Subway station foundation pit construction method combining open excavation and cover excavation from top to bottom

Abstract

A subway station foundation pit construction method combining open excavation and cover excavation from top to bottom combines processes and advantages of a traditional open excavation method and a cover excavation method, after underground diaphragm walls are installed, foundation pit top plates arranged at intervals are manufactured between the underground diaphragm walls on the two sides, open-air open grooves are reserved between the foundation pit top plates, open excavation is conducted at the positions of the open grooves, and the open excavation is conducted at the positions of the open grooves; cover excavation is conducted on the bottom of the foundation pit top plate, the overall construction technology is simple, rapid and economical, the influence of construction on surrounding traffic and environment can be limited within a certain time and space range, earthwork transportation is more convenient, the foundation pit top plate provides more construction site space for construction machinery, and the construction efficiency is improved. Meanwhile, the foundation pit top plate provides necessary support for the underground diaphragm walls on the two sides, additional arrangement of supporting components in the follow-up construction process can be effectively reduced, meanwhile, the foundation pit top plate can be used as a top plate of a subway station and does not need to be dismantled, and procedures and cost are greatly saved.

Description

Technical Field

[0001] The invention relates to the technical field of foundation pit construction, in particular to a top-down excavation and cover combined foundation pit construction method for a subway station. Background Art

[0002] Urban rail transit civil construction mainly includes the excavation and construction of stations and section tunnels, parking lot civil construction, track laying and related civil construction supporting construction. For subway construction, it is generally necessary to first construct the subway station foundation pit. The existing construction methods include open cut and covered cut. The open cut method is to excavate earth and stone from the ground to the designed elevation, then construct the main structure of the tunnel from the base upwards, and finally backfill the foundation pit and restore the ground. The advantage of the open cut method is that the construction technology is simple, fast and economical, but its disadvantages are also very obvious. The construction has a relatively large impact on the traffic around the construction area in terms of time and space. When it is necessary to ensure that the roads in the construction area are unobstructed, the construction of underground stations can adopt the cover and cut method. The cover and cut method is a construction method in which the ground is excavated downward to a certain depth, the top is closed, the ground is restored, and the entire lower engineering construction is carried out in a closed space. Although the cover and cut method limits the impact of urban rail transit civil construction on the surrounding traffic and environment to a certain time and space range, its earthwork transportation and processing are more cumbersome than the open cut method. In addition, both the open cut method and the cover and cut method require a large number of concrete structure supports between the ground-connected walls during the excavation process. Not only is the process operation more complicated, but the concrete structure supports will also be dismantled in the later construction process, resulting in varying degrees of waste. Summary of the invention

[0003] The purpose of the present invention is to provide a subway station foundation pit construction method that combines open excavation and covered excavation from top to bottom, combines the advantages of open excavation and covered excavation, and adopts a top-down structural construction method to pre-fabricate the foundation pit top plate as a supporting member, effectively reducing the addition of concrete structure supports in the subsequent construction process, thereby solving the problems in the prior art.

[0004] The technical solution adopted by the present invention to solve its technical problems is: a method for constructing a subway station foundation pit by combining open cover and excavation from top to bottom, comprising the following steps: ① digging a shallow pit downward in the area where the foundation pit is located, and excavating guide grooves downward on both sides of the shallow pit in the length direction, wherein the sum of the depths of the shallow pit and the guide groove is the same as the depth of the foundation pit; ② after the excavation of the guide grooves on both sides in step ① is completed, a plurality of groups of first prefabricated underground continuous walls and second prefabricated underground continuous walls arranged at intervals are installed in the guide grooves, wherein the length of the first prefabricated underground continuous wall is greater than that of the second prefabricated underground continuous wall; ③ after the prefabricated underground continuous walls in step ② are installed in the guide grooves, Drill several groups of holes downward on the ground between the prefabricated underground continuous walls, each group of holes is located between the second prefabricated underground continuous walls on both sides; ④ After the drilling in step ③ is completed, fill each group of holes with steel cages and pour concrete to make support columns; ⑤ After the support columns in step ④ are made, install templates between the prefabricated underground continuous walls on the upper side of each group of support columns, the length of the template is the length between the guide grooves on both sides, and the width of the template spans the joint position between the two ends of the second prefabricated underground continuous wall and the first prefabricated underground continuous wall; ⑥ After the template in step ⑤ is installed, place a steel cage in the template and pour concrete to make the foundation pit top plate, The top plate of the foundation pit is constructed as a whole with the supporting columns at the bottom, the first prefabricated underground continuous walls and the second prefabricated underground continuous walls on both sides, wherein the top plate of the foundation pit spans the joint positions at both ends of a group of second prefabricated underground continuous walls; ⑦ After the top plate of the foundation pit is completed in step ⑥, the template is removed, and the top plates of the foundation pit and the open trenches arranged at intervals are formed on the ground between the prefabricated underground continuous walls. Subsequently, an excavator is used to dig the pit at the position of the open trench, and the excavated soil is pulled away and transferred by the slag machine on the top plate of the foundation pit; ⑧ After the open trench position in step ⑦ is excavated downward to the set depth, the excavator at the bottom of the pit moves to the position at the bottom of the top plates of the foundation pit on both sides. Carry out excavation operations at the location, and use the slag machine at the bottom of the pit to transfer the earthwork to the pit excavated at the position of the open slot. The long-arm excavator on the top plate of the foundation pit transfers the earthwork in the pit to the slag machine on the top plate of the foundation pit, and the earthwork is pulled away and transferred by the slag machine; ⑨ Repeat steps ⑦ and ⑧ alternately until the open slot and the top plate of the foundation pit are both excavated to the depth of the foundation pit, and stop the excavation operation; ⑩ After the excavation of the foundation pit is completed, the top plate of the foundation pit is used as the top plate of the station, and the subway station structure is constructed inside the foundation pit. After the structural construction is completed, the top plate of the foundation pit is covered with earthwork and compacted, the initial road surface is restored, and the construction of the subway station foundation pit is completed. After the template is removed in step ⑦, connecting support components are installed between the two sides of each foundation pit top plate and the corresponding first prefabricated underground continuous wall. The connecting support component is a steel pipe internal support, a reinforced concrete frame internal support, or a steel composite support. Concrete corbel supports are provided on the inner sides of the first prefabricated underground continuous wall and the second prefabricated underground continuous wall, and the concrete corbel supports are located at the lower side of the foundation pit top plate.The length of the first prefabricated underground continuous wall is 8m, the length of the second prefabricated underground continuous wall is 4m, the width of the foundation pit top plate is 8m, the width of the open groove is 4m, and each foundation pit top plate is correspondingly arranged at the middle position of the second prefabricated underground continuous wall. The thickness of the foundation pit top plate is 700-900mm. The number of each group of support columns is four, and the four support columns are located at the four corners of the rectangle respectively. Each support column is aligned with the joint position at both ends of the second prefabricated underground continuous wall. The width distance between adjacent support columns is 4m, and the distance between the support column and the prefabricated underground continuous wall is the same as the length distance between adjacent support columns. The depth of the shallow pit pre-excavated in step ① is 1.5-3m. The set depth of downward excavation at the open groove position in step ⑧ is 1.5-2m. A first reserved steel bar is arranged on the top of the first prefabricated underground continuous wall, a second reserved steel bar is arranged on the top of the second prefabricated underground continuous wall, a third reserved steel bar is arranged on the top of the supporting column, and the first reserved steel bar, the second reserved steel bar and the third reserved steel bar are all located in the top plate of the foundation pit.

[0005] The positive effect of the present invention is that the subway station foundation pit construction method combining open excavation and covered excavation from top to bottom described in the present invention combines the processes and advantages of traditional open excavation and covered excavation. After the underground continuous wall is installed, the foundation pit top plates are made between the underground continuous walls on both sides. An open trench is left between the foundation pit top plates. Open excavation is carried out at the position of the open trench, and covered excavation is carried out at the bottom of the foundation pit top plate. Not only is the overall construction technology simple, fast and economical, but the impact of the construction on the surrounding traffic and environment can also be limited to a certain time and space range, and the transportation of earthwork is more convenient. The foundation pit top plate provides more construction site space for construction machinery. At the same time, the foundation pit top plate also provides necessary support for the underground continuous walls on both sides, which can effectively reduce the addition of supporting components in the subsequent construction process. At the same time, the foundation pit top plate can also be used as the top plate of the subway station without dismantling, which greatly saves the process and cost, and also improves the operation safety during the foundation pit construction process to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 It is a schematic diagram of the completion of step ① of the present invention; Figure 2 It is a schematic diagram of the completion of construction of step ② of the present invention; Figure 3 It is a schematic diagram of the completion of step ③ of the present invention; Figure 4 It is a schematic diagram of the completion of step ④ of the present invention; Figure 5 It is a schematic diagram of the completion of construction of step ⑤ of the present invention; Figure 6 It is a schematic diagram of the completion of step ⑥ of the present invention; Figure 7It is a construction state diagram of step ⑦ of the present invention; Figure 8 It is a construction status diagram of step ⑧ of the present invention. DETAILED DESCRIPTION

[0007] The present invention discloses a method for constructing a subway station foundation pit by combining excavation and cover from top to bottom. Figure 1-8 As shown, the following steps are included: ① Dig a shallow pit downward in the area where the foundation pit is located, and dig guide grooves 12 downward on both sides of the shallow pit in the length direction. The total depth of the shallow pit and the guide groove 12 is the same as the depth of the foundation pit; ② After the excavation of the guide grooves 12 on both sides in step ① is completed, a plurality of groups of first prefabricated underground continuous walls 1 and second prefabricated underground continuous walls 2 arranged at intervals are installed in the guide grooves 12, and the length of the first prefabricated underground continuous wall 1 is greater than the length of the second prefabricated underground continuous wall 2; ③ After the prefabricated underground continuous wall in step ② is installed in the guide groove 12, several groups of holes are punched downward on the ground between the prefabricated underground continuous walls, and each group of holes is located between the second prefabricated underground continuous walls 2 on both sides; ④ After the drilling in step ③ is completed, fill each group of holes with steel cages and pour concrete to make support columns 3; ⑤ After the support columns 3 in step ④ are manufactured, a template 6 is installed between the prefabricated underground continuous walls on the upper side of each group of support columns 3. The length of the template 6 is the length between the guide grooves 12 on both sides, and the width of the template 6 spans the joint position between the two ends of the second prefabricated underground continuous wall 2 and the first prefabricated underground continuous wall 1; ⑥ After the template 6 in step ⑤ is installed, a steel cage is placed in the template 6 and concrete is poured to make a foundation pit top plate 4, which is integrated with the support column 3 at the bottom, the first prefabricated underground continuous wall 1 and the second prefabricated underground continuous wall 2 on both sides, wherein the foundation pit top plate 4 spans the joint positions at both ends of a group of second prefabricated underground continuous walls 2; ⑦ After the foundation pit top plate 4 in step ⑥ is completed, the template 6 is removed, and the foundation pit top plate 4 and the open trench 5 arranged at intervals are formed on the ground between the prefabricated underground continuous walls. Subsequently, an excavator is used to dig a pit at the position of the open trench 5, and the excavated earth is pulled away and transferred by the slag machine on the foundation pit top plate 4; ⑧ After the open slot 5 in step ⑦ is excavated downward to the set depth, the excavator at the bottom of the pit performs excavation operations toward the bottom of the foundation pit top plate 4 on both sides, and uses the slag machine at the bottom of the pit to transfer the soil to the pit excavated at the open slot 5. The long-arm excavator on the foundation pit top plate 4 transfers the soil in the pit to the slag machine on the top of the foundation pit top plate 4, and the soil is pulled away and transferred by the slag machine; ⑨ Repeat steps ⑦ and ⑧ alternately until the open groove 5 and the top plate 4 of the foundation pit are both dug down to the depth of the foundation pit, and then stop the excavation operation; ⑩ After the excavation of the foundation pit is completed, the foundation pit top plate 4 is used as the top plate of the station, and the subway station structure is constructed inside the foundation pit. After the structural construction is completed, the foundation pit top plate 4 is covered with earth and compacted to restore the original road surface, completing the construction of the subway station foundation pit.

[0008] The purpose of digging a shallow pit downward in step ① is to avoid the pre-buried pipelines under the original road surface. After the construction of the subway facilities under the ground is completed, the shallow pit is backfilled with earth to restore the original road surface. The underground continuous wall in step ② is to support the soil on both sides before excavation to prevent the soil from collapsing into the foundation pit and ensure the safety of operations in the foundation pit. The underground continuous wall can be cast on site by concrete. In order to improve construction efficiency, a prefabricated ground continuous wall can also be directly used and placed directly in the adapted guide groove 12.

[0009] The purpose of digging holes downward to make support columns 3 in step ③ is to provide multi-point support for the foundation pit top plate 4, so that the support columns 3 and the ground-connected walls on both sides can provide necessary support for the foundation pit top plate 4 at the same time, thereby improving the compressive strength and bearing capacity of the foundation pit top plate 4, and allowing the ground-connected walls on both sides to provide necessary support for the soil. The foundation pit top plate 4 covers the joint positions at both ends of the second prefabricated underground continuous wall 2, which can further enhance the integrity of the first prefabricated underground continuous wall 1 and the second prefabricated underground continuous wall 2, and avoid deformation at the joint position. The setting of the support columns 3 and the foundation pit top plate 4 can not only play a necessary supporting role, but also do not need to be removed during the subsequent subway station construction process. The support columns 3 can continue to be used as columns in the station, and the foundation pit top plate 4 can be used as the top plate of the subway station, which saves the support structure and reduces the production cost.

[0010] During the downward excavation process, open excavation is carried out at the open slot 5 position, and covered excavation is carried out at the bottom of the foundation pit top plate 4. The earth at the bottom of the foundation pit top plate 4 can be first transferred to the pit at the open slot 5 position, and then transferred to the slag truck on the foundation pit top plate 4 through a long-arm excavator or a gantry crane and other mechanisms, and then pulled away for transfer. The entire excavation process combines the advantages of open excavation and covered excavation, will not affect the normal transportation of earth, and can also be constructed at multiple open slots 5 positions at the same time, and the construction at each position will not affect each other. It is not only easy to implement and safe, but also the excavation efficiency is effectively improved.

[0011] Furthermore, in order to improve the integrity between the foundation pit top plate 4 and the underground continuous walls on both sides, and to improve the supporting strength of the underground continuous walls on both sides, after the formwork 6 is removed in step ⑦, connecting support components 7 are installed between the two sides of each foundation pit top plate 4 and the corresponding first prefabricated underground continuous wall 1. The connecting support components 7 can not only realize the connection between the foundation pit top plate 4 and the ground-connected walls on both sides, but also realize the support of the ground-connected walls on both sides, thereby improving the anti-collapse performance of the ground-connected walls on the soil on both sides.

[0012] The connecting support member 7 can be an existing supporting rod column with connecting bolts and reinforcing ribs, or can be a steel pipe internal support, a reinforced concrete frame internal support or a steel composite support.

[0013] The steel pipe internal support can be made of 609 steel pipe, with different wall thicknesses to adapt to different loads. The steel pipe support is in the form of bracing or angle bracing. When the spacing between braces is large, a web can be set to form a frame-type support. The reinforced concrete internal support has high rigidity and small deformation, which can effectively control the deformation of the retaining wall and the surrounding ground. It can also be cast in situ layer by layer as the soil is excavated. The form can change with the shape of the foundation pit, which is suitable for deep foundation pits with high requirements for the surrounding environment.

[0014] The steel composite support can adopt the prestressed fish belly steel support technology based on the prestressed principle. Through a large number of engineering research and practical applications, a new type of deep foundation pit support internal support structure system has been developed to address the shortcomings of traditional concrete internal support and steel support. The fish belly beam and H-shaped steel are used as load-bearing beams, and standard components such as corner supports, columns, beams, tie rods, triangular joints, and pre-stressing and tightening devices are combined to apply prestress to form a plane prestressed support system and a three-dimensional structure system. Compared with traditional concrete, the overall rigidity and stability of the support system are greatly improved. Combined with the remote real-time monitoring system, the displacement of the foundation pit can be effectively and accurately controlled, greatly reducing the deformation of the foundation pit.

[0015] Furthermore, in order to enable the ground connecting walls on both sides to provide more support to the foundation pit top plate 4, concrete corbel supports 8 are provided on the inner sides of the first prefabricated underground continuous wall 1 and the second prefabricated underground continuous wall 2. The concrete corbel supports 8 are located at the lower side of the foundation pit top plate 4, and the bottom of the foundation pit top plate 4 can be cast with a limiting convex edge with the concrete corbel supports 8.

[0016] Furthermore, the length of the first prefabricated underground continuous wall 1 is 8m, the length of the second prefabricated underground continuous wall 2 is 4m, the width of the foundation pit top plate 4 is 8m, the width of the open groove 5 is 4m, and each foundation pit top plate 4 is arranged at the middle position of the second prefabricated underground continuous wall 2, and the installation position of the foundation pit top plate 4 relative to the ground walls on both sides is consistent.

[0017] Furthermore, in order to ensure the strength and bearing capacity of the foundation pit top plate 4 itself, allow it to be used as a working site for excavators and slag trucks during earth excavation and transportation, and have good seismic and compressive resistance as the top plate of the subway station after the subway station is built, the thickness of the foundation pit top plate 4 is 700-900mm.

[0018] Furthermore, in order to share the support of the ground-connected walls on both sides to the foundation pit top plate 4, the number of each group of support columns 3 is four, and the four support columns 3 are located at the four corners of the rectangle, and each support column 3 is aligned with the joint position at both ends of the second prefabricated underground continuous wall 2. The width distance between adjacent support columns 3 is 4m, and the distance between the support column 3 and the prefabricated underground continuous wall is the same as the length distance between adjacent support columns 3, that is, in the width direction of the foundation pit, the two support columns 3 divide the distance between the ground-connected walls on both sides into three equal parts. The support columns 3 arranged according to the above position can achieve a more uniform support point layout for the bottom of the foundation pit top plate 4.

[0019] Furthermore, in order to avoid interference with the layout of the original pipelines at the foundation pit excavation location, and also to facilitate backfilling and restore the initial road surface above the foundation pit, the depth of the shallow pit pre-excavated in step ① is 1.5-3m.

[0020] Furthermore, in order to facilitate the excavation work in the foundation pit layer by layer, the slag truck in the foundation pit can be used to transport and transfer the excavated earth. In step ⑧, the set depth of downward excavation at the position of the open groove 5 is 1.5-2m. Excavation in layers according to the above height will not affect the excavation and transportation of the earth.

[0021] Furthermore, in order to enhance the connection performance between the foundation pit top plate 4 and the ground connection walls on both sides and the support column 3, and enhance the integrity and support of the structure, a first reserved steel bar 9 is set on the top of the first prefabricated underground continuous wall 1, a second reserved steel bar 10 is set on the top of the second prefabricated underground continuous wall 2, and a third reserved steel bar 11 is set on the top of the support column 3. The first reserved steel bar 9, the second reserved steel bar 10 and the third reserved steel bar 11 are all located in the foundation pit top plate 4. When the template 6 is laid to cast the foundation pit top plate 4, the above-mentioned reserved steel bars are all located inside the template 6. After the foundation pit top plate 4 is manufactured, it can be firmly connected with the support column 3 and the ground connection walls on both sides through the reserved steel bars, thereby improving the support performance of the device.

[0022] The technical solution of the present invention is not limited to the scope of the embodiments described in the present invention. The technical contents not described in detail in the present invention are all well-known technologies.

Claims

1. A method for constructing a subway station foundation pit by combining open excavation and cover excavation from top to bottom, characterized in that: The method comprises the following steps: ① digging a shallow pit downward in the area where the foundation pit is located, and digging guide grooves (12) downward on both sides of the shallow pit in the length direction, wherein the sum of the depths of the shallow pit and the guide grooves (12) is the same as the depth of the foundation pit; ② After the excavation of the guide grooves (12) on both sides in step ① is completed, a plurality of groups of first prefabricated underground continuous walls (1) and second prefabricated underground continuous walls (2) arranged at intervals are installed in the guide grooves (12), and the length of the first prefabricated underground continuous wall (1) is greater than the length of the second prefabricated underground continuous wall (2); ③ After the prefabricated underground continuous wall in step ② is installed in the guide groove (12), a plurality of groups of holes are drilled downward on the ground between the prefabricated underground continuous walls, each group of holes being located between the second prefabricated underground continuous walls (2) on both sides; ④ After the drilling in step ③ is completed, fill each group of holes with steel cages and pour concrete to make support columns (3); ⑤ After the support columns (3) in step ④ are manufactured, a template (6) is installed between the prefabricated underground continuous walls on the upper side of each group of support columns (3), the length of the template (6) being the length between the guide grooves (12) on both sides, and the width of the template (6) spanning the joint positions between the two ends of the second prefabricated underground continuous wall (2) and the first prefabricated underground continuous wall (1); ⑥ After the template (6) in step ⑤ is installed, a steel cage is placed in the template (6) and concrete is poured to form a foundation pit top plate (4), wherein the foundation pit top plate (4) is integrated with the support column (3) at the bottom, the first prefabricated underground continuous wall (1) and the second prefabricated underground continuous wall (2) on both sides, wherein the foundation pit top plate (4) spans the joint positions at both ends of a set of second prefabricated underground continuous walls (2); ⑦ After the foundation pit top plate (4) in step ⑥ is completed, the template (6) is removed, and the foundation pit top plates (4) and the open trench (5) arranged at intervals are formed on the ground between the prefabricated underground continuous walls. Subsequently, an excavator is used to dig a pit at the position of the open trench (5), and the excavated earth is pulled away and transferred by the slag truck on the foundation pit top plate (4); ⑧ After the open groove (5) position in step ⑦ is excavated downward to a set depth, the excavator at the bottom of the pit performs excavation operations toward the bottom of the foundation pit top plate (4) on both sides, and uses the slag machine at the bottom of the pit to transfer the soil to the pit excavated at the position of the open groove (5). The long-arm excavator on the foundation pit top plate (4) transfers the soil in the pit to the slag machine on the top of the foundation pit top plate (4), and the soil is pulled away and transferred by the slag machine; 9. Repeating steps 7 and 8 alternately until the open groove (5) and the top plate (4) of the foundation pit are both excavated to the depth of the foundation pit, and then stopping the excavation operation; ⑩ After the excavation of the foundation pit is completed, the foundation pit top plate (4) is used as the top plate of the station, and the subway station structure is constructed inside the foundation pit. After the structural construction is completed, the foundation pit top plate (4) is covered with earth and compacted to restore the original road surface, thereby completing the construction of the subway station foundation pit.

2. The method for constructing a subway station foundation pit by combining excavation and cover from top to bottom according to claim 1, characterized in that: After the formwork (6) is removed in step ⑦, connecting support members (7) are installed between the two sides of each foundation pit top plate (4) and the corresponding first prefabricated underground continuous wall (1).

3. The method for constructing a subway station foundation pit by combining excavation and cover from top to bottom according to claim 2, characterized in that: The connecting support member (7) is a steel pipe internal support, a reinforced concrete frame internal support or a steel composite support.

4. The method for constructing a subway station foundation pit by combining excavation and cover from top to bottom according to claim 1 is characterized in that: Concrete corbel supports (8) are provided on the inner sides of the first prefabricated underground continuous wall (1) and the second prefabricated underground continuous wall (2), and the concrete corbel supports (8) are located at the lower side of the foundation pit top plate (4).

5. The method for constructing a subway station foundation pit by combining excavation and cover from top to bottom according to claim 1 is characterized in that: The length of the first prefabricated underground continuous wall (1) is 8 m, the length of the second prefabricated underground continuous wall (2) is 4 m, the width of the foundation pit top plate (4) is 8 m, the width of the open groove (5) is 4 m, and each foundation pit top plate (4) is correspondingly arranged at the middle position of the second prefabricated underground continuous wall (2).

6. The method for constructing a subway station foundation pit by combining excavation and cover from top to bottom according to claim 5, characterized in that: The thickness of the foundation pit top plate (4) is 700-900 mm.

7. The method for constructing a subway station foundation pit by combining excavation and cover from top to bottom according to claim 5, characterized in that: Each group of support columns (3) has four support columns (3), which are located at the four corners of the rectangle respectively. Each support column (3) is aligned with the joint positions at both ends of the second prefabricated underground continuous wall (2). The width distance between adjacent support columns (3) is 4m, and the distance between the support column (3) and the prefabricated underground continuous wall is the same as the length distance between adjacent support columns (3).

8. The method for constructing a subway station foundation pit by combining excavation and cover from top to bottom according to claim 1, characterized in that: The depth of the shallow pit pre-dug in step ① is 1.5-3m.

9. The method for constructing a subway station foundation pit by combining excavation and cover from top to bottom according to claim 1, characterized in that: The set depth of excavation downward at the position of the open slot (5) in step ⑧ is 1.5-2m.

10. The method for constructing a subway station foundation pit by combining excavation and cover from top to bottom according to claim 1, characterized in that: A first reserved steel bar (9) is arranged on the top of the first prefabricated underground continuous wall (1), a second reserved steel bar (10) is arranged on the top of the second prefabricated underground continuous wall (2), a third reserved steel bar (11) is arranged on the top of the support column (3), and the first reserved steel bar (9), the second reserved steel bar (10) and the third reserved steel bar (11) are all located in the foundation pit top plate (4).

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