A kind of underground structure constructed by pile digging and construction and its construction method

Abstract

The embodiments of the present application relate to the technical field of underground structure construction, and in particular to a pile-dig underground structure and its construction method. This construction method can avoid the transportation, processing, positioning, measurement, hoisting and fixing of steel pipe columns in narrow guide tunnels, and cancels the construction of the lower guide tunnel and the strip foundation in the lower guide tunnel. It can solve the construction difficulties of the existing "hole-column" construction method, such as high construction difficulty, poor working environment, high requirements for positioning accuracy and differential settlement control, complex beam-column node structure, narrow construction space under the slab, slow construction speed, and high construction difficulty, and can reduce temporary projects, speed up construction progress and reduce project costs.

Description

Technical Field

[0001] The present application relates to the technical field of underground structure construction, and in particular to an underground structure constructed by pile digging and concealed excavation and a construction method thereof. Background Art

[0002] In the 1990s, the pile method was successfully applied for the first time in Beijing Metro Fuba Line, achieving good ground control effects. It was subsequently widely used in Beijing Metro Line 4 and Line 10 Phase I, accumulating a wealth of experience. It has now become the mainstream construction method for Beijing Metro underground excavation stations.

[0003] At present, the construction sequence of the secondary lining of the "hole column" method includes three construction methods: full reverse construction, full forward construction, and half forward and half reverse construction. Among them, although the hole column reverse construction method saves a lot of temporary cross braces, the construction space is narrow and the construction speed is slow. In addition, due to space limitations at the reverse construction joints, there are difficulties in reserving and protecting waterproof boards during construction, and it is not easy to ensure the waterproof quality of the construction joints. Therefore, it is easy to cause water leakage at the reverse construction joints. When pouring concrete at the bottom of the construction joint of the reverse construction structure, due to the shrinkage of concrete solidification, it is difficult to pour densely at the construction joints, and gaps appear, which causes quality defects and safety hazards, affecting the quality of the structural entity and normal use.

[0004] The steel tube concrete column is the main load-bearing member in the structure, and the quality of the steel tube column concrete is related to the safety and stability of the entire structure. Due to the small cross-section of the pilot tunnel and the limited working space, the installation accuracy of the steel tube column and the quality of the steel tube column concrete construction are difficult to guarantee. Due to the clearance limit of the pilot tunnel, the steel tube column needs to be segmented, resulting in a large number of nodes. Therefore, the quality of the steel tube column connection nodes needs to be strictly controlled, and the middle column needs to use a steel tube column. The transportation, processing, positioning, measurement, hoisting and fixing of the steel tube column are carried out in a very narrow pilot tunnel. The construction is difficult, the working environment is poor, the positioning accuracy and differential settlement control requirements are high, and the beam-column node structure is complex. Whether the node can achieve effective transmission of internal force depends on the structural design, construction accuracy and construction quality of the node.

[0005] The traditional method of building columns in a cave often uses horizontal steel supports. The transportation and installation of steel supports in a closed environment are difficult, the construction speed is slow, and the cost is high.

[0006] In summary, the existing "hole-column" construction method adopts the reverse construction method, which has the disadvantages of great difficulty in the transportation and processing, positioning and measurement, hoisting and fixing of steel pipe columns, poor working environment, high requirements for positioning accuracy and differential settlement control, complex beam-column node structure, narrow construction space under the slab, slow construction speed and great construction difficulty; while the traditional forward construction method has the disadvantages of great difficulty in transporting and installing the horizontal steel support, slow construction speed and high cost. Summary of the invention

[0007] The embodiment of the present application provides a tunnel pile dark excavation and construction method for an underground structure. Since the construction method can avoid the operations of transportation, processing, positioning, measurement, hoisting and fixing of steel pipe columns in a narrow guide tunnel, and cancels the lower guide tunnel and the strip foundation construction in the lower guide tunnel, it can solve the construction difficulties of the existing "tunnel column" construction method, such as high construction difficulty, poor working environment, high requirements for positioning accuracy and differential settlement control, complex beam-column node structure, narrow construction space under the slab, slow construction speed, and high construction difficulty. It can also reduce temporary projects, speed up construction progress and reduce project costs.

[0008] The present invention provides a method for constructing an underground structure by dark excavation of piles, which method comprises the following steps:

[0009] A pilot tunnel is excavated through the cross passage, and the end of the pilot tunnel is sealed after it is dug to the end;

[0010] Temporary columns, permanent columns and side piles are constructed downwards in the pilot tunnel, and the crown beam is cast on the top of the side piles, and the top longitudinal beam and waterproof layer are cast on the top of the temporary columns and permanent columns. The steel bars of the main arch secondary lining and top arch are reserved for connection, and the waterproof layer is reserved for joints. The primary support of the main arch in the pilot tunnel on the top side of the side piles is constructed, and the backfill in the pilot tunnel is constructed;

[0011] A conduit for the main arch crown is drilled in the transverse passage, and the conduit for the main arch crown is pre-grouted to reinforce the stratum. The excavation is symmetrical to the steps on both side arches and the middle arch, and support is provided.

[0012] Continue to excavate the side arches and the steps under the middle arch, and close the initial support;

[0013] Construct the secondary lining, side walls and waterproof layer of the main arch, reserve steel bars for connection with subsequent structures, and reserve joints for the waterproof layer;

[0014] Excavate in steps to 0.5m below the diagonal brace, and construct steel waist beams and diagonal braces until the excavation reaches the base;

[0015] Lay the waterproof layer, cast the permanent columns and the bottom longitudinal beams at the bottom of the permanent columns, and remove the temporary columns from top to bottom after the permanent columns reach the design strength;

[0016] Level the ground formwork, backfill the fertilizer tank, lay the cushion layer and waterproof layer, and cast the remaining base plate structure;

[0017] Backfill the fertilizer tank, lay the waterproof layer from bottom to top, and cast the side walls and middle plate;

[0018] The fertilizer trough is backfilled, a waterproof layer is laid, the remaining side walls are poured, and the main structure is closed.

[0019] Preferably, before excavating the guide tunnel through the transverse passage, the method further includes: installing a large pipe shed, a conduit or deep hole grouting to reinforce the stratum, and reinforcing the transverse passage in the breach entry area;

[0020] The construction of the pilot tunnel through the cross channel includes:

[0021] First dig the side guide tunnel, then the middle guide tunnel, and carry out real-time monitoring and measurement.

[0022] Preferably, the temporary columns, permanent columns and pile foundations of the side piles are all constructed using a mechanical hole-forming process, and the temporary columns and permanent columns are staggered in arrangement.

[0023] Preferably, the permanent columns are cast-in-place piles, the pile foundations of the permanent columns below the base are cast-in-place pile foundations, the permanent columns above the base use steel lattice columns as supports for the top longitudinal beams, and the pile holes are backfilled with fine sand.

[0024] Preferably, the pile foundation of the permanent column adopts a single pile or multiple piles. When the pile foundation of the permanent column adopts the form of multiple piles, the bottom longitudinal beam is a multiple pile cap.

[0025] Preferably, when symmetrically excavating to the steps on both side arches and the middle arch and performing support, the construction of the middle arch and the side arch are staggered by a certain distance.

[0026] Preferably, after closing the initial support and before constructing the secondary lining of the main arch, the side wall and the waterproof layer, it also includes:

[0027] After the primary support of the main arch reaches the designed strength, the guide tunnel grid within the permanent structure section is removed.

[0028] Preferably, the main arch secondary lining is constructed by segmented construction to form a permanent transverse load-bearing multi-arch and multi-span structure located at the top of the proposed underground space, and connected with the crown beam at the top of the side piles to form a permanent transverse arch cover-side pile-temporary column bearing system.

[0029] Preferably, excavation is performed in steps to 0.5 m below the diagonal support, specifically including:

[0030] Mechanical excavation is used to reach 300mm above the cushion layer, and the rest is removed manually;

[0031] During the excavation, the mesh spraying support between the piles is constructed.

[0032] Preferably, when pouring the permanent column and the bottom longitudinal beam at the bottom of the permanent column, the concrete at the beam-column joint is vibrated to ensure that the pouring is dense and the top longitudinal beam and the permanent column, as well as the pile under the permanent column and the bottom longitudinal beam are tightly connected;

[0033] When pouring the side wall, the joint between the first poured side wall part and the later poured side wall part is constructed by funnel pouring method, a grouting pipe and two layers of water-swelling polyurethane water-stop glue are used at the construction joint, and a cement-based penetrating crystalline waterproof coating is applied on the surface of the construction joint.

[0034] In addition, the embodiment of the present application further provides a hole pile dark excavation and construction underground structure, which is constructed by any one of the construction methods provided by the above technical solutions and includes a bottom plate, a side wall, a main arch secondary lining, a main arch primary support, a middle plate, side piles and a middle pile;

[0035] The bottom plate, the side wall, the main arch secondary lining, the side piles, the middle piles and the middle plate are cast as an integrated structure and surround to form a tunnel; the side wall is supported between the bottom plate and the main arch secondary lining; the main arch primary support is formed on the top of the main arch secondary lining; the middle plate is horizontally fixedly connected between the side walls;

[0036] The side piles are arranged on the outside of the side wall to support the ends of the secondary lining of the main arch and the primary support of the main arch;

[0037] The middle pile is arranged between the side walls and is formed by permanent columns for supporting the secondary lining of the main arch.

[0038] Preferably, a steel waist beam is provided on the side of the side piles facing the side wall, and a diagonal brace is connected to the steel waist beam;

[0039] Concrete is poured in the fertilizer trough between the side piles and the side wall.

[0040] Preferably, the diagonal brace is an anchor cable.

[0041] Preferably, the main arch secondary lining includes a middle arch and a side arch;

[0042] Top longitudinal beams are arranged between the middle arches and between the middle arches and the side arches; a crown beam is arranged at the other end of the side arch;

[0043] The top longitudinal beam is located on the top of the middle pile and connects the middle pile and the secondary lining of the main arch into an integrated structure; concrete is filled between the top longitudinal beam and the primary support of the main arch;

[0044] The crown beam is located on the top of the side piles and connects the side piles and the main arch secondary lining into an integrated structure.

[0045] Preferably, a guide hole is provided on the top of the side pile, and the space enclosed by the guide hole, the crown beam and the primary support of the main arch is filled with concrete;

[0046] A plurality of conduits for internal grouting are distributed on the top of the pilot tunnel and the top of the primary support of the main arch.

[0047] Preferably, a plurality of the conduits are evenly arranged along the top of the guide tunnel and the top of the primary branch of the main arch.

[0048] Preferably, the side piles and the center piles are both formed by mechanical drilling and casting construction.

[0049] Preferably, the bottom of the side pile is embedded below the bottom plate.

[0050] The technical solution provided in the embodiment of the present application can avoid the transportation, processing, positioning, measurement, hoisting and fixing of steel pipe columns in narrow guide tunnels, and cancel the construction of the lower guide tunnel and the strip foundation in the lower guide tunnel. It can solve the construction difficulties of the existing "hole-column" construction method, such as high construction difficulty, poor working environment, high positioning accuracy and differential settlement control requirements, complex beam-column node structure, narrow construction space under the plate, slow construction speed, and high construction difficulty. It can also reduce temporary projects, speed up construction progress and reduce project costs. In addition, the bottom of the side pile is embedded below the base, which can avoid lateral displacement of the bottom of the side pile and reduce construction risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0052] Figure 1 A process flow chart of a method for constructing an underground structure by dark excavation of piles provided in an embodiment of the present application;

[0053] Figure 2-11 To adopt Figure 1 Schematic diagram of the process changes of the construction method provided in the construction process when forming an underground structure. DETAILED DESCRIPTION

[0054] In order to make the technical solutions and advantages in the embodiments of the present application more clearly understood, the exemplary embodiments of the present application are further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than an exhaustive list of all the embodiments. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0055] The construction method provided in the embodiment of the present application is used to form an underground structure in underground construction. The underground structure can be used in the construction process of a subway or in other underground construction processes.

[0056] Embodiment 1

[0057] The construction method of the underground structure provided by the embodiment of the present application is as follows: Figure 1 As shown, the construction method comprises the following steps:

[0058] Step S10, excavating a pilot tunnel through a transverse passage, and sealing the end of the pilot tunnel after the end is dug; Figure 2As shown in the structure, four guide holes were dug for construction, including two side guide holes and a middle guide hole located between the two side guide holes. When the guide holes are excavated through the cross channel, the side guide holes can be excavated first, and then the middle guide hole can be excavated, and support, real-time monitoring and measurement can be carried out; before the guide holes are excavated through the cross channel, the following can also be included: installing a large pipe shed, a conduit or deep hole grouting to reinforce the stratum, and reinforcing the cross channel in the breach area; the structure formed after construction can refer to Figure 2 ,like Figure 2 The guide tubes located at the top of each pilot tunnel in the structure have been installed before the pilot tunnel is excavated, and grouting is injected into the guide tubes to reinforce the bottom layer of the pilot tunnel, thereby improving the safety of construction; during construction, grouting is promptly backfilled behind the primary support, and real-time monitoring and measurement are carried out, and the end of the pilot tunnel is promptly sealed after it reaches the end;

[0059] Step S20, construct temporary columns, permanent columns and side piles downward in the pilot tunnel, cast a crown beam on the top of the side piles, cast a top longitudinal beam and a waterproof layer on the top of the temporary columns and permanent columns, reserve the main arch secondary lining top arch steel bar connection, reserve the waterproof layer joint, construct the main arch primary support in the pilot tunnel on the top side of the side piles, and backfill the pilot tunnel; Figure 3 As shown in the structure, the construction of the side piles, temporary columns and permanent columns all starts from the pilot hole, and the top beam is cast on the top of the side piles to form a crown beam, and the top longitudinal beam is cast on the top of the temporary columns and permanent columns to form a top longitudinal beam; in order to improve the firmness and stability of the underground structure foundation, temporary columns are provided with temporary column lower piles, permanent columns are provided with permanent column lower piles, and side piles are provided with side pile lower piles; and in the process of constructing temporary columns, permanent columns and side piles, the pile foundations of temporary columns, permanent columns and side piles can all be constructed by mechanical hole-forming technology, and the temporary columns and permanent columns are staggered; permanent columns can be in the form of cast-in-place piles, the pile foundations of permanent columns below the base are cast-in-place pile foundations, and the permanent columns above the base use steel lattice columns as the supports of the top longitudinal beams, and the pile holes are backfilled with fine sand; the pile foundations of permanent columns are single piles or multiple piles, and when the pile foundations of permanent columns are in the form of multiple piles, the bottom longitudinal beam can be a multi-pile cap;

[0060] Step S30, a main arch crown conduit is set in the transverse passage, and the conduit of the main arch crown is pre-grouted to reinforce the stratum, and symmetrical excavation is performed to the steps of the two side arches and the middle arch and support is performed; when symmetrical excavation is performed to the steps of the two side arches and the middle arch and support is performed, the construction of the middle arch and the construction of the side arch are staggered by a certain distance; during the construction, grouting is performed in time behind the primary support and real-time monitoring and measurement are performed; Figure 4 As shown in the structure, the stratum of the vault is reinforced by setting a grouting conduit at the vault of the main arch;

[0061] Step S40, continue to excavate the side arches and the steps under the middle arch, and close the initial support; Figure 5As shown in the structure, after excavating the side arches and the steps under the middle arch, the excavation surface is made flush with the bottom surface of the pilot tunnel, and the initial support at the top forms a complete structure;

[0062] Step S50, after the primary support of the main arch reaches the designed strength, the guide hole grid within the permanent structure section is removed; the secondary lining, side wall and waterproof layer of the main arch are constructed, and steel bars are reserved for connection with subsequent structures, and joints are reserved for the waterproof layer; the structure after the secondary lining of the main arch is constructed as shown in FIG. Figure 6 As shown in the figure, when dismantling the guide tunnel grid steel frame, the longitudinal dismantling length should be strictly controlled according to monitoring measurement, and the dismantling length should not be greater than 6m; in the process of constructing the main arch secondary lining, the segmented construction method is adopted to make the main arch secondary lining form a permanent transverse force-bearing multi-arch and multi-span structure located at the top of the proposed underground space, and connected with the crown beam at the top of the side pile to form a permanent transverse arch cover-side pile-temporary column bearing system;

[0063] Step S60, excavate step by step to 0.5m below the diagonal brace, and construct steel waist beams and diagonal braces until the excavation reaches the base; Figure 7 As shown in the structure, one end of the diagonal brace is fixedly connected to the steel waist beam to support the steel waist beam to strengthen the structural strength; the diagonal brace can be supported by anchor cables or other rigid or flexible structures; during the excavation process, in order to avoid a large disturbance of the bottom soil of the pit, mechanical excavation can only be dug to a position 300mm above the cushion layer, and the rest is excavated manually, and mesh spraying support is carried out between piles during the excavation construction;

[0064] Step S70, laying a waterproof layer, casting permanent columns and bottom longitudinal beams at the bottom of permanent columns, and breaking temporary columns from top to bottom after the permanent columns reach the design strength; Figure 8 As shown in the structure, during the construction process, in order to improve the reliability and safety of the support during the construction process, multiple temporary columns are set between the permanent columns. The temporary columns and the permanent columns are staggered. When digging to the base, a waterproof layer is laid on the base, and then the permanent columns and the bottom longitudinal beams at the bottom of the permanent columns are cast. After the structural strength of the permanent columns reaches the design strength, the temporary columns are removed from top to bottom. The temporary columns are the process support columns. When casting the permanent columns and the bottom longitudinal beams at the bottom of the permanent columns, the concrete at the beam-column joints is vibrated to ensure that the casting is dense, and the top longitudinal beams and the permanent columns, as well as the piles under the permanent columns and the bottom longitudinal beams are tightly connected.

[0065] Step S80, leveling the ground form, backfilling the fertilizer tank, laying the cushion layer and waterproof layer, and pouring the remaining base plate structure; Fig. 9 As shown in the structure, the entire bottom plate structure is cast, and a partial side wall is formed on the side of the bottom plate close to the side pile, and a fertilizer trough is formed between the side wall and the side pile, and the fertilizer trough is backfilled, which can be backfilled with concrete;

[0066] Step S90, backfill the fertilizer tank, lay a waterproof layer from bottom to top, and cast the side walls and middle plate; Fig.10 As shown in the structure, on the basis of casting to form the bottom plate structure, the lower side wall and the middle plate are cast continuously. The middle plate is horizontally arranged between the two side walls and cast as an integrated structure with the side wall. A fertilizer trough is formed between the lower side wall and the side piles, and the fertilizer trough is backfilled to prevent the formation of gaps between the side wall and the side piles, which affects the firmness and safety of the underground structure.

[0067] Step S100, backfill the fertilizer tank, lay a waterproof layer, cast the remaining side walls, and close the main structure; Fig.11 As shown in the structure, the remaining side wall between the lower side wall and the second lining of the main arch is cast to form an integral structure of the side wall, and the main structure is closed to form an underground space in the middle; when casting the side wall, the joint between the first cast side wall part and the later cast side wall part is constructed by funnel casting method, and a grouting pipe and two layers of water-swelling polyurethane water-stopping glue are used at the construction joint, and a cement-based penetrating crystalline waterproof coating is applied on the surface of the construction joint.

[0068] The above construction method can form Fig.11 The underground structure shown in the figure can avoid the transportation, processing, positioning, measurement, hoisting and fixing of steel pipe columns in narrow guide tunnels by adopting the above-mentioned construction method, and cancel the construction of the lower guide tunnel and the strip foundation in the lower guide tunnel. It can solve the construction difficulties of the existing "tunnel-column" construction method, such as high construction difficulty, poor working environment, high requirements for positioning accuracy and differential settlement control, complex beam-column node structure, narrow construction space under the slab, slow construction speed and high construction difficulty, and can also reduce temporary projects, speed up construction progress and reduce project costs.

[0069] In addition, the bottom of the side pile is embedded below the base, which can prevent the bottom of the side pile from shifting sideways and reduce construction risks.

[0070] Embodiment 2

[0071] The present application also provides a method for constructing an underground structure by digging piles in a hole, such as Fig.11 As shown in the structure, the underground structure of pile excavation is constructed by any one of the construction methods provided in the above embodiments, and includes a bottom plate, side walls, a main arch secondary lining, a main arch primary support, a middle plate, side piles and a middle pile; the bottom plate, the side walls, the main arch secondary lining, the side piles, the middle piles and the middle plate are cast as an integrated structure, and surround to form a tunnel; the side walls are supported between the bottom plate and the main arch secondary lining; the main arch primary support is formed at the top of the main arch secondary lining; the middle plate is horizontally fixedly connected between the side walls; the side piles are arranged on the outside of the side walls for supporting the ends of the main arch secondary lining and the main arch primary support; the middle piles are arranged between the side walls and are formed by permanent columns for supporting the main arch secondary lining.

[0072] The strip foundation of the base is eliminated in the above-mentioned underground structure constructed by dark excavation of piles. Therefore, the construction of the lower guide tunnel and the strip foundation in the lower guide tunnel can be eliminated during the construction process, so that when constructing the above-mentioned underground structure, the construction difficulty can be reduced, the construction progress can be accelerated, the construction speed can be increased, and the project cost can be reduced; and the bottom of the side piles is embedded below the base, which can avoid lateral displacement of the bottom of the side piles, which is beneficial to reducing construction risks.

[0073] In a specific implementation manner, Fig.11 As shown in the structure, a steel waist beam is provided on the side of the side pile facing the side wall, and a diagonal brace is connected to the steel waist beam; concrete is poured in the fertilizer trough between the side pile and the side wall. The diagonal brace is used to support the side pile to enhance the structural strength and rigidity of the side pile and the underground structure. The diagonal brace can be a flexible component such as an anchor cable or a rigid component.

[0074] Specifically, Figure 5 and Figure 6 As shown in the structure, the main arch secondary lining may include a plurality of middle arches and side arches; top longitudinal beams are arranged between the middle arches and between the middle arches and the side arches; a cap beam is arranged at the other end of the side arch; the top longitudinal beam is located on the top of the middle pile, and connects the middle pile with the main arch secondary lining into an integrated structure; concrete is filled between the top longitudinal beam and the primary support of the main arch; the cap beam is located on the top of the side pile, and connects the side pile with the main arch secondary lining into an integrated structure.

[0075] Since the secondary lining of the main arch includes multiple middle arches and side arches, the segmented construction method can be adopted in the process of pouring the secondary lining of the main arch, which is beneficial to reducing the span and height of the middle arch, thereby reducing the difficulty of construction and enhancing the structural strength of the secondary lining of the main arch, so that the secondary lining of the main arch forms a permanent transverse force-bearing multi-arch and multi-span structure located at the top of the proposed underground space, and is connected with the crown beam on the top of the side pile to form a permanent transverse arch cover-side pile-temporary column bearing system.

[0076] For the convenience of construction, a guide hole is set at the top of the side pile, and the space surrounded by the guide hole, the crown beam and the primary support of the main arch is filled with concrete; multiple conduits for internal grouting are distributed on the top of the guide hole and the top of the primary support of the main arch. The conduits can be steel pipes. Multiple conduits are evenly arranged along the top of the guide hole and the top of the primary support of the main arch. The side piles and the middle piles are formed by mechanical drilling and pouring. The bottom of the side pile is embedded below the bottom plate.

[0077] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0078] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A construction method for underground structure by dark excavation of piles, characterized in that: The following steps are involved: Install large pipe sheds, conduits or deep hole grouting to reinforce the strata, and reinforce the transverse passages in the breach entry area; Excavating a pilot tunnel through a transverse passage, and sealing the end of the pilot tunnel after the end is excavated; Excavating a pilot tunnel through a transverse passage specifically includes: first excavating a side pilot tunnel, then excavating a middle pilot tunnel, and performing real-time monitoring and measurement; Temporary columns, permanent columns and side piles are constructed downwards in the pilot tunnel, and a crown beam is cast on the top of the side piles, and a top longitudinal beam and a waterproof layer are cast on the top of the temporary and permanent columns. Reinforcement connection of the main arch secondary lining and top arch is reserved, and joints are reserved for the waterproof layer. The primary support of the main arch in the pilot tunnel on the top side of the side piles is constructed, and backfill construction is carried out in the pilot tunnel; the pile foundations of temporary columns, permanent columns and side piles are constructed using mechanical hole-forming technology, and the temporary columns and permanent columns are arranged staggered; permanent columns are cast-in-place piles, and the pile foundations of permanent columns below the base are cast-in-place pile foundations, and the permanent columns above the base use steel lattice columns as the support of the top longitudinal beam, and the pile holes are backfilled with fine sand; the pile foundations of permanent columns are single piles or multiple piles. When the pile foundations of permanent columns are multiple piles, the bottom longitudinal beam is a multi-pile cap; The main arch crown conduit is set in the transverse passage, and the conduit at the main arch crown is pre-grouted to reinforce the stratum. The excavation is symmetrical to the steps on both side arches and the middle arch and support is provided. The construction of the middle arch and the side arch is staggered at a certain distance. Continue to excavate the side arches and the steps under the middle arch, and close the initial support; After the primary support of the main arch reaches the designed strength, the guide tunnel grid within the section of the permanent structure shall be removed; Construct the secondary lining, side walls and waterproof layer of the main arch, reserve steel bars for connection with subsequent structures, and reserve joints for the waterproof layer; Excavate in steps to 0.5m below the diagonal brace, and construct steel waist beams and diagonal braces until the excavation reaches the base; Lay the waterproof layer, cast the permanent columns and the bottom longitudinal beams at the bottom of the permanent columns, and remove the temporary columns from top to bottom after the permanent columns reach the design strength; Level the ground formwork, backfill the fertilizer tank, lay the cushion layer and waterproof layer, and cast the remaining base plate structure; Backfill the fertilizer tank, lay the waterproof layer from bottom to top, and cast the side walls and middle plate; The fertilizer trough is backfilled, a waterproof layer is laid, the remaining side walls are poured, and the main structure is closed.

2. The construction method according to claim 1, characterized in that: The secondary lining of the main arch is constructed by segmented construction method to form a permanent transverse load-bearing multi-arch and multi-span structure located at the top of the proposed underground space, and connected with the crown beam at the top of the side piles to form a permanent transverse arch cover-side pile-temporary column bearing system.

3. The construction method according to claim 1, characterized in that: Excavate in steps to 0.5m below the diagonal support, including: Mechanical excavation is used to reach 300mm above the cushion layer, and the rest is removed manually; During the excavation, the mesh spraying support between the piles is constructed.

4. The construction method according to any one of claims 1 to 3, characterized in that: When pouring permanent columns and bottom longitudinal beams at the bottom of permanent columns, focus on vibrating the concrete at the beam-column joints to ensure that the pouring is dense and that the top longitudinal beam and permanent columns, as well as the piles under the permanent columns and the bottom longitudinal beams are tightly connected; When pouring the side wall, the joint between the first poured side wall part and the later poured side wall part is constructed by funnel pouring method, a grouting pipe and two layers of water-swelling polyurethane water-stop glue are used at the construction joint, and a cement-based penetrating crystalline waterproof coating is applied on the surface of the construction joint.

5. An underground structure constructed by the construction method according to any one of claims 1 to 4, characterized in that: It includes the bottom plate, side wall, secondary lining of main arch, primary support of main arch, middle plate, side piles and middle piles; The bottom plate, the side wall, the main arch secondary lining, the side piles, the middle piles and the middle plate are cast as an integrated structure and surround to form a tunnel; the side wall is supported between the bottom plate and the main arch secondary lining; the main arch primary support is formed on the top of the main arch secondary lining; the middle plate is horizontally fixedly connected between the side walls; The side piles are arranged on the outside of the side wall to support the ends of the secondary lining of the main arch and the primary support of the main arch; The middle pile is arranged between the side walls and is formed by permanent columns for supporting the secondary lining of the main arch.

6. The underground structure according to claim 5, characterized in that A steel waist beam is provided on the side of the side piles facing the side wall, and a diagonal brace is connected to the steel waist beam; Concrete is poured in the fertilizer trough between the side piles and the side wall.

7. The underground structure according to claim 5, characterized in that The main arch secondary lining includes a middle arch and a side arch; Top longitudinal beams are arranged between the middle arches and between the middle arches and the side arches; a crown beam is arranged at the other end of the side arch; The top longitudinal beam is located on the top of the middle pile and connects the middle pile and the secondary lining of the main arch into an integrated structure; concrete is filled between the top longitudinal beam and the primary support of the main arch; The crown beam is located on the top of the side piles and connects the side piles and the main arch secondary lining into an integrated structure.

8. The underground structure according to claim 5, characterized in that: A guide hole is arranged on the top of the side pile, and the space enclosed by the guide hole, the crown beam and the primary support of the main arch is filled with concrete; A plurality of conduits for internal grouting are distributed on the top of the pilot tunnel and the top of the primary support of the main arch.

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