Large-section arch cover method for underground excavation construction of subway station

Abstract

The application discloses a subway station large-section arch cover method excavation construction method and relates to the technical field of subway station construction, which comprises the following steps: S1, constructing an advanced anchor rod; S2, excavating a small pilot tunnel; S3, constructing a pile foundation and a support column; S4, excavating an edge pilot tunnel; S5, constructing a top longitudinal beam; S6, constructing a bottom longitudinal beam; S7, removing an initial support and constructing a secondary lining; and S8, excavating soil layers in stages. The application has the effect of shortening the construction period of the arch cover method.

Description

Technical Field

[0001] This application relates to the technical field of subway station construction, and in particular to the method of large-section arch cover tunnel construction for subway stations. Background Technology

[0002] The arch cap method is a tunneling construction method developed based on the PBA method, suitable for soft-overhead, hard-underlying, weathered rock strata. The core idea of ​​this method is to fully utilize the bearing capacity and stability of the underlying rock. Under conditions of no blasting or weak blasting, the initial support arch is constructed using the small pilot tunnel form of the PBA method, while a large arch foot scheme replaces the side piles in the PBA method. The initial support and secondary lining structure of the arch are supported on stable bedrock on both sides, forming an arch cap. Under the protection of the arch cap, underground cut-and-cover construction can be carried out in either reverse or forward direction.

[0003] like Figure 1 The diagram illustrates the traditional arch-type construction process. First, multiple small pilot tunnels are excavated within the rock strata. Then, support columns are constructed between upper and lower pilot tunnels. Pilot tunnels are continued to be excavated, connecting the multiple small pilot tunnels to form an arch. Secondary lining is then constructed within the pilot tunnels. Finally, a foundation pit is excavated downwards within the arch until the designed bottom elevation is reached. If the traditional arch-type construction method is used, multiple small pilot tunnels need to be constructed. If the soil is relatively hard, the construction period is long and the cost is high. Summary of the Invention

[0004] In order to shorten the construction period of the arch-type construction method under good soil conditions, this application provides a method for the underground excavation of large-section arch-type subway stations.

[0005] This application provides a method for the cut-and-cover construction of large-section arched subway stations, employing the following technical solution:

[0006] The method for constructing subway stations using the large-section arch cover tunnel method includes the following steps:

[0007] S1. Construct advanced anchor bolts around the outline of the small pilot tunnel to be excavated;

[0008] S2. Excavate a small pilot tunnel and implement initial support;

[0009] S3. Construct pile foundations and support columns inside the pilot tunnel;

[0010] S4. Construct advanced anchor bolts around the outline of the pilot tunnel to be excavated, and excavate the pilot tunnels on both sides of the small pilot tunnel to construct the initial support of the pilot tunnel.

[0011] S5. Construct the top longitudinal beam inside the small pilot tunnel. The top longitudinal beam is supported by the support column and is poured along the longitudinal direction of the small pilot tunnel.

[0012] S6. Bottom longitudinal beam of the construction side guide tunnel;

[0013] S7. Remove the initial support of the side walls on both sides of the small pilot tunnel and construct the secondary lining of the pilot tunnel.

[0014] S8. Excavate the soil layer downwards in stages to the design bottom slab elevation.

[0015] By adopting the above-mentioned technical solution, and considering that the subway station foundation pit is being excavated in rock strata with relatively good soil conditions, and the cross-sectional span of the foundation pit at the subway station platform is larger than that of a conventional single-tube tunnel, it is extremely important that the arch cap has sufficient strength and stability to support the overburden during construction. Traditional shield tunneling methods cannot meet the stability support requirements within the tunnel. The arch cap method, a related technology, requires the simultaneous excavation of multiple small tunnels, and the construction of pile foundations and support columns within these tunnels. After the pile foundations and support columns are completed, the various pilot tunnels are connected to complete the construction. This process is complex and has a long construction period.

[0016] Large-section arched construction in rock strata with good soil conditions is costly if the arched construction method is used.

[0017] The method for constructing a large-section arched subway station using the cut-and-cover method provided in this application involves constructing pile foundations and top longitudinal beams within the small pilot tunnel during excavation. Due to the favorable soil conditions, side pilot tunnels connected to the small pilot tunnel can be directly excavated on both sides. The top longitudinal beams, the secondary linings within the small and side pilot tunnels are then cast as a single unit, allowing the pile foundations and top longitudinal beams to serve as the support system for the final arched structure. Since the arch structure itself has a certain bending moment resistance, and the support system ensures the stability of the large-section arched structure, the construction process is simple, the construction speed is fast, and it has good economic benefits.

[0018] Optionally, both the small pilot tunnel and the side pilot tunnel are excavated using the step method.

[0019] By adopting the above technical solution, the excavation method is optimized from the conventional central partition wall method to the bench method, which is used for tunnel excavation in rock strata with good foundation soil. This makes the construction faster and reduces the construction cost.

[0020] Optionally, in step S3, the pile hole is first excavated and the pile hole sidewall concrete is poured. Then, the pile foundation under the central column is poured from the bottom of the pile hole upwards, and the steel pipe column is hoisted into the pile hole. The steel pipe column is connected and fixed to the pile foundation under the central column. After the pile foundation under the central column is poured, the core concrete of the steel pipe column is poured to form a steel pipe concrete column.

[0021] By adopting the above technical solution, since the construction of pile foundations and support columns needs to be carried out in the small pilot tunnel, the clearance height of the small pilot tunnel is limited. However, the soil conditions of the foundation are good, and pile holes can be formed by manual excavation. Then, pile foundation concrete is first driven into the pile holes, and then steel pipe concrete columns are hoisted and poured to finally form a pile column support system. The support of the upper arch structure is achieved by setting up the pile column support system.

[0022] Optionally, the first stage of secondary lining can be poured simultaneously during the pouring of the top longitudinal beam.

[0023] By adopting the above technical solution, the positioning of the steel grating formwork is more accurate when the secondary lining of the small guide tunnel and other parts of the side guide tunnel is laid during the later pouring, which facilitates the construction of the joints of the secondary lining in the top longitudinal beam and the guide tunnel, and the construction and forming effect is better.

[0024] Optionally, the earthwork in the two side guide tunnels can be excavated simultaneously, and the excavation progress of the working faces of the adjacent small guide tunnels and side guide tunnels can be staggered by no less than 10m.

[0025] By adopting the above technical solution, the earthwork in the two side tunnels is excavated simultaneously, which makes the construction progress faster and shortens the construction period. At the same time, the excavation faces of adjacent tunnels are staggered by no less than 10m to enhance the safety during the construction process.

[0026] Optionally, during the initial support construction and the secondary lining formwork, grouting steel pipes need to be pre-embedded between the initial support and the sidewall of the pilot tunnel, and between the secondary lining and the initial support.

[0027] By adopting the above technical solution, since construction errors are inevitable during the excavation of the pilot tunnel, there will be gaps between the initial support and the sidewall of the pilot tunnel, or between the secondary lining and the initial support. During construction, grouting steel pipes are pre-embedded to facilitate the injection of concrete into the gaps later to fill them.

[0028] Optionally, there is a gap between the top of the top longitudinal beam and the initial support of the small guide tunnel. The gap is backfilled and compacted with micro-expansion concrete of the same grade as the main structure.

[0029] By adopting the above technical solution, there is no gap between the top of the longitudinal beam and the tunnel sidewall, which reduces the impact of soil collapse on the longitudinal beam. In addition, the use of micro-expansion concrete of the same grade ensures the support strength of each part of the arch.

[0030] Optionally, the secondary lining arch foot of the side tunnel is supported above the bottom longitudinal beam.

[0031] By adopting the above technical solution and constructing the arch cover method according to the relevant technology, it is necessary to construct the pile foundation supporting the arch foot in the side guide tunnel. However, due to the good soil conditions, the support scheme is optimized to support the arch foot by supporting the side guide tunnel with the bottom longitudinal beam. This not only meets the stress requirements, but also reduces the construction cost and simplifies the construction process. It is an optimized construction measure that is suitable for the construction conditions of this application.

[0032] Optionally, the construction of pile foundations and support columns inside the small pilot tunnel can be carried out simultaneously with the excavation of the side pilot tunnel and the construction of the bottom longitudinal beam.

[0033] By adopting the above technical solution, due to the good quality of the foundation soil, the earthwork excavation of the side guide tunnel can be carried out during the construction of pile foundation and support columns. Due to the stress characteristics of the arch itself, that is, the bending moment inside the arch is less than the bending moment of the beam with the same span, the inner wall of the foundation pit can remain stable during the excavation of the side guide tunnel, which shortens the construction period and reduces the construction cost.

[0034] In summary, this application includes at least one of the following beneficial effects:

[0035] 1. This application provides a method for the construction of a subway station arch cover by tunnel excavation in areas with good soil conditions. This method can meet the stress stability requirements of large-section subway station construction, and it saves more construction time compared with traditional methods. Moreover, the construction steps are simplified and the economic benefits are better.

[0036] 2. When excavating small pilot tunnels and side pilot tunnels, the excavation method is optimized to the bench method. This method can satisfy the construction space of the excavation machinery and the stability of the surrounding strata. Compared with the central diaphragm wall method, the construction period is shorter and the economic benefits are better.

[0037] 3. The support system of pile foundation plus support column plus top longitudinal beam can provide stable support for the large-section three-guide tunnel. In combination with relatively hard foundation soil, it forms a new arch cover construction technology suitable for good soil conditions. Under the premise of meeting construction safety, the construction period is shorter, the construction procedures are fewer, and the construction cost is lower. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the construction process of the arch method in related technologies;

[0039] Figure 2 This is a schematic cross-sectional view of the small pilot tunnel after the excavation is completed in step S2 of the embodiment of this application;

[0040] Figure 3 This is a schematic diagram of the transverse cross-section after the construction of the top longitudinal beam in the small guide tunnel is completed in step S5 of the embodiment of this application;

[0041] Figure 4This is a schematic cross-sectional view of the arch after the construction of step S7 of the embodiment of this application is completed;

[0042] Figure 5 This is a schematic cross-sectional view of the subway station after step S8 of the embodiment of this application is completed.

[0043] Explanation of reference numerals in the attached drawings: 1. Small pilot tunnel; 2. Side pilot tunnel; 3. Top longitudinal beam; 4. Bottom longitudinal beam; 5. Secondary lining; 51. First stage secondary lining; 52. Second stage secondary lining; 6. Pile-column support system; 61. Pile foundation under the middle column; 62. Steel-concrete composite column; 63. Pile hole; 7. Void; 8. Grouting steel pipe; 9. Initial support. Detailed Implementation

[0044] The following is in conjunction with the appendix Figure 1-5 This application will be described in further detail.

[0045] The large-section arch-cover method for tunnel construction of subway stations disclosed in this application involves excavating pilot tunnels and constructing arches in moderately weathered or slightly weathered silty mudstone, characterized by relatively hard rock, relatively intact rock mass, slightly developed joints and fissures, and a relatively underdeveloped surface water system. The arch span reaches 25.1m. Compared to the span of most tunnels, this application's embodiment represents a large-section arch construction, making the full-cycle stress stability of the arch a crucial factor to consider. Furthermore, as it involves subway station construction within an urban area, the disturbance to the surrounding soil and construction noise must be taken into account.

[0046] The construction method disclosed in this application includes the excavation of three pilot tunnels, as referred to... Figure 2 and Figure 3 The pilot tunnel in the middle is called the small pilot tunnel 1, and the pilot tunnels on both sides of the small pilot tunnel 1 are called the side pilot tunnels 2. The small pilot tunnel 1 is excavated first, and then the side pilot tunnels 2 are excavated.

[0047] Specifically, the large-section arch cover method for underground construction of subway stations disclosed in this application includes the following steps:

[0048] S1. Pre-construction anchor bolts: Refer to... Figure 2 At the front of the excavation of the small pilot tunnel 1, along the outline of the small pilot tunnel 1 to be excavated, advanced anchor rods are driven radially in front of the excavation face with a large outward insertion angle to form pre-anchoring of the rock strata to be excavated, thereby strengthening the soil stability of the sidewall of the small pilot tunnel 1 and reducing the occurrence of soil collapse on the sidewall of the small pilot tunnel 1 during the excavation process.

[0049] S2. Excavate the pilot tunnel 1 and implement initial support 9: Refer to Figure 3A single-arm tunneling machine was used for earthwork excavation, and the step method was employed during the excavation of the pilot tunnel 1. The excavation step distance was the same as the spacing of the steel frame and steel grid supporting the sidewalls of the pilot tunnel 1. Since the construction site was located in an urban area, blasting methods could not be used. The use of a single-arm tunneling machine provided high flexibility for excavation and met the requirements of fractured rock strata.

[0050] During the excavation of the small pilot tunnel 1, the initial support 9 of the sidewall of the small pilot tunnel 1 was constructed simultaneously with the excavation. The initial support 9 was supported by wire mesh and shotcrete. Since the earthwork excavation was carried out in the rock strata with good soil quality, the use of wire mesh and shotcrete was sufficient to meet the requirements of the initial support 9.

[0051] When installing the mesh for the initial support 9 on the side wall of the small pilot tunnel 1, the grouting steel pipe 8 is pre-embedded. After the initial support 9 is shotcreted, the pre-embedded grouting steel pipe 8 facilitates the backfilling and injection of concrete into the gap between the initial support 9 and the surrounding rock strata of the small pilot tunnel 1.

[0052] S3. Construct multiple pile foundations and support columns within the pilot tunnel 1: Refer to... Figure 3 During the excavation of the small pilot tunnel 1, multiple pile holes 63 are manually excavated along the longitudinal direction of the small pilot tunnel 1, and the pile hole 63 retaining wall construction is carried out. In the embodiment of this application, the pile is that 150mm thick C30 concrete is poured on the side wall of the hole. In other embodiments, the specific concrete pouring thickness and concrete grade are determined according to the actual engineering geological conditions. After the construction of the retaining wall of pile hole 63 is completed, the pile foundation 61 of the middle column is poured into pile hole 63. After pouring to the corresponding elevation, the top hanger and the lower locking device are installed in the small guide hole 1. After the steel pipe column is hoisted into place section by section, the pile foundation 61 of the middle column is poured to the design elevation. The steel pipe column and the pile foundation 61 of the middle column are fixed by pouring the steel pipe column part into the concrete of the pile foundation 61 of the middle column. After the construction of the pile foundation 61 of the middle column is completed, fine sand is backfilled into the gap between the side wall of pile hole 63 and the steel pipe column. After the fine sand is compacted, the column core concrete is poured to complete the construction of the steel pipe concrete column 62 and form the pile column support system 6.

[0053] S4. Excavate the side guide tunnels 2 on both sides of the small guide tunnel 1: Refer to Figure 3 Due to favorable geological conditions, the excavation of the side tunnels 2 on both sides of the small pilot tunnel 1 can be carried out simultaneously during the construction of the pile foundation and steel-concrete composite columns 62 within the small pilot tunnel 1. Before the excavation of the side tunnels 2, pre-anchor bolts are installed around the excavation outline of the side tunnels 2, and the earthwork excavation of the side tunnels 2 also adopts the bench method using a single-arm tunneling machine. To improve the construction safety during the excavation of the side tunnels 2, the excavation progress of the adjacent small pilot tunnels 1 and side tunnels 2 is staggered by no less than 10m. The initial support 9 of the side tunnels 2 is constructed simultaneously with the excavation of the side tunnels 2, and the initial support 9 method of the side tunnels 2 is the same as that of the small pilot tunnels 1.

[0054] S5. Construct the top longitudinal beam 3 inside the small pilot tunnel 1: Refer to Figure 3 After the construction of the central column pile foundation 61 and the steel-concrete composite column 62 in the small pilot tunnel 1 is completed, a pile-column support system 6 is formed. A top longitudinal beam 3 is constructed at the top of the steel-concrete composite column 62 along the longitudinal direction of the small pilot tunnel 1. The reinforcing bars in the top longitudinal beam 3 are anchored to the reinforcing bars in the steel-concrete composite column 62 according to relevant specifications. During the pouring of the top longitudinal beam 3, part of the secondary lining 5 of the final arched roof slab is poured simultaneously. This construction of the secondary lining 5 is the first stage of secondary lining 51 construction. Because the structure formed by one-time pouring is more stable, the connection between the top longitudinal beam 3 and the final arched roof slab is better, and the soil pressure on the tunnel sidewall slab borne by the final arched roof slab can be better transferred to the top longitudinal beam 3.

[0055] After the completion of the construction of the top longitudinal beam 3 and the first-stage secondary lining 51, a gap 7 is formed between the top longitudinal beam 3 and the initial support 9 of the small pilot tunnel 1. The gap 7 is backfilled and compacted with micro-expansion concrete of the same grade as the main structure. This gives the entire arch structure good strength and reduces the possibility of soil collapse on the tunnel sidewalls and soil directly falling onto the top longitudinal beam 3.

[0056] S6. Bottom longitudinal beam 4 of construction side guide tunnel 2: Refer to Figure 4 After the initial support 9 in the side tunnel 2 is connected to the initial support 9 in the small tunnel 1, the bottom longitudinal beam 4 in the side tunnel 2 is constructed. The bottom longitudinal beam 4 is constructed at the arch foot of the side tunnel 2. The bottom longitudinal beam 4 is poured along the excavation path of the side tunnel 2 and the pouring section of the bottom longitudinal beam 4 includes an inclined surface for joining with the secondary lining 5 of the side tunnel 2.

[0057] S7. Remove the initial support 9 on both sides of the small pilot tunnel 1, and construct the secondary lining 5 of the pilot tunnel 2: Refer to Figure 4 After the construction of the top longitudinal beam 3, the first-stage secondary lining 51, the initial support 9, and the bottom longitudinal beam 4 in the side guide tunnel 2 are completed, the initial support 9 between the small guide tunnel 1 and the side guide tunnel 2 is removed. At this time, the small guide tunnel 1 and the side guide tunnel 2 are connected to form a continuous three-arch end face. Then, the secondary lining 5 in the side guide tunnel 2 is constructed. This construction is the second-stage secondary lining 52 construction. One end of the second-stage secondary lining 52 is connected to the first-stage secondary lining 51 constructed in step S5, and the other end is connected to the bottom longitudinal beam 4 at the arch foot. During the formwork construction of the secondary lining 5, grouting steel pipes 8 are pre-embedded. After the secondary lining 5 is poured and reaches its design strength, concrete is backfilled and injected between the secondary lining 5 and the initial support 9 through the pre-embedded grouting steel pipes 8 to strengthen the connection between the secondary lining 5 and the initial support 9.

[0058] S8. Excavate downwards: Refer to... Figure 5After the completion of the second phase of secondary lining 52, a continuous arch was formed. Once the arch concrete reached its design strength, the construction was divided into several sections along the longitudinal direction of the subway station. Excavation was carried out layer by layer down to the bottom elevation of the subway station's foundation slab, and a cushion layer was poured. The sidewall support and waterproofing layer of the foundation slab were then constructed in sections. The sidewall support of the foundation pit was achieved using a wire mesh and shotcrete method.

[0059] After construction is completed, the subway station's base slab, base beams, and side walls will be constructed to complete the main structure of the station.

[0060] The implementation principle of the large-section arch cover method for underground excavation of subway stations in this application embodiment is as follows: By setting up a central column pile foundation 61 and a steel pipe concrete column 62 in the small pilot tunnel 1 to support the upper longitudinal beam 3, the secondary lining 5 of the side pilot tunnel 2 and the upper longitudinal beam 3 are cast into one piece. This allows the lateral pressure of the surrounding rock strata reached by the arch cover system provided in this application to be transferred to the foundation through the upper longitudinal beam 3 and the pile support system 6, making the large-section arch cover structure stress-balanced and stable. Only one central small pilot tunnel 1 is excavated, and the side pilot tunnel 2 connected to the small pilot tunnel 1 is directly excavated. The excavation process of the side pilot tunnel 2 is carried out simultaneously with the construction of the pile support system 6 and the upper longitudinal beam 3. Compared with the traditional arch cover method construction, the construction procedures are simplified and the construction period is short. The construction method of this application provides a method for underground excavation of large-section arch cover in rock strata with good geological conditions and less developed surface water. It not only meets the need to shorten the construction period, but also simplifies the construction procedures, creating good economic benefits for the construction of subway stations.

[0061] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for constructing subway stations using the large-section arch cover method with tunnel excavation, characterized in that: The construction method includes the excavation of three pilot tunnels, with the middle pilot tunnel being a single small pilot tunnel (1), and the pilot tunnels on both sides of the small pilot tunnel (1) being side pilot tunnels (2); the construction method includes: S1. Construct advanced anchor bolts around the outline of the small pilot tunnel (1) to be excavated; S2. Excavate a small pilot tunnel (1) and perform initial support (9). S3. Excavate multiple pile holes (63) downward along the longitudinal direction of the small guide tunnel (1) in the small guide tunnel (1), and construct pile foundations and support columns in sequence from the bottom of the pile holes (63) upward, without constructing the lower guide tunnel; S4. Construct advanced anchor bolts around the outline of the side guide tunnel (2) to be excavated, and excavate the side guide tunnels (2) on both sides of the small guide tunnel (1) and construct the initial support (9) of the side guide tunnel (2). S5. Construct the top longitudinal beam (3) inside the small guide tunnel (1). The top longitudinal beam (3) is supported by the support column and is poured along the longitudinal direction of the small guide tunnel (1). S6. The bottom longitudinal beam (4) of the construction side guide tunnel (2); S7. Remove the initial support (9) on both sides of the small pilot tunnel (1) and construct the secondary lining (5) of the pilot tunnel (2). S8. Excavate the soil layer downwards in stages to the design bottom slab elevation.

2. The method for constructing a subway station using the large-section arch cover method with tunnel excavation as described in claim 1, characterized in that: Both the small pilot tunnel (1) and the side pilot tunnel (2) are excavated using the step method.

3. The method for constructing a subway station using the large-section arch cover method with tunnel excavation as described in claim 1, characterized in that: In step S3, the pile hole (63) is excavated and the side wall of the pile hole (63) is poured first. Then, the pile foundation (61) of the middle column is poured from the bottom of the pile hole (63) upwards, and the steel pipe column is hoisted into the pile hole. The steel pipe column is connected and fixed to the pile foundation (61) of the middle column. After the pile foundation (61) of the middle column is poured, the core concrete of the steel pipe column is poured to form a steel pipe concrete column (62).

4. The method for constructing a subway station using the large-section arch cover method with tunnel excavation as described in claim 1, characterized in that: During the pouring of the top longitudinal beam (3), the first stage secondary lining (51) is poured simultaneously.

5. The method for constructing a subway station using the large-section arch cover method with tunnel excavation as described in claim 1, characterized in that: Simultaneously excavate the earthwork in the two side guide tunnels (2), and the excavation progress of the adjacent small guide tunnels (1) and side guide tunnels (2) is staggered by no less than 10m.

6. The method for constructing a subway station using the large-section arch cover method with tunnel excavation as described in claim 1, characterized in that: When constructing the initial support (9) and the secondary lining (5), grouting steel pipes (8) need to be pre-embedded between the initial support (9) and the side wall of the guide tunnel, and between the secondary lining (5) and the initial support (9).

7. The method for constructing a subway station using the large-section arch cover method with tunnel excavation as described in claim 1, characterized in that: There is a gap (7) between the top of the top longitudinal beam (3) and the initial support (9) of the small guide tunnel (1). The gap (7) is backfilled and compacted with micro-expansion concrete of the same grade as the main structure.

8. The method for constructing a subway station using the large-section arch cover method with tunnel excavation as described in claim 1, characterized in that: The arch foot of the secondary lining (5) of the side guide tunnel (2) is supported above the bottom longitudinal beam (4).

9. The method for constructing a subway station using the large-section arch cover method with tunnel excavation as described in claim 1, characterized in that: The construction of the pile foundation and support columns inside the small pilot tunnel (1) can be carried out simultaneously with the excavation of the side pilot tunnel (2) and the construction of the bottom longitudinal beam (4).

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