A construction method for ultra-shallow buried large-span underground excavation subway stations

Abstract

The present invention discloses a construction method for an ultra-shallow buried, large-span, underground excavation subway station. The method comprises first excavating an open excavation pit to the underground excavation working surface and installing a pipe curtain. Then, according to design requirements, two side guide tunnels are excavated and side piles and crown beams are installed. Then, two middle guide tunnels are excavated and a secondary lining arch cover is installed. Then, the rock and soil under the arch cover is excavated and concrete and steel supports are erected to the bottom surface of the station tunnel. Finally, a cushion layer is poured, waterproof panels are laid, and the main structure is rebuilt to close the gap. This construction method effectively solves the impact of pipeline relocation, traffic diversion, etc. on the road surface. Compared with the traditional side tunnel method and PBA construction method, the construction process is simpler, the support system is simpler, the amount of abandoned work is reduced, and the long-span structure and waterproofing quality are more easily guaranteed, thereby achieving the advantages of large construction space, high efficiency, short construction period, and low risk. Compared with the traditional arch cover method, the structure is buried at a shallower depth, the structural system is more stable, and the stratum applicability is wider.

Description

Technical Field

[0001] The invention relates to the technical field of underground engineering construction and discloses a construction method for an ultra-shallow buried large-span underground excavation subway station. Background Art

[0002] With the development of rail transit in major cities across China, an increasing number of subway stations are located at busy intersections and in areas with dense underground pipelines. To minimize disruption to surface traffic and reduce pipeline relocation, more and more stations are being constructed using shallow-buried, underground excavation methods at intersections. However, stations in urban areas are typically buried at relatively shallow depths, which can lead to long construction periods, high risks, and high costs. For subway stations at intersections where full open-cut construction is not feasible, side tunnels, PBAs, and arch-cover methods can be used. However, each of these methods has its pros and cons, making the choice of construction method a key factor in ensuring rapid, safe, and economical construction.

[0003] The side tunnel method is a construction technique that uses excavation and support simultaneously. This method uses two central partition walls to divide the entire tunnel into multiple sections: left, center, and right. The left and right pilot tunnels are constructed first, followed by the center pilot tunnel. After the initial support arch forms a ring, the temporary supports on both sides of the pilot tunnel are removed, leaving the full section. However, the side tunnel method has significant disadvantages. First, the excavation section is divided into multiple sections, causing significant disturbance, and the initial support and full section closure takes a long time. Second, the construction during underground excavation is difficult, slow, and expensive.

[0004] The PBA method is a construction method that combines the characteristics of the traditional shallow-buried, covered-and-cut method with the characteristics of the covered-and-cut method. This method uses side piles, central columns, top and bottom beams, and arch covers to form an integrated support system to withstand the loads during construction. The secondary lining structure is then constructed sequentially or reversely under the protection of the arch covers. However, the PBA method has many drawbacks. First, it requires multiple pilot tunnels and multiple processes, which disturbs many layers of ground. Second, the support system is complex, with frequent removal of primary supports, resulting in a large amount of abandoned work, slow progress, and high costs. Third, the numerous connection points between pilot tunnels make the support system relatively weak. Fourth, the main structure has multiple longitudinal joints, posing a risk of leakage in the later stages. Fifth, it requires high verticality of the central columns.

[0005] The arch capping method is a concealed excavation construction method suitable for soft-top, hard-bottom, and rocky strata. This method fully utilizes the bearing capacity and stability of the underlying surrounding rock. With no or minimal blasting, it uses a small pilot tunnel for primary support and buckle arch construction. Simultaneously, a large arch footing scheme is employed, supporting the primary arch support and secondary lining structure on stable bedrock on both sides to form an arch cap. Under the protection of the arch cap, underground cover excavation is carried out in either reverse or forward directions. However, the arch capping method requires high surrounding rock strength and is only suitable for rocky strata. In soft-top, hard-bottom strata, the arch cap footing must be located on stable bedrock, and blasting excavation below the arch footing is difficult to control and protect. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the defects of the existing technology in the construction of underground excavation subway stations, such as complex procedures, great construction difficulty, long construction period, high risk and high cost, and provide a construction method for ultra-shallow buried large-span underground excavation subway stations.

[0007] The present invention solves the above technical problems through the following technical solutions:

[0008] A construction method for an ultra-shallow buried large-span underground excavation subway station comprises the following steps:

[0009] S1. Excavate the open excavation pit to the underground excavation working surface according to the design requirements, erect internal supports and construct the pipe curtain guide wall. After the pipe curtain guide wall reaches the design strength, install the pipe curtain and perform grouting and filling reinforcement;

[0010] S2. Break the piles and open the portals of the lateral guide tunnels on both sides. Set up multiple primary supports at the portals and excavate two lateral guide tunnels according to the design requirements. Set up the primary supports of the lateral guide tunnels in the tunnels and drive the first anchor pipe.

[0011] S3, grouting to reinforce the stratum and grouting behind the primary support of the side guide tunnel. After the side guide tunnels on both sides are connected, side piles are installed, crown beam steel bars are tied, and concrete is poured;

[0012] S4. Construct the primary support of the arch cover in the side guide tunnel. After the primary support reaches the designed strength, backfill the cavity behind the primary support with plain concrete.

[0013] S5. Break the piles and open the portals of the central guide tunnel on both sides. Attach multiple primary supports at the portals and excavate two central guide tunnels according to the design requirements. Set up the primary supports of the central guide tunnels and drive the second anchor pipes.

[0014] S6. Grouting to reinforce the stratum and grouting behind the primary support of the middle guide tunnel;

[0015] S7. After the middle pilot tunnel is penetrated, the temporary middle partition wall is removed and the secondary lining arch cover is constructed;

[0016] S8. After the secondary lining arch cover reaches the designed strength, the rock and soil are excavated to the bottom of the station tunnel, and concrete supports and steel supports are installed in sequence;

[0017] S9. Pour the cushion layer, lay the waterproof board, and pour the secondary lining base plate, secondary lining middle plate and secondary lining side wall. Remove the steel support and concrete support after the concrete reaches the design strength.

[0018] In this proposal, the aforementioned construction method effectively addresses the impacts of pipeline relocation and traffic diversion on the road surface. Compared with the side tunnel method, the main arch can be completed earlier, reducing construction risks such as pilot tunnel collapse caused by heavy loads on the station arch and low initial support stiffness. Furthermore, large-scale machinery can be used to excavate the lower section of the station, significantly shortening the construction period. Compared with the PBA method, the arch can be formed in one step, eliminating the need for center columns and pilot tunnels under them, shortening the construction period and reducing project investment. Furthermore, the reduced number of arch connection nodes ensures the quality of the main structure and waterproofing, reducing the risk of leakage at these nodes during operation. Compared with the arch cap method, the side piles reduce the station's burial depth and avoid construction quality issues such as cracking of the main structure caused by large deformation of the arch foot. Furthermore, the side piles enhance the stability of the arch foot and the bearing capacity of the end. The internal supports under the arch cap effectively control the deformation of the side piles, ensuring the stability of the arch cap and the underlying foundation pit. This method is applicable to both soil and rock strata, expanding its applicability.

[0019] Preferably, the following steps are further included before S1:

[0020] S10. Construct retaining piles, top ring beams and concrete supports for the open excavation pit of the station.

[0021] In this scheme, the above-mentioned construction method is adopted, so that before the excavation of the open excavation pit, the stability of the open excavation pit is increased by setting up retaining piles, top ring beams and foundation pit concrete supports, effectively ensuring the safety of the construction process, and the setting of retaining piles, top ring beams and foundation pit concrete supports also determines the construction position for the open excavation pit, ensuring the accuracy and quality of the construction.

[0022] Preferably, steel bars for connecting to the pipe curtain guide wall are pre-embedded in the retaining piles, and locking ribs are provided along the circumferential direction at the ends of the pipe curtain for anchoring connection with the pipe curtain guide wall.

[0023] In this solution, the above-mentioned structural form is adopted, which effectively increases the stability and convenience of the installation of the pipe curtain guide wall, and also makes the connection between the pipe curtain and the pipe curtain guide wall more firmly, ensuring the safety and quality of the construction process.

[0024] Preferably, in said S1, the grouting filling reinforcement is to perform grouting through said pipe curtain to reinforce the ground layer and fill said pipe curtain.

[0025] In this solution, the above-mentioned construction method is adopted to carry out grouting and filling above the dark-excavated pilot tunnel through the pipe curtain, so that the stratum is reinforced, avoiding the risk of rock and soil falling between the arch pipe curtain during the pilot tunnel excavation stage, and ensuring the safety of the construction process.

[0026] Preferably, the following steps are further included between S2 and S3:

[0027] S20, constructing a first small advance guide tube at the top of the side guide tunnel, constructing a hollow grouting anchor rod at the straight wall section of the side guide tunnel, and performing grouting to reinforce the stratum through the first small advance guide tube and the hollow grouting anchor rod.

[0028] Preferably, the following steps are further included between S5 and S6:

[0029] S30, constructing a second small advance guide tube at the top of the middle guide tunnel, and reinforcing the stratum by grouting through the second small advance guide tube.

[0030] Preferably, the step S7 specifically includes the following steps:

[0031] S71, first excavate the middle pilot tunnel on the left side to three times the pilot tunnel excavation width;

[0032] S72, excavating the middle pilot tunnel on the right side to twice the pilot tunnel excavation width;

[0033] S73, constructing the secondary lining arch cover within a range of one times the pilot tunnel excavation width from the tunnel opening, and continuing to excavate the middle pilot tunnel;

[0034] S74: After the middle guide holes on both sides are connected, the remaining secondary lining arch covers are constructed.

[0035] In this plan, the above-mentioned construction method is adopted to first construct a second lining arch cover at the dark excavation entrance to lock the boundary between the open and dark excavation, ensuring the stability of the soil covering the upper part of the entrance arch and the safety of subsequent construction.

[0036] Preferably, the step S8 specifically includes the following steps:

[0037] S81, after the secondary lining arch cover is completed and reaches the designed strength, excavate the rock and soil to the bottom surface of the crown beam;

[0038] S82, constructing the concrete support, and after the concrete support reaches the designed strength, continuing to excavate downward to the position of the steel support;

[0039] S83. Erect the steel support, and continue excavating downward to the bottom surface of the station tunnel after the steel support is stable.

[0040] In this solution, the above-mentioned construction method is adopted, and through the setting of concrete supports and steel supports, during the excavation of the rock and soil under the secondary lining arch cover, the crown beam, concrete supports and the side piles on both sides form a stable portal structure, thereby ensuring the safety of excavation of the upper secondary lining arch cover and the foundation pit under the arch cover; in addition, through the setting of steel supports, the side piles on both sides are further constrained, ensuring that the bottom of the side piles is stable when excavating downward; in addition, the construction process is simple and has fewer steps, which makes it have the characteristics of short construction period, high efficiency and low risk.

[0041] Preferably, when constructing the crown beam, a steel bar connector for the concrete support is reserved. In S8, the concrete support is connected to the crown beam through the steel bar connector; the steel support is tightened against the side piles through steel surrounding purlins.

[0042] Preferably, the step S9 specifically includes the following steps:

[0043] S91, pouring the cushion layer on the bottom surface of the station tunnel and laying the waterproof board;

[0044] S92, casting the second lining plate on the cushion layer, and casting part of the second lining side wall;

[0045] S93, after the concrete reaches the design strength, remove the steel support;

[0046] S94, continue laying the waterproof board and continue pouring the secondary lining side wall and the secondary lining middle plate;

[0047] S95. After the concrete reaches the designed strength, the concrete support is removed, and the waterproof board is laid and the remaining part of the secondary lining side wall is poured, and the main structure is closed to complete the construction.

[0048] The positive progress effect of the present invention is:

[0049] The support structure for an ultra-shallow buried, large-span underground excavation subway station disclosed in this solution effectively solves the impact of pipeline relocation, traffic diversion, etc. on the road surface. Compared with the traditional side tunnel method and PBA method, the construction process is simpler, the support system is simpler, the amount of abandoned projects is less, and the large-span structure and waterproofing quality are easier to ensure, thereby achieving the advantages of large construction space, high efficiency, short construction period and low risk. Compared with the traditional arch cover method, the structure is buried deeper, the structural system is more stable, and the stratum applicability is wider. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 The present invention provides a flowchart of a method for constructing an ultra-shallow buried, large-span, underground excavation subway station.

[0051] Figure 2Schematic cross-sectional view of the open excavation pit, pipe curtain guide wall and pipe curtain of a subway station in an embodiment of the present invention.

[0052] Figure 3 It is a cross-sectional schematic diagram of the initial support structure of the side guide tunnels on both sides in an embodiment of the present invention.

[0053] Figure 4 It is a cross-sectional schematic diagram of the side piles, crown beams and initial support of the arch cover in the side guide tunnel and the backfilling of the cavity in an embodiment of the present invention.

[0054] Figure 5 Schematic cross-sectional view of the initial support structure of the middle guide tunnels on both sides in an embodiment of the present invention.

[0055] Figure 6 It is a cross-sectional schematic diagram of the second lining arch cover buckle arch in an embodiment of the present invention.

[0056] Figure 7 It is a cross-sectional schematic diagram of excavating earthwork below the secondary lining arch cover and erecting supports in an embodiment of the present invention.

[0057] Figure 8 It is a cross-sectional schematic diagram of the closure of the second lining arch cover and the lower main structure in an embodiment of the present invention.

[0058] Description of reference numerals:

[0059] Retaining pile 1

[0060] Top ring beam 2

[0061] Foundation pit concrete support 3

[0062] Open excavation pit 4

[0063] Internal support 5

[0064] Dark excavation working face 6

[0065] Tube curtain guide wall 7

[0066] Tube curtain 8

[0067] Locking rib 9

[0068] First side guide hole 10

[0069] Second side guide hole 11

[0070] Side guide tunnel primary support 12

[0071] First locking foot anchor pipe 13

[0072] First advance small catheter 14

[0073] Hollow grouting anchor 15

[0074] Side Stake 16

[0075] Crown Beam 17

[0076] Hole edge beam 18

[0077] Arch cover initial support 19

[0078] Plain concrete 20

[0079] First middle guide hole 21

[0080] Second middle guide hole 22

[0081] Middle guide tunnel primary branch 23

[0082] Second locking foot anchor pipe 24

[0083] Second advanced small catheter 25

[0084] Second lining arch cover 26

[0085] Temporary next door 27

[0086] Concrete support 28

[0087] Steel support 29

[0088] Tunnel bottom 30

[0089] Steel purlin 31

[0090] Pad 32

[0091] Second substrate 33

[0092] Secondary lining side wall 34

[0093] Second lining plate 35 DETAILED DESCRIPTION

[0094] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples.

[0095] like Figures 2 to 8 As shown, this embodiment discloses a support structure for an ultra-shallow buried large-span underground excavation subway station, including an open excavation foundation pit support structure and a underground excavation support structure. The open excavation foundation pit support structure is arranged at both ends of the underground excavation pilot tunnel. The open excavation foundation pit support structure includes retaining piles 1, top ring beams 2 and foundation pit concrete supports 3. The retaining piles 1 are vertically arranged around the open excavation foundation pit 4, the top ring beams 2 are arranged on the top of the retaining piles 1, and the foundation pit concrete supports 3 are erected on the side of the top ring beam 2; the underground excavation support structure includes an advanced support structure and an initial support structure for the side guide tunnel and the middle guide tunnel, and a support structure under the secondary lining arch cover 26. The advanced support structure is an advanced small guide tube arranged at the top of the guide tunnel, the initial support structure is a steel frame and mesh sprayed concrete arranged around the guide tunnel after the guide tunnel is excavated, and the support structure under the secondary lining arch cover 26 is a concrete support 28 and a steel support 29 arranged on the inner side of the side piles 16.

[0096] This support structure effectively addresses the impacts of pipeline relocation and traffic diversion on the road surface. Compared with the side tunnel method, the main arch can be completed earlier, reducing construction risks such as pilot tunnel collapse caused by heavy loads on the station arch and low initial support stiffness. At the same time, large-scale machinery can be used to excavate the lower section of the station, significantly shortening the construction period. Compared with the PBA method, the arch can be formed in one step, eliminating the need for center columns and pilot tunnels under the center columns, shortening the construction period and reducing project investment. At the same time, the reduction in arch connection nodes ensures the quality of the main structure and waterproofing, reducing the risk of leakage at nodes during operation. Compared with the arch cover method, the role of the side piles 16 can reduce the station's burial depth and avoid construction quality issues such as cracking of the main structure caused by large deformation of the arch foot. At the same time, the side piles 16 increase the stability of the arch foot and the bearing capacity of the end. The support under the arch cover effectively controls the deformation of the side piles 16, ensuring the stability of the arch cover and the underlying foundation pit. It is applicable to both soil and rock strata, expanding the scope of application.

[0097] In a preferred embodiment, Figure 2 As shown, the advanced support structure also includes a pipe curtain guide wall 7, a pipe curtain 8 and a locking rib 9. The pipe curtain guide wall 7 is arranged on the inner side of the open excavation pit 4 and is a reinforced concrete beam. The pipe curtain 8 is a hot-rolled seamless steel pipe with a diameter of not less than 300 mm. The locking rib 9 is arranged at the end of the pipe curtain 8 along the circumferential direction. The pipe curtain guide wall 7 and the pipe curtain 8 are anchored and connected by the locking rib 9.

[0098] In a preferred embodiment, Figure 3 As shown, the side guide tunnel support structure includes a side guide tunnel primary branch 12, a first locking foot anchor pipe 13, a first advance small guide pipe 14 and a hollow grouting anchor rod 15. The side guide tunnel primary branch 12 is arranged around the side guide tunnel. The first advance small guide pipe 14 passes through the side guide tunnel primary branch 12 from the top of the guide tunnel and is then driven into the stratum. The first locking foot anchor pipe 13 is arranged at the bottom of the side guide tunnel primary branch 12, and the hollow grouting anchor rod 15 is arranged in the straight wall section of the side guide tunnel.

[0099] In a preferred embodiment, Figure 4 As shown, the initial support structure also includes side piles 16, crown beams 17, hole edge beams 18, arch cover primary supports 19 and plain concrete 20. The side piles 16 are implemented after the side guide tunnel is penetrated and extend to below the second base slab 33. The crown beams 17 are set on the top of the side piles 16. The hole edge beams 18 are set at the connection between the side piles 16 and the primary support at the bottom of the side guide tunnel. One end of the arch cover primary support 19 is connected to the side guide tunnel primary support 12, and the other end is connected to the crown beam 17. Plain concrete 20 is filled between the side guide tunnel primary support 12 and the arch cover primary support 19.

[0100] In a preferred embodiment, the side piles 16 are reinforced concrete piles or steel pipe piles. The aperture side beams 18 are formed by providing longitudinal connecting bars between steel frames to improve the overall stability after the primary support is disconnected. The plain concrete 20 should be non-shrinkage concrete.

[0101] In a preferred embodiment, Figure 5 As shown, the middle guide tunnel support structure includes the middle guide tunnel primary branch 23, the second locking foot anchor pipe 24, the second advance small guide pipe 25 and the temporary middle partition wall 27. The middle guide tunnel primary branch 23 is arranged around the middle guide tunnel, the temporary middle partition wall 27 is arranged at the connection between the two middle guide tunnels, the second locking foot anchor pipe 24 is arranged at the bottom of the temporary middle partition wall 27, and the second advance small guide pipe 25 passes through the middle guide tunnel primary branch 23 and the temporary middle partition wall 27 and is driven into the formation.

[0102] In a preferred embodiment, Figure 6 As shown, the middle guide tunnel further includes a secondary lining arch cover 26, which is arranged on the inner side of the primary support 23 of the middle guide tunnel and extends to both ends of the dark-excavated guide tunnel to form a top arch of the dark-excavated guide tunnel.

[0103] In a preferred embodiment, Figure 7 As shown, the supporting structure under the secondary lining arch cover 26 includes concrete supports 28 and steel supports 29. The concrete supports 28 are connected to the crown beam 17 through steel connectors reserved in the crown beam 17. The steel supports 29 are arranged between the concrete supports 28 and the bottom surface 30 of the station tunnel. The steel supports 29 are tightened against the side piles 16 on both sides through steel purlins 31.

[0104] In a preferred embodiment, Figure 8 As shown, the station also includes a cushion layer 32, a waterproof board, a secondary lining base plate 33, a secondary lining middle plate 35 and a secondary lining side wall 34. The cushion layer 32 is cast on the tunnel bottom surface 30, the waterproof board is laid on the cushion layer 32, the secondary lining base plate 33 is arranged on the waterproof board, the secondary lining side wall 34 is arranged on the inner side of the side pile 16, and the secondary lining middle plate 35 is arranged between the secondary lining arch cover 26 and the secondary lining base plate 33, so as to separate the subway station into two floors.

[0105] In addition, if Figures 1 to 8As shown, the present embodiment also discloses a construction method for an ultra-shallow buried large-span underground excavation subway station, which comprises the following steps: S1, excavating an open excavation foundation pit 4 to an underground excavation working surface 6 according to design requirements, erecting internal supports 5 and constructing a pipe curtain guide wall 7, after the pipe curtain guide wall 7 reaches the design strength, driving a pipe curtain 8 and performing grouting filling and reinforcement; S2, breaking piles and opening the side guide hole portals on both sides, setting up multiple primary supports at the portals and excavating two side guide holes according to design requirements, erecting the side guide hole primary support 12 in the hole and driving the first locking foot anchor pipe 13; S3, grouting reinforcement of the stratum and grouting behind the side guide hole primary support 12, after the side guide holes on both sides are connected, constructing side piles 16, tying the crown beam 17 steel bars and pouring concrete; S4, constructing the side guide hole inner arch cover primary support 19, after the arch cover primary support 19 reaches the design strength After the strength is calculated, the cavity behind the primary support 19 of the arch cover is backfilled with plain concrete 20; S5, the piles are broken and the portals of the middle guide tunnel on both sides are opened. Multiple primary supports are connected at the portals and two middle guide tunnels are excavated according to the design requirements. The primary support 23 of the middle guide tunnel is erected in the tunnel and the second locking anchor pipe 24 is driven; S6, grouting is performed to reinforce the stratum and grouting is performed behind the primary support 23 of the middle guide tunnel; S7, after the middle guide tunnel is penetrated, the temporary middle partition wall 27 is removed and the secondary lining arch cover 26 is constructed; S8, after the secondary lining arch cover 26 reaches the design strength, the rock and soil are excavated to the bottom surface 30 of the station tunnel, and concrete supports 28 and steel supports 29 are constructed in sequence; S9, the cushion layer 32 is poured and the waterproof board is laid, and the secondary bottom slab 33, the secondary lining middle plate 35 and the secondary lining side wall 34 are poured. After the concrete reaches the design strength, the steel support 29 and concrete support 28 are removed.

[0106] like Figure 1 As shown in the figure, this construction method effectively solves the impact of pipeline relocation, traffic diversion, etc. on the road surface. Compared with the traditional side tunnel method and PBA method, the construction process is simpler, the support system is simpler, the amount of abandoned projects is less, and the large-span structure and waterproofing quality are easier to ensure, thus achieving the advantages of large construction space, high efficiency, short construction period and low risk. Compared with the traditional arch cover method, the structure is shallower, the structural system is more stable, and the stratum applicability is wider.

[0107] In a preferred embodiment, Figure 2 As shown, before S1, the following steps are also included: S10, constructing the retaining piles 1, top ring beams 2 and foundation pit concrete supports 3 of the open excavation pit 4 of the station, and setting internal supports 5 according to actual construction conditions.

[0108] like Figure 2 As shown, before the open excavation pit 4 is excavated, the stability of the open excavation pit 4 is increased by setting the retaining piles 1, the top ring beam 2 and the foundation pit concrete support 3, which effectively ensures the safety of the construction process. In addition, the setting of the retaining piles 1, the top ring beam 2 and the foundation pit concrete support 3 also determines the construction position for the open excavation pit 4, ensuring the accuracy and quality of the construction.

[0109] In a preferred embodiment, the pipe curtain 8 uses a hot-rolled seamless steel pipe with a diameter of not less than 300 mm. In actual application, the diameter and circumferential spacing of the pipe curtain 8 can be set according to the specific conditions and requirements during construction. In addition, in the actual construction process, the sizes of the retaining piles 1, the top ring beam 2 and the foundation pit concrete support 3 are set accordingly according to the actual size of the open excavation pit 4 and the specific requirements of the construction. Therefore, in this embodiment, no excessive restrictions are made, and the sizes of the pipe curtain 8, the retaining piles 1, the top ring beam 2 and the foundation pit concrete support 3 are not limited to the range disclosed in this embodiment.

[0110] In a preferred embodiment, Figure 2 As shown, steel bars for connecting to the pipe curtain guide wall 7 are pre-embedded in the retaining pile 1 , and locking ribs are provided along the circumferential direction at the end of the pipe curtain 8 for anchoring connection to the pipe curtain guide wall 7 .

[0111] By pre-embedding steel bars in the retaining piles 1 and providing locking ribs at the ends of the pipe curtain 8, the stability and convenience of the installation of the pipe curtain guide wall 7 are effectively increased. At the same time, the connection between the pipe curtain 8 and the pipe curtain guide wall 7 is also made more secure, ensuring the safety and quality of the construction process.

[0112] In a preferred embodiment, in S1, grouting and filling reinforcement is performed through the pipe curtain 8 to reinforce the ground and fill the pipe curtain 8. The grouting slurry is cement slurry, which is injected through the pipe curtain 8 above the dark-excavated pilot tunnel to reinforce the ground, thereby avoiding the risk of rock and soil falling between the arch pipe curtain during the pilot tunnel excavation phase, and ensuring the safety of the construction process.

[0113] In other embodiments, according to actual construction requirements, corresponding slurry materials and proportions are selected and the corresponding filling coefficient is ensured. Therefore, the type of grouting slurry is not limited to the scope disclosed in this embodiment.

[0114] In a preferred embodiment, Figure 3 and Figure 4 As shown, the following steps are also included between S2 and S3: S20, constructing a first advance small guide tube 14 at the top of the side guide tunnel, constructing a hollow grouting anchor rod 15 in the straight wall section of the side guide tunnel, grouting to reinforce the stratum through the first advance small guide tube 14 and the hollow grouting anchor rod 15, and grouting behind the primary support 12 of the side guide tunnel.

[0115] During the actual construction process, the models of the first advance small tube 14 and the hollow grouting anchor rod 15 are selected according to the design requirements. In this embodiment, the grouting slurry used to reinforce the first advance small tube 14 and the hollow grouting anchor rod 15 can be selected as single-liquid slurry or double-liquid slurry according to the on-site engineering and hydrogeological conditions.

[0116] In a preferred embodiment, the first side pilot tunnel 10 and the second side pilot tunnel 11 are staggered by a distance that is no less than twice the pilot tunnel excavation width. In step S2, breaking piles and opening the side pilot tunnel portals on both sides involves first breaking the retaining piles 1 within half the pile diameter. After the primary support is constructed, the remaining retaining piles 1 are broken and multiple primary supports are constructed.

[0117] In a preferred embodiment, the primary support 12 of the side guide tunnel includes a steel frame and mesh shotcrete. During the actual construction process, the steel frame is selected to be a single-layer steel frame or a double-layer steel frame composed of a grid steel frame and a steel frame according to the situation of the top arch covering. The model of the steel frame is finally calculated and determined based on the vertical and horizontal loads and adverse working conditions in the excavation sequence, and taking into account the effect of the pipe curtain 8; the mesh shotcrete includes a double-layer steel mesh and wet shotcrete.

[0118] In a preferred embodiment, during the erection phase of the primary supports 12 of the side guide tunnels before constructing the side piles 16 in S3, structural measures are required to ensure stability in the event that the primary supports 12 are removed within the area of ​​the side piles 16. These structural measures include installing longitudinal connecting bars between the steel frames to form aperture side beams 18, which enhance overall stability after the steel frames are disconnected. The crown beam 17 serves as a support at the arch foot of the arch cap. The cross-section of the crown beam 17 is determined based on the construction of the arch foot, and its dimensions are calculated based on vertical and horizontal loads and adverse conditions during the excavation sequence. Furthermore, after the side piles 16 are completed, the reinforcement of the crown beam 17 is tied and concrete is poured. In actual construction, the side piles 16 can be reinforced concrete piles or steel pipe piles, depending on the actual geological conditions. Depending on the geological conditions, the side piles 16 can be excavated mechanically or manually. Parameters such as the diameter and longitudinal spacing of the side piles 16 are calculated based on the actual geology, vertical and horizontal loads, and adverse conditions during the excavation sequence.

[0119] In a preferred embodiment, Figure 4 As shown in S4, the primary support of the arch cover should be welded or bolted to the connecting steel plates reserved in the primary support 12 of the side guide tunnel and the crown beam 17. Plain concrete 20 should be backfilled with non-shrinkage concrete to ensure that the backfill is dense.

[0120] In a preferred embodiment, Figure 5 As shown, in S5, when breaking piles and opening the central guide tunnel portals on both sides, the first central guide tunnel 21 and the second central guide tunnel 22 are required to be staggered by a distance of at least twice the tunnel excavation width. The requirements for breaking piles, the model of the steel frame for the central guide tunnel primary support 23 and the second advance small guide tube 25, and the grouting requirements are the same as those for the side guide tunnel excavation and are therefore not further described.

[0121] In a preferred embodiment, Figure 5 and Figure 6As shown, the following steps are also included between S5 and S6: S30, constructing a second advance small pipe 25 on the top of the primary branch 23 of the middle guide tunnel, and grouting and reinforcing the stratum through the second advance small pipe 25.

[0122] In a preferred embodiment, Figure 5 and Figure 6 As shown, S7 specifically includes the following steps: S71, first excavating the first middle guide tunnel 21 on the left side to three times the guide tunnel excavation width; S72, then excavating the second middle guide tunnel 22 on the right side to one times the guide tunnel excavation width; S73, constructing the second lining arch cover 26 within the range of one times the guide tunnel excavation width from the tunnel opening, and continuing to excavate the middle guide tunnel; S74, after the middle guide tunnels on both sides are connected, constructing the remaining second lining arch covers 26.

[0123] A secondary lining arch cover 26 is first constructed at the entrance of the underground excavation to lock the boundary between the open and underground excavation. This ensures the stability of the soil covering the top of the entrance arch and the safety of subsequent construction. In actual construction, the temporary intermediate partition wall 27 should be removed longitudinally and sectionally based on calculation results and monitoring results before the secondary lining arch cover 26 is installed.

[0124] In a preferred embodiment, Figure 7 As shown, S8 specifically includes the following steps: S81, after the secondary lining arch cover 26 is completed and reaches the design strength, the rock and soil are excavated to the bottom surface of the crown beam 17; S82, the concrete support 28 is constructed, and after the concrete support 28 reaches the design strength, the excavation is continued downward to the position of the steel support 29; S83, the steel support 29 is erected, and after the steel support 29 is stable, the excavation is continued downward to the bottom surface 30 of the station tunnel.

[0125] By setting the concrete supports 28 and the steel supports 29, during the excavation of the rock and soil below the secondary lining arch cover 26, the crown beam 17, the concrete supports 28 and the side piles 16 on both sides form a stable portal structure, thereby ensuring the safety of excavation of the upper secondary lining arch cover and the foundation pit under the arch cover; in addition, by setting the steel supports 29, the side piles 16 on both sides are further constrained, ensuring that the bottom of the side piles 16 is stable when excavating downward; in addition, the construction process is simple and has fewer steps, which makes it have the characteristics of short construction period, high efficiency and low risk.

[0126] In a preferred embodiment, Figure 7 As shown, when constructing the crown beam 17, concrete support steel bar connectors are reserved. In S8, the concrete supports 28 are connected to the crown beam 17 via the steel bar connectors, and the steel supports 29 are tightened against the side piles 16 via the steel purlins 31. In actual construction, the cross-sectional dimensions and longitudinal spacing of the concrete supports 28 and steel supports 29, as well as the cross-sectional dimensions of the steel purlins 31, should be determined based on the horizontal load and adverse working conditions during the excavation sequence.

[0127] In a preferred embodiment, Figure 8 As shown, S9 specifically includes the following steps: S91, pouring the cushion layer 32 located at the bottom surface 30 of the station tunnel and laying the waterproof board; S92, pouring the secondary lining slab 33 on the cushion layer 32, and pouring part of the secondary lining side wall 34; S93, removing the steel support 29 after the concrete reaches the design strength; S94, continuing to lay the waterproof board and continue to pour the secondary lining side wall 34, and pour the secondary lining middle plate 35; S95, removing the concrete support 28 after the concrete reaches the design strength, and continuing to lay the waterproof board and pour the remaining part of the secondary lining side wall 34, closing the main structure, and completing the construction.

[0128] Although specific embodiments of the present invention have been described above, those skilled in the art will appreciate that these are merely illustrative and that the scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, and such changes and modifications are intended to fall within the scope of the present invention.

Claims

1. A construction method for an ultra-shallow buried large-span underground excavation subway station, characterized in that: It includes the following steps: S1. Excavate the open excavation pit to the underground excavation working surface according to the design requirements, erect internal supports and construct the pipe curtain guide wall. After the pipe curtain guide wall reaches the design strength, install the pipe curtain and perform grouting and filling reinforcement; S2. Break the piles and open the portals of the lateral guide tunnels on both sides. Attach multiple primary supports at the portals and excavate two lateral guide tunnels according to the design requirements. Set up the primary supports of the lateral guide tunnels in the tunnels and drive the first anchor pipe. S3, grouting to reinforce the stratum and grouting behind the primary support of the side guide tunnel. After the side guide tunnels on both sides are connected, side piles are installed, crown beam steel bars are tied, and concrete is poured; S4. Construct the primary support of the arch cover in the side guide tunnel. After the primary support reaches the designed strength, backfill the cavity behind the primary support with plain concrete. S5. Break the piles and open the portals of the central guide tunnels on both sides. Set up multiple primary supports at the portals and excavate two central guide tunnels according to the design requirements. Set up the primary supports of the central guide tunnels and drive the second anchor pipes. S6. Grouting to reinforce the bottom layer and grouting behind the primary support of the middle guide tunnel; S7, after the middle pilot tunnel is penetrated, the temporary middle partition wall is removed and the secondary lining arch cover is constructed; S8. After the secondary lining arch cover reaches the designed strength, the rock and soil are excavated to the bottom of the station tunnel, and concrete supports and steel supports are installed in sequence; S9, pour the cushion layer, lay the waterproof board, and pour the secondary lining base plate, secondary lining middle plate and secondary lining side wall. After the concrete reaches the design strength, remove the steel support and concrete support; The S7 specifically includes the following steps: S71, first excavate the middle pilot tunnel on the left side to three times the pilot tunnel excavation width; S72, excavating the middle pilot tunnel on the right side to twice the pilot tunnel excavation width; S73, constructing the secondary lining arch cover within a range of one times the pilot tunnel excavation width from the tunnel opening, and continuing to excavate the middle pilot tunnel; S74: After the middle guide holes on both sides are connected, the remaining second lining arches are constructed.

2. The construction method of an ultra-shallow buried large-span underground excavation subway station according to claim 1, characterized in that: Before S1, the method further includes the following steps: S10. Construct retaining piles, top ring beams and concrete supports for the open excavation pit of the station.

3. The construction method of an ultra-shallow buried large-span underground excavation subway station according to claim 2, characterized in that: Steel bars for connecting to the pipe curtain guide wall are pre-embedded in the retaining piles, and locking ribs are provided along the circumferential direction at the ends of the pipe curtain for anchoring and connecting to the pipe curtain guide wall.

4. The construction method of an ultra-shallow buried large-span underground excavation subway station according to claim 1, characterized in that: In said S1, grouting filling reinforcement is carried out by grouting through the said pipe curtain to reinforce the stratum and fill the said pipe curtain, and the said pipe curtain is a hot-rolled seamless steel pipe with a diameter of not less than 300mm; in said S2, the retaining piles within half the pile diameter should be broken before the pile breaking to open the tunnel door, and the remaining retaining piles should be broken and the primary support should be erected after the primary support is constructed; in said S3, structural measures need to be reserved in the primary support erection stage before the construction of the side piles, and the structural measures refer to the setting of longitudinal connecting bars between the steel frames to form the hole edge beams to improve the overall stability after the steel frame is disconnected.

5. The construction method of an ultra-shallow buried large-span underground excavation subway station according to claim 1, characterized in that: The following steps are also included between S2 and S3: S20, constructing a first small advance guide tube at the top of the side guide tunnel, constructing a hollow grouting anchor rod at the straight wall section of the side guide tunnel, and performing grouting to reinforce the stratum through the first small advance guide tube and the hollow grouting anchor rod.

6. The construction method of an ultra-shallow buried large-span underground excavation subway station according to claim 1, characterized in that: The following steps are also included between S5 and S6: S30, constructing a second small advance guide tube at the top of the middle guide tunnel, and performing grouting to reinforce the stratum through the second small advance guide tube.

7. The construction method of an ultra-shallow buried large-span underground excavation subway station according to claim 1, characterized in that: The S8 specifically includes the following steps: S81, after the secondary lining arch cover is completed and reaches the designed strength, excavate the rock and soil under the arch cover to the bottom surface of the crown beam; S82, constructing the concrete support, and after the concrete support reaches the designed strength, continuing to excavate downward to the position of the steel support; S83. Erect the steel support, and continue excavating downward to the bottom surface of the station tunnel after the steel support is stable.

8. The construction method of an ultra-shallow buried large-span underground excavation subway station according to claim 1, characterized in that: When constructing the crown beam, a steel bar connector for the concrete support is reserved. In S8, the concrete support is connected to the crown beam through the steel bar connector, and the steel support is tightened against the side piles through the steel surrounding purlin.

9. The construction method of an ultra-shallow buried large-span underground excavation subway station according to claim 1, characterized in that: The S9 specifically includes the following steps: S91, pouring the cushion layer on the bottom surface of the station tunnel and laying the waterproof board; S92, casting the second lining plate on the cushion layer, and casting part of the second lining side wall; S93, after the concrete reaches the design strength, remove the steel support; S94, continue laying the waterproof board and continue pouring the secondary lining side wall and the secondary lining middle plate; S95. After the concrete reaches the designed strength, the concrete support is removed, and the waterproof board is laid and the remaining part of the secondary lining side wall is poured, and the main structure is closed to complete the construction.

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