Large-section tunneling construction method for pre-construction of permanent structure before excavation

Abstract

The application discloses a large-section tunnel excavation construction method for pre-construction of permanent structures before excavation, which is suitable for large-section tunnel excavation and construction in soft rock or soil layers. The method comprises the following steps: providing a support effect by constructing a permanent structure in a small range of strata, excavating a large-section tunnel, pre-designing a permanent structure capable of supporting a support force after tunnel excavation before full-section underground excavation of the tunnel, arranging a plurality of freezing pipes on the two sides of the position of the designed permanent structure, freezing the position of the designed permanent structure and surrounding soil into a frozen soil curtain by using the freezing pipes, digging a construction permanent structure space with a relatively small section in the formed frozen soil curtain, installing steel bars in the construction permanent structure space and pouring concrete, and waiting for solidification to perform full-section excavation of soil in the interior of the permanent structure to form a tunnel. The method does not need a temporary support structure in the construction process, is simple in construction, safe and reliable, and high in construction efficiency.

Description

Technical Field

[0001] This invention relates to a method for the pre-construction of permanent structures in large-section tunnels using the cut-and-cover method, applicable to large-section tunnel construction projects in soft rock or soil layers, and belongs to the field of underground engineering construction. Background Technology

[0002] The difference between underground engineering and surface structural engineering lies in the lack of construction space. Therefore, the conventional construction procedure for underground engineering generally involves first creating the structural construction space through tunneling, and then constructing the underground structure using concrete pouring methods similar to those used in surface structural engineering. During the tunneling phase of constructing underground space, temporary supports and anchor bolts are typically installed around the excavation section to maintain the stability of the surrounding strata and balance the water and soil pressure around the excavation area. As the excavation cross-section increases, the technical requirements for the initial support structures to maintain the stability of the surrounding strata become increasingly sophisticated. For example, in the construction of large-section tunnels, the difficulty of maintaining the stability of soft strata after excavation is significant due to the large cross-section, necessitating high-strength and large-sized initial support structures as temporary measures during the excavation phase, which greatly increases the project's investment. Especially during tunnel excavation in soft strata, due to the large cross-sectional area of ​​the tunnel, temporary intermediate support structures such as CD and CRD are generally required to control the deformation of the surrounding strata. These structures are used to divide the tunnel excavation section, reduce deformation, and maintain the stability of the excavation face. After the entire cross-section is excavated and connected, the permanent structure is constructed around the perimeter of the tunnel. Once the strength of the permanent structure meets the design requirements, the internal intermediate support walls are removed. Therefore, all initial support structures are only temporary maintenance measures during the excavation stage. Their function is only to maintain the stability of the surrounding soil during the underground excavation process and does not affect the form and function of the permanent structure. Moreover, the construction of initial support structures and temporary intermediate support walls within the tunnel complicates the organization of the excavation and permanent structure construction process. Therefore, the construction of initial support structures as temporary measures increases project investment and prolongs the construction period, especially when the excavation cross-section is large, where the construction problems are more pronounced. Summary of the Invention

[0003] To address the shortcomings of existing technologies, a method for the pre-construction of permanent structures before excavation in large-section tunnels is provided. This method is simple to construct, safe, reliable, and efficient, and can solve the problems of complex work organization and low efficiency in the construction of large-section underground engineering projects, such as the use of temporary supports for support and subsequent dismantling.

[0004] To achieve the above objectives, the present invention provides a method for pre-constructing permanent structures for large-section tunnel excavation. Before full-section tunnel excavation, a permanent structure capable of supporting the tunnel excavation is pre-designed. Then, multiple freezing pipes are installed around the designed permanent structure on both the inner and outer sides, following the tunnel's direction. These freezing pipes freeze the designed permanent structure location and the surrounding soil into a frozen soil curtain. Space for constructing the permanent structure is excavated within this curtain. As excavation progresses, two layers of frozen walls are formed on both the inner and outer sides of this space under the action of the two layers of freezing pipes. This ensures that the frozen walls can block water and soil pressure and isolate groundwater during excavation. Reinforcing steel is then installed and concrete is poured into the space containing the permanent structure. Once the reinforced concrete solidifies, it provides support, eliminating the need for temporary support at the excavation face. The internal soil is excavated within the permanent structure, and the tunnel is formed after penetration.

[0005] The specific steps are as follows:

[0006] a. Plan the tunnel to be excavated in advance and pre-determine the location of the full cross-section of the tunnel construction stratum; design a permanent structure at the outer edge of the pre-determined full cross-section of the tunnel construction stratum to ensure support for the tunnel construction, the permanent structure being an arch structure;

[0007] b. Drive multiple freezing pipes matching the permanent structure into both the inner and outer sides of the designed permanent structure according to the tunnel direction, thereby forming two layers of freezing pipes according to the design outline of the permanent structure.

[0008] c. Refrigerant is introduced into the freezing pipe to freeze the soil around the permanent structure to form a frozen soil curtain. Under the protection of the frozen soil curtain, the ground is excavated at the location of the designed permanent structure.

[0009] d. As the construction space of the permanent structure is excavated, the frozen soil curtain forms two layers of frozen walls located inside and outside the construction space. After the frozen soil in the pre-designed permanent structure is completely excavated, steel bars are installed in the construction space of the permanent structure and tied to form a steel mesh. Then, the inner and outer frozen walls are used as formwork to pour concrete.

[0010] e. Once the concrete has hardened and formed a permanent structure, stop the freezing pipes from releasing cold and allow the soil to thaw naturally.

[0011] f. Under the support of the permanent structure, the excavation of the internal strata of the tunnel is carried out inside the permanent structure. Since the permanent structure can resist external water and soil pressure and isolate groundwater, the internal strata do not bear external water and soil pressure. The excavation of the internal strata is based on the standard of convenient construction organization and no additional countermeasures are required.

[0012] g. Once all the strata inside the tunnel (1) have been excavated, the tunnel can be completed and the tunnel construction can be finished.

[0013] Furthermore, the length of the permanent structure during each construction is constrained by the length of the refrigeration pipe. When long-distance tunnel excavation is required, segmented construction is necessary.

[0014] Furthermore, as the strata inside the tunnel are excavated, the frozen pipes that affect the construction will be cut off in sections. Once the soil excavation of the entire tunnel area is completed, the tunnel can be connected and the tunnel construction can be completed.

[0015] Furthermore, the freezing pipe can be installed using a pipe jacking machine.

[0016] Furthermore, the thickness of the permanent structure of the tunnel is 1 / 10 of the preset tunnel cross-sectional size, and the thickness of the permanent structure of tunnels with a span of 10 to 15m is 1 to 2m.

[0017] Furthermore, the layout, spacing, and other parameters of the freezing pipes around the permanent structure can be adjusted according to the location and burial depth of the permanent structure. By arranging some freezing pipes inside the permanent structure location, the excavation range of the permanent structure location can be divided, realizing the zonal excavation and segmented concrete pouring construction of the permanent structure, reducing the cross-sectional size of the permanent structure construction, improving the stability of the excavation cross-section, and reducing the impact on the surrounding environment.

[0018] Beneficial effects:

[0019] By first freezing the soil to form a frozen soil curtain, then excavating the construction space for the permanent structure within this curtain, and finally using the frozen soil as a formwork to construct the permanent structure with reinforced concrete, the scope and cross-sectional dimensions of the tunnel excavation were significantly reduced, lowering the difficulty of underground engineering excavation. The permanent structure replaced the load-bearing function of temporary supports in segmented construction, saving on temporary support construction costs. The entire tunnel excavation process was carried out under the support of the permanent structure, reducing deformation of the surrounding strata during excavation, simplifying the complexity of the excavation process, and facilitating construction organization. Attached image description:

[0020] Figure 1 This is a schematic diagram of the construction method for the pre-construction of permanent structures before excavation of large-section tunnels according to the present invention.

[0021] Figure 2 This is a schematic cross-sectional view of the strata during tunnel construction in accordance with the present invention.

[0022] In the diagram: 1-Tunnel construction stratum; 2-Freezing pipe; 3-Permanent structure; 4-Excavation face; 5-Freezing wall; 6-Internal soil; Detailed Implementation

[0023] The following description of the embodiments is taken with reference to the accompanying drawings, which illustrate specific embodiments in which the invention can be implemented.

[0024] This invention discloses a method for pre-constructing permanent structures in large-section tunnels using the cut-and-cover method. This involves pre-constructing permanent structures within the strata, then using the support of these permanent structures to excavate the entire internal soil section, directly forming the tunnel after breakthrough. The construction of the permanent structures can be achieved through traditional methods such as freezing or grouting to reinforce the strata before excavation and concrete construction, or through methods like jacking precast structures. Specifically, this involves temporarily improving the stability of a small area of ​​the strata surrounding the tunnel using grouting or artificial freezing reinforcement methods. Through small-scale excavation and construction, a permanent structure 3 is pre-formed around the tunnel excavation section, replacing the temporary support structures arranged in sections during excavation to maintain the stability of the surrounding soft strata and block groundwater. Under the support of the permanent structure 3, tunnel excavation is carried out, and once the excavation is completed, the entire tunnel construction process is finished, eliminating the need for further concrete pouring.

[0025] Before the excavation of the large-section tunnel, a ring of horizontal freezing pipes 2 parallel to the tunnel is arranged inside and outside the permanent structure 3 outside the tunnel excavation section. The freezing reinforcement effect of the freezing pipes 2 is used to improve the stability of the strata. Under its protection, the excavation of the weak rock or soil layer at the location of the permanent structure 3 is carried out. Then, the concrete permanent structure 3 is constructed in the excavation space.

[0026] Once the strength of the permanent concrete structure 3 meets the design requirements, it can provide support and water sealing for the surrounding strata. Under the support of the permanent structure 3, the excavation of the tunnel construction stratum 1 inside the tunnel permanent structure 3 can be carried out.

[0027] During the excavation of the internal strata of the tunnel, the permanent structure 3 formed around the perimeter can provide support for the surrounding weak rock or soil layers, eliminating the need for additional temporary initial support structures, saving on project investment, and greatly facilitating the excavation organization of the internal strata. Simultaneously, by adding a small number of freezing pipes 2 between the two rings of freezing pipes 2, the excavation area of ​​the permanent structure 3 can be divided into zones for excavation and structural construction, thereby further reducing the excavation cross-section, improving its stability, reducing the difficulty of underground excavation, and facilitating the organization of excavation and structural construction. The method of pre-constructing the permanent structure 3 for large-section tunnel excavation can significantly reduce the excavation cross-section area, improve its stability, reduce the need for layered and sectional construction organization and temporary support structure construction during large-section tunnel excavation, simplify the construction process, and save on project costs. It can ensure the construction quality of the permanent structure 3, increase the excavation speed of the strata, and effectively reduce the impact of the excavation process on the surrounding environment.

[0028] Example 1

[0029] like Figure 1 andFigure 2 As shown, on the cross-section of the tunnel to be excavated, the soft soil requiring support is reinforced using artificial freezing. Freezing pipes 2 are arranged around the designed location of the permanent structure 3, spaced at the same angle, dividing the frozen wall 5 into sections. Adjacent sections are separated by intersecting freezing pipes 2. Low-temperature refrigerant is injected into the freezing pipes 2 to form the frozen wall 5. Under the load-bearing capacity of the frozen wall 5, the permanent structure 3 is constructed between the two rows of freezing pipes 2. The location of the permanent structure 3 is determined according to its designed outline. The soil around the excavation face is maintained sequentially until the permanent structure 3 completely surrounds the excavation face 4. This construction mode utilizes the support of the permanent structure 3 for excavation. The permanent structure 3 bears the load of the surrounding soil and prevents water infiltration. After the permanent structure 3 is constructed, it bears the load of the surrounding soil and prevents groundwater from flowing into the excavation face 4 during excavation. In subsequent construction, no temporary support is needed for the excavation face; excavation can continue under the support of the permanent structure until the tunnel is penetrated.

[0030] The specific steps are as follows:

[0031] a. Two rows of freezing pipes 2 are arranged outside the soil to be excavated, along the design position of the permanent structure 3. Separating freezing pipes can be set between the two rows of freezing pipes 2 to divide the frozen wall 5 into multiple segmented areas, which facilitates the construction of the permanent structure 3 in different areas and further reduces the cross-sectional area and size of the permanent structure excavation. The arrangement parameters of the freezing pipes 2 are based on meeting the strength requirements of the frozen wall and are related to the strength of the structure and the magnitude of water and soil pressure.

[0032] b. Inject low-temperature refrigerant into freezing pipe 2 to form a frozen wall 5 in the tunnel construction stratum 1. Under the protection of the frozen wall 5, excavate the soil layer in the area of ​​permanent structure 3 and construct permanent structure 3 in the formed space. The thickness of permanent structure 3 is determined according to the bearing requirements of the tunnel.

[0033] c. Under the support of the permanent structure 3, the internal soil 6 is excavated. During the excavation process, any internal frozen pipes that affect the construction are cut off as needed.

[0034] d. Continue to excavate the soil inside the tunnel. Once the tunnel is completed, the tunnel structure construction can be finished. The permanent structure 3 will bear the load of the surrounding soil.

[0035] Specifically, this method changes the traditional construction sequence of underground engineering. Instead of the conventional approach of first creating the construction space and then constructing the structure within that space, it first constructs a permanent structure. This permanent structure then provides structural support to balance the water and soil pressure during tunnel excavation. Compared to tunnel construction, the pre-constructed permanent structure has a smaller cross-sectional size, is less difficult to construct, and is less affected by the surrounding environment. During construction, various methods such as freezing, grouting, and pipe jacking can be used to create the necessary conditions for permanent structure construction, meeting the requirements for permanent structures. Furthermore, the pre-constructed permanent structure can serve as a long-term support structure for the tunnel and can also replace temporary support during excavation, saving on construction investment, reducing the difficulty of underground structural engineering, and minimizing the impact of construction on the surrounding environment.

Claims

1. A method for the pre-construction of permanent structures before excavation in the construction of large-section tunnels using the cut-and-cover method, characterized in that: Before the full-section tunnel excavation, a permanent structure (3) that can provide sufficient support after the tunnel is excavated is designed in advance. Then, two layers of multiple freezing pipes (2) are set on the inner and outer sides of the outline of the designed permanent structure (3) according to the tunnel direction. The freezing pipes (2) are used to freeze the location of the designed permanent structure (3) and the surrounding soil into a frozen soil curtain. The space for the construction of the permanent structure (3) is excavated in the frozen soil curtain. The inner and outer sides of the space for the construction of the permanent structure (3) form two layers of frozen walls (5) under the action of the two layers of freezing pipes (2), ensuring that the frozen walls (5) can block the water and soil pressure and isolate groundwater during the excavation process. Then, steel bars are installed in the space for the construction of the permanent structure (3) and concrete is poured. After the reinforced concrete of the permanent structure (3) solidifies and forms a support, freezing is stopped. There is no need to provide temporary support for the excavation face. The internal soil (6) is excavated in the permanent structure (3) to form a tunnel. The specific steps are as follows: a. Plan the tunnel to be excavated in advance and pre-determine the location of the full cross-section of the tunnel construction stratum (1); design a permanent structure (3) at the outer edge of the pre-determined full cross-section of the tunnel construction stratum (1) to ensure support for the tunnel construction. The permanent structure (3) can be an arch structure. b. Drive multiple freezing pipes (2) that match the structure of the permanent structure (3) into the inner and outer sides of the designed permanent structure (3) according to the tunnel direction, so as to form two layers of freezing pipes (2) in accordance with the design outline of the permanent structure (3). c. Cold medium is introduced into the freezing pipe (2) to freeze the soil around the permanent structure (3) to form a frozen wall (5). Under the protection of the frozen wall (5), the ground is excavated at the location of the designed permanent structure (3). d. As the construction space of the permanent structure (3) is excavated, the frozen soil curtain forms two layers of frozen walls (5) located inside and outside the construction space and provides a protective effect against the surrounding water and soil pressure. When the frozen soil in the pre-set permanent structure (3) is completely excavated, steel bars are set into the construction space of the permanent structure (3) and tied to form a steel mesh. Then, the inner and outer frozen walls (5) are used as templates to pour concrete. e. After the reinforced concrete solidifies and forms a permanent structure (3), stop the freezing pipe (2) to release cold, allow the soil to thaw naturally, and then remove the freezing pipe (2). f. Under the support of the permanent structure (3), the excavation of the tunnel stratum (1) is carried out inside the permanent structure (3). Since the permanent structure (3) can resist external water and soil pressure and isolate groundwater, the internal stratum does not bear external water and soil pressure. The full-section excavation method of the tunnel stratum (1) is based on the standard of convenient construction organization and no additional countermeasures are required. g. Once all the strata inside the tunnel (1) have been excavated, the tunnel can be completed and the tunnel construction can be finished.

2. The method for constructing large-section tunnels using the cut-and-cover method according to claim 1, characterized in that: The length of the permanent structure (3) during each construction is constrained by the length of the freezing pipe. When long-distance tunnel excavation is required, segmented construction is necessary.

3. The method for constructing large-section tunnels using the cut-and-cover method according to claim 2, characterized in that: As the strata (1) inside the tunnel are excavated, the frozen pipes (2) that affect the construction will be cut off in sections. Once the soil excavation of the entire tunnel area is completed, the tunnel can be connected and the tunnel construction can be completed.

4. The method for constructing large-section tunnels using the cut-and-cover method according to claim 1, characterized in that: The thickness of the permanent structure (2) of the tunnel is 1 / 10 of the preset tunnel cross-sectional size. The thickness of the permanent structure of a tunnel with a span of 10~15m is 1~2m.

5. The method for constructing large-section tunnels using the cut-and-cover method according to claim 1, characterized in that: The arrangement and spacing of the freezing pipes (2) around the permanent structure (3) are adjusted according to the location and burial depth of the permanent structure (3). By arranging some freezing pipes (2) inside the location of the permanent structure (3), the excavation range of the permanent structure (3) can be divided, realizing the partitioned excavation of the permanent structure and the segmented concrete structure pouring construction, further reducing the size of the excavation section, improving the stability of the excavation section, and reducing the impact on the surrounding environment.

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