A method for concealed excavation of a three-layer six-hole subway station

Abstract

The present invention belongs to the field of subway stations, and particularly relates to a method for the concealed excavation of a three-story and six-hole subway station, which includes the following steps: constructing a pipe roof, with the pipe roof arranged in an inverted "冖" shape; excavating the lower Z2 pilot tunnel and the three upper Z1 pilot tunnels; constructing a bottom longitudinal beam in the Z2 pilot tunnel, constructing a top longitudinal beam in the middle Z1 pilot tunnel, and manually excavating holes to construct steel pipe columns; constructing a C-shaped crown beam; constructing the Z3 pilot tunnel; excavating the soil downward to the bottom surface position of the middle plate on the first basement floor; excavating in sections and constructing the middle plate on the first basement floor, the first middle longitudinal beam, the upper side walls, the temporary support positions, and the first temporary support; excavating downward to the bottom surface position of the middle plate on the second basement floor, and constructing the middle plate on the second basement floor, the second middle longitudinal beam, and the upper side wall structure in sections; excavating downward, erecting the second temporary support, and pouring the floor slab; pouring the lower side walls and the middle columns, and constructing the remaining side walls to complete the construction of the station main body; the top plate of the present invention occupies a small space of the soil body of the station main body and is suitable for the construction of concealed excavation stations near the ground.

Description

Technical Field

[0001] The present invention belongs to the technical field of subway station construction, and particularly relates to a method for mined tunneling of a three-story and six-hole subway station. Background Art

[0002] The construction of many subway stations is carried out after the construction of the city, with complex surrounding environments and numerous underground pipelines. There are open cut methods and mined tunneling methods for subway station construction. When the ground traffic and pipeline and other environmental conditions do not allow open cut, mined tunneling methods need to be adopted.

[0003] For three-story mined tunneling subway stations, due to the large cross-sectional span and high height, an arched roof structure is usually adopted. There are signal pipelines, gas pipelines, drainage pipelines, water supply pipelines, etc. buried in the urban roads, and some pipelines are buried at about 3.5 meters. This places many restrictions on the shallow-buried three-story subway station, and the construction conditions for the arched roof are not available.

[0004] Therefore, it is necessary to provide an improved technical solution for the deficiencies of the above-mentioned existing technologies. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the existing technologies and provide a method for mined tunneling of a three-story and six-hole subway station.

[0006] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0007] A method for mined tunneling of a three-story and six-hole subway station, which adopts the open cut method + pipe roof and pilot shaft method for construction, and includes the following steps:

[0008] In the first step, the open cut sections at both ends of the mined tunneling section of the station are used as pipe roof launching and receiving wells for pipe jacking operations; the pipe roof is arranged in a "冖" shape. After the pipe roof is jacked in place, self-compacting concrete is filled in the pipe; by using the structure of the existing station open cut section, the construction process is simplified and the construction efficiency is improved; the pipe roof is arranged in a "冖" shape, strengthening the support effect on the soil at the corners;

[0009] In the second step, after the pipe roof construction is completed, the lower Z2 pilot tunnel is excavated. After the lower Z2 pilot tunnel is贯通, the three upper Z1 pilot tunnels are constructed in the order of first the sides and then the middle; the three Z1 pilot tunnels are respectively located on both sides and in the middle of the upper side, and the middle Z1 pilot tunnel is directly above the Z2 pilot tunnel; as the excavation progresses forward, initial support construction is carried out for the pilot tunnels, and the grids of the three upper Z1 pilot tunnels are tightly pressed against the pipe roof; after the pilot tunnels are closed into a ring, backfill grouting should be carried out in time behind the initial support, which helps to maintain the stability of the chamber and prevent ground deformation;

[0010] The third step is to construct the bottom longitudinal beam in the Z2 pilot tunnel, the top longitudinal beam in the middle Z1 pilot tunnel, and manually dig holes and construct steel pipe columns; construct side piles in the Z1 pilot tunnels on both sides, and the side piles are mechanically bored piles; then construct the cap beam on the top of the pile, and the cap beam is a C-shaped cap beam;

[0011] The fourth step is to construct the Z3 pilot tunnel between the Z2 pilot tunnel in the middle and the Z1 pilot tunnels on both sides and perform the initial support construction; after the penetration, according to the monitoring situation, part of the Z1 pilot tunnel and the initial support of the Z3 pilot tunnel will be dismantled in sections horizontally and vertically, the waterproof layer will be laid, and the top plate and part of the side wall secondary lining will be cast in formwork;

[0012] Step 5: After the top plate reaches the designed strength, excavate the soil downward to the bottom of the underground first floor middle plate; construct the underground first floor middle plate, the first middle longitudinal beam, the upper side wall in sections, and construct the side wall waterproof layer and structure;

[0013] Step 6: When the concrete strength of the middle slab reaches the design, continue to excavate the soil downward to the temporary support position in the middle of the span; lay the side wall waterproof layer and erect the first temporary support after constructing the side wall, and continue to excavate downward to the bottom surface of the middle slab of the negative second floor;

[0014] Step 7: Construct the negative second floor middle plate, the second middle longitudinal beam, the upper side wall structure in sections, and construct the side wall waterproof layer and structure;

[0015] Step 8: Continue to excavate downwards, set up the negative second temporary support at the same time, and carry out the mesh spraying support between the piles during the excavation; after excavating to the design elevation, the foundation pit should be leveled in time, and the plain concrete cushion layer should be applied in time to seal the foundation pit, and then the waterproof layer should be laid and the bottom plate should be poured;

[0016] Step 9: Remove the second support, cast the lower side walls and center columns, construct the remaining side walls, waterproof layer and structure, and remove the first support.

[0017] Furthermore, in the first step, during the pipe jacking operation, laser-guided deviation correction measures are adopted; the middle and corner pipes are jacked in first, and the top and side steel pipes are jacked in sequence from the middle pipe to both sides. The accuracy and direction of the pipe jacking are strictly controlled during the jacking process, and no deviation or deflection is allowed.

[0018] Furthermore, in the second step, the Z2 pilot tunnel base is reinforced by grouting with a reinforcement depth of 1.5m. After the pilot tunnel is closed into a ring, the primary support and the foundation should be backfilled and grouted in time. The slurry adopts cement-water glass double liquid slurry, and the diffusion radius of the grouting slurry is 0.5m. After reinforcement, the unconfined compressive strength of the soil is not less than 0.8MPa.

[0019] Furthermore, during the construction of the pilot tunnel, when constructing the pilot tunnel from the open excavation section to the dark excavation section, a single small guide tube with a length of 6m and a circumferential spacing of 300mm is installed at the horse head gate before opening the tunnel. The stratum is reinforced by pre-grouting before the tunnel gate retaining piles can be excavated. First, remove 1 / 2 of the concrete piles, cut off the main reinforcement in the grille range, erect a grille, and spray concrete in time. Then remove the remaining 1 / 2 of the concrete piles, cut off the main reinforcement of the piles, erect a steel grille in close spacing, spray concrete in time, and use copper buckles to closely connect the three-grade grilles. The grilles should be firmly welded to the cut-off retaining main reinforcement.

[0020] Furthermore, in the fourth step, the top slab concrete is poured in multiple times with each pouring length of 9m~10m in the long direction. The concrete is poured in layers and vibrated to be dense in layers by manual vibrating rods or the vibration system of the trolley.

[0021] Furthermore, in the first step, during the construction of the pipe curtain, two water drills drill holes continuously in the order from the middle to both sides. The initial hole drilling cannot be more than 4 times the pipe curtain spacing. When drilling holes at the receiving end, the initial and receiving holes are no more than 3m. After the pipe curtain passes, the reinforcement of the retaining piles and the pipe curtain steel pipes are connected in time, with a connection rate of 50% and an unconnected length of no more than 5 pipe curtains.

[0022] Furthermore, the pipe curtain has two layers, the first layer of the pipe curtain is supported along the top surface of the contour line of the Z1 guide tunnel and the Z3 guide tunnel, and the second layer of the pipe curtain is supported on the upper part of the side of the contour line of the Z1 guide tunnel.

[0023] Furthermore, in the fifth step, when constructing the middle plate and side walls of the first underground floor, the bottom is cleared manually when the excavation surface is 10 centimeters away from the bottom of the middle plate, and a frog-type rammer is used to compact the bottom while cleaning to control the flatness and elevation of the entire base surface; square timber and formwork are laid on the compacted and leveled sand layer base to form an earth formwork system for casting the middle plate of the first underground floor, the first middle longitudinal beam, and the upper side walls.

[0024] Furthermore, the diameter of the side pile body is 1000mm, and the expanded bottom diameter is 1400mm; the side pile drilling is constructed by a reverse circulation drilling rig, and the drilling is carried out in batches with two holes per interval; the construction sequence is divided into two times as a whole, and the driving sequence is unidirectional to ensure that the steel pipe column construction is as far away from the side pile construction as possible.

[0025] Furthermore, in the third step, the gaps around the steel pipe columns are backfilled with fine sand; in the fifth step, after the top plate reaches the designed strength, the gap between the C-shaped crown beam and the upper Z1 guide hole is backfilled with C20 concrete.

[0026] The beneficial effects of the present invention are:

[0027] The top plate of the station main structure of the present invention is horizontal. Compared with the traditional arched top plate, the top plate occupies less space in the soil body of the station main body, enabling the station to be applicable to the construction of mined - out stations near pipelines and near the ground. During the construction process, through "冖"-shaped pipe - curtain support, side - pile construction, sectional construction, primary support construction, etc., the risks during the construction process are reduced, the stability of the surrounding soil body is ensured, and potential safety hazards are minimized. When constructing the pilot tunnels, the lower - layer Z2 pilot tunnel is constructed first, then the three upper - layer Z1 pilot tunnels are constructed in sequence, and finally the Z3 pilot tunnel is constructed. This construction sequence helps to reasonably distribute the construction load and reduce stratum disturbance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The schematic drawings forming a part of this application are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not unduly limit the present invention. Among them:

[0029] Figure 1 is the construction process of the subway station in the embodiment of the present invention Figure 1 .

[0030] Figure 2 is the construction process of the subway station in the embodiment of the present invention Figure 2 .

[0031] Figure 3 is the construction process of the subway station in the embodiment of the present invention Figure 3 .

[0032] Figure 4 is the construction process of the subway station in the embodiment of the present invention Figure 4 .

[0033] Figure 5 is the construction process of the subway station in the embodiment of the present invention Figure 5 .

[0034] Figure 6 is the construction process of the subway station in the embodiment of the present invention Figure 6 .

[0035] Figure 7 is the construction process of the subway station in the embodiment of the present invention Figure 7 .

[0036] Figure 8 is the construction process of the subway station in the embodiment of the present invention Figure 8 .

[0037] Fig. 9 is the construction process of the subway station in the embodiment of the present invention Figure 9 .

[0038] Fig.10 is the schematic diagram of the construction sequence of the side piles in the embodiment of the present invention.

[0039] In the figure: 1. pipe curtain; 2. crown beam; 3. side piles; 4. steel pipe column; 5. top plate; 6. side wall; 7. middle plate of the first negative floor; 8. middle plate of the second negative floor; 9. first temporary support; 10. second temporary support; 11. bottom plate; 12. top longitudinal beam; 13. bottom longitudinal beam; 14. bottom grouting reinforcement area; 15. first middle longitudinal beam; 16. second middle longitudinal beam; 17. first construction scope of side piles; 18. Z1 pilot tunnel; 19. Z2 pilot tunnel; 20. Z3 pilot tunnel. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0041] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0042] The present invention takes the A Street subway station as an example for explanation. The main body of the A Street subway station is 170 meters long, a three-story single-column double-span box-type structure (double-column three-span at the expanded end), with open-cut sections of 67.7m and 64.3m at both ends, a dark-cut section of 38m, a standard section width of 20.9m, and a bottom plate buried depth of about 25.99m. According to on-site investigations, the surrounding environment of the station mainly includes: DN200 signal pipelines, DN250 / DN300 / DN400 / DN500 gas pipes, DN200 communication pipes, DN300 drainage pipelines, and DN400 water supply pipelines. Among them, the DN500 medium-pressure gas pipe has a maximum buried depth of 3.57m, and the top of the pipe curtain is 473mm away from the bottom of the gas pipe.

[0043] Next, the construction method of the main dark excavation section of the station is taken as an example to specifically illustrate the dark excavation method of the three-layer six-hole subway station of the present invention.

[0044] The main structure of the station is constructed by open excavation + pipe curtain hole pile method. The length of the underground excavation section of the station is 38 meters, the width is 21 meters, the excavation depth is about 26 meters, the soil cover is 5.0 meters (to the top plate of the structure), there are three underground floors, single column double span 7.5 meters column span, from top to bottom reverse construction. The underground excavation section is a three-story underground excavation. The construction of the underground excavation section adopts the pipe curtain hole pile method. After the pipe curtain is set up in the upper part of the open excavation working well, the upper guide tunnel adopts I25b steel frame, and the lower guide tunnel adopts a small guide tube of a steel grid steel frame to supplement grouting, and precipitation is carried out in advance before construction.

[0045] Specifically, a method for underground excavation of a three-layer six-hole subway station includes the following steps:

[0046] The first step: Construction of the pipe roof 1: After the open-cut main structure at both ends of the station is completed, dewatering is carried out in the area for the mined tunneling construction. After dewatering, equipment is installed in the working shaft foundation pit. Using the open-cut sections at both ends of the station as the launching shaft and receiving shaft for the pipe roof 1, pipe jacking operations are carried out; for the mined tunneling section, the spiral earth-excavating pipe jacking process is adopted, selecting a pipe roof of Φ457×16mm, with laser-guided deviation correction measures; during pipe jacking operations, first jack in the middle and corner pipes, and then jack in the top and lateral steel pipes from the middle pipe to both sides in sequence. During the jacking process, strictly control the pipe jacking accuracy and direction, without deviation or deflection. After the steel pipes are jacked in place, seal the two ends of the steel pipes with 10mm steel plates, and reserve grouting holes and exhaust holes at the pipe jacking ports. Then, use a pump truck to fill the inside of the pipes with C30 self-compacting concrete; during grouting, the filling operation is tentatively scheduled to start 5 pipes behind the pipe roof, and adjust it in real time according to the actual situation on site and the detection data. Figure 1 It is a schematic diagram of the pipe roof 1 after construction. The pipe roof 1 is arranged in a "冖" shape. In addition to supporting the soil mass at the top of the designed position of the station main body, it can also play a good supporting role for the soil mass at the corners.

[0047] The second step: After the construction of the pipe roof 1 is completed, excavate the lower Z2 pilot tunnel 19. After the lower Z2 pilot tunnel 19 is贯通, then construct the upper Z1 pilot tunnel 18 in the order of first the sides and then the middle, and the longitudinal spacing between each pilot tunnel is ≥15m. The bench method is adopted for the pilot tunnel, and the bench length is 3m - 5m. As the excavation progresses forward, carry out the initial support construction for the longitudinal pilot tunnel, and the grid of the upper Z1 pilot tunnel is tightly pressed against the pipe roof 1. After the pilot tunnel is closed into a ring, backfill grouting should be carried out in time behind the initial support (including the foundation), and supplementary grouting should be carried out according to the monitoring situation. Figure 2 It is a schematic diagram of the positions of the Z1 pilot tunnel 18 and the Z2 pilot tunnel 19. The excavation direction of each pilot tunnel is along the direction of the pipe roof 1. The pipe roof 1 provides additional support, which helps to reduce the disturbance of the surrounding strata during the excavation of the pilot tunnel and helps to control the ground settlement.

[0048] The third step: Construct the concrete structure of the bottom longitudinal beam 13 (including part of the floor 11 structure) in the Z2 pilot tunnel 19 (the lower middle pilot tunnel), and reserve steel pipe column positioning bolts at the top of the bottom longitudinal beam 13. Construct manual dug piles at the position of the structural columns in the upper middle Z1 pilot tunnel 18, connect the upper middle Z1 pilot tunnel 18 at the position of the structural columns with the Z2 pilot tunnel 19, and complete the installation of the steel pipe column 4 and the concrete pouring in the piles; construct the top longitudinal beam 12 (including part of the roof 5 structure) at the top of the steel pipe column 4. The top longitudinal beam 12, the bottom longitudinal beam 13, and the steel pipe column 4 form a stable spatial stress system, forming a cross-middle support structure. Construct side piles 3 in the upper side Z1 pilot tunnel 18 as the retaining structure for the mined tunneling in reverse, and construct a C-shaped capping beam 2, part of the main body side wall 6, and the roof 5 at the top of the piles. Excavate one side pile 3 every three, the side piles 3 are mechanically drilled piles, the side piles 3 adopt C35 concrete, and the protective layer thickness of the side piles 3 is 70mm; construct a capping beam 2 at the top of the piles, the capping beam 2 is a C-shaped top capping beam, adopting C35 concrete, and the protective layer thickness of the capping beam 2 is 35mm - 40mm. Figure 3 is a schematic diagram of the structure after the third step of construction; in this embodiment, Fig.10 As shown, only one row of steel pipe columns 4 is provided in the middle of the station.

[0049] Step 4: excavate the soil between the upper Z1 pilot tunnel 18 and the upper middle Z1 pilot tunnel 18 and close the primary support, then construct the Z3 pilot tunnel 20 between the upper Z1 pilot tunnel 18 and the upper middle Z1 pilot tunnel 18; erect a temporary middle partition wall when necessary according to the monitoring situation, and after the connection is completed, remove part of the primary supports and middle partition walls of the Z1 and Z3 pilot tunnels in sections horizontally and vertically according to the monitoring situation (the removal of the middle partition wall requires the main body strength to reach 75% in the first step), lay a waterproof layer, and erect molds to cast the top plate 5 and part of the side wall secondary lining. Figure 4 This is a schematic diagram of the structure after the fourth step of construction is completed.

[0050] Step 5: After the top plate 5 reaches the design strength and the construction of the top plate 5 is completed, backfill the gap between the C-shaped crown beam and the upper Z1 guide hole 18 with C20 concrete; at the same time, excavate the soil downward to the bottom surface of the negative first layer middle plate 7. Spray the mesh between the piles as the excavation is carried out, cut off the steel pipe column 4 guard arm, and protect the steel pipe column 4 to avoid collision with the excavation machinery. The earth excavation should be constructed by the method of pulling grooves in the middle and cutting edges at the end. Construct the negative first layer middle plate 7, the first middle longitudinal beam 15, and the upper side wall 6 in sections, and construct the side wall waterproof layer and structure. Before construction, the middle beam node of the steel pipe column 4 should be cleaned, and the beam and plate reinforcement should be effectively connected to the steel pipe column 4 node according to the design requirements. When constructing the negative first floor middle plate 7 and side wall 6, the bottom is cleared manually when the excavation surface is 10 cm away from the bottom of the middle plate, and a frog-type rammer is used to compact the bottom while cleaning to control the flatness and elevation of the entire base surface; square timber and formwork are laid on the compacted and leveled sand layer base to form an earth formwork system for casting the negative first floor middle plate 7, the first middle longitudinal beam 15, and the upper side wall 6. Figure 5 This is a schematic diagram of the structure after the fifth step of construction is completed. It can be seen that the top surface of the top plate 5 is slightly higher than the top surface of the C-type crown beam. After the C20 concrete is backfilled, the C20 concrete structure, the top plate 5, and the C-type crown beam form a whole, which enhances the overall stiffness of the corner structure of the station body and improves the bearing capacity of the structure.

[0051] Step 6: When the concrete strength of the middle plate reaches 100% of the design, continue to excavate the soil downward to the temporary support position in the middle of the span; after laying the side wall waterproof layer and constructing the side wall 6, set up the first temporary support 9, and continue to excavate downward to the bottom surface of the negative second floor middle plate 8, spray the net between the piles as the excavation progresses, cut off the steel pipe column 4 arm guard, and protect the steel pipe column 4 to avoid collision with the excavation machinery; the earthwork excavation should be constructed by the method of middle grooving and rear edge cutting. The first temporary support 9 adopts steel support, and the steel support is installed by fixing a chemical anchor bolt on the top of the corresponding retaining pile of the steel support. In this step, it is also possible to excavate to the bottom of the track top air duct, first construct the track top air duct, and after the construction of the track top air duct is completed, backfill and compact the soil around the track top air duct. In this embodiment, the pre-loaded axial force of the first temporary support 9 is 100kN / m, and the designed axial force is 1790.81kN. Figure 6 This is a schematic diagram of the structure after the sixth step of construction is completed.

[0052] Step 7: Construct the negative second floor middle plate 8, the second middle longitudinal beam 16, and the upper side wall 6 structure in sections, and construct the side wall waterproof layer and structure. Before construction, the middle beam node of the steel pipe column 4 should be cleaned, and the beam, plate reinforcement and the steel pipe column 4 node should be effectively connected according to the design requirements. The negative second floor side wall 6 is constructed with steel formwork, and the support system uses a tripod. Figure 7 This is a schematic diagram of the structure after the seventh step of construction is completed.

[0053] Step 8: Continue to excavate the soil downward to a position 300mm above the foundation pit cushion layer, and remove the rest manually, and set up a second temporary support 10 at the mid-span; carry out mesh spraying support between piles during excavation; the pre-added axial force of the second temporary support 10 is 150kN / m, and the designed axial force is 2661.123kN; after excavating to the designed elevation, the foundation pit should be leveled in time, and a plain concrete cushion layer should be applied in time to seal the foundation pit, and the geological conditions, soil quality and bearing capacity of the base should be checked to see if they are consistent with the design. If the bearing capacity is insufficient, measures such as base replacement can be adopted; then, lay a waterproof layer and cast the bottom plate 11. Figure 8 This is a schematic diagram of the structure after the eighth step of construction is completed.

[0054] Step 9: Remove the second support, cast the lower side wall 6 and the middle column, construct the remaining side wall 6, waterproof layer and structure, and remove the first support. Fig. 9 This is a schematic diagram of the structure after the ninth step of construction is completed.

[0055] Furthermore, in the above method, the overall construction process of the pipe curtain 1 construction is: operating platform installation → measurement and setting out → pile breaking → equipment guided jacking → pipe curtain 1 jacking → end sealing → pouring concrete into the pipe. The pile breaking adopts a diamond drill (water drill) with a water source to drill holes. The spacing of the pipe curtain 1 is 500mm and the drilling diameter is 550mm. The scope of each breaking of the tunnel door enclosure should be carried out according to the needs and after the jacking equipment is in place. It shall not be broken all at once, nor should it be broken in advance. In this embodiment, there are 53 holes in total, and two water drills drill holes continuously from the middle to both sides. Specifically, the holes are arranged from one end to the other in order of 1 to 53. Then, one water drill drills holes from the middle 27 to 1, and the other water drill drills holes from 28 to 53; holes 2 to 52 are the upper contours of the first row adjacent to the Z1 guide hole 18 and the Z3 guide hole 20, and holes 1 and 53 are the outer contours of the second row adjacent to the upper Z1 guide hole. The initial opening cannot be more than 4 times the spacing of the pipe curtain 1. When the receiving end opens the hole, the initial and receiving openings are not more than 3m. After the pipe curtain 1 passes, the reinforcement of the retaining pile and the steel pipe of the pipe curtain 1 are connected in time, with a connection rate of 50% and an unconnected length of no more than 5 pipe curtains 1. "Eating holes" are set on both sides of the first section of the pipe curtain 1 steel pipe to "eat" the soil between the pipe curtain 1 steel pipe and the hole gap into the pipe and discharge it, effectively reducing the friction between the outer wall of the pipe curtain 1 steel pipe and the soil. Figures 1 to 9 The completed pipe curtain 1 structure and position can be seen in the figure. The top plate 5 of the Z1 guide tunnel, Z3 guide tunnel and the station body are all designed to be flat, which provides the premise for the pipe curtain 1 and the station body to be close to the ground.

[0056] Furthermore, in the third and fourth steps of the above method, the top plate 5 concrete is poured in four times with a length of 9.5 m in the long direction each time. Observation holes and exhaust holes are set during the pouring of concrete to ensure the quality of concrete pouring. Concrete is poured in layers and vibrated to be dense in layers, and vibrated by manual vibrating rods or the vibrating system of the trolley; a pouring hole is left on the arch template 1 m away from the plugs on both sides, and observation holes are set on the arch plugs on both sides.

[0057] Furthermore, in the pilot tunnel construction of the above method, in order to avoid the group tunnel effect, the Z2 pilot tunnel 19 is constructed first, and then the Z1 pilot tunnel 18 is constructed. The Z1 pilot tunnel 18 can be constructed only after the pipe curtain 1 is fully constructed; finally, the Z3 pilot tunnel 20 is constructed. The Z3 pilot tunnel 20 can be constructed only after the top longitudinal beam 12 and the main structure of the Z1 pilot tunnel 18 are completed. This construction sequence helps to reasonably distribute the construction load and reduce the stratum disturbance. When constructing a pilot tunnel from the open excavation section to the dark excavation section, a single small guide tube is set at the horse head gate before the tunnel is opened. The small guide tube is 6m long and 300mm in circumferential spacing. The stratum is reinforced by pre-grouting before the tunnel gate retaining piles can be excavated; first, 1 / 2 of the pile concrete is removed, and the main reinforcement of the grid range is cut off, a grid is erected, and concrete is sprayed in time; then the remaining 1 / 2 of the pile concrete is removed, and the main reinforcement of the pile is cut off, and a steel grid is erected closely, and concrete is sprayed in time. The copper buckles are closely connected to form three-grade grids, and the grid should be welded firmly to the main reinforcement of the enclosure after being cut off. Specifically, the construction process of the pilot tunnel is: grouting of the small guide tube in advance → breaking the horse head gate (excavation of the pilot tunnel) → installing the grid steel frame → locking the anchor pipe → hanging the mesh and spraying → grouting behind the primary support.

[0058] Furthermore, during the construction of the pilot tunnel, the advance small conduit grouting includes: before the horse head gate is broken, the upper part of the upper pilot tunnel (Z1 pilot tunnel 18 and Z3 pilot tunnel 20) needs to be reinforced with advance small conduit grouting, and cement-water glass double liquid slurry is injected. The lower pilot tunnel (Z2 pilot tunnel 19) uses cement-water glass double liquid slurry injected into the small conduit. The cement-water glass double liquid slurry uses PO 42.5 cement + water glass slurry, and the slurry mix ratio is cement slurry: water glass = 1:1. A single row of small conduit pipe curtain 1 is used. The small conduit uses DN32×3.25mm seamless steel pipe, a single length of 2m, and an annular spacing of 300mm. The two small conduit pipe curtains 1 are set upward at an angle of 16° in the forward direction, and the longitudinal spacing is the same as the grid spacing. The front end of the small conduit is made into a 20cm long cone to facilitate insertion and prevent the slurry from rushing forward. In the middle of the small conduit, symmetrical holes of 6mm~8mm in diameter are opened every 15cm in a plum blossom shape (to prevent dead corners during grouting). No holes are drilled within 0.5m of the tail to prevent leakage (no holes are opened).

[0059] Small conduit grouting is to advance into the tunnel arch with a perforated steel pipe, and inject various slurries suitable for different strata at high pressure to penetrate into the effective range of the stratum. As long as the grouting pressure exceeds the minimum shear strength of the injected soil, the slurry can quickly penetrate into the soil in the form of veins, and discharge the air and moisture in it, making the slurry veins denser and thicker, and densifying the soil. Subsequently, the slurry undergoes a gelling reaction, causing the fluid plastic clay to cement and harden, turning it into hard plastic, forming a consolidated body with a certain strength and impermeability with the slurry vein as the skeleton, thereby improving the strength, stability and impermeability of the surrounding rock, improving the stress condition of the lining, and achieving the purpose of preventing mud and water gushing in the tunnel, surface subsidence and construction safety. In this embodiment, the small conduit and locking foot are installed by the hole-leading top-in method, and the installation steps are as follows:

[0060] ① Use YT-28 pneumatic drill or special hydraulic trolley to drill holes; before drilling the small conduit, mark the position of the small conduit on the arch frame according to the design requirements, and place the tail of the small conduit on the belly of the steel frame and spot weld it to increase the common support capacity;

[0061] ②Insert the small catheter and the locking foot rivet tube. If it is difficult to insert, you can use a YT-28 pneumatic drill with an impact hammer to push it in or directly use a heavy hammer to drive it in. If there is a steel arch frame, the small catheter must be inserted through its abdomen;

[0062] ③ Use a blower to blow out the sand and gravel in the conduit or use a digging hook to hook it out;

[0063] ④ Use plastic mud to seal the cracks around the conduit and the working surface, or spray 8cm~10cm thick concrete around the conduit and the working surface to seal. The grouting volume, proportion, and grouting pressure are determined according to field tests, and the grouting diffusion radius is required to be no less than 0.25m. After the grouting is completed, the grouting effect must be checked, and the weak parts of the grouting must be re-grouted;

[0064] ⑤ After the locking foot anchor pipe and the small duct are installed, they are welded to the main reinforcement of the grille. The exposed spray surface is 100mm~200mm. Double-liquid slurry is used for the advanced small duct, and single-liquid slurry is used for the locking foot rivet pipe.

[0065] Furthermore, during the construction of the pilot tunnel, the removal of the horse head gate includes the following steps:

[0066] (1) After breaking the piles within the upper step of the upper guide tunnel at the horse head gate, after excavating one advance, hang steel mesh and erect a grid steel frame in time. The grid steel frame is connected to the main reinforcement of the broken pile; and spray C25 concrete to seal it; then, in this order, erect three grids closely at the tunnel gate and spray them for support; among them, the arch frame connecting reinforcement is connected by single-sided welding, and the connecting reinforcement is arranged in double rows inside and outside with a circumferential spacing of 1m. The connecting reinforcement and the main reinforcement of the arch frame must be welded firmly; one grid is overlapped between the steel meshes, and the connection between the steel mesh and the arch frame is overlapped by binding; before spraying concrete, clean the scum, loose soil and other debris on the surface of the original concrete; the centerline deviation of the arch frame is ±20mm, the elevation deviation is ±15mm, the longitudinal deviation is ±30mm, and the verticality deviation is controlled within 0.5%. The arch frame advance is 50cm and the deviation is controlled within ±3cm;

[0067] (2) When excavating the pilot tunnel using the step method, the core soil is retained during excavation to prevent the collapse of the heading face. The staggered distance between the upper and lower steps of the same pilot tunnel is 3m to 5m, and the staggered distance between adjacent pilot tunnels is 15m. The position of the embedded parts is accurately located to ensure that the grid cannot be connected during subsequent installation, thereby affecting the stress of the primary support structure. The core soil length is 2m, and the core soil is excavated after the primary support of the arch is completed.

[0068] (3) After the upper step is constructed 3m to 5m forward, the retaining piles of the open-cut section within the lower step are removed, and the first grid of the lower step is quickly constructed to form a ring of steel grids for the upper guide tunnel door and connect them to the piles;

[0069] Note that excavation must be carried out under water-free conditions. If a large amount of seepage and water gushing occurs during excavation, excavation must be stopped immediately, the tunnel face must be closed in time, and pre-grouting reinforcement must be performed on the soil in front of the excavation.

[0070] In the above step (1), the concrete of the retaining piles at the tunnel entrance must be broken during construction, which destroys the stress of the entire structure and causes stress redistribution at the tunnel entrance, which is most likely to cause the soil at this location to become unstable. In order to ensure the structural safety of the horse head gate, the horse head gate is reinforced with three closely spaced grids, and the main reinforcement exposed from the retaining piles of the open-cut section is welded to the horse head gate grid. At the same time, the first steel grid of the tunnel gate must be welded to the main reinforcement of the side wall to form a whole, to ensure the safety of the tunnel gate.

[0071] Furthermore, the step method is used in tunnel construction. The step method construction method is as follows:

[0072] (1) Advance support by grouting small pipes in the construction arch;

[0073] (2) Excavate the upper section, reserve core soil, spray concrete initially, erect grid steel frame, install locking anchor pipes, and spray concrete again;

[0074] (3) Excavate the lower section, spray concrete initially, erect grid steel frame, and spray concrete again; after the initial support converges and stabilizes, grouting is performed behind the initial support to make the initial support fit closely with the stratum. The initial support adopts a combination of spray concrete + steel mesh + grid steel frame.

[0075] Furthermore, during the excavation of the pilot tunnel, the advance of each excavation cycle must be strictly controlled not to exceed the spacing between two adjacent steel grilles. After excavation, the initial support should be carried out in time. The initial support adopts the joint support of shotcrete + steel mesh + grid steel frame. During construction, a double-layer steel mesh is set in the initial support of 350mm in the initial support shotcrete, and a single-layer steel mesh is set in the initial support of 300mm. The mesh overlap length is 150mm, and it is reliably connected to the grid. Longitudinal connecting bars (Φ22mm) are set on the inside and outside of the front and rear grids, with a circumferential spacing of 1.0m. The longitudinal connecting bars are connected by single-sided 10d welding. The connecting bars must be reliably welded with the main bars of the grid. After the grid joint plate is installed in place on site, the welding bars are constructed and welded with the main bars on both sides for 10d on one side. After the grid steel frame is erected, two locking foot grouting anchor rods are set at each longitudinal grid. The specifications of the locking foot grouting anchor rods are Φ32×3.25mm and the length is 2.0m.

[0076] Furthermore, the grid steel frame is tested before being used in the project. The erection meets the design requirements, the connecting bolts must be tightened, the number meets the design, and the connecting plates are closely aligned. When installing the arch frame, the arch foot should be placed on the bedrock, original soil or pads, and must not be placed on loose soil. It is strictly forbidden to be suspended in the air. The error of the arch frame installation shall not exceed plus or minus 5cm, and the installation inclination shall not exceed 2°. The grid steel frame of Z1 guide hole 18 and Z3 guide hole 20 is made of I25b I-beam into a square grid. The Z1 reserved steel plate and M24 bolt hole are connected to the Z3 guide hole 20. In order to ensure the integrity of the connection, the length of each grid is strictly controlled during the construction process. The surveyors give reference points for each guide hole on site, and check every five frames. Finally, it is ensured that the completed steel frame is on the same horizontal plane.

[0077] Furthermore, the grouting behind the initial support is carried out after the initial support of the entire section is closed, following the excavation working face. The grouting pipe uses a DN32×3.25mm welded steel pipe, which is arranged along the tunnel arch and side wall, with an annular spacing (at the same time, it is required to arrange no less than 1 hole and no more than 5 holes above the arch line): 2.0m for the arch and 3.0m for the side wall; the longitudinal spacing is 3.0m, arranged in a plum blossom shape, using high-strength micro-expansive cement slurry, backfill grouting pressure ≤0.2MPa, slurry diffusion distance 2m~3m; grouting is repeated when necessary according to the deformation and leakage of the bottom layer. Grouting reinforcement of the foundation is only required when the bearing capacity of the lower soil is insufficient. To improve the bearing capacity of the natural soil, the foundation of the Z2 pilot tunnel 19 can be reinforced with small conduit grouting, with a reinforcement depth of 1.5m. Figures 1 to 9 The bottom grouting reinforcement area 14 in the figure is a schematic diagram of the foundation reinforcement of the Z2 pilot tunnel 19; after the pilot tunnel is closed into a ring, the primary support (including the foundation) should be backfilled and grouted in time.

[0078] Furthermore, in this embodiment, the underground excavation station has 53 side piles (hole piles), with a pile length of about 29.89m, a pile body diameter of 1000mm, and a bottom diameter of 1400mm. The drilling of the side piles (hole piles) is carried out using a reverse circulation drilling rig. The side piles 3 are constructed in batches with skip holes, and two holes are constructed per interval during the construction of bored piles. The construction sequence is divided into two times as a whole, and the order of driving is from south to north, ensuring that the construction of the artificial excavated piles (steel pipe columns 4) is as far away from the construction of the side piles 3 as possible. Fig.10The first construction scope 17 of the side pile is schematically drawn in the figure. When the side pile 3 is constructed on one side, the manually dug steel pipe column 4 is constructed on the other side first. According to the space and geological conditions in the cave, the side pile 3 adopts the method of special reverse circulation drilling rig and impact drilling, segmented lifting of steel cage, and string tube pouring. The construction process is as follows: measurement and layout → leveling the site → pile position layout → burying casing → drilling rig in place → slurry making, punching, slag removal, sampling, punching → hole acceptance → first hole cleaning → lowering steel cage → second hole cleaning → pouring underwater concrete. The slump of concrete pouring is 18cm~22cm. The initial setting time of the first batch of concrete pouring shall not be earlier than the completion time of all concrete pouring of the bored pile. The pouring time should be shortened as much as possible and the operation should be continuous.

[0079] Furthermore, the steel cage is divided into sections according to the conditions in the hole. The single sections are mechanically connected with the same section using a first-level joint, and the main reinforcement and stirrups are spot welded. For the convenience of lifting, the steel cage is made in sections in advance, and the length of each section is about 2.5m~3m, and it is connected on site at the hole mouth; the two sections of the steel cage are connected by a connecting sleeve, and the steel cage is connected by positive wire. The lower section of the steel cage is pulled with 27 buckles of full wire and put into the sleeve, and the upper section of the steel cage is pulled with 13 buckles for docking. The steel cage is lowered by a manual hoist. In order to ensure that the steel cage does not deform during lifting, two-point lifting is adopted, and wooden poles are temporarily added in the steel cage before lifting. The lifting point is set at the connection between the stirrups of the steel cage and the main reinforcement, and the lifting points are symmetrical and lifted at one time.

[0080] Furthermore, the construction of the main structure of the station's underground excavation will begin after the construction of the C-shaped crown beam is completed. The construction of the main structure of the underground excavation section is completed in eight steps. For details, please refer to the part about the construction of the underground excavation structure in the underground excavation method of the three-story six-hole subway station in the previous article. The concrete of the main structure of the underground excavation of the station uses commercial concrete, with a grade of C40P10 waterproof concrete. The on-site construction concrete method is the self-flowing form of ground pump + pump pipe to the working surface. The pump pipe is installed to the innermost side before pouring, and the pouring is completed and removed after one section is completed, and the pouring is backward.

[0081] The waterproofing of the main structure of the dark excavation adopts a fully wrapped flexible waterproof layer on the outside of the station structure. The waterproof structure of the top plate 5 is waterproof coating + isolation layer + concrete protective layer; the waterproof structure of the side wall 6 is cement mortar leveling layer + waterproof membrane; the waterproof structure of the bottom plate 11 is concrete cushion + waterproof membrane + concrete protective layer. In the construction of the dark excavation structure, the initial support base of the sprayed concrete is rough and uneven, the small pipe head is exposed, and there is water seepage in some parts, which has a great impact on the quality of laying the waterproof layer. For this reason, the base surface of the waterproof layer must be leveled, such as dealing with burrs and protrusions, and the laying weight must be not less than 400g / m 2 Geotextile buffer layer and other measures.

[0082] Furthermore, in this embodiment, the diameter of the pipe curtain 1 of the dark excavation section is 457mm, and the spacing is 500mm; the upper five guide holes (3 Z1 guide holes + 2 Z3 guide holes) use the I25b steel frame, and the lower guide hole (Z2 guide hole) uses the steel grid steel frame; the side piles 3 are mechanically bored cast-in-place piles, the middle column adopts the manual hole digging process, and the main structure adopts the reverse construction method. There are a total of about 53 steel pipe curtains 1 for top advance support. The side pile 3 is a φ1000mm@1400mm mechanically bored reinforced concrete bored pile with a depth of 12m; the upper pilot hole (Z1 pilot hole 18 and Z3 pilot hole 20) is 4.5m wide, 4.5m high, and the initial support thickness is 350mm. The temporary support (the first temporary support 9 and the second temporary support 10) uses 25b I-beams; the lower pilot hole (Z2 pilot hole) is 4.0m wide, 5.0m high, and the initial support thickness is 300mm. DN32 small pipe advance support. The main structure top plate 5 is 900mm thick, the middle plate is 400mm thick, the bottom plate 11 is 1000mm thick, and the side wall 6 is 800mm thick.

[0083] Furthermore, the water level before construction was outside the pit, and the water level was 0.5m~1m below the bottom plate 11. During the construction of the dark excavation section, the water level of the shield construction of the open excavation section was continuously reduced, and the water level of the entire station was below the bottom plate 11, which was considered to meet the construction requirements.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A method for underground excavation of a three-layer six-hole subway station, characterized in that: It includes the following steps: In the first step, use the open-cut sections at both ends of the mined section of the station as the pipe roof launching and receiving wells for pipe jacking operations; the pipe roof is arranged in a "冖" shape. After the pipe roof is jacked into place, self-compacting concrete is filled inside the pipes; In the second step, after the pipe roof construction is completed, excavate the lower Z2 pilot tunnel. After the lower Z2 pilot tunnel is贯通, then construct the three upper Z1 pilot tunnels in the order of first the sides and then the middle; the three Z1 pilot tunnels are located on the upper sides and in the middle respectively, and the middle Z1 pilot tunnel is directly above the Z2 pilot tunnel; as the excavation progresses forward, carry out initial support construction for the pilot tunnels, and the grids of the three upper Z1 pilot tunnels are tightly pressed against the pipe roof; after the pilot tunnels are closed into a ring, backfill grouting should be carried out in time behind the initial support; In the third step, construct the bottom longitudinal beam in the Z2 pilot tunnel, construct the top longitudinal beam in the middle Z1 pilot tunnel, dig by hand and construct steel pipe columns; construct side piles in the two side Z1 pilot tunnels, and the side piles are bored piles formed by machinery; then construct the capping beam on the pile tops, and the capping beam is a C-shaped top capping beam; In the fourth step, construct the Z3 pilot tunnel and carry out initial support construction between the middle Z2 pilot tunnel and the two side Z1 pilot tunnels; after贯通, according to the monitoring situation, horizontally and longitudinally segmentally拆除部分Z1导洞、Z3导洞初支, lay the waterproof layer, formwork and pour the top plate and part of the side wall secondary lining; In the fifth step, after the top plate reaches the design strength, excavate the soil downward to the position of the bottom surface of the middle plate on the first basement floor; segmentally construct the middle plate on the first basement floor, the first middle longitudinal beam, and the upper side wall, and construct the waterproof layer and structure of the side wall; In the sixth step: after the concrete strength of the middle plate reaches the design, continue to excavate the soil downward to the position of the temporary support at the mid-span; lay the waterproof layer of the side wall and construct the side wall, then erect the first temporary support, and continue to excavate downward to the position of the bottom surface of the middle plate on the second basement floor; In the seventh step: segmentally construct the middle plate on the second basement floor, the second middle longitudinal beam, and the upper side wall structure, and construct the waterproof layer and structure of the side wall; In the eighth step: continue to excavate downward, and at the same time erect the second temporary support, and carry out shotcrete support between piles during excavation; after excavating to the design elevation, level the foundation pit in time, timely construct the plain concrete cushion to seal the foundation pit, then, lay the waterproof layer and pour the bottom plate; In the ninth step:拆除第二道支撑, pour the lower side wall and the middle column, construct the remaining side wall, waterproof layer and structure, and拆除第一道支撑.

2. The method for underground excavation of a three-layer six-hole subway station according to claim 1 is characterized in that: In the first step, during the pipe jacking operation, adopt laser guidance deviation correction measures; first jack the middle and corner pipes, and jack the top and lateral steel pipes from the middle pipe to both sides in sequence. During the jacking process, strictly control the pipe jacking accuracy and direction, and there shall be no deviation or deflection.

3. The method for underground excavation of a three-layer six-hole subway station according to claim 1 is characterized in that: In the second step, grouting reinforcement is carried out on the base of the Z2 pilot tunnel, and the reinforcement depth is 1.5m. After the pilot tunnel is closed into a ring, backfill grouting should be carried out in time behind the initial support and on the foundation; the grout is a cement-sodium silicate double-fluid grout, the diffusion radius of the grouting slurry is 0.5m, and the unconfined compressive strength of the soil after reinforcement is not less than 0.8MPa.

4. The method for underground excavation of a three-layer six-hole subway station according to claim 1 is characterized in that: During the construction of the pilot tunnel, when constructing the pilot tunnel from the open excavation section to the dark excavation section, a single small guide tube with a length of 6m and a circumferential spacing of 300mm is set at the horse head gate before digging the tunnel. The stratum is reinforced by pre-grouting before the tunnel gate retaining piles can be dug. First, remove 1 / 2 of the concrete pile, cut off the main reinforcement in the grille range, erect a grille, and spray concrete in time. Then, remove the remaining 1 / 2 of the concrete pile, cut off the main reinforcement of the pile, erect a steel grille in close arrangement, spray concrete in time, and use copper buckles to closely connect the three-grade grille. The grille should be firmly welded to the cut-off retaining main reinforcement.

5. The method for underground excavation of a three-layer six-hole subway station according to claim 1 is characterized in that: In the fourth step, the top slab concrete is poured in multiple times with each pouring length of 9m~10m in the long direction. The concrete is poured in layers and vibrated to make it dense. It is vibrated by manual vibrating rods or the vibration system of the trolley.

6. The method for underground excavation of a three-layer six-hole subway station according to claim 1 is characterized in that: The first step is that during the construction of the pipe curtain, two water drills will drill holes continuously in the order from the middle to both sides. The initial hole opening cannot be more than 4 times the pipe curtain spacing. When opening holes at the receiving end, the initial and receiving holes should not be more than 3m. After the pipe curtain passes, the reinforcement of the retaining piles and the pipe curtain steel pipes should be connected in time, with a connection rate of 50% and an unconnected length of no more than 5 pipe curtains.

7. The method for underground excavation of a three-layer six-hole subway station according to claim 1, characterized in that: The pipe curtain consists of two layers. The first layer of pipe curtain is supported along the top surface of the contour line of the Z1 guide tunnel and the Z3 guide tunnel, and the second layer of pipe curtain is supported on the upper part of the side of the contour line of the Z1 guide tunnel.

8. The method for underground excavation of a three-layer six-hole subway station according to claim 1, characterized in that: In the fifth step, when constructing the middle plate and side walls of the first underground floor, the bottom is cleared manually when the excavation surface is 10 cm away from the bottom of the middle plate, and a frog-type rammer is used to compact the bottom while cleaning to control the flatness and elevation of the entire base surface; square timber and formwork are laid on the compacted and leveled sand layer base to form an earth formwork system for pouring the middle plate of the first underground floor, the first middle longitudinal beam, and the upper side walls.

9. The method for underground excavation of a three-layer six-hole subway station according to claim 1, characterized in that: The diameter of the side pile body is 1000mm, and the expanded bottom diameter is 1400mm. The side pile drilling is constructed by reverse circulation drilling rig, and the drilling is carried out in batches with skip holes at intervals. The bored piles are constructed with two holes per interval. The construction sequence is divided into two times as a whole, and the driving sequence is unidirectional to ensure that the steel pipe column construction is as far away from the side pile construction as possible.

10. The method for underground excavation of a three-layer six-hole subway station according to claim 1, characterized in that: In the third step, the gap around the steel pipe column is backfilled with fine sand; in the fifth step, the gap between the C-shaped crown beam and the upper Z1 guide hole is backfilled with C20 concrete.

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