Construction method for large-span subway tunnel with large and small sections connected in water-rich sand layer

Abstract

The invention relates to the technical field of subway tunnel construction, in particular to a construction method for a large-span large-small-section-connected subway tunnel in a water-rich sand layer, and provides targeted construction technologies such as water-rich sand layer excavation face radiation range precipitation and interval large-span large-small-section-connected sequential construction. The whole set of large-span large-section and small-section connected tunnel construction method for the water-rich sand layer is formed, the purpose of safe and efficient precipitation is achieved, the influence of underground water of the strong-permeability stratum on construction is reduced, and the influence of construction on the safety of existing buildings is reduced. Meanwhile, the problem of rapid conversion of the large section and the small section is solved, adverse effects caused by stress conversion of the variable-section structure are eliminated, and the site construction time is shortened.

Description

Technical Field

[0001] The invention relates to the technical field of subway tunnel construction, and in particular to a subway tunnel construction method in which a water-rich sand layer has large spans and large and small sections connected. Background Art

[0002] Water-rich sandy strata are unstable and weak surrounding rocks that are easily damaged. Their basic characteristics are loose structure, lack of bonding, and strong permeability. The risk of water inrush and sand burst during tunnel construction in such strata is huge. In addition, with the continuous expansion of the scale of urban subway network construction, the number of large-span and variable-section tunnel construction designs in subway sections is increasing. The shallow buried and dark excavation sections are large, and the sequential construction of dark excavation pilot tunnels using multiple methods causes multiple mutual disturbances between soil bodies, making ground settlement difficult to control, making construction organization difficult, and construction risks high. The sections change frequently from large to small, and the structural force conversion is very complex. The excavation process transition at the sudden change of the section is complex, and the safety risk is high, which brings great difficulty to the construction. Summary of the invention

[0003] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a subway tunnel construction method with large spans and large and small sections in water-rich sand layers. Targeted construction technologies such as precipitation in the radiation range of the excavation surface of the water-rich sand layer and sequential construction of large spans and large and small sections in the interval are proposed to form a complete set of tunnel construction methods with large spans and large and small 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 large and small sections in a water-rich sand layer, comprising the following steps:

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

[0007] Before tunnel excavation, dewatering wells are set up in sections on both sides of the tunnel section to pump out groundwater. The number of dewatering wells to be pumped out increases with the distance of tunneling along the main line. Water level observation holes are 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 the half section of the arch to reinforce the stratum, and a single row of small pipes are set up for advance grouting support;

[0010] 4) Excavation of the large section of the tunnel to the junction of the large and small sections: the large section is excavated by the double-side wall pilot method. After each cavern is excavated, concrete is sprayed to seal the heading face, and initial support and temporary support are immediately carried out. After that, the temporary steel frame is removed according to the monitoring situation, and a waterproof layer and secondary lining are applied;

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

[0012] 6) Temporary blocking of the junction of large and small sections: If the caverns where large and small sections are connected are expanded, the junction with the small section pilot tunnel should be temporarily blocked. After the construction of the large section pilot tunnels is completed and formed into a ring, the temporary blocking wall is broken, and then the small section pilot tunnel is constructed;

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

[0014] 8) Dowel bars should be reserved at the node distribution excavation and the intersection of the small section and the large section. The large section grid should be installed at the overlap of the small section and the large section steel grid, and the small section grid should be cancelled. The main bars of the small section grid and the large section grid should 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 is drilled on the surface with a drilling rig, and the diameter of the hole is not less than 80 mm, and then the prepared monitoring mark is buried, and the threaded steel mark point is fixed to the surrounding original soil with concrete at the bottom, and then filled with fine sand around, and a protective cover and a cover plate are set at the same time.

[0017] As the preferred technical solution of the present invention, in step 1), a water level monitoring hole is selected to be drilled outside the tunnel structure. A drilling rig is first used to drill a hole with a diameter of 100 mm on the ground. The water level pipe has a diameter of about 70 mm and a pipe body densely covered with small holes. A dense net is wrapped around the outside of the water level pipe to prevent the water level pipe from entering 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. Necessary protective devices are set at the water level pipe mouth.

[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; 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 a stop 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. The grouting pipe adopts DN32 anchor pipe grouting 10, L=2m, and the spacing is 1.0m×1.0m in a plum blossom shape. 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 beneficial effects of the present invention are as follows:

[0021] The present invention achieves the purpose of safe and efficient precipitation, reduces the impact of groundwater in highly permeable strata on construction, and reduces the impact of construction on the safety of existing buildings. At the same time, it solves the problem of rapid conversion of large and small sections, eliminates the adverse effects caused by the force conversion of variable section structures, and shortens the on-site construction time. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0025] Figure 4 This is a schematic plan view of the initial support plugging wall with large and small sections connected by 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-semi-section deep hole grouting; 4-advanced small duct grouting; 5-middle partition wall; 6-middle partition board; 7-locking anchor rod; 10-anchor pipe grouting; 11-plug wall; 12-the overlap between the small-section and large-section steel gratings; 13-large-section steel frame; 14-small-section steel grating. DETAILED DESCRIPTION

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

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

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

[0030] like Figure 1 As shown in the figure, before tunnel excavation, dewatering wells were set up on both sides of the section along the line. A total of 64 wells were designed on both sides of the tunnel, and the wells were located as far away from the edge of the foundation pit as possible by 3 to 4 meters. Dewatering well 1 in the construction scope of the vertical shaft and the horizontal passage was set up with 10 dewatering wells at intervals of 5 to 10 meters, and the depth of the dewatering wells was 36 meters; the interval of dewatering well 2 in the main line of the section was 15 meters apart and 32 meters deep.

[0031] According to the current specifications and design requirements, measurement and positioning, drilling rig placement, hole forming, laying of well pipe, filling of filter material, laying of submersible pump, and water testing are carried out in sequence. They will not be described in detail in this embodiment, and the focus will be on the implementation method of the method involved in 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, reinforcement or recharge and other corresponding emergency rescue measures that meet the working conditions should be implemented in time.

[0033] The buried ground settlement observation points should penetrate the surface structure 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 on the surface with a diameter of not less than 80mm, and then bury the prepared monitoring mark (rebar with a diameter of 18-22mm). The rebar mark point is fixed to the surrounding original soil with concrete at the bottom. The consolidation length of the bottom concrete should be 50mm, and then the surrounding area is filled with fine sand. At the same time, a protective cover and cover plate are set. When arranging the measuring points, the location, direction, burial depth and other information of the underground pipelines should be found 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 put a water level meter probe into 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 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 net 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. 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 in the vertical shaft and the horizontal passage maintain precipitation to ensure that the precipitation radiation range before and after the operation surface is ≥15m. The water level is observed through the observation well and the water level line is controlled to be 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. Water level observation should be carried out well and problems should be dealt with in a timely manner when discovered.

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

[0040] 3) Advance support of excavation surface: 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.

[0041] like Figure 2 As shown, half-section deep hole grouting 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 3 has 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.

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

[0043] 4) Excavation of large-section tunnel to the junction of large and small sections: Double-side wall pilot tunnel method is used to excavate large sections. After each cavern is excavated, concrete is sprayed to seal the heading face, and initial support and temporary support are immediately carried out, including the erection of steel grids and temporary steel frames (middle partitions, middle partitions), and the installation of locking anchors 7. Afterwards, the temporary steel frames are dismantled according to the monitoring situation, and waterproof layers and secondary linings are applied.

[0044] The double side wall pilot method excavates the section, staggering the distance of one time the tunnel diameter to excavate the caverns in sequence ①→②→③→④→⑤→⑥( Figure 2 The excavation spacing of the upper and lower adjacent small pilot tunnels ①②, ③④, ⑤⑥ is 5-6m, and the excavation spacing of the ②③, ④⑤ pilot tunnels is 10m. After each cavern is excavated, the middle partition 6, the middle partition wall 5 and the initial support are constructed.

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

[0046] 6) Temporary blocking of the junction of large and small sections: If the small section guide 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 forward into the small-section pilot tunnel without temporary blocking; if there is expansion ( Figure 3 The connection between the large-section guide holes and the small-section guide holes should be temporarily blocked. The thickness of the temporary blockage is the same as the thickness of the middle partition wall. After the large-section guide holes are completed and formed into a ring, the temporary blockage wall is broken, and then the small-section guide holes are constructed.

[0047] 7) A plug wall 11 is set up at the vacant space where the tunnel section suddenly changes: the main part of the plug wall 11 is reinforced with anchor pipe grouting 10. The grouting pipe adopts DN32 (t = 3.25mm) anchor pipe grouting 10, L = 2m, and the spacing is 1.0m × 1.0m in a plum blossom arrangement. The grouting liquid is the same as the advanced support. A large-section steel grid is placed on the outside of the plug 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 plug wall 11 (such as Figure 4 shown).

[0048] 8) Dowel bars should be reserved at the node distribution excavation and the intersection of the small section and the large section. The length of dowel bars is determined according to the on-site construction conditions. The large section grid is constructed at the overlap of the small section and the large section steel grid, and the small section grid is cancelled. The main bars of the small section grid and the large section grid are welded before the grid overlaps.

[0049] 9) The subsequent small-section caverns of 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 heading direction, the temporary support of the transition section is removed one by one according to the inspection results, and the lateral excavation construction conversion is finally completed when the tunnel section suddenly changes to a large-span section.

[0050] The above contents are merely examples and explanations of the concept of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described 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 protection scope 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 in the radiation range of excavation surface of water-rich sand layer: Before tunnel excavation, dewatering wells are set up in sections on both sides of the tunnel section to pump out groundwater. The number of dewatering wells to be pumped out increases with the distance of tunneling along the main line. Water level observation holes are 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 the half section of the arch to reinforce the stratum, and a single row of small pipes are set up for advance grouting support; 4) Excavation of the large section of the tunnel to the junction of the large and small sections: the large section is excavated by the double-side wall pilot method. After each cavern is excavated, concrete is sprayed to seal the heading face, and initial support and temporary support are immediately carried out. After that, the temporary steel frame is removed according to the monitoring situation, and a waterproof layer and secondary lining are applied; 5) Reinforcement of the face where large and small sections meet: For the pilot tunnel that will be expanded later, anchor pipe grouting reinforcement of the face is carried out after the large-section pilot tunnel is constructed; 6) Temporary blocking of the junction of large and small sections: If the caverns where large and small sections are connected are expanded, the junction with the small section pilot tunnel should be temporarily blocked. After the construction of the large section pilot tunnels is completed and formed into a ring, the temporary blocking wall is broken, and then the small section pilot tunnel is constructed; 7) A plugging wall is set up at the vacant part where the tunnel section changes suddenly, and anchor pipe grouting is used for reinforcement; 8) Dowel bars should be reserved at the node distribution excavation and the intersection of the small section and the large section. The large section grid should be installed at the overlap of the small section and the large section steel grid, and the small section grid should be cancelled. The main bars of the small section grid and the large section grid should 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 large spans and large and small sections in water-rich sand layers as claimed in claim 1, characterized in that: In step 1), the buried ground 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, drill a hole in the ground with a drilling rig with a diameter of not less than 80mm, and then bury the prepared monitoring mark. At the bottom, fix the threaded steel mark point to the surrounding original soil with concrete, 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 large spans and large and small sections in water-rich sand layers 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. A 100mm diameter hole is first 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 net 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. Necessary protective devices are set at the water level pipe mouth.

4. The method for constructing a subway tunnel with large spans and large and small sections in water-rich sand layers 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 a stop 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 large spans and large and small sections in water-rich sand layers 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 the spacing is 1.0m×1.0m in a plum blossom shape. 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 primary 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.

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