A method for designing a second lining of an ultra-shallow pipe roof tunnel

Abstract

The application provides a design method for a second lining of a super-shallow buried pipe roof tunnel, which comprises the following steps: calculating vertical loads of three characteristic points of a vault top, a haunch and a maximum excavation width side wall position; calculating horizontal loads of the vault top and an inverted arch bottom; assuming second lining design parameters, establishing a load structure model, and performing normal use limit state design on the load structure model by using 100% load corresponding combination; performing bearing capacity limit state checking on the load structure model by using 70% load corresponding combination; judging rationality of the second lining design normal use limit state and the bearing capacity limit state, and adjusting the second lining design parameters if there is a problem in the rationality of the normal use limit state and the bearing capacity limit state, and repeating the above steps until the design parameters that make the normal use limit state and the bearing capacity limit state of the second lining reasonable are obtained. The method provides a theoretical guidance for the second lining design of the super-shallow buried pipe roof tunnel under complex environmental conditions.

Description

Technical Field

[0001] This invention relates to the field of transportation engineering technology, specifically to a design method for the secondary lining of an ultra-shallow buried pipe tunnel. Background Technology

[0002] With China's economic development, engineering construction conditions, especially in urban surrounding environments, are becoming increasingly complex. Case studies of ultra-shallow buried tunnel projects using pipe-jacking excavation under complex conditions are increasing. The Chongqing Railway Hub East Ring Line is located on the outskirts of the city, with extremely complex environmental conditions. It passes under highways in several locations, such as the Xinbaiyangwan double-track tunnel passing under the Chongqing Ring Expressway with a 4m clearance; the Maoyakou and Qiaozibao No. 2 single-track tunnels passing parallel to each other with a 2-3m clearance passing under the Yuyi Expressway embankment; the Jinyu single-track tunnel passing under the Jinyu Avenue embankment with a 7m clearance; the Jinshan double-track tunnel (HMDK14+540~+595) passing under a 20m thick spoil heap on the side of the Jinshan Avenue embankment; and the Jinshan tunnel exit section passing under the Zhaojiaxi Interchange area with a 10m clearance. The roads affected by these underpasses are all major urban traffic arteries in Chongqing with huge traffic volumes. Furthermore, due to geological conditions and burial depth, the engineering risks are extremely high. Open-cut construction would involve enormous costs related to road relocation and reconstruction, and relocating highways would require partial road closures or road interruptions, resulting in speed limits on highways, significant social impact, high safety risks, and extremely difficult management and coordination. Taking all factors into consideration, the above-mentioned work sites all adopted the ultra-shallow buried tunnel pipe jacking excavation technology.

[0003] To address the technical challenges of tunnel excavation using pipe jacking in complex conditions for ultra-shallow buried tunnels in the Chongqing East Ring Railway, China Railway Eryuan Engineering Group Co., Ltd. developed a series of patents, including "A Calculation Model for Pipe Jacking Structure in Shallow Buried Tunnels under Complex Environmental Conditions (ZL201910647078.5)," "A Full-Section Construction Method for Pipe Jacking in Shallow Buried Tunnels under Complex Environmental Conditions (ZL201910647079.X)," and "A Structure for Longitudinal Connection Joints of Pipe Jacking Steel Pipes Using Bolted Welding (ZL201920590483.3)." They also published a paper titled "Discussion on the Principle and Application of Tunnel Pipe Jacking Method" in the journal *High-Speed ​​Railway Technology*, and released a Chongqing municipal-level QC achievement, "Optimization Research on Construction Method of Ultra-Shallow Buried Railway Tunnels Passing Under Highway Subgrade." These research findings suggest that a rigid support system is the most fundamental principle of ultra-shallow buried tunnel pipe jacking excavation technology. The widely used New Austrian Tunneling Method (NATM) and shallow-buried tunneling methods primarily utilize the coordinated deformation of the surrounding rock and the initial support structure to jointly serve as the main load-bearing structure. This allows for a certain amount of deformation in the surrounding rock to release ground pressure, and the coordinated deformation of the initial support and the surrounding rock achieves the purpose of joint load-bearing, thus forming a flexible support system. In contrast, the ultra-shallow tunneling pipe jacking technology aims to maximize the control of surrounding rock deformation. To ensure the safety of existing structures, the circumferential and longitudinal supports completely bear the surrounding rock pressure, without considering the coordinated deformation of the surrounding rock and the support, thus forming a rigid support system.

[0004] Regarding the calculation methods for composite lining secondary lining in mined tunnels, Peng Xin from Shijiazhuang Railway University, in his article "Research on Calculation Model and Mechanical Principles of Composite Lining in Tunnels," mainly proposed the following three methods: The first method is to establish a structural system model in which the initial support and secondary lining share the load, with the load acting on the initial support; the second method is to establish a separate structural system model for the secondary lining, with the initial support and secondary lining sharing the surrounding rock load in a certain proportion; the third method is to use the initial support as the main load-bearing structure and the secondary lining as a safety reserve. The first method is relatively complex, and the interaction between the primary support and the secondary lining in the model is difficult to accurately simulate, so it is rarely used at present. The third method considers the secondary lining as a safety reserve, but given the importance of the secondary lining, it is rarely used in China. Although the New Austrian Tunneling Method (NATM) design concept has been adopted in China, almost all of them use a load structure model that considers the secondary lining bearing part of the surrounding rock pressure, i.e., the second calculation method mentioned above. The corresponding surrounding rock pressure is mainly based on the loose body theory, using the collapse arch or Terzaghi method to calculate the loose surrounding rock pressure, or using the surrounding rock pressure calculation method based on industry experience, such as the load calculation methods for deep and shallow buried tunnels specified in Appendices D and E of the "Code for Design of Railway Tunnels" (TB10003-2016). At present, the design of the secondary lining structure of conventional cut-and-cover tunnels using load structure models for stress and deformation calculation is relatively mature. Based on this, the bearing capacity and serviceability limit state design are carried out according to the calculation results of the load structure model.

[0005] Compared with traditional calculation models for the secondary lining of mined tunnels, the support system and load patterns of ultra-shallow buried pipe jacking tunnels under complex environmental conditions differ significantly. The design methods for their secondary lining structures mainly suffer from the following problems:

[0006] (1) Differences in Loading Modes: In traditional load-structure models, the surrounding rock pressure is mainly based on loose body theory, using methods such as the collapse arch or Terzaghi method to calculate the loose surrounding rock pressure. For example, in the literature with application number 201811496389.8, entitled "A Design Method for Composite Lining of Tunnels Based on the Total Safety Factor Method," the secondary lining design uses similar surrounding rock pressure. When calculating the loads in traditional load-structure models, the influence of the surrounding rock is considered. For example, when calculating the vertical load of shallow-buried tunnels, the frictional force of the surrounding rock is considered, and when calculating the horizontal load, the active earth pressure under the condition of large horizontal deformation is used. However, under the ring and longitudinal rigid support system of pipe-jacking tunnels, the deformation of the surrounding rock is minimal, and the conditions for the formation of frictional force and active earth pressure are not present.

[0007] (2) In traditional support load calculations, the load is shared between the primary support and the secondary lining in a certain proportion, as shown in Table 10.3.3 of the "Design Specifications for Highway Tunnels" (JTG / TD70-2010). However, in ultra-shallow buried pipe liner tunnels under complex environmental conditions, the secondary lining is required to keep pace. Due to the durability of the primary support, the secondary lining will inevitably bear a large earth pressure in the later stages. Further research is needed to determine the load when the primary support bears 100% of the load and the secondary lining follows closely.

[0008] (3) Traditional cut-and-cover tunnel secondary linings employ a load-structure model, simultaneously designing for bearing capacity and serviceability limit state. In pipe-jacking cut-and-cover tunnels, considering the initial support bearing 100% of the load, the secondary lining theoretically only needs to be considered as a safety reserve in terms of bearing capacity. Simultaneously, due to the characteristics of shotcrete, the initial support cannot meet the serviceability limit state requirements; therefore, the serviceability limit state must be met through the secondary lining. Overall, theoretically, in the design of the support structure for pipe-jacking cut-and-cover tunnels, the initial support meets the ultimate bearing capacity limit state, while the secondary lining serves only as a safety reserve, but must still meet the serviceability limit state requirements. Considering the poor durability of the initial support and the high safety and reliability requirements of the support structure for ultra-shallow buried pipe-jacking cut-and-cover tunnels under complex environmental conditions, further research is needed on how to design the secondary lining under these circumstances. Summary of the Invention

[0009] In order to overcome the defects in the existing technology, the purpose of this invention is to provide a design method for the secondary lining of ultra-shallow buried pipe tunnels, which provides theoretical guidance for the design of secondary lining of ultra-shallow buried pipe tunnels under complex environmental conditions.

[0010] To achieve the above-mentioned objectives of this invention, this invention provides a method for designing the secondary lining of an ultra-shallow buried pipe tunnel, comprising the following steps:

[0011] S1, determine the location of the tunnel's crown, arch waist, and the sidewall at the maximum excavation width, and calculate the vertical loads at these three characteristic points respectively.

[0012] The horizontal load between the arch crown and the bottom of the invert varies linearly. Calculate the horizontal load between the arch crown and the bottom of the invert.

[0013] S2, assuming secondary lining design parameters, determine the geometric and physical parameters in the load structure model, establish the load structure model, and use the corresponding combination of 100% load for normal service limit state design.

[0014] S3, the load-bearing capacity limit state verification of the load-structure model is performed using a 70% load combination;

[0015] S4. Determine the rationality of the serviceability limit state and ultimate limit state design of the secondary lining. If there are problems with the rationality of the serviceability limit state and ultimate limit state design, adjust the secondary lining design parameters and repeat steps S2, S3, and S4 until the design parameters that make the serviceability limit state and ultimate limit state design of the secondary lining reasonable are obtained.

[0016] This method employs a differential load design approach, where the secondary lining is designed under normal service limit state with 100% load and verified under ultimate limit state with 70% load. This approach ensures the secondary lining structure possesses sufficient safety and reliability, providing theoretical guidance for the design of secondary linings in ultra-shallow buried pipe tunnels under complex environmental conditions.

[0017] In a preferred scheme of the design method for the secondary lining of the ultra-shallow buried pipe curtain tunnel, when establishing the load structure model, the secondary lining is simulated by beam elements, and the interaction between the initial support and the surrounding rock is simulated by only compressed springs. Based on the Winkel foundation model, it is assumed that the pressure intensity p at any point on the foundation is proportional to the foundation settlement s at that point, i.e., p = k·s, where k is the elastic resistance coefficient of the surrounding rock; the springs are set in the invert arch and sidewall areas.

[0018] In a preferred scheme of the design method for the secondary lining of the ultra-shallow buried pipe curtain tunnel, when the serviceability limit state design is carried out using the corresponding combination of 100% load, the stress condition of the secondary lining is calculated by numerical analysis through the finite element calculation model; the serviceability limit state design, i.e. crack resistance verification, is carried out based on the stress condition of the secondary lining, and the reinforcement parameters that meet the crack resistance requirements are obtained.

[0019] When performing ultimate limit state verification of the load structure model using the corresponding combination of 70% load, numerical analysis is performed through the finite element calculation model to calculate the stress condition of the secondary lining at this time; the reinforcement parameters are then verified for ultimate limit state of bearing capacity based on the stress condition of the secondary lining at this time.

[0020] In a preferred scheme of the secondary lining design method for ultra-shallow buried pipe curtain tunnels, when judging the rationality of the serviceability limit state and ultimate limit state of the secondary lining design, it is necessary to judge whether the reinforcement parameters are reasonable, whether the reinforcement is feasible, and whether the ultimate limit state of the bearing capacity is reasonable.

[0021] In a preferred scheme of the design method for the secondary lining of the ultra-shallow buried pipe curtain tunnel, the horizontal load is the at-rest earth pressure.

[0022] In a preferred scheme of the design method for the secondary lining of the ultra-shallow buried pipe curtain tunnel, the horizontal load of the arch crown is e1=k0·p1, and the horizontal load of the invert bottom is e2=e1+k0·γz, where k0 is the static earth pressure coefficient, γ is the unit weight of the surrounding rock, z is the height difference between the arch crown and the invert bottom on the outer side of the initial support, and p1 is the vertical load of the arch crown.

[0023] The beneficial effects of this invention are as follows: Based on the traditional load structure model, this invention proposes a load mode adapted to the stress characteristics of ultra-shallow buried pipe curtain tunnel support under complex environmental conditions. Specifically, the vertical load uses the resultant force of soil gravity and surface load, while the horizontal load uses at-rest earth pressure. Considering the initial support characteristics and durability factors, and to ensure the safety and reliability of the support structure, the secondary lining is designed under 100% load for the serviceability limit state and verified under 70% load for the ultimate limit state. This invention overcomes the differences between the traditional load structure model and the stress characteristics of ultra-shallow buried pipe curtain tunnel structures. The differential load design method, which designs the secondary lining under 100% load for the serviceability limit state and verifies it under 70% load for the ultimate limit state, ensures that the secondary lining structure possesses sufficient safety and reliability. This method has a clear approach and simple calculations. It can be used to guide the design of secondary lining for ultra-shallow buried tunnels under complex environmental conditions. It helps to form a theoretical system for ultra-shallow buried tunnel pipe jacking technology, ensuring the safety of engineering construction and operation. At the same time, it provides theoretical and technical support for the further large-scale promotion and application of pipe jacking technology, and has significant economic and social benefits.

[0024] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0025] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0026] Figure 1 This is a schematic diagram of the structural model of the secondary lining of an ultra-shallow buried pipe tunnel under complex environmental conditions, under normal service limit state load. Detailed Implementation

[0027] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0028] Considering the poor durability of the initial support and the high safety and reliability requirements of the support structure for ultra-shallow buried pipe tunnels under complex environmental conditions, and based on the stress and deformation characteristics of the rigid support system for ultra-shallow buried pipe tunnels under complex environmental conditions, this invention provides an embodiment of a secondary lining design method for ultra-shallow buried pipe tunnels. This embodiment, based on the traditional load structure model, proposes a load mode adapted to the stress characteristics of the support structure for ultra-shallow buried pipe tunnels under complex environmental conditions. Specifically, the vertical load uses the resultant force of soil gravity and surface load, and the horizontal load uses at-rest earth pressure. Considering the characteristics and durability factors of the initial support, the secondary lining is designed under the serviceability limit state at 100% load and verified under the ultimate limit state at 70% load. This method is particularly suitable for the design of secondary linings for ultra-shallow buried pipe tunnels under complex environmental conditions.

[0029] Specifically, the following steps are included:

[0030] S1, as Figure 1 As shown, the vertical load is the resultant force of the weight of the upper soil and the surface load. Since the tunnel is arc-shaped, the upper load is calculated at the arch crown, arch waist, and the maximum excavation width sidewall. Therefore, the arch crown, arch waist, and the maximum excavation width sidewall are determined first. The vertical load varies linearly between the arch crown and arch waist, and between the arch waist and the maximum excavation width sidewall. The vertical loads at these three characteristic points, namely the arch crown, arch waist, and the maximum excavation width sidewall, are calculated and denoted as p1, p2, and p3, respectively.

[0031] The horizontal load between the arch crown and the invert bottom varies linearly. The horizontal load between the arch crown and the invert bottom is calculated using the at-rest earth pressure.

[0032] The horizontal load at the top of the arch is e1=k0·p1, and the horizontal load at the bottom of the invert is e2=e1+k0·γz, where k0 is the static earth pressure coefficient, γ is the unit weight of the surrounding rock, and z is the height difference between the top of the arch and the bottom of the invert on the outer side of the initial support.

[0033] S2, assuming secondary lining design parameters, which can be assumed based on engineering experience, determines the geometric and physical parameters in the load-structure model, and then establishes the load-structure model, such as... Figure 1As shown, the secondary lining is simulated using beam elements, and the interaction between the initial support and the surrounding rock is simulated using only compression springs. Based on the Winkler foundation model, it is assumed that the pressure intensity p at any point on the foundation is proportional to the foundation settlement s at that point, i.e., p = k·s, where k is the elastic resistance coefficient of the surrounding rock; the springs are placed in the invert arch and sidewall areas. After the geometric and physical parameters in the load structure model are determined, due to the cumbersome calculation of the geometric analytical solution, its application remains unchanged. In actual engineering applications, numerical analysis is performed using the finite element calculation model to calculate the stress condition of the secondary lining under the corresponding combination of 100% load. Based on the stress condition of the secondary lining at this time, the serviceability limit state design is carried out using the corresponding combination of 100% load, mainly for crack resistance verification, to obtain reinforcement parameters that meet the crack resistance requirements.

[0034] S3. The ultimate limit state of the load-bearing capacity of the load-bearing structural model is verified using the corresponding combination of 70% load. Specifically, numerical analysis is performed using a finite element calculation model to calculate the stress condition of the secondary lining under the corresponding combination of 70% load; the reinforcement parameters are then verified for ultimate limit state of bearing capacity based on the stress condition of the secondary lining at this time.

[0035] S4. Determine the rationality of the serviceability limit state and ultimate limit state of the secondary lining design, such as whether the reinforcement parameters are reasonable, whether the reinforcement is feasible, and whether the ultimate limit state is reasonable. If there are problems with the rationality of the serviceability limit state and ultimate limit state design, adjust the secondary lining design parameters and repeat steps S2, S3, and S4 until the design parameters that make the serviceability limit state and ultimate limit state of the secondary lining reasonable are obtained.

[0036] Before implementing this embodiment, it is necessary to determine parameters such as tunnel engineering parameters and surrounding rock unit weight. When implementing this embodiment, these parameters can be substituted into the above steps. The specific calculations of each step in this embodiment are all existing technologies and will not be described in detail here.

[0037] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0038] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A design method for secondary lining of ultra-shallow buried pipe tunnels, characterized in that, Includes the following steps: S1, determine the location of the tunnel's crown, arch waist, and the sidewall at the maximum excavation width, and calculate the vertical loads at these three characteristic points respectively. The horizontal load between the arch crown and the invert bottom varies linearly. The horizontal load between the arch crown and the invert bottom is calculated. The horizontal load is the at-rest earth pressure. The horizontal load at the arch crown is e1=k0·p1, and the horizontal load at the invert bottom is e2= e1+ k0·γz, where k0 is the at-rest earth pressure coefficient, γ is the unit weight of the surrounding rock, z is the height difference between the arch crown and the invert bottom on the outer side of the initial support, and p1 is the vertical load at the arch crown. S2, assuming the secondary lining design parameters, determine the geometric and physical parameters in the load structure model, establish the load structure model, and conduct normal serviceability limit state design using 100% load corresponding combination; when establishing the load structure model, the secondary lining is simulated using beam elements, and the interaction between the initial support and the surrounding rock is simulated using only compression springs. Based on the Winkel foundation model, it is assumed that the pressure intensity p at any point on the foundation is proportional to the foundation settlement s at that point, i.e., p = k·s, where k is the elastic resistance coefficient of the surrounding rock; the springs are set in the invert arch and sidewall areas; S3, the load-bearing capacity limit state verification of the load-structure model is performed using a 70% load combination; S4. Determine the rationality of the serviceability limit state and ultimate limit state of the secondary lining design. If there are problems with the rationality of the serviceability limit state and ultimate limit state, adjust the secondary lining design parameters and repeat steps S2, S3, and S4 until design parameters that make the serviceability limit state and ultimate limit state of the secondary lining reasonable are obtained.

2. The design method for secondary lining of ultra-shallow buried pipe curtain tunnels according to claim 1, characterized in that, When using the 100% load combination for serviceability limit state design, numerical analysis is performed using a finite element calculation model to calculate the stress condition of the secondary lining at this time; based on the stress condition of the secondary lining at this time, serviceability limit state design, i.e. crack resistance verification, is performed to obtain reinforcement parameters that meet crack resistance requirements; When performing ultimate limit state verification of the load structure model using the corresponding combination of 70% load, numerical analysis is performed through the finite element calculation model to calculate the stress condition of the secondary lining at this time; the reinforcement parameters are then verified for ultimate limit state of bearing capacity based on the stress condition of the secondary lining at this time.

3. The design method for secondary lining of ultra-shallow buried pipe curtain tunnels according to claim 1, characterized in that, When judging the rationality of the serviceability limit state and ultimate limit state of the secondary lining design, it is necessary to determine whether the reinforcement parameters are reasonable, whether the reinforcement is feasible, and whether the ultimate limit state is reasonable.

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