angle curve. θ That is, when the tunnel exhibits convergent deformation, the deformation amount D is... vThe bending stiffness value of the lower shield joint is k θ When the deformation value D v When k changes θ It will also change accordingly.

[0072] like Figure 7 As shown, this step constructs a shell-spring model of a staggered shield tunnel structure based on a joint stiffness library to improve the calculation efficiency of shield tunnel bearing deformation and analyze the full-stage deformation resistance of shield tunnels under different design conditions.

[0073] Specifically, step D includes the following steps:

[0074] The principle of dual control of construction performance and waterproof performance of rubber sealing gaskets is proposed. Taking into account the waterproof performance, material hardness and closing compression force performance of the sealing gasket, field tests are carried out to optimize the design of tunnel waterproof sealing gaskets and ensure the waterproof effect of shield tunnel joints.

[0075] like Figure 8a , Figure 8b and Figure 8c As shown in the figure, this embodiment presents three gasket design schemes. Scheme 1 is a composite gasket of water-swellable rubber and EPDM, Scheme 2 is a double-row perforated EPDM gasket, and Scheme 3 is a single-row perforated EPDM gasket. The gasket parameters are shown in Table 1 below. This study is used to test and compare the closing compression force and hardness performance. Considering the comprehensive waterproofing ability, hardness test, and closing compression force test, Scheme 3 (single-row perforated) waterproof gasket is recommended.

[0076] Table 1 Gasket Parameters

[0077]

[0078] Based on the above analysis steps, this embodiment ultimately designs a resilient main structure for a staggered-joint shield tunnel that adapts to the environmental changes in soft soil areas, as follows: Figure 9 As shown, the designed resilient structural segment has an inner diameter of 5.9m, an outer diameter of 6.7m, and a segment thickness of 400mm. The tongue and groove joints use a circumferential seam design, the bolts are grade 8.8, and single-row perforated EPDM rubber gaskets with a cross-sectional area of ​​448mm² are used. 2 The cross-sectional area of ​​the trench is 460 mm². 2 The cross-sectional area of ​​the trench / cross-sectional area of ​​the sealing gasket is 1.027. Compared with conventional staggered shield tunnels, the toughness of the main structure of the designed staggered shield tunnel can be increased by 37% and 141% respectively under the lateral unloading failure condition.

[0079] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept. The scope of protection of this invention is not limited to the specific forms stated in the implementation examples, but also includes equivalent technical means that can be conceived by those skilled in the art based on the inventive concept.

Claims

1. A method for designing the resilient structure of a shield tunnel in soft soil strata, characterized in that, The design methodology specifically includes the following steps: A. Establish a refined numerical model including a full-ring shield tunnel and calculate the reasonable thickness-to-diameter ratio of the shield tunnel to adapt to the environmental changes of soft soil strata; B. Establish a three-dimensional refined nonlinear finite element model of the shield tunnel joint and carry out optimized construction of the shield tunnel joint under the conditions of the entire service life; C. A cross-iteration method of joint stiffness internal force-deformation is proposed to calculate the shield bearing deformation and analyze the shield tunnel's deformation resistance under different design conditions; D. Conduct on-site experiments, propose the principle of dual control of the construction performance and waterproof performance of rubber sealing gaskets, and optimize the design of tunnel waterproof sealing gaskets.

2. The method for designing a resilient structure for a shield tunnel in soft soil strata according to claim 1, characterized in that, Step A specifically includes the following steps: A1. Establish a refined numerical model of the whole-ring shield tunnel and study the cross-sectional deformation characteristics of the shield tunnel under different thickness-to-diameter ratio designs. A2. Analyze the impact of foundation pit excavation on the deformation of shield tunnel structure, and obtain the deformation resistance of shield tunnel segments with different thickness-to-diameter ratios; A3. Calculate the appropriate thickness-to-diameter ratio of shield tunnels to adapt to the environmental changes of soft soil strata, and enhance the deformation resistance of subway shield tunnel structures.

3. The method for designing a resilient structure for a shield tunnel in soft soil strata according to claim 1, characterized in that, Step B specifically includes the following steps: B1. Establish a three-dimensional refined nonlinear finite element model of the shield tunnel joint, including the concrete segments, reinforcing bars, bolts, handholes, joint tenons and mortises, and groove details on both sides of the joint. B2. Study the influence of the tenon and mortise joint construction on the overall structural deformation and the opening and misalignment of the joints; B3. Based on the failure characteristics and critical conditions of the joint throughout its entire life cycle, optimize the joint parameters of the tongue and groove joints in shield tunnels in soft soil areas, including length, depth, and inclination angle, to improve the damage resistance of the segment structure.

4. The method for designing a resilient structure for a shield tunnel in soft soil strata according to claim 1, characterized in that, Step C specifically includes the following steps: C1. Establish a library of bending and shear stiffness for circumferential and longitudinal joints of shield tunnels, and propose a cross-iteration method for joint stiffness internal force-deformation. C2. Construct a shell-spring model of staggered shield tunnel structure based on joint stiffness library to improve the calculation efficiency of shield tunnel bearing deformation, and analyze the full-stage deformation resistance of shield tunnel under different design conditions.

5. The method for designing a resilient structure for a shield tunnel in soft soil strata according to claim 4, characterized in that, The cross-iteration method for joint stiffness internal force-deformation in step C1 specifically includes the following steps: C11. Based on the given tunnel convergence deformation D v Assume the neutral axis function of the joint is: In the formula, y n The corresponding convergent deformation D at the joint v The position of the neutral axis at time A, y0 and t are unknown coefficients, which can be solved by iterative methods; C12. According to the continuous rotation method, it is assumed that only the overall displacement of the tunnel and the rotation of the tunnel segments will occur, thus based on the convergence deformation D v Determine the joint rotation angles θ1, θ2, and θ3, as well as the joint opening amounts x1 and x2; C13. Based on the joint deformation, a mechanical analysis model is established, assuming that the joint rotation deformation is small relative to the segment and that the contact and separation surfaces of the segment after loading are both planes. The stress state of the joint under this convergent deformation condition is obtained, and a new neutral axis function is derived. C14. Determine whether the derived joint neutral axis function is consistent with the assumed joint neutral axis function: If there is a discrepancy, the parameters need to be adjusted and the iteration needs to be repeated. If they match, the mechanical parameters of the joint, namely axial force N, bending moment M, and rotation angle θ, can be obtained by combining the stress state of the joint. The bending stiffness k of the joint can then be obtained by tangent slope analysis of the bending moment-rotation angle curve. θ That is, when the tunnel exhibits convergent deformation, the convergent deformation D v The bending stiffness value of the lower shield joint is k θ When the convergence deformation D v When k changes θ It will also change accordingly.

6. The method for designing a resilient structure for a shield tunnel in soft soil strata according to claim 1, characterized in that, Step D specifically includes the following steps: D1. The principle of dual control of construction performance and waterproof performance of rubber sealing gaskets is proposed. The waterproof performance, material hardness and closing compression performance of the sealing gasket are comprehensively considered. Field tests are carried out to optimize the design of tunnel waterproof sealing gaskets and ensure the waterproof effect of shield tunnel joints. D2. Based on the above analysis steps, the final design is a resilient main structure for staggered-joint shield tunnels that adapts to the environmental changes in soft soil areas.

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