Shield tunnel structure reliability evaluation method based on joint safety reserve

Abstract

The invention relates to a shield tunnel structure reliability evaluation method based on joint safety reserve. The method comprises the steps that corresponding geological exploration data and tunnel design materials are collected for a to-be-evaluated tunnel; selecting a plurality of sections, and determining and calculating section parameters and shield tunnel structure joint internal forces under different burial depths; according to the stress state of the joint, constructing an ultimate bearing capacity curve of the section of the shield tunnel joint with different burial depths and different positions; and calculating a joint reliability coefficient Kj through the ultimate bearing capacity curve, and evaluating the reliability of the shield tunnel in combination with the joint reliability coefficient Kj. According to the method for evaluating the reliability of the shield tunnel structure, the reliability of the joints of the shield tunnel structure at different burial depths and different positions can be analyzed by calculating the reliability coefficient Kj of the joint of the plurality of calculated sections in the future, and a new thought is provided for reliability evaluation and real-time early warning of the shield tunnel structure in the future.

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 vigorous development of urban rail transit, more and more cities will use shield tunnels assembled from prefabricated concrete segments as the main structural form of urban rail transit. Monitoring of shield tunnels during operation found that tunnel structural defects such as lateral convergence deformation, segment joint opening and misalignment, joint water leakage and segment damage are seriously threatening the safety of tunnel structures. The reliability evaluation of operating tunnel structures has received more and more attention and attention. At present, the reliability evaluation of shield tunnel structures is mostly analyzed from two aspects: normal use safety state and bearing capacity limit state. Through the collation 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 an 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 tunnel structure, the present invention proposes a joint reliability coefficient K for safety reserve j The definition and calculation method of is proposed, and then a reliability evaluation method of 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 cross-sections and different positions, and conducts reliability analysis on each joint section, providing a new idea for 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 structure based on joint safety reserve 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 to determine the calculation section parameters and the internal forces of the 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 joint section of the shield tunnel at different burial depths and different positions is constructed. The curve is calculated by formula (1):

[0010]

[0011] Where A1, A2, B1, B2, C1, C2 are coefficients, which are 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 boundary 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 coordinates, 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, and its value is taken according to 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 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 reliability of shield tunnel structure joints at different burial depths and locations is analyzed by calculation, which provides a new idea for the reliability evaluation and real-time early warning of shield tunnel structures in the future. 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 compared with 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 the shield tunnel structure. 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 be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work 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 the 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 joint section of the shield tunnel at different burial depths and different positions is constructed, such as Figure 2 The above curve is the curve of the pipe segment joint under different pressures N ju When the bending bearing capacity of the joint section is 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 limit 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 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 tendon. When calculating the bearing capacity of the joint, the design value of the tensile strength of the bolt 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 then 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 coordinate origin.

[0039] Embodiment 1

[0040] A tunnel in a certain area was selected for safety evaluation. First, geological survey data and tunnel design materials were collected, and three sections were selected for safety evaluation. The calculation parameters of each section are shown in Table 1 and Table 2. The design conditions of the calculation section (taking calculation section 1 as an example) are summarized 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 force calculation of the lining structure is carried out according to the plane strain treatment, and a 1m long lining ring is taken along the longitudinal direction of the tunnel for calculation. The internal force of the lining structure is calculated using the elastic equation method, and the cross-sectional internal forces M, N, and V calculated by each load are superimposed. The calculation results are shown in Table 3.

[0057] Table 3 Calculation results of 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 joint section of the shield tunnel at different burial depths and different positions is constructed as follows: Figure 3 As shown. And further calculate the joint reliability coefficient K through formula (3) j The results are shown in Table 4.

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

[0062]

[0063] According to the above calculation results, when the lining form is certain, the smaller the tunnel burial depth, the greater the joint reliability coefficient, and the safer the tunnel structure. The lining type in the example is not suitable for subway tunnels with a burial depth of more than 20m. Under the same burial depth, different joint positions have different reliability coefficients. Specifically, for the same calculation section, the joint reliability coefficient has the rule of bottom joint> waist joint> top joint. Therefore, if the ground is overloaded or other working conditions occur, the top joint with the smallest safety reserve should be considered as the key research object.

[0064] It is obvious 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 features of the present invention. Therefore, the embodiments should be considered as exemplary and non-restrictive in all respects.

Claims

1. A method for evaluating the reliability of shield tunnel structure based on joint safety reserve, 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 to determine the calculation section parameters and the internal forces of the shield tunnel structure joints at different burial depths; S3. According to the stress state of the joint, the ultimate bearing capacity curve of the joint section of the shield tunnel at different burial depths and different positions is constructed. The curve is calculated by formula (1): Where A1, A2, B1, B2, C1, C2 are coefficients, which are 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 boundary 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 coordinates, combined with the joint reliability coefficient K j , and evaluate the reliability of shield tunnels.

2. The method for evaluating the reliability of shield tunnel structure based on joint safety reserve according to claim 1 is characterized in that: The coefficients A1, A2, B1, B2, C1, and C2 in formula (1) are obtained by formula (2): Among them, α1 is a coefficient, and its value is taken according to 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 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.

3. The method for evaluating the reliability of shield tunnel structure 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.

4. The method for evaluating the reliability of shield tunnel structure based on joint safety reserve according to claim 1 is characterized in that: Tunnel structure joint reliability factor K j Calculated by 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 coordinate origin.

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