Shallow-buried tunnel excavation and support method

Abstract

The present invention discloses an excavation support method and a support structure for a shallow-buried tunnel passing through a water-rich stratum, which relates to the field of tunnel engineering and aims to improve the advanced drainage efficiency and the stability of the support structure. The technical solution adopted by the present invention is as follows: for the excavation support method of a shallow-buried tunnel, drill holes at the working face directly above the tunnel, use the drill holes as drainage wells for drainage, lower the groundwater level, then excavate the tunnel and drill tie rod holes, place steel skeletons and tie rod steel bars in the drill holes and tie rod holes, and pour concrete to form an integral support structure, and the support structures are arranged at intervals along the axis of the tunnel. The support structure of the shallow-buried tunnel is obtained by constructing through the above-mentioned excavation support method of the shallow-buried tunnel. The present invention uses the drill holes as drainage wells for drainage, with high advanced drainage efficiency and no occupation of the straight construction period; the support structure is buried in the soil body, which is not only safe but also has good stability. The present invention is used for the excavation support of a shallow-buried tunnel passing through a water-rich stratum.

Description

Technical Field

[0001] The invention relates to the field of tunnel engineering, in particular to an excavation support method and a support structure for a shallow-buried deep tunnel passing through a water-rich stratum. Background Art

[0002] The excavation of shallow buried deep tunnels through water-rich strata is difficult, the construction process is relatively complex, and it is easy to cause safety accidents such as tunnel collapse. At present, the main construction process is the combination of advanced drainage and advanced support. Advanced drainage holes are drilled on the face to pre-drain groundwater. After the tunnel is excavated, steel supports, steel mesh and shotcrete are used for initial support to achieve the purpose of smooth excavation.

[0003] The above construction technology has the following shortcomings: First, the effect of advance drainage is limited, especially for tunnel sections with abundant groundwater. It takes a long time to advance drainage at the face and it is impossible to accurately judge the time of groundwater discharge, resulting in delayed construction progress and increased construction costs. Second, the advance support construction occupies the linear construction period, slowing down the construction progress. Third, the steel support needs to be prefabricated into the designed shape and size. The steel support often cannot fit closely with the tunnel excavation contour, and the support effect is not good. Fourth, the steel mesh is laid on the outside of the steel support, and there is a large gap between it and the surrounding rock, which is not conducive to the long-term stability of the surrounding rock on the top of the tunnel. Fifth, when the tunnel is excavated by blasting, the steel support close to the face is easily damaged, causing damage to the support structure and leading to safety hazards. Sixth, the bottom of the steel support is easily hollowed out under the immersion of groundwater and the rolling of slag transport vehicles, causing a major safety hazard. Summary of the invention

[0004] The present invention firstly provides a shallow buried deep tunnel excavation support method, the purpose of which is to improve the advance drainage efficiency and improve the stability of the support structure.

[0005] The technical solution adopted by the present invention to achieve the above-mentioned purpose is: a shallow buried deep tunnel excavation support method, comprising the following steps:

[0006] S1. Level the site and determine the drilling points: Clear the working surface on the surface directly above the tunnel, and arrange the drilling points outside the projection of the working surface along the tunnel side wall.

[0007] Specifically: there are at least two rows of drilling points, both rows of drilling points are arranged along the axis of the tunnel, the distance between each row of drilling points and the vertical plane of the adjacent tunnel side wall is 20 to 40 cm, and the horizontal spacing between each row of drilling points is 50 to 150 cm.

[0008] S2. Casings are buried at each drilling point and the static mud wall drilling process is used to drill the holes. The bottom elevation of the holes is lower than the elevation of the tunnel floor.

[0009] For example, the inner diameter of the casing is 20 - 40 cm larger than the pile diameter, and the burial depth of the casing is 200 - 400 cm.

[0010] S3. Clear the drilled hole and lower the water level: Clear the drilled hole, and after clearing, use it as a drainage well to drain water and lower the water level.

[0011] For example, after the drilled hole reaches the designed depth, check the hole depth and hole position and clear the hole. The hole is cleared by the pumping method; after clearing, place the well pipe into the drilled hole, then place the drainage pipe into the well pipe, and connect the drainage pipe to a water pump for drainage.

[0012] S4. Tunnel excavation construction: After the water levels of the drilled holes within the single - cycle excavation length range of the tunnel are all lower than the elevation of the tunnel floor, conduct single - cycle excavation of the tunnel until the designed cross - sectional dimensions are reached.

[0013] S5. Select one drilled hole on each side of the tunnel axis to form a group. Select at least one group of drilled holes in the tunnel section of single - cycle excavation, and place steel skeletons in each group of drilled holes.

[0014] Furthermore: The distances from the centerlines of the two drilled holes in the same group to the tunnel axis are equal.

[0015] Furthermore: The vertical plane where the centerlines of the two drilled holes in the same group are located is perpendicular to the tunnel axis.

[0016] Furthermore: The drilled holes in each group are arranged at equal horizontal intervals along the tunnel axis.

[0017] For example, the steel skeleton includes main bars arranged vertically and stirrups arranged along the horizontal plane. The steel skeleton is rectangular in the horizontal cross - section, and the long side of the rectangle is parallel to the vertical plane where the centerlines of the two drilled holes are located.

[0018] Specifically: The length of the long side of the rectangle is 50 - 100 mm smaller than the drilled - hole diameter.

[0019] S6. Drill tie - rod holes in the tunnel and install tie - rod steel bars: Drill tie - rod holes on the tunnel wall along the cross - section corresponding to the two drilled - hole points in the same group. The tie - rod holes are drilled into the corresponding drainage well on one side, then place tie - rod steel bars into the tie - rod holes. The front end of the tie - rod steel bar is fixedly connected to the steel skeleton, and the rear end of the tie - rod steel bar is located outside the orifice of the tie - rod hole. After the installation of the tie - rod steel bars is completed, seal the orifice corresponding to the rear end of the tie - rod steel bar.

[0020] Furthermore: The tie - rod holes in the same cross - section of the tunnel are arranged axially symmetrically along the vertical centerline of the tunnel, and the extension lines of the centerlines of the tie - rod holes in the same cross - section of the tunnel all pass through the center of the tunnel arch crown.

[0021] For example: a hook is set at the front end of the tie rod steel bar to connect with the steel bar skeleton, and the rear end of the tie rod steel bar is welded and connected to the steel mesh. The number of tie rod holes in the same section of the tunnel is 4 to 8, and is an even number.

[0022] S7. Tunnel support construction: A steel mesh is hung on the inner wall of the tunnel. The steel mesh is fixedly connected to the rear end of the tie rod steel bar. After the steel mesh is hung, initial support construction is carried out, for example, the initial support construction is shotcrete.

[0023] S8. After the initial support reaches the designed strength, concrete is poured into the drilled holes on the working surface, and the drilled holes and tie rod holes form an integral support structure.

[0024] S9. After the support structure reaches the designed strength, the next cycle of construction is carried out according to steps S4 to S8 until the tunnel passes through the water-rich stratum.

[0025] The present invention also provides a shallow buried deep tunnel support structure, which is obtained by the shallow buried deep tunnel excavation support method, and the purpose is also to improve the advanced drainage efficiency and improve the stability of the support structure. The shallow buried deep tunnel support structure, a vertical pile hole is respectively set on the outer side of the two side walls of the tunnel, the upper end of the pile hole passes through the ground surface, and the lower end of the pile hole is lower than the elevation corresponding to the tunnel bottom plate, at least two tie rod holes are set between the tunnel wall and the pile hole on the same side, the center line of the tie rod hole is located on the vertical plane where the two pile holes are located, a steel skeleton is set in the pile hole, and a tie rod steel bar is set in the tie rod hole. The front end of the tie rod steel bar is connected to the steel skeleton, and concrete is poured into the drill hole and the tie rod hole to form an integral support structure. The support structure is arranged at intervals along the axis of the tunnel; a steel mesh is hung on the inner wall of the tunnel, and the steel mesh is fixedly connected to the rear end of the tie rod steel bar. The steel mesh is the initial support structure of the tunnel.

[0026] Furthermore, the distance between the center lines of the two pile holes of the same supporting structure and the tunnel axis is equal. For example, the distance between the pile hole and the vertical plane where the adjacent tunnel side wall is located is 20 to 40 cm.

[0027] Furthermore, the vertical planes where the supporting structures are located are parallel to each other.

[0028] Furthermore, the plane where the center lines of the two pile holes of the same supporting structure are located is perpendicular to the axis of the tunnel.

[0029] Furthermore, each supporting structure is arranged at equal intervals along the axis of the tunnel, for example, the spacing between adjacent supporting structures is 50 to 150 cm.

[0030] Specifically: the steel skeleton in the pile hole includes main bars arranged vertically and stirrups arranged along the horizontal plane. The steel skeleton is rectangular in the horizontal section, and the long side of the rectangle is parallel to the vertical plane where the center lines of the two pile holes are located.

[0031] Specifically: a hook is provided at the front end of the tie bar reinforcement and is connected to the steel bar framework, and the rear end of the tie bar reinforcement is welded to the steel bar mesh.

[0032] Furthermore: the tie holes of the support structure are arranged axially symmetrically along the vertical center line of the tunnel, and the extension lines of the center lines of the tie holes all pass through the center of the circle of the tunnel crown.

[0033] Specifically: the number of tie holes of the same support structure is 4 to 8, and is an even number.

[0034] Specifically: the initial support structure is a structure formed by shotcrete.

[0035] The beneficial effects of the present invention are as follows: in the present invention, a working face directly above the tunnel is drilled, and the drilled hole is first used as a drainage well for drainage to lower the groundwater level within the single-cycle excavation length range of the tunnel, with high advance drainage efficiency and no occupation of the straight construction period. In the later stage of the present invention, a steel bar framework is placed in the drilled hole, tie holes are drilled and tie bar reinforcements are installed in the tie holes, and concrete is poured into the drilled hole and the tie holes to form an integral reinforced concrete support structure. There is no problem that the bottom of the support structure is hollowed out by the rolling of muck trucks, improving the stability of the support structure; at the same time, the support structure is buried in the soil body, avoiding or reducing the damage to the support structure caused by blasting excavation, and improving the quality and construction efficiency of the support structure. In the present invention, a steel bar mesh is directly hung and fixed on the inner wall of the tunnel, and the steel bar mesh is closely attached to the surrounding rock. There is no gap between the steel bar mesh of the initial support and the surrounding rock, which is beneficial to the long-term stability of the tunnel surrounding rock.

[0036] The tie holes of the same cross-section of the tunnel are arranged axially symmetrically along the vertical center line of the tunnel, that is, the tie holes of the support structure are arranged axially symmetrically along the vertical center line of the tunnel; the extension lines of the center lines of the tie holes of the same cross-section of the tunnel pass through the center of the crown circle, that is, the extension lines of the center lines of the tie holes of the support structure all pass through the center of the circle of the tunnel crown. Both limitations are beneficial to balancing the forces on both sides of the support structure and can improve the stability of the support structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the support structure of the shallow-buried tunnel of the present invention.

[0038] Figure 2 is Figure 1 a schematic diagram of the steel bar framework in the horizontal cross-section in

[0039] Reference numerals: working face 1, drainage well 2, steel bar framework 3, tie hole 4, tie bar reinforcement 5, initial support 6. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The present invention is applicable to the excavation support of shallow buried deep tunnels passing through water-rich strata, and is generally applicable to tunnel sections with a burial depth of less than 50m. The water-rich strata are rich in groundwater and have soft and broken surrounding rocks such as carbonaceous slate and mudstone. The present invention is further described below in conjunction with the accompanying drawings.

[0041] See also Figure 1 The shallow buried deep tunnel excavation support method of the present invention comprises the following steps:

[0042] S1. Level the site and determine the drilling points: Clear the working surface 1 on the surface directly above the tunnel, and arrange the drilling points outside the projection of the working surface 1 along the tunnel side wall.

[0043] The working surface 1 is generally a plane, which is used for drilling construction and also for subsequent concrete pouring construction. Measurement and positioning are performed on the working surface 1 to determine the position of each drilling point. The drilling points are used for drilling, and each drilling point corresponds to a drill hole, which is used for advance drainage. All the drill holes are first used for drainage, and then all the steel skeletons 3 are lowered and concrete is poured to form a support structure; or, all the drill holes are first used for drainage, and then a part of the drill holes are selected to subsequently lower the steel skeleton 3 and pour concrete to form a support structure.

[0044] Since the support structure needs to span both sides of the tunnel, it is distributed on both sides of the tunnel. For example, there are two rows of drilling points, and both rows of drilling points are arranged along the axis of the tunnel, that is, the line connecting the two rows of drilling points is parallel to the axis of the tunnel. The boreholes corresponding to the two rows of drilling points are used to form the support structure. The distance between each row of drilling points and the vertical surface of the adjacent tunnel side wall is 20 to 40 cm, and the horizontal spacing between each row of drilling points is 50 to 150 cm. In addition to these two rows of drilling points, additional drilling points can be appropriately arranged, and the resulting boreholes are only used for drainage.

[0045] S2. Casings are buried at each drilling point and the static mud wall drilling process is used to drill the holes. The bottom elevation of the holes is lower than the elevation of the tunnel floor.

[0046] The bottom elevation of the borehole is lower than the elevation of the tunnel floor, ensuring that the groundwater in the tunnel excavation area can be lowered below the tunnel floor. The construction of step S2 is carried out according to the existing process, and the drilling construction is carried out according to the approved construction plan and operating procedures until the designed depth.

[0047] For example, for the boreholes that form the support structure, the inner diameter of the casing is 20 to 40 cm larger than the pile diameter, and the buried depth of the casing is 200 to 400 cm. The center line of the casing is vertical and should coincide with the center line of the borehole. Unless otherwise specified in the design, the allowable error of the plane is 50 mm, and the vertical line inclination is not more than 1%. When the drilling rig is in place, measures should be taken to ensure that the center of the drill tool and the center of the drilling point coincide, and the deviation should not be greater than 20 mm. After the drilling rig is in place, it should be flat and stable, and measures should be taken to fix it to ensure that there is no displacement and shaking during the drilling process. The mud is mainly made of water, clay and additives in a certain proportion. It can be mixed evenly in the mud pool and the borehole by machinery, and the mud specific gravity is controlled at 1.15 to 1.20. Before drilling, align the center line and verticality, and press the casing. Pour mud into the hole, and always keep the liquid level in the hole 1.5 to 2.0 m above the groundwater level and 0.3 m below the top surface of the casing to prevent overflow.

[0048] S3, cleaning the borehole and lowering the water level: cleaning the borehole, and after cleaning, using the borehole as a drainage well 2 to drain water and lower the water level.

[0049] When the borehole reaches the designed depth, the hole depth, hole position, etc. are checked and the hole is cleaned. For example, the hole is cleaned by the slurry extraction method, and the mud in the hole is extracted by a mud pump, and the drilling cuttings in the hole are discharged together. After the hole is cleaned, the pre-processed well pipe is connected on the ground and placed into the borehole. When hoisting it in, it should be inserted vertically in line with the center of the borehole to prevent it from touching the hole wall. The process of lowering the well pipe into the hole should be slow and smooth, and the operation should be continuous. After the well pipe is installed, the drainage pipe is placed in the well pipe, and the seepage water in the hole is drained to the ground drainage ditch by a water pump for drainage.

[0050] Drainage can be carried out through drilling holes, either only through the drill holes within the single-cycle excavation length of the tunnel to be drained and its surroundings, or through all the drill holes.

[0051] S4. Tunnel excavation construction: After the water level of the boreholes within the single-cycle excavation length of the tunnel is lower than the elevation of the tunnel floor, the single-cycle excavation of the tunnel is carried out to the designed cross-sectional dimensions. The single-cycle excavation length of the tunnel is determined comprehensively based on the working conditions, and the excavation of the tunnel is carried out according to the existing technology.

[0052] S5. Select one borehole on each side of the tunnel axis and form a group. Select at least one group of boreholes in the tunnel section of single-cycle excavation, and place a steel skeleton 3 in each group of boreholes.

[0053] The two boreholes in a group are used to form an integral reinforced concrete support structure, so the two boreholes in the same group are located on both sides of the tunnel axis. The center lines of the two boreholes in the same group are vertical, and the distances between the center lines of the two boreholes and the tunnel axis are equal or unequal. In order to make the forces on both sides of the support structure consistent, the distances between the center lines of the two boreholes and the tunnel axis are preferably equal.

[0054] The centerlines of two boreholes in the same group are both vertical, so a vertical plane can be formed, which is obliquely or perpendicularly intersected with the axis of the tunnel. When it is perpendicular, the size of a single support structure is relatively small, the tunnel penetrates a certain length of water-rich stratum, and the number of support structures is relatively large. When it is obliquely intersected, the size of a single support structure is relatively large, and the tunnel penetrates the same length of water-rich stratum, and the number of support structures is relatively small.

[0055] The boreholes in each group can be arranged at equal or unequal intervals. When the properties of the water-rich stratum are uniform, the support structures can be arranged at equal intervals along the axis of the tunnel. Otherwise, the support structures can be appropriately densified at the weak links. Generally, the vertical plane where the centerlines of two boreholes in the same group are located is perpendicular to the axis of the tunnel, and the boreholes in each group are arranged at equal horizontal intervals along the axis of the tunnel. For example, the horizontal interval between adjacent two groups of boreholes is 100 - 200 cm.

[0056] The steel bar cage 3 can be prefabricated in advance. Before putting the steel bar cage 3 into the borehole, the drainage device in the borehole needs to be taken out. For example, the drain pipe and the well pipe are taken out of the borehole in sequence, and then the prefabricated steel bar cage 3 is hoisted into the borehole. According to the force borne by the support structure, the steel bar cage 3 is preferably of the following structure. See Figure 2 , the steel bar cage 3 includes main bars arranged vertically and stirrups arranged along the horizontal plane. The steel bar cage 3 is rectangular in the horizontal cross-section, and the long side of the rectangle is parallel to the vertical plane where the centerlines of two boreholes in the same group are located. In order to ensure that the steel bar cage 3 can be smoothly put into the borehole, the long side of the steel bar cage 3 is 50 - 100 mm smaller than the borehole diameter.

[0057] S6. Drill the tie rod holes 4 in the tunnel and install the tie rod steel bars 5.

[0058] In the tunnel, the wall of the tunnel is measured and positioned, and the tie rod holes 4 are constructed along the corresponding sections of two boreholes in the same group. The tie rod holes 4 stop drilling when they reach the corresponding drainage well 2 on one side. The tie rod holes 4 and two boreholes in the same group are located in the same plane. See Figure 1 . When the tie rod holes 4 reach the corresponding drainage well 2 on one side, that is, as long as the tie rod holes 4 are communicated with two boreholes in the same group. In order to balance the force borne by the support structure, the tie rod holes 4 in the same cross-section of the tunnel are axially symmetrically arranged along the vertical centerline of the tunnel, and the extension lines of the centerlines of the tie rod holes 4 in the same cross-section of the tunnel all pass through the center of the circle of the tunnel arch crown. See Figure 1 . The support structure corresponding to the tie rod holes 4 mainly bears tension, and the aperture of the tie rod holes 4 is smaller than the aperture of two boreholes in the same group. The number of the tie rod holes 4 is generally 4 - 8, and preferably an even number to achieve axial symmetry arrangement.

[0059] After the rod hole 4 is drilled, a rod reinforcement 5 is placed in the rod hole 4, and the front end of the rod reinforcement 5 is fixedly connected to the reinforcement frame 3, for example, a hook is provided at the front end of the rod reinforcement 5 to connect to the reinforcement frame 3; the rear end of the rod reinforcement 5 is located outside the hole of the rod hole 4. One or more rod reinforcements 5 are placed in each rod hole 4. After the rod reinforcement 5 is installed, the hole corresponding to the rear end of the rod reinforcement 5 is blocked.

[0060] S7, tunnel support construction: a steel mesh is hung on the inner wall of the tunnel, and the steel mesh is fixedly connected to the rear end of the tie rod steel bar 5, for example, the steel mesh is welded to the rear end of the tie rod steel bar 5. After the steel mesh is hung, initial support 6 is constructed at the steel mesh, for example, the initial support 6 is constructed as shotcrete.

[0061] S8. After the initial support 6 reaches the design strength, concrete is poured into each group of boreholes at the working face 1, so that the boreholes and tie rod holes 4 form an integral support structure. The concrete pouring construction is for the boreholes corresponding to each group of borehole points within the single cycle excavation length. The concrete fluidity should meet the construction requirements to ensure that the boreholes and tie rod holes 4 are filled densely. For the boreholes corresponding to the excavated tunnel section that are only used for drainage, they can be backfilled.

[0062] S9. After the support structure reaches the designed strength, the next cycle of construction is carried out according to steps S4 to S8 until the tunnel passes through the water-rich stratum.

[0063] The present invention also provides a shallow buried deep tunnel support structure, which is constructed by the shallow buried deep tunnel excavation support method. Figure 1 , a shallow buried deep tunnel support structure, a vertical pile hole is set on the outer side of each of the two side walls of the tunnel, the upper end of the pile hole passes through the ground surface, and the lower end is lower than the elevation corresponding to the tunnel bottom plate, and the two pile holes are a group of drilled holes determined in the above step S5. At least two tie rod holes 4 are set between the tunnel wall and the pile hole on the same side, at least one tie rod hole 4 connects the tunnel with one pile hole, and at least one tie rod hole 4 connects the tunnel with another pile hole. The center line of the tie rod hole 4 is located in the vertical plane where the two pile holes are located, that is, the tie rod hole 4 and the pile hole are located in the same vertical plane.

[0064] A steel bar skeleton 3 is arranged in the pile hole. Figure 2 The steel skeleton 3 includes a main bar arranged vertically and stirrups arranged along a horizontal plane. The steel skeleton 3 is rectangular in horizontal cross section, and the long side of the rectangle is parallel to the vertical plane where the center lines of the two pile holes are located. Tie rod steel bars 5 are arranged in the tie rod holes 4, and the front ends of the tie rod steel bars 5 are connected to the steel skeleton 3. For example, a hook is arranged at the front end of the tie rod steel bar 5 to be connected to the steel skeleton 3, and there is at least one tie rod steel bar 5 in each tie rod hole 4.

[0065] Concrete is poured into the drilling holes and tie rod holes 4 to form an integral support structure, and the support structures are arranged at intervals along the axis of the tunnel. To balance the forces on a single support structure, the distances from the centerlines of the two pile holes of the same support structure to the tunnel axis are equal. Specifically, the distance between the pile hole and the vertical plane where the adjacent tunnel side wall is located is 20 - 40 cm.

[0066] To optimize the forces on a single support structure, the tie rod holes 4 of the support structure are arranged axially symmetrically along the vertical centerline of the tunnel, and the support structures are arranged axially symmetrically along the vertical centerline of the tunnel. For example, the number of tie rod holes 4 of the same support structure is 4 - 8, and is an even number. To optimize the forces on a single support structure, the extension lines of the centerlines of each tie rod hole 4 all pass through the center of the tunnel arch crown.

[0067] Each support structure is arranged along the tunnel axis direction. The vertical planes where each support structure is located are generally parallel to each other and perpendicular to the tunnel axis. For example, each support structure is arranged at equal intervals along the tunnel axis, and the distance between adjacent support structures is 50 - 150 cm.

[0068] A steel mesh is hung on the inner wall of the tunnel, and the steel mesh is fixedly connected to the rear end of the tie rod steel bar 5. For example, the rear end of the tie rod steel bar 5 is welded to the steel mesh. The steel mesh is the primary support 6 structure of the tunnel. The primary support 6 structure is generally a structure formed by shotcrete, and the steel mesh is a part of the primary support 6.

Claims

1. A method for excavation and support of shallow-buried tunnels, characterized in that, It includes the following steps: S1. Level the site and determine the drilling points: Clear the working surface (1) on the ground directly above the tunnel, and arrange the drilling points outside the projection of the working surface (1) along the side walls of the tunnel. The drilling points are distributed on both sides of the tunnel; S2. Bury casing for each drilling point and drill holes using the static mud wall protection drilling process. The bottom elevation of the drilled hole is lower than the elevation of the tunnel floor; S3. Clean the drilled holes and dewater: Clean the drilled holes, and after cleaning, use them as drainage wells (2) for drainage to lower the water level; S4. Tunnel excavation construction: After the water levels of the drilled holes within the single-cycle excavation length of the tunnel are all lower than the elevation of the tunnel floor, conduct single-cycle excavation of the tunnel until the designed cross-sectional dimensions are reached; S5. Select one drilling hole on each side of the tunnel axis to form a group. The distances from the centerlines of the two drilling holes in the same group to the tunnel axis are equal, and the vertical plane where the centerlines of the two drilling holes in the same group are located is perpendicular to the tunnel axis. Select at least one group of drilling holes in the tunnel section of single-cycle excavation, and place steel skeletons (3) in each group of drilling holes; S6. Drill tie rod holes (4) in the tunnel and install tie rod steel bars (5): Drill tie rod holes (4) on the tunnel wall along the cross-section corresponding to the two drilling points in the same group. The tie rod holes (4) are drilled into the corresponding drainage well (2). The tie rod holes (4) on the same cross-section of the tunnel are arranged axially symmetrically along the vertical centerline of the tunnel. Then place tie rod steel bars (5) in the tie rod holes (4). The front end of the tie rod steel bar (5) is fixedly connected to the steel skeleton (3), and the rear end of the tie rod steel bar (5) is located outside the orifice of the tie rod hole (4). After the installation of the tie rod steel bar (5) is completed, seal the orifice corresponding to the rear end of the tie rod steel bar (5); S7. Tunnel support construction: Hang steel mesh on the inner wall of the tunnel, and fixedly connect the steel mesh to the rear end of the tie rod steel bar (5). After the steel mesh is hung, conduct initial support (6) construction; S8. After the initial support (6) reaches the designed strength, pour concrete into the drilling holes from the working surface (1). The drilling holes and the tie rod holes (4) form an integral support structure; S9. After the support structure reaches the designed strength, carry out the construction of the next cycle according to steps S4 - S8 until the tunnel passes through the water-rich stratum.

2. The shallow-buried tunnel excavation and support method according to claim 1, characterized in that: In step S1, the drilling points are arranged in two columns, both columns of drilling points are arranged along the axis direction of the tunnel. The distance between each column of drilling points and the vertical plane where the adjacent tunnel side wall is located is 20 - 40 cm, and the horizontal spacing between each column of drilling points is 50 - 150 cm.

3. The shallow-buried tunnel excavation and support method according to claim 1, characterized in that: In step S2, the inner diameter of the casing is 20 - 40 cm larger than the pile diameter, and the burial depth of the casing is 200 - 400 cm.

4. The shallow-buried tunnel excavation and support method according to claim 1, characterized in that: In step S3, when the drilling reaches the designed depth, check the hole depth and hole position and clean the hole. The hole cleaning is carried out by the pumping method. After hole cleaning, place the well pipe into the drilling hole, then place the drainage pipe into the well pipe, and the drainage pipe is externally connected to a water pump for drainage.

5. The shallow-buried tunnel excavation and support method according to claim 1, characterized in that: In step S5, each group of drilling holes is arranged at equal horizontal intervals along the axis of the tunnel.

6. The shallow-buried tunnel excavation and support method according to any one of claims 1 to 5, characterized in that: In step S5, the steel bar cage (3) includes vertically arranged main bars and horizontally arranged stirrups. The steel bar cage (3) is rectangular in the horizontal cross-section, and the long side of the rectangle is parallel to the vertical plane where the center lines of the two drill holes are located.

7. The shallow-buried tunnel excavation and support method according to claim 6, characterized in that: In step S5, the length of the long side of the rectangle is 50 - 100 mm smaller than the drill hole diameter.

8. The shallow-buried tunnel excavation and support method according to any one of claims 1 to 5, characterized in that: In step S6, the extension lines of the center lines of the tie holes (4) in the same cross-section of the tunnel all pass through the center of the tunnel arch crown.

9. The shallow-buried tunnel excavation and support method according to claim 8, characterized in that: In step S6, a hook is provided at the front end of the tie bar (5) to connect with the steel bar cage (3), the rear end of the tie bar (5) is welded to the steel bar mesh, and the number of tie holes (4) in the same cross-section of the tunnel is 4 - 8 and is an even number.

10. The shallow-buried tunnel excavation and support method according to any one of claims 1 to 5, characterized in that: In step S7, the initial support (6) construction is shotcrete.

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