Stress analysis method for super-large-span tunnel lining supporting structure

Abstract

The invention relates to the technical field of tunnel reinforcement, in particular to a super-large-span tunnel lining support structure stress analysis method, which analyzes the internal force of a super-large-span tunnel lining structure by establishing a set of simplified three-dimensional numerical model and adopting a comparison method combining numerical analysis and field actual measurement monitoring, and improves the stability of the internal force of the super-large-span tunnel lining support structure. The sharing ratio of a primary support structure to secondary and tertiary lining loads is revealed, safety construction of the tunnel is guaranteed, and the construction period and quality are further guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel reinforcement, in particular to a stress analysis method for a super-large span tunnel lining support structure. Background Art

[0002] Composite lining structures are widely used in tunnel construction. They are generally composed of primary support and secondary lining. That is, after the excavation of the tunnel soil, anchor rods and shotcrete are promptly applied as primary support to control the deformation of the surrounding rock and bear the construction load. After the deformation of the surrounding rock is basically stable, the secondary lining is applied. The two initial layers are also called primary support and secondary lining, and the last layer of permanent lining structure is called tertiary lining.

[0003] At present, there is no unified understanding of the load sharing ratio of composite linings in various countries. Based on the understanding that secondary lining is constructed after the primary support is stable, the Japanese tunnel construction specification believes that the initial support bears most of the load, while European countries such as Germany pay particular attention to the bearing function of the secondary lining and design it according to the secondary lining bearing all loads. In my country's highway tunnel specifications, the design of the support bearing surrounding rock pressure is considered according to the surrounding rock grade. When the surrounding rock stability is good, the primary support mainly bears the surrounding rock pressure; when the surrounding rock stability is poor, the secondary lining bears more surrounding rock pressure. The worse the stability of the surrounding rock, the higher the surrounding rock pressure shared by the secondary lining. At present, the design of support structures in my country is still mainly based on engineering analogy, combined with finite element method for verification, and the determination of its design parameters still depends mainly on engineering experience.

[0004] At present, the stress on the lining structure of super-large tunnels is still unclear, and it is necessary to study the stress characteristics of the initial support and secondary lining (tertiary lining) structure of the tunnel.

[0005] Therefore, it is necessary to design a stress analysis method for the lining support structure of ultra-large span tunnels. The internal forces of the lining structure of ultra-large span tunnels are analyzed by combining numerical analysis with field measurements to reveal the load sharing ratio between the initial support structure and the secondary and tertiary lining loads. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a stress analysis method for a super-large span tunnel lining support structure. The internal force of the super-large span tunnel lining structure is analyzed by combining numerical analysis with on-site measurement, revealing the sharing ratio of the initial support structure and the secondary and tertiary lining loads.

[0007] In order to achieve the above object, the present invention provides a method for analyzing the stress of a lining support structure of a super-large span tunnel: The following steps are involved: S1, numerical model design: S1-1, three-dimensional numerical model establishment: A simplified model of a 2m tunnel length was established based on quasi-plane strain considerations, and the forces between the supporting structures were analyzed. The simplified model satisfies: The tunnel secondary lining adopts an equivalent method of replacing the material properties of the primary support plate elements; The load sharing on the tertiary lining surface is considered through the interface element; The ground surface is assumed to be horizontal and the strata are homogeneous to ensure that the ground stress is continuous and the same along the tunnel direction; The meshing of the three-dimensional numerical model uses 10-node high-order tetrahedral elements, and the mesh is encrypted near the structure, with a total of 7275 solid elements and 14578 nodes; S1-2, model parameters: The rock mass is assumed to be an ideal elastic-plastic material, moderately weathered granite, and is simulated using the Mohr-Coulomb model, with its strength index reduced by considering the strength of the structural surface; The primary shotcrete and surrounding rock are closely combined without any contact surface. The small conduit is simulated by Embedded pile unit, and its own interface is used to simulate the interaction between the conduit body and the surrounding rock; the interface strength is automatically generated according to the strength and stiffness of the adjacent strata; the small conduit itself is a linear elastic material; The tertiary lining is assumed to be an ideal elastic material, the material is C35 concrete with a thickness of 70 cm; the Young's modulus is 3.15E7 kN / m 2 , Poisson's ratio 0.15; S1-3, simulation method: According to the double-sidewall pilot tunnel construction method, the construction process of step-by-step excavation and support was simulated, and 18 construction stages were set. Except for the upper step excavation stage, the stress release coefficient was set to 0.5 before support. In other stages, the stress was released at one time, and then the plate unit was activated in a separate stage to simulate the initial support. S2, analysis of calculation results of primary support and secondary and tertiary lining loads: S2-1, initial support internal force after secondary lining: After the secondary lining is constructed, it is combined with the primary support, and the primary support and the secondary lining are output together. Since the bending moment and shear force are small, the axial force is used as a representative to consider the change of the internal force of the primary support; S2-2, the interface unit is used as the contact between the tertiary lining and the primary support, and the output structural surface unit normal stress reflects the contact force between the tertiary lining and the primary support; S3, actual measurement and analysis of internal forces of lining structure: S3-1, surrounding rock and initial support pressure: Monitoring point 1: Pressure monitoring points are set at the left and right waists and the invert arch to monitor the pressure of the surrounding rock on the initial support structure; Monitoring data analysis 1: Based on the on-site measurement results, the pressure monitored for three consecutive days was extracted and compared with the pressure values ​​at the same location in the numerical model; S3-2, pressure between primary support and secondary lining: Monitoring point 2: After the primary support is constructed, three pressure monitoring points are set between the primary support and the secondary lining: the invert, left waist and right waist; Monitoring data analysis 2: similarly extract the monitoring pressure between the primary support and the secondary lining for three consecutive days as in monitoring data analysis 1, and compare it with the pressure value of the same part of the numerical model; The measured results of the loads of surrounding rock on primary support and the loads of primary support on secondary lining in S3-1 and S3-2 are statistically analyzed.

[0008] Compared with the prior art, the present invention has the following beneficial effects: The present invention establishes a simplified three-dimensional numerical model and adopts a comparative method of numerical analysis combined with on-site measurement and monitoring to analyze the internal force of the lining structure of the extra-large span tunnel, revealing the sharing ratio of the initial support structure and the secondary and tertiary lining loads, which provides a guarantee for the safe construction of the tunnel and further ensures the construction period and quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 Schematic diagram of the three-dimensional geometry of the numerical model of the embodiment of the present invention.

[0010] Figure 2 A schematic diagram of dividing a three-dimensional grid model according to an embodiment of the present invention.

[0011] Figure 3 It is a model diagram of the construction process of the double-side wall pilot pit method according to an embodiment of the present invention.

[0012] Figure 4 This is the initial axial force distribution diagram of the embodiment of the present invention.

[0013] Figure 5 It is a schematic diagram of the force distribution of the interface unit according to an embodiment of the present invention.

[0014] Figure 6 This is the initial axial force distribution diagram of the embodiment of the present invention.

[0015] Figure 7 This is a cross-sectional layout diagram of surrounding rock pressure monitoring according to an embodiment of the present invention.

[0016] Figure 8 This is a pressure curve diagram of the surrounding rock acting on the primary support structure in an embodiment of the present invention.

[0017] Fig. 9 This is a diagram of the pressure monitoring arrangement between the primary support and the secondary lining according to an embodiment of the present invention.

[0018] Fig.10It is a curve diagram of the pressure value between the primary support and the secondary liner in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] See also Figures 1 to 10 The present invention is now further described in conjunction with the accompanying drawings. The present invention provides a method for analyzing the stress of a lining support structure of a super-large span tunnel: In this embodiment, the tunnel portal section is designed as a Class IV shallow buried reinforced section. The initial support uses C25 shotcrete with a thickness of 28 cm and I22b steel support; the second layer of initial support uses shotcrete with a thickness of 15 cm and a 12×15 cm grid steel frame; the third lining uses 65 cm thick waterproof reinforced concrete. The initial support and the second layer of initial support shotcrete are sprayed using the wet spraying method.

[0020] After excavation, 4cm thick concrete shall be sprayed in time, steel support and anchor rods shall be erected, and then 24cm thick concrete shall be sprayed again to complete the initial support; after the initial support is closed into a ring, the second layer of initial support shall be applied in time to ensure the stability of the surrounding rock and tunnel structure before the third lining forms strength. The radial system anchor rods adopt radial D25mm hollow grouting anchor rods (L=5.0m), which are arranged in a plum blossom shape with a spacing of 50cm*100cm (longitudinal*ring); ^42*4mm locking foot anchor pipes are set at the arch at the foot of the side wall, L-4.0m, with the same longitudinal spacing as the steel arch frame, and are firmly welded to the steel arch frame.

[0021] The steel mesh layout range is the arch wall part above the structural design baseline. When using double-layer steel mesh, a certain distance should be maintained between the two layers of mesh, and the second layer of steel mesh must be laid after the first layer of steel mesh is completely covered by sprayed concrete.

[0022] The reserved deformation amount is considered to be 15cm, which can be adjusted according to the actual deformation situation during construction; over-excavation and under-excavation should be strictly controlled during construction, and the over-excavation part should be backfilled and compacted with concrete of the same grade.

[0023] 1. Numerical model design: 1.1 Establishment of three-dimensional numerical model: Due to the construction design and control, the secondary and tertiary linings are less disturbed by excavation, so they can be considered as quasi-plane strain. A simplified model of a 2m tunnel length is established to analyze the forces between the support structures. The stratum is moderately weathered granite. ,like Figure 1 The model size is X×Y×Z=60m×2m×45m.

[0024] This embodiment mainly analyzes the stress of primary support and secondary lining in the construction of double-side wall pilot pit method. Under the premise of grasping the main contradiction, the influence of minor and small factors is simplified as much as possible to highlight the main research object and improve the calculation efficiency. The numerical model is simplified as follows: (1) The secondary lining of the tunnel adopts an equivalent method of replacing the material properties of the primary support plate elements.

[0025] (2) The load sharing on the tertiary lining surface is considered through the interface unit.

[0026] (3) The ground surface is assumed to be horizontal and the strata are uniform, thus ensuring that the ground stress is continuous and the same along the tunnel direction.

[0027] The 3D solid model mesh is divided using 10-node high-order tetrahedron elements, and the mesh is encrypted near the structure, with a total of 7275 solid elements and 14578 nodes. Figure 2 shown.

[0028] 1.2 Model parameters: The rock mass is assumed to be an ideal elastic-plastic material, and the medium-weathered granite The Mohr-Coulomb model (MC) is used for simulation, and its strength index is reduced by taking into account the strength of the structural surface. The physical and mechanical parameters of the rock and soil are shown in Table 1: Table 1: Physical and mechanical parameters of rock and soil

[0029] Initial support C25 shotcrete. In addition, considering the contact characteristics between the initial support shotcrete and the surrounding rock, it is considered that the two are closely combined and no contact surface is set. The small conduit is simulated by the Embedded pile unit, and the built-in interface is used to simulate the interaction between the conduit body and the surrounding rock. The interface strength is automatically generated according to the strength and stiffness of the adjacent strata. The small conduit itself is a linear elastic material, as shown in Table 2: Table 2: Small catheter parameters

[0030] The tertiary lining is assumed to be an ideal elastic material. The material is C35 concrete with a thickness of 70 cm. The Young's modulus is 3.15E7 kN / m2 and the Poisson's ratio is 0.15.

[0031] 1.3 Simulation method: According to the double-side wall pilot tunnel construction scheme, the construction process of step-by-step excavation and support is simulated. A total of 18 construction stages are set. Except for the upper step excavation stage, the stress release coefficient is set to 0.5 before support. The stress is released once in other stages, and then the plate unit is activated in a separate stage to simulate the initial support. Figure 3 shown.

[0032] 2. Analysis of calculation results of primary support, secondary and tertiary lining loads: 2.1 Initial support internal force after secondary lining: After the secondary lining is constructed, it is combined with the primary support. Therefore, the primary support and the secondary lining are output together, and are collectively referred to as the primary support below. The bending moment and shear force are small, so the axial force is used as a representative to consider the changes in the internal forces of the primary support, such as Figure 4 shown.

[0033] from Figure 4 It can be seen that after the tunnel is fully excavated, the maximum axial force reaches 1231kN / m 2 , mainly concentrated in the initial support of the side walls on both sides, the axial force of the arch is relatively small, and the axial force of the invert arch is almost non-existent. When the temporary partition wall is removed, the initial support internal force of the tunnel increases significantly to 1314kN / m 2 The changes in the initial axial force caused by the three-tier lining of the invert and the two-tier lining of the invert are relatively small. The axial force of the arch crown increases to 1473 kN / m due to the three-tier lining of the arch. 2 Therefore, it is analyzed that the initial internal force is redistributed under the action of the demolition of the temporary partition wall and the self-weight of the tertiary lining.

[0034] 2.2 Third lining load sharing and internal force: The interface unit is used as the contact between the tertiary lining and the primary support. The output structural surface unit normal stress reflects the contact force between the tertiary lining and the primary support, such as Figure 5 shown.

[0035] from Figure 5 It can be seen that the cast tertiary lining of the invert is in full contact with the primary support of the tunnel invert under its own weight, and the reaction force of the primary support structure (surrounding rock) on the tertiary lining is -24.84kN / m 2 ; The third lining of the arch is poured, and the reaction force of the surrounding rock at the invert position of the third lining increases to -70.65kN / m 2 The arch position is detached from the surrounding rock and is not subject to stress.

[0036] The internal forces of the tertiary lining are simulated using the built-in plate element with a reduced stiffness of 1 / 1000, so the output internal forces should be multiplied by 1000 times, such as Figure 6 shown.

[0037] from Figure 6 It can be seen that the maximum axial force of the tertiary lining is -730 kN / m2, which is located in the side walls, while the vault and invert are subject to certain tension.

[0038] In summary, the three-time lining of the arch was completed, and the reaction force of the surrounding rock at the invert position of the three-time lining increased to -70.65kN / m2. The arch position was separated from the surrounding rock, and the maximum axial force of the three-time lining was -730kN / m2, located on the side wall.

[0039] 3. Actual measurement and analysis of internal forces of lining structure: 3.1 Surrounding rock and initial support pressure: 3.1.1 Monitoring points: In order to monitor the pressure of the surrounding rock on the initial support structure, pressure monitoring points are set at the left and right waists and the invert position, such as Figure 7 shown.

[0040] 3.1.2 Monitoring data analysis: Based on the on-site measurement results, the monitoring pressures on November 12, 13, and 14, 2021 were extracted and compared with the pressure values ​​at the same locations in the numerical model. Figure 8 As shown in the figure, the measured surrounding rock pressures of the invert, left waist and right waist are 335kPa, 269kPa and 289kPa respectively; the calculated surrounding rock pressures of the invert, left waist and right waist are 420kPa, 265kPa and 278kPa respectively. The numerical simulation results of the invert position are too large (due to stress concentration), and the calculated values ​​of the two waists are basically consistent with the measured values. Overall, the stress of the surrounding rock pressure acting on the primary support is less than the initial ground stress of the surrounding rock (the overburden at the measuring point is about 600kPa of deadweight), which shows that the self-stabilizing capacity of the surrounding rock bears part of the surrounding rock load.

[0041] 3.2 Pressure between initial support and secondary lining: 3.2.1 Monitoring points: After the primary support is constructed, three pressure monitoring points, namely, the invert, left waist and right waist, are set between the primary support and the secondary lining, as shown in 9.

[0042] 3.2.2 Monitoring data analysis: The monitoring pressure between the primary support and the secondary lining on November 12, 13, and 14, 2021 was also extracted and compared with the pressure values ​​at the same location in the numerical model, such as Fig.10 As shown in the figure, the measured surrounding rock pressures of the invert, left waist and right waist are 56kPa, 27kPa and 29kPa respectively; the calculated surrounding rock pressures of the invert, left waist and right waist are 60kPa, 24kPa and 24kPa respectively. The measured results are basically consistent with the monitoring results, verifying the rationality of the numerical simulation.

[0043] The measured results of the loads of the surrounding rock on the primary support and the loads of the primary support on the secondary lining are statistically analyzed as shown in Table 3 below: Table 3: Load comparison

[0044] It can be seen that the measured values ​​of the left and right waists are basically consistent with the calculated values. The primary support shares about 90% of the surrounding rock load, and the sharing ratio at the foot of the invert arch is between 85.7% and 94%. It is not difficult to find that the primary support shares the surrounding rock load very well.

[0045] The above are only preferred embodiments of the present invention, which are only used to help understand the method and core ideas of the present application. The protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention. The above embodiments can be implemented in whole or in part by software or hardware. When implemented using software, the above embodiments can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions or computer programs. When a computer instruction or computer program is loaded or executed on a computer, a process or function according to an embodiment of the present application is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. Computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another computer-readable storage medium.

[0046] The present invention solves the deficiency in the prior art that the stress of the lining structure of a super-large tunnel is still unclear. By adopting the method of numerical analysis combined with on-site measurement, the internal force of the lining structure of a super-large span tunnel is analyzed, and the sharing ratio of the initial support structure and the secondary and tertiary lining loads is revealed, which provides a guarantee for the safe construction of the tunnel and further guarantees the construction period and quality.

Claims

1. A method for analyzing the stress of a super-long span tunnel lining support structure, characterized in that: The following steps are involved: S1, numerical model design: S1-1, three-dimensional numerical model establishment: A simplified model of a 2m tunnel length is established according to quasi-plane strain considerations, and the forces between the supporting structures are analyzed. The simplified model satisfies: The tunnel secondary lining adopts an equivalent method of replacing the material properties of the primary support plate elements; The load sharing on the tertiary lining surface is considered through the interface element; The ground surface is assumed to be horizontal and the strata are homogeneous to ensure that the ground stress is continuous and the same along the tunnel direction; The three-dimensional numerical model meshes using 10-node high-order tetrahedron units, with meshes encrypted near the structure, with a total of 7275 entity units and 14578 nodes; S1-2, model parameters: The rock mass is assumed to be an ideal elastic-plastic material, moderately weathered granite, and is simulated using the Mohr-Coulomb model, with its strength index reduced by considering the strength of the structural surface; The primary shotcrete and surrounding rock are closely combined without any contact surface. The small conduit is simulated by Embedded pile unit, and its own interface is used to simulate the interaction between the conduit body and the surrounding rock; the interface strength is automatically generated according to the strength and stiffness of the adjacent strata; the small conduit itself is a linear elastic material; The tertiary lining is assumed to be an ideal elastic material, the material is C35 concrete with a thickness of 70cm; Young's modulus is 3.15E7kN / m 2 , Poisson's ratio 0.15; S1-3, simulation method: According to the double-sidewall pilot tunnel construction method, the construction process of step-by-step excavation and support was simulated, and 18 construction stages were set. Except for the upper step excavation stage, the stress release coefficient was set to 0.5 before support. In other stages, the stress was released at one time, and then the plate unit was activated in a separate stage to simulate the initial support. S2, analysis of calculation results of primary support and secondary and tertiary lining loads: S2-1, initial support internal force after secondary lining: After the secondary lining is constructed, it is combined with the primary support, and the primary support and the secondary lining are output together. Since the bending moment and shear force are small, the axial force is used as a representative to consider the change of the internal force of the primary support; S2-2, the interface unit is used as the contact between the tertiary lining and the primary support, and the output structural surface unit normal stress reflects the contact force between the tertiary lining and the primary support; S3, actual measurement and analysis of internal forces of lining structure: S3-1, surrounding rock and initial support pressure: Monitoring point 1: Pressure monitoring points are set at the left and right waists and the invert arch to monitor the pressure of the surrounding rock on the initial support structure; Monitoring data analysis 1: Based on the on-site measurement results, the pressure monitored for three consecutive days was extracted and compared with the pressure values ​​at the same location in the numerical model; S3-2, pressure between primary support and secondary lining: Monitoring point 2: After the primary support is constructed, three pressure monitoring points are set between the primary support and the secondary lining: the invert, left waist and right waist; Monitoring data analysis 2: similarly extract the monitoring pressure between the primary support and the secondary lining for three consecutive days as in the monitoring data analysis 1, and compare it with the pressure value of the same part of the numerical model; The measured results of the loads of the surrounding rock on the primary support and the loads of the primary support on the secondary lining in S3-1 and S3-2 are statistically analyzed.

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