A method for constructing a subway tunnel with large spans and connected sections in a water-rich sand layer

Abstract

A method for constructing a subway tunnel with large spans and connected sections in a water-rich sand layer relates to the technical field of subway tunnel construction. The present invention proposes targeted construction techniques, including dewatering within the excavation surface of the water-rich sand layer and sequential construction of connected sections with large spans and small sections. This complete method achieves safe and efficient dewatering, reduces the impact of groundwater in highly permeable strata on construction, and minimizes the impact of construction on the safety of existing buildings. Furthermore, it solves the problem of rapid conversion between large and small sections, eliminates the adverse effects caused by force conversion in variable-section structures, and shortens on-site construction time.

Description

Technical Field

[0001] The present invention relates to the technical field of subway tunnel construction, in particular to a method for constructing a subway tunnel with a water-rich sand layer having a large span and connected large and small sections. Background Art

[0002] Water-rich sandy strata are unstable, weak surrounding rocks that are easily damaged. Their fundamental characteristics are a loose, uncohesive structure and high permeability. Tunnel construction in such strata carries a significant risk of water inrush and sand bursts. Furthermore, with the continuous expansion of urban subway network construction, the design of large-span, variable-section tunnels within subway sections is increasing. These shallow, excavated sections are large, and the sequential construction of multiple-method excavation pilot tunnels causes multiple disturbances between the soil masses, making ground subsidence difficult to control. Construction organization is challenging, construction risks are high, and sections frequently change from large to small, leading to complex structural force transitions. The excavation process at sudden changes in section is complex, posing high safety risks and presenting significant construction challenges. Summary of the Invention

[0003] In view of the shortcomings of the aforementioned prior art, the present invention aims to provide a method for constructing subway tunnels with large spans and interconnected sections in water-rich sand layers. This method proposes targeted construction techniques, including dewatering within the excavation surface of the water-rich sand layer and sequential construction of interconnected sections with large spans and interconnected sections, forming a complete method for constructing tunnels with large spans and interconnected sections in water-rich sand layers.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A method for constructing a subway tunnel with a large span and connected small and large sections in a water-rich sand layer comprises the following steps:

[0006] 1) Method of precipitation operation within the radiation range of the excavation surface of the water-rich sand layer:

[0007] Before tunnel excavation, dewatering wells were drilled at sections along both sides of the tunnel section to pump out groundwater. The number of dewatering wells pumped increased with the distance of the mainline excavation. Water level observation holes were set up outside the foundation pit to monitor the changes in water level and settlement outside the pit in a timely manner.

[0008] 2) Excavation surface dewatering operation: according to the excavation depth, the dewatering well pump in the corresponding range is continuously opened to maintain dewatering;

[0009] 3) Advance support of excavation face: deep hole grouting is carried out on half section of arch to reinforce the stratum, and a single row of small guide tubes are installed for advance grouting support;

[0010] 4) Excavation of the large tunnel section to the junction of the large and small sections: The large section is excavated using the double-side wall pilot method. After each cavern is excavated, the tunnel face is sealed with sprayed concrete, and initial support and temporary support are immediately carried out. Afterwards, the temporary steel frame is removed based on monitoring results, and a waterproof layer and secondary lining are applied.

[0011] 5) Reinforcement of the tunnel face where large and small sections meet: For pilot tunnels that will be expanded later, anchor pipe grouting reinforcement of the tunnel face will be carried out after the large section pilot tunnel is constructed;

[0012] 6) Temporary blocking of the junction of large and small sections: If the cavern where the large and small sections meet is excavated, the junction with the small section pilot tunnel shall be temporarily blocked. After the large section pilot tunnels are completed and form a ring, the temporary blocking wall shall be broken, and then the small section pilot tunnel shall be constructed;

[0013] 7) A plug wall is set up at the vacant part where the tunnel section changes suddenly, and anchor pipe grouting is used for reinforcement;

[0014] 8) Inserted reinforcement shall be reserved at the node distribution excavation and the intersection of the small section and large section middle partition wall; large section grid shall be installed at the overlap of small section and large section steel grid, and the small section grid shall be cancelled. The main reinforcement of small section grid and large section grid shall be welded before the grid overlaps;

[0015] 9) The subsequent small-section caverns in the transition section are excavated, initially supported and temporarily supported in the same order as the large-section construction, and finally the lateral excavation construction conversion is completed when the tunnel section suddenly changes to a large-span section.

[0016] As a preferred technical solution of the present invention, in step 1), the surface settlement observation point should be buried through the surface structural layer and buried in a relatively solid stratum with a burial depth of not less than 150 cm; first, a hole should be drilled on the surface with a drill rig, and the diameter of the hole should be not less than 80 mm. Then, the prepared monitoring mark should be buried, and the threaded steel mark point at the bottom should be fixed to the surrounding original soil with concrete, and then filled with fine sand around it, and a protective cover and a cover plate should be set at the same time.

[0017] As a preferred technical solution of the present invention, in step 1), a water level monitoring hole is selected to be drilled on the outside of the tunnel structure. First, a hole with a diameter of 100 mm is drilled on the ground with a drilling rig. The water level pipe has a diameter of about 70 mm and is densely covered with small holes. A dense mesh is wrapped around the outside of the water level pipe to prevent mud and sand from entering the water level pipe and blocking the measuring hole. A 1m sedimentation section is set at the bottom of the water level pipe. After the hole is formed at the measuring point, the water level pipe is placed in and clean water is injected into the water level pipe. The water level pipe mouth is equipped with necessary protective devices.

[0018] As a preferred technical solution of the present invention, in step 3), four rings of grouting holes are drilled on the working face, and the drilling angles of the first to fourth rings are 37°, 28°, 21°, and 17° respectively; the horizontal spacing of the holes is 500mm, and the vertical spacing of the rings is 1000mm. The holes are drilled radially from the working face to the excavation direction, forming a grouting reinforcement body with a grouting range of 0.5m inside the initial support contour line to 3m outside the contour line, with a total thickness of 3.5m; half-section deep hole grouting is carried out in a cycle section of 12m along the tunnel excavation direction; after a grouting section is completed, 2m is left unexcavated as a grouting rock plate for the next cycle; a ring of advance small guide tubes is drilled on the arch top, the small guide tubes are 2.0m long, with a circumferential spacing of 0.3m and an inclination of 16°.

[0019] As the preferred technical solution of the present invention, in step 7), the main part of the plugging wall is reinforced by anchor pipe grouting, and the grouting pipe adopts DN32 anchor pipe grouting 10, L=2m, and a plum blossom-shaped arrangement with a spacing of 1.0m×1.0m, and the slurry is the same as the advanced support; a large-section steel grating is placed on the outside of the plugging wall, and a small-section steel grating is placed on the inside. When the initial lining steel grating crosses and overlaps, the small-section steel grating is cut off, and the main reinforcement of the small-section steel grating is anchored into the large-section steel frame and welded to the main reinforcement of the large-section steel frame, and concrete is sprayed in time to permanently seal the plugging wall.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention achieves the goal of safe and efficient water reduction, reduces the impact of groundwater in highly permeable strata on construction, and minimizes the impact of construction on the safety of existing buildings. It also solves the problem of rapid conversion between large and small sections, eliminates the adverse effects caused by force conversion in variable-section structures, and shortens on-site construction time. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the layout of the dewatering wells according to the method of the present invention.

[0023] Figure 2 This is a schematic diagram of cross-section grouting reinforcement and excavation using the method of the present invention.

[0024] Figure 3 This is a schematic diagram of the construction of connecting large and small sections using the method of the present invention.

[0025] Figure 4 This is a plan view of the primary support plugging wall where large and small sections are connected using the method of the present invention.

[0026] The meanings of the reference numerals in the figure are: 1-dewatering wells within the construction scope of vertical shafts and horizontal passages; 2-dewatering wells on the main line of the section; 3-dewatering wells on the half-section deep hole; 4-advanced small-duct grouting; 5-middle partition wall; 6-middle partition board; 7-locking anchor rods; 10-anchor pipe grouting; 11-head wall; 12-the overlap between the small-section and large-section steel grilles; 13-large-section steel frame; 14-small-section steel grilles. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with embodiments and drawings.

[0028] This embodiment proposes a method for constructing a subway tunnel with a large span and connected sections in a water-rich sand layer, and the steps are as follows:

[0029] 1) Method of precipitation operation within the radiation range of the excavation surface of the water-rich sand layer:

[0030] like Figure 1 As shown, before tunnel excavation, dewatering wells were drilled on both sides of the tunnel section. A total of 64 wells were designed on both sides of the tunnel, and the wells were located as far as possible from the foundation pit edge by 3-4 meters. Dewatering well 1 within the vertical shaft and cross passage construction area was drilled with 10 dewatering wells spaced 5-10 meters apart, with a depth of 36 meters. Dewatering well 2 within the section mainline was drilled with a spacing of 15 meters and a depth of 32 meters.

[0031] According to the current specifications and design requirements, measurement and positioning, drilling rig placement, hole formation, laying of well pipe, filling of filter material, laying of submersible pump, and water testing are carried out in sequence. This embodiment will not be repeated here, and the focus will be on the implementation method of the present invention.

[0032] Water level observation holes are set up outside the foundation pit and a settlement monitoring network is established to timely monitor changes in the water level and settlement outside the pit. When the settlement reaches the alarm value, corresponding emergency rescue measures such as reinforcement or recharge that are in line with the working conditions should be implemented in a timely manner.

[0033] The buried surface settlement observation points should penetrate the surface structural layer and be buried in a relatively solid stratum with a burial depth of not less than 150cm. First, use a drilling rig to drill a hole in the ground with a diameter of not less than 80mm. Then bury the prepared monitoring marker (rebar with a diameter of 18-22mm). Fix the rebar marker point with concrete and the surrounding original soil at the bottom. The bottom concrete consolidation length should be 50mm. Fill the surrounding area with fine sand and set a protective cover and cover plate. When arranging the measuring points, the location, direction, burial depth and other information of the underground pipelines should be ascertained in advance to avoid damaging the existing pipelines when arranging the points.

[0034] Building settlement monitoring points use embedded L-shaped threaded steel marking points or adhesive direct monitoring points, and are observed using a level.

[0035] The groundwater level observation equipment uses an electronic water level meter. Its working principle is to place a water level meter probe in the buried water level pipe. The groundwater level observation equipment uses an electric water level meter. When the probe contacts the groundwater, the alarm sends an alarm signal. At this time, the scale connected to the probe is read. This reading is the vertical distance between the water level and the fixed measurement, and then converted into the water level depth and water level elevation from the ground through the elevation of the fixed measuring point and its relative position to the ground.

[0036] The water level monitoring hole in this section is chosen to be drilled outside the tunnel structure. First, a 100mm diameter hole is drilled on the ground with a drilling rig. The water level pipe has a diameter of about 70mm and is densely covered with small holes. A dense mesh is wrapped around the outside of the water level pipe to prevent mud and sand from entering the pipe and blocking the hole. A 1m sedimentation section is set at the bottom of the water level pipe. After the hole is drilled at the measuring point, the water level pipe is placed in and clean water is injected into the water level pipe. Necessary protective devices are set at the water level pipe mouth to prevent debris or off-site sewage from entering the pipe.

[0037] During the process of breaking the horse head gate, the precipitation wells within the vertical shaft and horizontal passage are maintained to ensure that the precipitation radiation range before and after the operation surface is ≥15m, and the water level is observed through the observation well to control the water level line to 1m below the bottom plate.

[0038] Pre-precipitation should be carried out within 15m along the excavation direction of the main line of the section. The precipitation well pump in the opposite direction should keep running to maintain precipitation, to ensure that there is no water 1m below the excavation surface. Carry out water level observation and deal with problems in a timely manner when they are discovered.

[0039] 2) Dewatering operation on the excavation surface: according to the excavation depth, continuously open the dewatering well pump in the corresponding range to maintain dewatering.

[0040] 3) Advance support of excavation surface: deep hole grouting is performed on half section of arch to reinforce the stratum, and a single row of small guide tubes are installed for advance grouting support.

[0041] like Figure 2 As shown, semi-section deep hole grouting 3: Four rings of grouting holes are drilled in the working face, with the first to fourth rings drilled at angles of 37°, 28°, 21°, and 17°, respectively. The holes are spaced 500mm apart horizontally and 1000mm apart vertically. The holes are drilled radially from the working face toward the excavation direction, creating a grouting reinforcement extending from 0.5m inside the primary support contour to 3m outside it, with a total thickness of 3.5m. Semi-section deep hole grouting 3 is performed in 12m-long cycles along the tunneling direction. After each grouting cycle, 2m of unexcavated rock is left as a stop rock for the next cycle.

[0042] Advance small conduit grouting 4 support: a ring of advance small conduits (DN32 (t = 3.25mm)) is set on the arch top. The small conduits are 2.0m long, with an annular spacing of 0.3m and an inclination angle of 16°.

[0043] 4) Excavation of the large tunnel section to the junction of the large and small sections: The large section is excavated using the double-sidewall pilot method. After each chamber is excavated, the tunnel face is sealed with sprayed concrete. Initial and temporary support are immediately implemented, including the installation of steel grids and temporary steel frames (middle partitions and middle partitions), and the installation of 7 locking anchors. The temporary steel frames are then removed based on monitoring results, and a waterproof layer and secondary lining are applied.

[0044] Double side wall pilot method excavation section, staggered by one time the hole diameter spacing to excavate the cave chambers ①→②→③→④→⑤→⑥ ( Figure 2 (As shown in the figure), the spacing between adjacent small pilot tunnels ①②, ③④, ⑤⑥ is 5-6 meters, and the spacing between pilot tunnels ②③, ④⑤ is 10 meters. After each cavern excavation, the middle partition 6, the middle partition wall 5, and the initial support are installed.

[0045] 5) Reinforcement of the tunnel face where large and small sections meet: For the pilot tunnel that will be expanded later, the tunnel face will be reinforced by anchor pipe grouting 10 after the construction of the large-section pilot tunnel. The grouting pipe uses DN32 (t=3.25mm) anchor pipe grouting 10, L=2m, and a plum blossom-shaped arrangement with a spacing of 1.0m×1.0m.

[0046] 6) Temporary blocking of the junction of large and small sections: If the small section pilot hole connected does not have expansion ( Figure 3 As shown in position A in the middle), you can continue to construct from this pilot tunnel into the small-section pilot tunnel without temporary blocking; if there is expansion ( Figure 3 The connection between it and the small-section pilot hole should be temporarily blocked. The thickness of the temporary blocking is the same as the thickness of the middle partition wall. After the large-section pilot holes are completed and formed into a ring, the temporary blocking wall should be broken, and then the small-section pilot hole should be constructed.

[0047] 7) A plugging wall 11 is set up at the vacant part of the tunnel section: the main part of the plugging wall 11 is reinforced with anchor pipe grouting 10. The grouting pipe adopts DN32 (t=3.25mm) anchor pipe grouting 10, L=2m, and is arranged in a plum blossom shape with a spacing of 1.0m×1.0m. The slurry is the same as the advanced support. A large-section steel grid is placed on the outside of the plugging wall 11, and a small-section steel grid is placed on the inside. When the primary lining steel grid crosses and overlaps, the small-section steel grid is cut off. The main reinforcement of the small-section steel grid 14 is anchored into the large-section steel frame 13 and welded to the main reinforcement of the large-section steel frame 13. Concrete is sprayed in time to permanently seal the plugging wall 11 (such as Figure 4 shown).

[0048] 8) Dowels must be reserved at the node distribution excavation and the intersection of the small section and large section partition walls. The dowel length is determined according to the on-site construction conditions. Where the small section and large section steel grilles overlap, the large section grille is installed and the small section grille is eliminated. The main reinforcement of the small section grille and the large section grille are welded before the grilles overlap.

[0049] 9) The subsequent small-section caverns in the transition section are excavated, initially supported and temporarily supported in the same order as the large-section construction. Finally, as the construction progresses in the direction of the heading face, the temporary support of the transition section is removed one by one according to the inspection results, and the horizontal excavation construction conversion is finally completed when the tunnel section suddenly changes to a large-span section.

[0050] The above content is merely an example and explanation of the concept of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A method for constructing a subway tunnel with large spans and large and small sections in a water-rich sand layer, characterized in that: The following steps are involved: 1) Method of precipitation operation within the radiation range of the excavation surface of the water-rich sand layer: Before tunnel excavation, dewatering wells were drilled at sections along both sides of the tunnel section to pump out groundwater. The number of dewatering wells pumped increased with the distance of the mainline excavation. Water level observation holes were set up outside the foundation pit to monitor the changes in water level and settlement outside the pit in a timely manner. 2) Excavation surface dewatering operation: according to the excavation depth, the dewatering well pump in the corresponding range is continuously opened to maintain dewatering; 3) Advance support of excavation face: deep hole grouting is carried out on half section of arch to reinforce the stratum, and a single row of small guide tubes are installed for advance grouting support; 4) Excavation of the large tunnel section to the junction of the large and small sections: The large section is excavated using the double-side wall pilot method. After each cavern is excavated, the tunnel face is sealed with sprayed concrete, and initial support and temporary support are immediately carried out. Afterwards, the temporary steel frame is removed based on monitoring results, and a waterproof layer and secondary lining are applied. 5) Reinforcement of the tunnel face where large and small sections meet: For pilot tunnels that will be expanded later, anchor pipe grouting reinforcement of the tunnel face will be carried out after the large section pilot tunnel is constructed; 6) Temporary blocking of the junction of large and small sections: If the cavern where the large and small sections meet is excavated, the junction with the small section pilot tunnel shall be temporarily blocked. After the large section pilot tunnels are completed and form a ring, the temporary blocking wall shall be broken, and then the small section pilot tunnel shall be constructed; 7) A plug wall is set up at the vacant part where the tunnel section changes suddenly, and anchor pipe grouting is used for reinforcement; 8) Inserted reinforcement shall be reserved at the node distribution excavation and the intersection of the small section and large section middle partition wall; large section grid shall be installed at the overlap of small section and large section steel grid, and the small section grid shall be cancelled. The main reinforcement of small section grid and large section grid shall be welded before the grid overlaps; 9) The subsequent small-section caverns in the transition section are excavated, initially supported and temporarily supported in the same order as the large-section construction, and finally the lateral excavation construction conversion is completed when the tunnel section suddenly changes to a large-span section.

2. The method for constructing a subway tunnel with a large span and large and small sections in a water-rich sand layer as claimed in claim 1, characterized in that: In step 1), the surface settlement observation point should be buried through the surface structural layer and buried in a relatively solid stratum with a burial depth of not less than 150 cm; first, use a drill to drill a hole in the surface with a diameter of not less than 80 mm, then bury the prepared monitoring mark, fix the threaded steel mark point to the surrounding original soil with concrete at the bottom, and then fill it with fine sand around it, and set a protective cover and cover plate at the same time.

3. The method for constructing a subway tunnel with a large span and large and small sections in a water-rich sand layer as claimed in claim 1, characterized in that: In step 1), a water level monitoring hole is selected to be drilled outside the tunnel structure. First, a hole with a diameter of 100mm is drilled on the ground with a drilling rig. The diameter of the water level pipe is about 70mm, and the pipe body is densely covered with small holes. A dense mesh is wrapped around the water level pipe to prevent the water level pipe from entering the mud and blocking the measuring hole. A 1m sedimentation section is set at the bottom of the water level pipe. After the hole is formed at the measuring point, the water level pipe is placed in and clean water is injected into the water level pipe. The water level pipe mouth is equipped with necessary protective devices.

4. The method for constructing a subway tunnel with a large span and large and small sections in a water-rich sand layer as claimed in claim 1, characterized in that: In step 3), four rings of grouting holes are drilled on the working face, and the drilling angles of the first to fourth rings are 37°, 28°, 21°, and 17° respectively; the horizontal spacing of the holes is 500mm, and the vertical spacing of the rings is 1000mm. The holes are drilled radially from the working face to the excavation direction, forming a grouting reinforcement body with a grouting range of 0.5m inside the initial support contour line to 3m outside the contour line, with a total thickness of 3.5m; the half-section deep hole grouting is a cycle section of 12m along the tunnel excavation direction; after a grouting section is completed, 2m is left unexcavated as the grouting rock plate for the next cycle; a ring of advance small guide tubes is drilled on the arch top, the small guide tubes are 2.0m long, with a circumferential spacing of 0.3m and an inclination of 16°.

5. The method for constructing a subway tunnel with a large span and large and small sections in a water-rich sand layer as claimed in claim 1, characterized in that: In step 7), the main part of the plugging wall is reinforced by anchor pipe grouting. The grouting pipe adopts DN32 anchor pipe grouting 10, L=2m, and a plum blossom-shaped arrangement with a spacing of 1.0m×1.0m. The slurry is the same as the advanced support. A large-section steel grille is placed on the outside of the plugging wall, and a small-section steel grille is placed on the inside. When the primary lining steel grille crosses and overlaps, the small-section steel grille is cut off, and the main reinforcement of the small-section steel grille is anchored into the large-section steel frame and welded to the main reinforcement of the large-section steel frame. Concrete is sprayed in time to permanently seal the plugging wall.

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