A structural reliability evaluation method for shield tunnels based on joint safety reserve

Abstract

The present invention relates to a method for evaluating the reliability of shield tunnel structures based on joint safety reserves, comprising: collecting relevant geological survey data and tunnel design materials for the tunnel to be evaluated; selecting a number of sections, determining and calculating section parameters and internal forces of shield tunnel structure joints at different burial depths; constructing ultimate bearing capacity curves of shield tunnel joint sections at different burial depths and locations based on the joint stress state; and calculating the joint reliability coefficient K using the ultimate bearing capacity curves. j , combined with the joint reliability coefficient K j The present invention establishes a method for evaluating the reliability of shield tunnel structures. By calculating the reliability coefficients Kj of several calculated section joints, it will be possible to analyze the reliability of shield tunnel structure joints at different burial depths and locations, providing a new approach for future shield tunnel structure reliability evaluation and real-time early warning.

Description

Technical Field

[0001] The invention relates to the field of shield tunnel reliability evaluation, in particular to a shield tunnel structure reliability evaluation method based on joint safety reserve. Background Art

[0002] With the rapid development of urban rail transit, more and more cities are adopting shield tunnels assembled from precast concrete segments as the primary structural form of urban rail transit. Monitoring of shield tunnels during operation has revealed that tunnel structural defects such as lateral convergence deformation, segment joint opening and misalignment, joint leakage, and segment damage are seriously threatening the safety of tunnel structures. The reliability evaluation of operating tunnel structures is receiving increasing attention and attention. Currently, the reliability evaluation of shield tunnel structures is mostly analyzed from two aspects: the normal use safety state and the ultimate bearing capacity state. Through the review of the research results of relevant scholars in recent years, the common reliability evaluation indicators of shield tunnel structures are mainly the following: bearing capacity index, structural deformation index, durability index, and other indicators such as anti-seepage pressure.

[0003] Since the deformation of the tunnel is easy to measure, the existing methods for evaluating the reliability of shield tunnel structures are mainly based on deformation indicators, while there are few studies on the reliability evaluation of tunnel structures based on the bearing capacity of the lining structure. From the perspective of the structure itself, the safety problem of the tunnel structure will only arise when the force on the tunnel structure exceeds the bearing capacity of the material. The bearing capacity of the tunnel structure is the most important indicator for evaluating the reliability of the tunnel structure, and the structural deformation is only an appearance. Considering that the obvious feature of the shield tunnel is that there are a large number of joints between the segments, and the actual stiffness of the joints is less than the stiffness of the segments themselves, which is a weak position in the bearing capacity of the tunnel structure, the present invention proposes a joint reliability coefficient K for the safety reserve j The definition and calculation method of joint safety reserve are proposed, and then a reliability evaluation method for shield tunnel structure based on joint safety reserve is constructed, which provides a new idea for reliability evaluation and real-time early warning of shield tunnel structure. Summary of the Invention

[0004] The present invention establishes a shield tunnel structure reliability evaluation method based on joint safety reserve. The present invention considers the shield tunnel joint structure and safety reserve and proposes a shield tunnel joint reliability coefficient K. j The definition and calculation method of this method calculates the safety reserve of tunnel structure joints at different burial depths, different sections and different positions, and performs reliability analysis on each joint section, providing a new idea for the reliability evaluation and real-time early warning of shield tunnel structures.

[0005] The present invention adopts the following technical solutions:

[0006] A method for evaluating the reliability of shield tunnel structures based on joint safety reserves comprises the following steps:

[0007] S1. Collect relevant geological survey data and tunnel design materials for the tunnel to be evaluated;

[0008] S2. Select several sections and determine the calculation section parameters and the internal forces of shield tunnel structure joints at different burial depths;

[0009] S3. According to the stress state of the joint, the ultimate bearing capacity curve of the shield tunnel joint section at different burial depths and different positions is constructed. The curve is calculated by formula (1):

[0010]

[0011] Where A1, A2, B1, B2, C1, and C2 are coefficients determined by the concrete structure design code; N ju is the pressure on the segment joint, M ju is the bending bearing capacity of the joint section, N ju1 is the dividing value of different joint ultimate load states;

[0012] S4. Calculate the joint reliability coefficient K through the ultimate bearing capacity curve j , joint reliability coefficient K j It is obtained by calculating the minimum distance between the actual joint internal force point and the joint ultimate bearing capacity curve and the distance between the actual joint internal force point and the origin of the curve coordinate, combined with the joint reliability coefficient K j , and evaluate the reliability of shield tunnels.

[0013] The coefficients A1, A2, B1, B2, C1, and C2 in formula (1) are obtained by formula (2):

[0014]

[0015] Among them, α1 is a coefficient, the value of which is based on the concrete structure design code; β1 is the neutral axis height coefficient when the height of the compression zone of the rectangular stress diagram is assumed to be a flat section; f c is the design value of the concrete axial compressive strength; w is the width of the joint section; h is the height of the joint section; e is the effective height of the joint section; ζb is the height of the relative limit pressure zone; f by is the design value of tensile strength of prestressed tendons; σ b0 is the initial bolt preload; A b is the corresponding bolt cross-sectional area.

[0016] In step S2, the elastic equation method is used to calculate the internal forces of the shield tunnel structure joints at different burial depths.

[0017] Tunnel structure joint reliability factor Kj Calculated by formula (3):

[0018]

[0019] Where, |AA′| is the actual joint internal force point A(M j , N j ) is the minimum distance between the internal force calculation point A and the coordinate origin.

[0020] The beneficial effects of the present invention are as follows: the present invention establishes a method for evaluating the reliability of shield tunnel structures, which can be used to calculate the reliability coefficient K of several cross-section joints in the future. j The calculation is used to analyze the reliability of shield tunnel structure joints at different burial depths and locations, providing a new approach for future shield tunnel structure reliability evaluation and real-time early warning. Compared with other analysis methods, it has the following characteristics:

[0021] (1) The present invention proposes a joint reliability coefficient K based on safety reserve j . The reliability evaluation index system of shield tunnels has been broadened.

[0022] (2) The present invention adopts a reliability evaluation index based on bearing capacity, which can more directly reflect the reliability of the tunnel structure than the deformation index.

[0023] (3) The present invention can effectively consider the safety reserves of shield tunnel joints at different burial depths, different sections and different positions, which is of great significance for the reliability evaluation and real-time early warning of shield tunnel structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a flow chart of a method for evaluating the reliability of a shield tunnel structure based on joint safety reserve.

[0025] Figure 2 To construct the ultimate bearing capacity curve of shield tunnel joint sections at different burial depths and locations.

[0026] Figure 3 This is a schematic diagram of the ultimate bearing capacity curve and reliability coefficient calculation of a joint in the example. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] like Figure 1 A method for evaluating the reliability of a shield tunnel structure based on joint safety reserve is shown, comprising the following steps:

[0029] S1. Collect relevant geological survey data and tunnel design materials for the tunnel to be evaluated;

[0030] S2. Select several sections, determine the calculation section parameters, and use the elastic equation method to calculate the internal forces of shield tunnel structure joints at different burial depths;

[0031] S3. According to the stress state of the joint, the ultimate bearing capacity curve of the shield tunnel joint section at different burial depths and positions is constructed, such as Figure 2 The above curve is the pipe segment joint under different pressure N ju When the bending bearing capacity of the joint section M ju , the calculation method of the curve is shown in formula (1):

[0032]

[0033] In the formula, A1, A2, B1, B2, C1, C2 are coefficients, N ju is the joint section pressure, N ju1 is the boundary value of different joint ultimate load states, when N ju >N ju1 When N ju ≤N ju1 When , the component is in the ultimate bearing state 2; the calculation method of each coefficient is shown in formula (2):

[0034]

[0035] Among them, α1 is a coefficient, and its value is taken in accordance with the concrete structure design code; β1 is the neutral axis height coefficient when the height of the compression zone of the rectangular stress diagram is assumed to be a flat section, and its specific value is taken in accordance with the concrete code; f c is the design value of the concrete axial compressive strength; w is the width of the joint section; h is the height of the joint section; e is the effective height of the joint section; ζb is the height of the relative limit compression zone; the bolts applying pre-tightening force are regarded as prestressed tendons, f by is the design value of the tensile strength of the prestressed tendons. When calculating the bearing capacity of the joints, the design value of the tensile strength of the bolts is taken; σ b0 is the initial bolt preload; A b is the corresponding bolt cross-sectional area.

[0036] S4. Calculate the joint reliability coefficient K through the ultimate bearing capacity curve j , based on the joint reliability coefficient Kj , the reliability of each joint section is evaluated and analyzed, and the safety status of the tunnel structure is obtained. Figure 2 As shown, the tunnel structure joint reliability factor K j Calculated by formula (3):

[0037]

[0038] Where, |AA′| is the actual joint internal force point A(M j , N j ) is the minimum distance between the internal force calculation point A and the ultimate bearing capacity curve of the joint, which can be considered as a bearing capacity safety reserve. |OA| is the distance between the internal force calculation point A and the coordinate origin.

[0039] Example 1

[0040] A tunnel in a certain area was selected for safety evaluation. First, geological survey data and tunnel design materials were collected. Three sections were selected for safety evaluation. The calculation parameters of each section are shown in Tables 1 and 2. The design conditions of the calculation section (taking calculation section 1 as an example) were calculated. The summarized geometric and stratigraphic parameters are as follows:

[0041] Segment inner diameter: D i =5500mm

[0042] Segment outer diameter: D0=6200mm

[0043] Segment centroid radius: R c =2925mm

[0044] Segment elastic modulus: E c =3.55×10 7 kPa

[0045] Concrete segment weight: γ c =26kN*m -3

[0046] Cross-sectional area: A = bh = 1 × 0.35 = 0.35 m 2

[0047] Sectional moment of inertia: I c =bh 3 / 12=3.573×10 -3 m -4

[0048] Bending stiffness: E c I c =1.268×10 5 kN*m 2

[0049] Formation resistance coefficient: k = 6000kN*m-3

[0050] Joint stiffness coefficient: η = 0.7

[0051] Joint moment transfer coefficient: ζ=0.4

[0052] Table 1 Parameters of the selected calculation sections

[0053] Section number Center elevation / m Ground elevation / m Top burial depth / m 1 -17.05 1.05 15 2 -18.05 2.05 17 3 -20.05 3.05 20

[0054] Table 2 Physical and mechanical parameters of soil in the stratum where section 1 is located

[0055]

[0056] The internal forces of the lining structure were calculated using plane strain methods, with a 1-meter-long lining ring along the tunnel longitudinal direction. The elastic equation method was used to calculate the internal forces of the lining structure, and the cross-sectional internal forces (M, N, and V) calculated from the various loads were superimposed. The results are shown in Table 3.

[0057] Table 3 Calculation results of cross-section internal forces

[0058]

[0059]

[0060] Substituting the above data into formula (1) and formula (2), according to the stress state of the joint, the ultimate bearing capacity curve of the shield tunnel joint section at different burial depths and different positions is constructed as follows: Figure 3 As shown. And further calculate the joint reliability coefficient K by formula (3) j The results are shown in Table 4.

[0061] Table 4 Reliability coefficient K of joints at different burial depths and positions j

[0062]

[0063] Based on the above calculation results, for a given lining type, the smaller the tunnel depth, the greater the joint reliability coefficient and the safer the tunnel structure. Therefore, the lining type used in the calculation example is not suitable for subway tunnels with a depth exceeding 20m. At the same burial depth, the reliability coefficient varies depending on the joint location. Specifically, within the same calculation section, the joint reliability coefficient follows a pattern: bottom joint > waist joint > top joint. Therefore, if ground conditions such as overload occur, the top joint, with its minimal safety margin, should be the focus of research.

[0064] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered in all respects as exemplary and non-restrictive.

Claims

1. A method for evaluating the reliability of shield tunnel structures based on joint safety reserves, characterized in that: The following steps are involved: S1. Collect relevant geological survey data and tunnel design materials for the tunnel to be evaluated; S2. Select several sections and determine the calculation section parameters and the internal forces of shield tunnel structure joints at different burial depths; S3. According to the stress state of the joint, the ultimate bearing capacity curve of the shield tunnel joint section at different burial depths and different positions is constructed. The curve is calculated by formula (1): Formula (1) Where A1, A2, B1, B2, C1, and C2 are coefficients determined by the concrete structure design code; N ju is the pressure on the segment joint, M ju is the bending bearing capacity of the joint section, N ju1 is the dividing value of different joint ultimate load states; S4. Calculate the joint reliability coefficient K through the ultimate bearing capacity curve j , joint reliability coefficient K j It is obtained by calculating the minimum distance between the actual joint internal force point and the joint ultimate bearing capacity curve and the distance between the actual joint internal force point and the origin of the curve coordinate, combined with the joint reliability coefficient K j , to evaluate the reliability of shield tunnels; The coefficients A1, A2, B1, B2, C1, and C2 in formula (1) are obtained by formula (2): Formula (2) Among them, α1 is a coefficient, the value of which is based on the concrete structure design code; β1 is the neutral axis height coefficient when the height of the compression zone of the rectangular stress diagram is assumed to be a flat section; f c is the design value of the concrete axial compressive strength; w is the width of the joint section; h is the height of the joint section; e is the effective height of the joint section; ζb is the height of the relative limit pressure zone; f by is the design value of tensile strength of prestressed tendons; σ b0 is the initial bolt preload; A b is the corresponding bolt cross-sectional area; Tunnel structure joint reliability factor K j Calculated by formula (3): Formula (3) Where, |AA′| is the actual joint internal force point A (M j , N j ) is the minimum distance between the internal force calculation point A and the ultimate bearing capacity curve of the joint, and |OA| is the distance between the internal force calculation point A and the coordinate origin.

2. The method for evaluating the reliability of shield tunnel structures based on joint safety reserve according to claim 1 is characterized in that: In step S2, the elastic equation method is used to calculate the internal forces of the shield tunnel structure joints at different burial depths.

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