Three-pilot-tunnel shallow-buried excavation subway station construction method

Abstract

The invention relates to a construction method for a three-pilot-tunnel shallow-buried excavation subway station. The construction method comprises the steps that advance supporting is conducted on a middle pilot tunnel and side pilot tunnels; reinforcing the stratum at the middle partition wall of the middle pilot tunnel by adopting a small conduit; the middle pilot tunnel and the side pilot tunnels are excavated through a benching method, and pilot tunnel excavation is conducted at intervals in a staggered progress mode; synchronously carrying out primary support construction on the middle pilot tunnel and the side pilot tunnel; buckle arches in the middle piles, the side piles, the pile top beams and the side pilot tunnels are constructed; a small guide pipe is adopted to carry out advance support on a buckling arch between pilot tunnels; excavating a buckling arch between pilot tunnels and carrying out primary support construction; the pilot tunnel side wall is cut off in a segmented mode, and secondary lining construction is conducted on the structure vault; and excavation of each layer of earth, floor construction, side wall waterproofing and structure construction are carried out. According to the shallow-buried excavation subway station and the construction method, the excavation section can be reduced, pilot tunnel construction can be conducted in a staggered mode, and therefore uneven ground surface settlement caused by pilot tunnel excavation is reduced, and the structural stability is improved.

Description

Technical Field

[0001] The present application relates to a technical field related to subway station construction, and in particular to a method for constructing a three-guide tunnel shallow buried dark excavation subway station. Background Art

[0002] The construction of subway stations near urban commercial areas often brings various engineering problems due to the complex surrounding environment, high-rise buildings, dense pipelines, traffic road networks, and soil cover thickness. For this type of construction, the shallow buried underground excavation (PBA) method is currently used for construction, but it is still difficult to pass through water-rich soft strata and the surrounding rock and soil have poor self-stability.

[0003] On the one hand, since the distances between the three guide tunnels in the existing three-guide tunnel construction method are relatively close, the construction of one guide tunnel may have an impact on the adjacent guide tunnels during the excavation and support process, such as causing the surrounding rock of the adjacent guide tunnels to loosen and the support structure to deform, which increases the complexity and difficulty of the construction.

[0004] On the other hand, since the bearing capacity of the water-rich soft stratum itself is low, the unloading effect on the stratum is obvious when each pilot tunnel is excavated. The larger excavation plane will cause large and uneven surface settlement.

[0005] Therefore, in this context, how to provide a shallow buried underground excavation subway station and construction method to reduce the excavation section and stagger the pilot tunnel construction, thereby reducing the uneven surface settlement caused by the pilot tunnel excavation and improving the structural stability, is a technical problem to be solved. Summary of the invention

[0006] In view of the above problems of the prior art, the present application provides a three-pilot-tunnel shallow buried underground excavation subway station construction method, which can reduce the excavation section and stagger the pilot tunnel construction, thereby reducing the uneven surface settlement caused by the pilot tunnel excavation and improving the structural stability.

[0007] To achieve the above-mentioned purpose, the first aspect of the present application provides a three-pilot-tunnel shallow buried dark excavation subway station construction method, comprising:

[0008] S1: Provide advance support for the middle and side guide tunnels;

[0009] S2: using a small conduit to reinforce the stratum at the middle partition wall of the middle guide tunnel;

[0010] S3: excavating the middle guide tunnel and the side guide tunnel by adopting the step method, and excavating the guide tunnels at intervals and staggered progress; wherein, during the excavation process, the initial support construction of the side walls and the vaults of the middle guide tunnel and the side guide tunnel is carried out simultaneously;

[0011] S4: constructing the middle pile in the middle guide tunnel and the side pile in the side guide tunnel, constructing the pile top crown beam on the upper end of the side pile; and constructing the buckle arch in the side guide tunnel above the pile top crown beam;

[0012] S5: Casting the column top longitudinal beam of the middle pile, and waterproofing and concrete pouring the vault of the middle guide tunnel;

[0013] S6: using a small guide tube to perform advance support on the buckle arch between the middle guide tunnel and the side guide tunnel; using the step method to dig the buckle arch between the middle guide tunnel and the side guide tunnel; and performing initial support construction and backfilling of the buckle arch between the middle guide tunnel and the side guide tunnel;

[0014] S7: Cutting off the side walls of the guide tunnel in sections, and performing waterproofing and concrete pouring on the buckle arches in the side guide tunnels and the buckle arches between the middle guide tunnel and the side guide tunnels;

[0015] S8: Carry out earth excavation, floor slab construction, side wall waterproofing and structure construction at each level of the subway station.

[0016] From the above, compared with the traditional three-pilot tunnel, the construction of adjacent pilot tunnels can be avoided by staggered excavation, reducing the impact of the stratum caused by the vibration of adjacent pilot tunnel excavation. However, compared with the traditional four-pilot tunnel, it has the advantages of smaller excavation section and lower support cost. Compared with the conventional six- and eight-pilot tunnel, while ensuring construction safety, it can effectively reduce the precipitation cycle, reduce engineering risks such as large deformation and sudden water inrush, save resources and reduce pollution. The use of small guide tubes to reinforce the stratum at the partition wall of the middle pilot tunnel can ensure the stability of the middle partition wall when the middle pilot tunnel is excavated; after completing the construction of the pilot tunnel and the buckle arch in the pilot tunnel, the stratum is supported again in advance to ensure the stability of the earthwork between the pilot tunnels; after completing all excavation, waterproof paving and concrete pouring are used to reduce the impact of underground seepage water when crossing the water-rich soft bottom layer.

[0017] As a possible implementation manner of the first aspect, the middle partition wall is located in the middle of the middle guide hole and has an arc-shaped side convex cross-section.

[0018] From the above, by dividing the middle pilot hole into two sections, a smaller pilot hole is obtained, thereby reducing the excavation section.

[0019] As a possible implementation of the first aspect, the net size of the middle guide tunnel is 8.6*5.650m, and the initial support thickness of the middle guide tunnel is 350mm; the size of the side guide tunnel is 4.0m*5.0m, and the initial support thickness of the side guide tunnel is 300mm.

[0020] From the above, by setting a relatively large middle guide hole size and a relatively small side guide hole size, an unconventional three-guide hole shallow buried dark excavation subway station construction can be achieved, wherein the size of the middle guide hole is roughly the same as the marshaling guide hole after being divided into two excavation sections. The initial support of the middle guide hole is thicker than that of the side guide hole, which can optimize the use of materials while ensuring the support effect.

[0021] As a possible implementation manner of the first aspect, the step S3 includes:

[0022] The middle guide tunnel and the side guide tunnel have two stages of earth excavation, upper and lower steps. The upper step is excavated first to reserve core soil, and then a steel grid is set up on the arch of the middle guide tunnel and concrete is sprayed. Wooden formwork is fixed on the side wall of the middle guide tunnel and the side guide tunnel and concrete is sprayed.

[0023] Then the lower steps are excavated, wooden formwork is set up on the side walls of the pilot hole, and concrete is sprayed;

[0024] Grouting is carried out on the outside of the primary support consisting of steel grid and shotcrete or wooden formwork and shotcrete;

[0025] The pilot tunnels are excavated at staggered progress, and the progress of adjacent pilot tunnel faces is staggered by no less than 10m; the length of the upper step is 3-5m, the length of the core soil retention is 2-3m, and the height and width of the core soil are not less than 1 / 2 of the excavation section.

[0026] From the above, the excavation area is small each time through the step method, which can reduce the exposure time of the surrounding rock and effectively control the deformation and relaxation of the surrounding rock. For the arch position of the middle guide hole, since it will not be broken later, steel grids are used as initial support, and wooden templates are used for other parts to facilitate the wall breaking during subsequent excavation. By staggering the progress of the face, the interference between adjacent guide holes can be reduced, while the construction period can be guaranteed.

[0027] As a possible implementation of the first aspect, the shotcrete uses C25 shotcrete, and the steel grating uses steel mesh with a spacing of 0.5m and a diameter of 8mm, and the size of each steel mesh is 150mm*150mm.

[0028] From the above, the use of C25 shotcrete can effectively resist the impact of loose rocks or small pieces falling, and the use of steel grids makes the stress distribution more uniform.

[0029] As a possible implementation of the first aspect, the construction of the buckle arch in the side guide tunnel above the pile top crown beam includes: along the extension direction of the guide tunnel, from inside to outside, above the pile top crown beam of the side pile, using steel grids and C25 shotcrete as initial support for the buckle arch;

[0030] Use C20 pumped concrete on the outside of the buckle arch in the side guide tunnel to backfill from the inside to the outside along the extension direction of the guide tunnel;

[0031] The back of the buckle arch in the side guide hole is grouted and backfilled with cement mortar.

[0032] As shown above, wooden formwork and shotcrete are used to complete the arch construction, and pumped concrete is used for backfilling, which has good fluidity and can ensure that the concrete is fully compacted. Since the strength of the backfill concrete is slightly smaller than the strength of the initial support concrete, it can offset part of the energy caused by the deformation of the surrounding rock, thereby improving the overall stability.

[0033] As a possible implementation manner of the first aspect, the advanced support described in step S1 includes:

[0034] According to the predetermined positions of the middle guide tunnel and the side guide tunnels on both sides of the middle guide tunnel, a large pipe shed is set up and grouting is performed to provide advance support for the primary lining buckle arch at the arch top position of the middle guide tunnel and the side guide tunnel;

[0035] According to the predetermined positions of the middle guide tunnel and the side guide tunnels on both sides of the middle guide tunnel, deep hole grouting is used to perform advance support on the excavation section positions of the middle guide tunnel and the side guide tunnels.

[0036] From the above, the large pipe-roof support can support the soil within a certain range above the tunnel to prevent collapse; deep space grouting injects slurry into the deep surrounding rock through drilling, and improves the physical and mechanical properties of the surrounding rock by filling the internal gaps and pores; the combination of the two can form a more comprehensive support range.

[0037] As a possible implementation of the first aspect, the large pipe shed adopts a pipe drilling construction method; wherein the steel pipe of the large pipe shed adopts a seamless steel pipe with a diameter of 108@400mm and a wall thickness of 6mm, the steel pipe joint adopts a threaded joint with a setting angle of 1°, and the number of joints in each section is less than 50%;

[0038] The range of the deep hole grouting is from 0.5m inside the excavation surface to 1.5m outside the excavation surface. Forward grouting or backward grouting is adopted. The depth of each ring of deep hole grouting is 10m, and the overlap of two adjacent grouting sections is 2m; the deep hole grouting pressure control value is 0.5~0.8MPa, and the grouting slurry adopts cement-water glass double liquid slurry with a diffusion radius of 0.5m; the unconfined compressive strength of the soil after grouting reinforcement is 0.5~0.8MPa, and the permeability coefficient is not greater than 1×10-6cm / s.

[0039] From the above, the use of the pipe drilling construction method can prevent the large pipe shed from drilling holes, and the use of steel pipes with larger diameters and wall thicknesses can provide higher strength and rigidity; the use of appropriate steel pipe spacing, installation angles, joint forms and the number of joints in the section can ensure that the large pipe shed can exert its bearing capacity well; deep hole grouting uses a suitable grouting range to ensure a stable area; forward grouting or backward grouting is selected according to different geological conditions to prevent slurry loss; through appropriate grouting depth, lap length, grouting pressure, and slurry type, the strength after grouting can be guaranteed to meet the requirements. The unconfined compressive strength and permeability coefficient of the soil behind the Pearl River ensure that the bearing capacity of the soil can withstand the surrounding rock pressure caused during the excavation process.

[0040] As a possible implementation of the first aspect, the middle pile adopts a steel tube concrete column with a diameter of 900 mm; the pile foundation under the middle pile has a diameter of 1800 mm and a length of 19.5-20.5 m, and is formed by underwater pouring of C35, 1.2 MPa concrete;

[0041] The side piles are bored cast-in-place columns with a diameter of 1000mm and an interval of 1600-1650mm.

[0042] As can be seen from the above, the middle pile adopts steel tube concrete column, which makes the internal concrete in a three-phase compression state, improving the compressive strength of the concrete. At the same time, the high strength and toughness of the steel tube itself make the middle pile have better bearing capacity under complex stress conditions; the side piles adopt bored cast-in-place columns, which can be closely combined with the shaft as the soil. The soil also provides lateral support for the side piles, which plays an important role in resisting lateral soil pressure and preventing the pile body from tilting.

[0043] As a possible implementation of the first aspect, the middle partition wall of the middle guide tunnel and the horse head gate of the side guide tunnel are supported in advance by small guide tubes;

[0044] The small conduit is a DN32, t=2.75mm welded steel pipe, with holes drilled alternately on the pipe wall every 200mm, the hole diameter is 6mm, and the circumferential spacing is 0.3m;

[0045] The small conduit used at the middle partition wall is 2m long and has an external insertion angle of 20-25°;

[0046] The small ducts used at the horse head gate of the side guide tunnel are double-row small ducts with a single length of 4.5m, which are laid horizontally.

[0047] From the above, a small conduit with certain strength and rigidity is used, and holes are set to improve the strength of the reinforcement. The horizontal small conduit can provide strong support for the surrounding rock in the horizontal direction in front of the horse head gate. The support cost of the small conduit is relatively low. It can reasonably utilize materials and construction resources and reduce unnecessary cost expenditures while ensuring the effect of advanced support. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a flow chart of the construction method of a three-pilot-tunnel shallow buried dark excavation subway station provided in the first embodiment of the present application;

[0049] Figure 2a It is a flow chart of a construction method of a three-pilot-tunnel shallow buried dark excavation subway station provided in the second embodiment of the present application;

[0050] Figure 2b It is a cross-sectional view of the construction of a three-pilot-tunnel shallow buried dark excavation subway station provided in the first embodiment of the present application;

[0051] Figure 2c It is a schematic diagram of the process of the construction method of a three-pilot-tunnel shallow buried dark excavation subway station provided in the second embodiment of the present application;

[0052] It should be understood that the size and shape of each block diagram in the above structural diagram are for reference only and should not constitute an exclusive interpretation of the embodiment of the present invention. The relative position and inclusion relationship between the blocks presented in the structural diagram are only schematic representations of the structural association between the blocks, and do not limit the physical connection method of the embodiment of the present invention. DETAILED DESCRIPTION

[0053] The technical solution provided by the present application is further described below with reference to the accompanying drawings and examples. It should be understood that the system structure and business scenarios provided in the examples of the present application are mainly to illustrate the possible implementation methods of the technical solution of the present application and should not be interpreted as the only limitation on the technical solution of the present application. It is known to those of ordinary skill in the art that with the evolution of the system structure and the emergence of new business scenarios, the technical solution provided by the present application is also applicable to similar technical problems.

[0054] It should be understood that the three-guide tunnel shallow buried dark excavation subway station solution provided in the embodiment of the present application includes a three-guide tunnel shallow buried dark excavation subway station construction method. Since the principles of solving the problems in these technical solutions are the same or similar, in the introduction of the following specific embodiments, some repetitions may not be repeated, but it should be regarded that these specific embodiments have been referenced to each other and can be combined with each other.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by technicians in the technical field of this application. In the event of any inconsistency, the meaning described in this specification or the meaning derived from the contents recorded in this specification shall prevail. In addition, the terms used herein are only for the purpose of describing the embodiments of the present application and are not intended to limit the present application. In order to accurately describe the technical content in this application and to accurately understand the present invention, the following explanations or definitions are given to the terms used in this specification before describing the specific embodiments:

[0056] 1) Small-Diameter Pipe Advanced Support: Small-Diameter Pipe Advanced Support is an important auxiliary construction method in tunnel and underground engineering construction. Specifically, before tunnel excavation, a small pipe is driven into the surrounding rock in front at a certain angle along the contour line of the tunnel arch. After driving, slurry is injected into the surrounding rock through the small pipe. The slurry will fill the cracks and pores in the surrounding rock and cement the loose surrounding rock into a whole, thereby improving the strength and self-stabilization ability of the surrounding rock. Its main function is to pre-reinforce the surrounding rock in front of the excavation face.

[0057] 2) Forward Grouting: Forward Grouting is a grouting method widely used in geotechnical engineering and underground engineering. During construction, instead of drilling the hole to the designed depth at one time and then grouting, grouting is performed while drilling. When the drill drills a certain distance, the newly formed hole is immediately grouted, and then drilling continues, and the cycle continues.

[0058] The three-pilot shallow-buried dark-cut subway station solution provided in the embodiment of the present application can be constructed by dividing the middle pilot hole in the conventional three-pilot hole into two parts using a middle partition wall, and excavating four pilot holes at intervals. This method provides a shallow-buried dark-cut subway station and construction method, which can reduce the excavation section, and can stagger the pilot hole construction, thereby reducing the uneven surface settlement caused by the pilot hole excavation and improving the structural stability. The embodiment of the present application can be applied to tunnel excavation, subway station construction and other construction in the fields of underground engineering and tunnel engineering. The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0059] The first embodiment of the present application provides a three-pilot-tunnel shallow buried dark excavation subway station construction method. Figure 1 Specifically, the implementation method of each step of the construction method of the three-pilot-tunnel shallow buried dark excavation subway station is described, including steps S10-S80.

[0060] S10: Provide advance support for the middle guide tunnel and side guide tunnel.

[0061] In some embodiments, the cross-section of the middle guide hole is divided into two parts by a middle partition wall, corresponding to the first middle guide hole and the second middle guide hole respectively; wherein the middle partition wall is located in the middle position of the middle guide hole and has an arc-shaped side convex cross-section; there are two side guide holes, namely the first side guide hole and the second side guide hole, which are located on both sides of the middle guide hole; wherein the middle guide hole and the side guide holes adopt a straight wall arch structure.

[0062] In some embodiments, the sizes of the first middle guide hole and the second middle guide hole are substantially equal, and are substantially equal to the sizes of the side guide holes 3 and 4 .

[0063] In some embodiments, the net size of the middle guide tunnel is 8.6*5.650m, and the initial support thickness of the middle guide tunnel is 350mm; the size of the side guide tunnel is 4.0m*5.0m, and the initial support thickness of the side guide tunnel is 300mm.

[0064] In some embodiments, the guide holes are, from left to right, the first side guide hole, the first middle guide hole, the second middle guide hole, and the second side guide hole.

[0065] In some embodiments, a variety of means may be used for advance support, including: according to the predetermined positions of the middle guide tunnel and the side guide tunnels on both sides of the middle guide tunnel, setting up a large pipe shed and injecting grout to provide advance support for the primary lining buckle arch at the arch top position of the middle guide tunnel and the side guide tunnel; according to the predetermined positions of the middle guide tunnel and the side guide tunnels on both sides of the middle guide tunnel, using deep hole grouting to provide advance support for the excavation section position of the middle guide tunnel and the side guide tunnel.

[0066] In some embodiments, the large pipe rack adopts a follow-pipe drilling construction method; wherein, the steel pipe of the large pipe rack adopts a seamless steel pipe with a diameter of 108@400mm and a wall thickness of 6mm, and the steel pipe joints are threaded with a punching angle of 1°, and the number of joints in each section is less than 50%; the range of the deep hole grouting is 0.5m inside the excavation surface to 1.5m outside, and forward grouting or backward grouting is adopted. The grouting depth of each ring of deep holes is 10m, and the overlap of two adjacent grouting sections is 2m; the deep hole grouting pressure control value is 0.5~0.8MPa, and the grouting slurry adopts cement-water glass double liquid slurry with a diffusion radius of 0.5m; the unconfined compressive strength of the soil after grouting reinforcement is 0.5~0.8MPa, and the permeability coefficient is not greater than 1×10-6cm / s.

[0067] In some embodiments, the grout used in the pipe-roof is cement sand, a one-time grouting process is adopted, and the MC6 pipe-roof drilling rig is used for drilling positioning and drilling. After the grouting operation orifice is discharged, the orifice is sealed, and then pressurized grouting is performed 1-3 times, and each pressure is less than 0.3MPa.

[0068] In some embodiments, the side guide tunnel is grouted with double rows of small conduits at the horse head gate. The small conduits are DN32, t=2.75mm welded steel pipes, with a single length of 4.5m and are laid horizontally.

[0069] S20: using a small conduit to reinforce the stratum at the middle partition wall of the middle guide tunnel;

[0070] In some embodiments, the stratum is reinforced by advanced small-duct grouting at the partition wall in the middle guide tunnel. The wall of the small-duct is staggered with holes every 200 mm, the hole diameter is 6 mm, the circumferential spacing is 0.3 m, the single length is 2 m, and the external insertion angle is 20-25°.

[0071] S30: excavating the middle guide tunnel and the side guide tunnel by adopting a step method, and excavating the guide tunnels at intervals and staggered progress; wherein, during the excavation process, the initial support construction of the side walls and the vaults of the middle guide tunnel and the side guide tunnel is carried out simultaneously;

[0072] In some embodiments, the middle guide tunnel and the side guide tunnel have two stages of earthwork excavation, upper and lower steps. The upper step is excavated first, the core soil is reserved, and then a steel grid is erected on the arch of the middle guide tunnel and concrete is sprayed. The wooden formwork is fixed on the side wall of the middle guide tunnel and the side guide tunnel and concrete is sprayed; then the lower step is excavated, and wooden formwork is erected on the side wall of the guide tunnel and concrete is sprayed; grouting is performed on the outside of the initial support composed of steel grid and sprayed concrete or wooden formwork and sprayed concrete; the guide tunnels are excavated at staggered progress, and the progress of adjacent guide tunnel faces is staggered by no less than 10m; the length of the upper step is 3-5m, the length of the core soil retention is 2-3m, and the height and width of the core soil are not less than 1 / 2 of the excavation section. Among them, the outer grouting uses cement slurry, the grouting pressure is 0.2MPa-0.4MPa, and the final pressure reaches 0.5MPa.

[0073] In some embodiments, excavation is performed in the order of a first middle guide tunnel, a second side guide tunnel, a second middle guide tunnel, and a first side guide tunnel.

[0074] In some embodiments, the shotcrete is C25 shotcrete, the steel grid is a steel mesh with a spacing of 0.5m and a diameter of 8mm, and the size of each steel mesh is 150mm*150mm. The thickness of the shotcrete is 350mm.

[0075] In some embodiments, C25 early-strength mesh sprayed concrete is used, and longitudinal connecting bars with a diameter of 22 mm are set between the steel grilles. The longitudinal lap welding connection is carried out, the lap length is not less than 10d, the circumferential spacing is 1.0m, and the connecting bars are arranged in a staggered manner inside and outside the main bars.

[0076] In some embodiments, after the concrete strength at the top of the side guide arch reaches 80% of the designed strength, back grouting is performed sequentially from high to low.

[0077] S40: constructing the middle pile in the middle guide tunnel and the side pile in the side guide tunnel, constructing the pile top crown beam on the upper end of the side pile; and constructing the buckle arch in the side guide tunnel above the pile top crown beam.

[0078] In some embodiments, the center pile adopts a steel tube concrete column with a diameter of 900mm; the pile foundation under the center pile is 1800mm in diameter and 19.5-20.5m in length, and is made of C35, 1.2MPa concrete poured underwater; the side piles adopt bored cast-in-place columns with a diameter of 1000mm and an interval of 1600-1650mm.

[0079] In some embodiments, during the construction of the side pile pilot pit, the opening section adopts the method of manual digging as the drilling casing, the minimum radius of the casing is 950mm, the outer diameter of the hole reinforcement lock ring is 2300mm, the thickness of the pilot pit wall is 150-200mm, and the depth is 2000mm. After the layout is completed, the initial support structure concrete of the pilot hole bottom plate is broken with the pile center as the center of the circle, and the breaking radius is 1150mm. The strength of the side pile opening lock and the pilot pit wall concrete is C25.

[0080] In some embodiments, the minimum radius of the guide pit wall protection structure during the construction of the side piles is 512.5mm, the outer diameter of the hole reinforcement locking ring is 1425mm, the thickness of the guide pit wall protection is 150-200mm, and the depth is 2000mm. Among them, the radius of concrete removal of the primary support structure of the guide tunnel bottom plate is 712.5mm.

[0081] In some embodiments, the pile foundations under the center piles and side piles can be mechanically drilled using a KYZ-180 crawler hydraulic high-power drilling rig, with one drill per four to be constructed.

[0082] In some embodiments, when pouring steel tube concrete, after fixing the steel pipe column, plain concrete support rings are set every 4-5m along the vertical direction of the pile hole, that is, a part of sand is filled to make support rings, and then sand is filled, and repeated until the steel tube is filled; at the same time, the outside of the steel pipe column is filled with fine sand, and finally concrete is poured.

[0083] In some embodiments, the column foundation adopts a static load test to determine the vertical bearing capacity of a single pile, and the number of test piles is not less than 3 and not less than 1% of the total number of piles; the single vertical bearing capacity determined by the static load test should be greater than 2 times of the characteristic value, wherein the characteristic value is Ra=8500KN.

[0084] In some embodiments, the crown beam is constructed in sections. Before construction, the pile head is cleaned to expose the fresh concrete surface, the bottom surface of the crown beam is leveled with cement mortar to the designed elevation, and the vertical bars of the steel cage are straightened to ensure that the length of the vertical bars anchored in the beam body is not less than the designed length. After the steel bars are processed and tied, the crown beam formwork is erected and concrete is poured.

[0085] In some embodiments, the cap beam is made of C30 reinforced concrete with a protective layer thickness of 30 mm;

[0086] In some embodiments, the construction of the buckle arch in the side guide tunnel above the pile top crown beam includes: using steel grating and C25 shotcrete as initial support for the buckle arch from inside to outside above the pile top crown beam of the side pile along the extension direction of the guide tunnel; and backfilling the outer side of the buckle arch in the side guide tunnel from inside to outside along the extension direction of the guide tunnel using C20 pumped concrete.

[0087] S50: Casting the column top longitudinal beam of the middle pile, and waterproofing and concrete pouring are performed on the arch of the middle guide hole.

[0088] In some embodiments, a wooden formwork or a steel formwork is installed and fixed on the top of the center pile, and after the main reinforcement and stirrups of the longitudinal beam are placed, pouring is performed by pumping concrete.

[0089] In some embodiments, cement mortar is used to apply a waterproof protective layer, and the arch of the middle guide hole is paved with waterproof membranes, such as polymer waterproof membranes, modified asphalt waterproof membranes, etc. Then, the template is laid outside the waterproof layer, and main reinforcement and stirrups are placed, and finally the structural arch is poured by pumping concrete.

[0090] S60: Use a small guide tube to perform advance support on the buckle arch between the middle guide tunnel and the side guide tunnel; use the step method to dig the buckle arch between the middle guide tunnel and the side guide tunnel; and perform initial support construction and backfilling of the buckle arch between the middle guide tunnel and the side guide tunnel.

[0091] In some embodiments, holes are staggered and drilled in the wall of the small conduit every 200 mm, the hole diameter is 6 mm, and the circumferential spacing is 0.3 m.

[0092] In some embodiments, the soil of the arch portions and the upper portions of the side walls between adjacent guide tunnels is excavated using a step method, and the initial support structure of the guide tunnels has to be destroyed during the construction process.

[0093] In some embodiments, the excavation step distance is the same as the thickness of the initial support of the arch.

[0094] S70: Cutting off the side walls of the guide tunnel in sections, and performing waterproof laying and concrete pouring on the buckle arches in the side guide tunnel and the buckle arches between the middle guide tunnel and the side guide tunnel.

[0095] In some embodiments, the concrete is poured backward from the inside to the outside along the extension direction of the guide tunnel, and the outer side of the buckle arch is backfilled and grouted at the same time. The backfill grouting can be performed by setting a grouting pipe by drilling and burying, and cement slurry or cement mortar is used for grouting.

[0096] S80: Carry out earth excavation of each layer, floor slab construction, side wall waterproofing and structure construction.

[0097] In some embodiments, after all the buckled arches or arch tops have reached the design strength, the station hall layer is excavated; it is divided into several construction sections along the extension direction of the guide tunnel, and excavated downward in layers. After each layer of soil is excavated, the soil between the piles is sprayed with mesh in time, and the station hall layer floor, side wall waterproof layer and side wall are constructed in sections according to the construction section until the station hall layer construction is completed; when the station hall layer floor and side wall reach the design strength, the platform layer is excavated in sections according to the construction section to the soil, and at the same time, the piles are sprayed with mesh concrete in the same way as the station hall layer; a cushion layer is applied to the base, a comprehensive grounding and a waterproof layer are laid, the bottom plate beam and bottom plate are applied, and finally the platform layer side wall is applied. Among them, the length of the construction section should not be greater than 20m.

[0098] The second embodiment of the present application provides a construction method for a three-pilot-tunnel shallow buried dark excavation subway station. Figure 2a , Figure 2b , Figure 2c For illustration, the method provided in the second embodiment includes the following steps S200-S310.

[0099] S200: A large pipe shed is used for advance support of the arches of the middle guide tunnel and the side guide tunnel.

[0100] First, the large pipe shed is installed on the external connecting wall of the open-cut structure side walls at both ends of the concealed excavation, and the trenchless pipe laying technology is used for one-time construction.

[0101] The steel pipe is a seamless steel pipe with a diameter of 108@400mm and a wall thickness of 6mm. The steel pipe joints are threaded with a setting angle of 1° to ensure that the number of joints in each section is less than 50%.

[0102] The MC6 pipe-roof drilling rig is used for drilling positioning and drilling, and the "one-time pipe drilling" construction method is selected. After drilling is completed, the borehole is thoroughly flushed to reduce residue in the hole, and then grouting operations are carried out.

[0103] The grouting adopts a one-time grouting process, and the slurry is cement slurry. After the slurry comes out of the hole, the hole is sealed, and then pressurized grouting is performed 1-3 times, with each pressure less than 0.3MPa.

[0104] S210: Deep hole grouting is used for advance support of the excavation sections of the central guide tunnel and the side guide tunnel.

[0105] The grouting range of the excavation position of the middle guide tunnel and the side guide tunnel is determined to be 0.5m inside the excavation surface to 1.5m outside; the location of the grouting hole is determined according to the construction method of deep hole grouting, and the ground connection wall is broken according to the drawings, and the hole is drilled, and then the drill rod is pulled back for grouting. Among them, the location of the grouting hole should ensure that the adjacent grouting sections overlap by 2m, and the grouting depth of each ring of deep holes is 10m.

[0106] For soil and sand layers that are prone to collapse, forward grouting is used, otherwise backward grouting is used. The grouting slurry uses cement-water glass double liquid slurry.

[0107] During the grouting process, under the premise of ensuring that the grouting hole meets the designed hole depth, the grouting flow rate decreases as the pressure rises during the grouting process. When the pressure reaches the final grouting pressure, the single-hole grouting can be ended. If the grouting pressure does not reach the designed final pressure, but the grouting volume has reached twice the designed grouting volume, the single-hole grouting can also be ended.

[0108] During the grouting process, the pressure is controlled at 0.5-0.8 MPa, and the diffusion radius is 0.5 m. When the grouting pressure suddenly rises or grout overflows from the hole wall or cross-section sand layer, the grouting should be stopped immediately, and the cause should be found out and measures such as adjusting the grouting parameters or shifting the grouting should be taken to restart the grouting.

[0109] After grouting reinforcement is completed, the unconfined compressive strength of the soil should be between 0.5 and 0.8 MPa, and its permeability coefficient should not be greater than 1×10-6 cm / s.

[0110] S220: Small conduits are used to reinforce the strata at the middle partition wall of the middle guide tunnel and the horse head gate of the side guide tunnel.

[0111] The small pipe in advance is used to reinforce the partition wall in the middle guide hole by grouting. The small pipe is a DN32, t=2.75mm welded steel pipe. The pipe wall is staggered with holes every 200mm. The hole diameter is 6mm, the circumferential spacing is 0.3m, the single pipe is 2m long, and the external insertion angle is 20-25°. Figure 2b As shown, the middle partition wall is located in the middle of the middle guide hole and has an arc-shaped side convex cross section. The middle partition wall divides the middle guide hole into middle guide hole 1 and middle guide hole 2.

[0112] Double rows of small ducts are used for grouting reinforcement at the horse head gate of the side guide tunnel. Each duct is 4.5m long and is laid horizontally.

[0113] S230: The middle guide tunnel and the side guide tunnel are excavated by the step method, and the initial support construction of the side walls and arches of the middle guide tunnel and the side guide tunnel is carried out simultaneously.

[0114] like Figure 2b As shown, the excavation of the guide tunnels is carried out in a staggered order of middle guide tunnel 1, side guide tunnel 4, middle guide tunnel 2, and side guide tunnel 3, and the progress of adjacent guide tunnel faces is staggered by no less than 10m.

[0115] Each pilot tunnel is divided into two steps, upper and lower, for excavation.

[0116] First, excavate the upper step of the middle guide tunnel 1 and reserve the core soil. Set up steel grids and spray concrete on the arch of the middle guide tunnel in time. The length of the upper step is 3-5m, the length of the core soil is 2-3m, and the height and width of the core soil are not less than 1 / 2 of the excavation section.

[0117] Then, excavate the lower steps, erect wooden formwork on the side walls and ground of the guide tunnel in time, and spray concrete.

[0118] The steel grating is a steel mesh with a spacing of 0.5m and a diameter of 8mm, and the size of each steel mesh is 150mm*150mm. The shotcrete is C25 shotcrete with a thickness of 350mm.

[0119] After the excavation of the middle guide tunnel 1 is started, the excavation of the side guide tunnel 4 can be carried out after the progress of the tunnel face 10m apart. Similarly, the excavation of the middle guide tunnel 2 and the side guide tunnel 3 is carried out in a staggered manner. The excavation steps in each guide tunnel are the same as those in the middle guide tunnel 1.

[0120] When the steel grid or wooden formwork and shotcrete complete the initial support and closure, and the concrete strength at the top of the side guide arch reaches 80% of the design strength, the soil on the outside (behind) is grouted (injected) from high to ground in time to ensure the density behind the initial support. Cement slurry is used for grouting on the outside, with a grouting pressure of 0.2MPa-0.4MPa and a final pressure of 0.5MPa.

[0121] In this step and the subsequent excavation and drilling process, deformation indicators should be monitored and feedback should be provided to prevent engineering risks.

[0122] S240: Construction of center piles and side piles is underway.

[0123] like Figure 2b As shown, the middle pile 8 is located in the middle pilot tunnel and adopts a steel tube concrete column with a diameter of 900 mm. The pile foundation under the column of the middle pile 8 is 1800 mm in diameter and 19.5-20.5 m in length, and is made of C35, 1.2 MPa concrete poured underwater.

[0124] Specifically, first, the pile foundation holes under the columns are drilled mechanically using a KYZ-180 crawler hydraulic high-power drilling rig, with construction being carried out at intervals of four.

[0125] Subsequently, the pile foundation steel cage and steel pipe column under the column were hoisted in turn.

[0126] Pour the pile foundation and adjust the position of the steel pipe column according to the data of settlement and position monitoring. When the pile foundation is poured to the designed elevation, fix the steel pipe column 7( Figure 2b ).

[0127] Then, a plain concrete support ring is set every 4-5m along the pile hole vertically, that is, a part of the sand is filled to make a support ring, and then the sand is filled again, and the process is repeated until the steel pipe is filled; at the same time, the outside of the steel pipe column is filled with fine sand. Finally, concrete is poured into the steel pipe column.

[0128] During the above construction process, a static load test should be conducted on the pile foundation under the column to determine the vertical bearing capacity of a single pile to check the quality of the pile foundation. The number of test piles shall not be less than 3 and shall not be less than 1% of the total number of piles; the vertical bearing capacity of a single pile determined by the static load test shall be greater than 2 times the characteristic value, wherein the characteristic value is Ra = 8500KN.

[0129] Middle pile 8 and side pile 5 ( Figure 2b ) can be constructed simultaneously, with the side piles located in the side guide holes and bored cast-in-place columns used.

[0130] First, the KYZ-180 crawler hydraulic high-power drilling rig is used to drill holes, with construction being carried out at intervals of four.

[0131] During the construction of the pilot pit, the side pile opening section uses artificial holes as drilling casings, and the hole positions should be well protected during the construction process. The thickness of the pilot pit wall is 150-200mm and the depth is 2000mm. The minimum wall radius of the casing is 512.5mm, and the outer diameter of the hole reinforcement lock ring is 1425mm.

[0132] Then, use a pneumatic pick or electric pick to break the initial support structure concrete of the pilot tunnel bottom plate with the pile center as the center of the circle, and the breaking radius is 712.5mm. The strength of the side pile opening lock and the pilot tunnel wall concrete is C25.

[0133] S250: constructing a cap beam on the top of the pile at the upper end of the side pile.

[0134] After the construction of the side piles is completed, the pile top crown beam 6 ( Figure 2b ).

[0135] Before construction, clean the pile head until the fresh concrete surface is exposed, use cement mortar to level the bottom surface of the crown beam to the designed elevation, straighten the vertical bars of the steel cage, and ensure that the length of the vertical bars anchored into the beam body is not less than the designed length; after the steel bar processing and binding are completed, erect the crown beam formwork and pour concrete.

[0136] Among them, the crown beam is made of C30 reinforced concrete with a protective layer thickness of 30mm.

[0137] S260: constructing a buckle arch in the side guide hole above the pile top crown beam.

[0138] Along the extension direction of the guide tunnel, from inside to outside, steel grids and C25 shotcrete are used above the crown beam of the side piles as the initial support for the side guide tunnel buckle arch.

[0139] After the initial support construction is completed, C20 pumped concrete is used to backfill from the inside to the outside along the extension direction of the guide tunnel on the outside of the side guide tunnel buckle arch.

[0140] S270: Casting the column top longitudinal beam of the middle pile, and waterproofing and concrete pouring are performed on the arch of the middle guide tunnel.

[0141] Install and fix the wooden or steel formwork on the top of the center pile, place the main reinforcement and stirrups of the longitudinal beam, and pour the center pile and the longitudinal beam by pumping concrete.

[0142] At the arch position of the middle guide tunnel, cement mortar is used to apply a waterproof protective layer, and waterproof membranes are laid, such as polymer waterproof membranes, modified asphalt waterproof membranes, etc. Then, the formwork is laid on the outside of the waterproof layer, and the main reinforcement and stirrups are placed, and finally the structural arch is poured by pumping concrete.

[0143] The formwork is removed after the pouring reaches the designed strength.

[0144] S280: Use small guide tubes to provide advance support for the buckle arch between the middle guide tunnel and the side guide tunnel.

[0145] In the transverse channel, an advanced small guide tube is used to buckle the arch 9( Figure 2b ) was reinforced by grouting at the excavation location, using DN32, t=2.75mm welded steel pipe. Holes were drilled alternately on the pipe wall every 200mm, with a hole diameter of 6mm and an annular spacing of 0.3m.

[0146] S290: using the step method to excavate the earth at the arch position, and to carry out the construction of the initial support of the guide tunnel arch and backfilling behind it.

[0147] The soil of the arches and the upper part of the side walls between the adjacent pilot tunnels is excavated by the step method, wherein the excavation step is the same as the thickness of the initial support of the arches. The initial support structure of the pilot tunnel has to be destroyed during the construction process.

[0148] The initial support of the arches between the guide tunnels is made of the same steel grating and shotcrete as the middle guide tunnel.

[0149] When the buckle arches between the guide holes are connected with the initial support of the middle guide hole and the side guide hole, backfill grouting is carried out in time. The steps are the same as the back grouting in S230.

[0150] S300: Cutting off the side walls of the guide tunnel in sections, and waterproofing and pouring concrete on the buckle arches in the side guide tunnels and the buckle arches between the guide tunnels;

[0151] The side walls and bottom surface of the pilot hole that are not needed in the segmentation stage. The waterproof protective layer and waterproof layer are applied to the arch of the main structure after penetration.

[0152] Pour concrete backwards from the inside to the outside along the extension direction of the guide tunnel, and at the same time backfill and grout the outside of the arch.

[0153] S310: Carry out earth excavation of each layer, floor slab construction, side wall waterproofing and structure construction.

[0154] After all the arches or vaults (main structure vaults) have reached the designed strength, excavation of the station hall layer will be carried out.

[0155] The extension direction of the guide tunnel is divided into several construction sections with a construction section length of no more than 20m, and the excavation is carried out downward in layers. After each layer of soil is excavated, the soil between the piles is meshed and sprayed with concrete in a timely manner.

[0156] After the excavation of the station hall soil is completed, the station hall bottom beam 11 ( Figure 2b ) The station hall floor slab 12, and the side wall waterproofing layer and side wall 10, until the station hall construction is completed.

[0157] When the floor slab and side walls of the station hall level reach the designed strength, the platform level is excavated in sections according to the construction sections to the soil, and at the same time, concrete is sprayed between the piles in the same way as the station hall level.

[0158] After the platform layer soil is excavated, the platform layer bottom beam 13 ( Figure 2b ) A cushion layer is applied to the base, a comprehensive grounding layer is laid, a waterproof layer is laid, a bottom plate beam and a bottom plate 14 are applied, and finally the side walls of the platform layer are applied.

[0159] At this point, the construction of the entire main structure has been completed.

[0160] The words "first, second, third, etc." or module A, module B, module C and other similar terms in the specification and claims are only used to distinguish similar objects and do not represent a specific ordering of the objects. It is understandable that the specific order or sequence can be interchanged where permitted so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0161] In the above description, the numbers representing the steps, such as S110, S120, etc., do not necessarily mean that the steps will be executed in this manner. If permitted, the order of the steps can be interchanged or they can be executed simultaneously.

[0162] The term "comprising" as used in the description and claims should not be interpreted as being limited to what is listed thereafter; it does not exclude other elements or steps. Therefore, it should be interpreted as specifying the presence of the features, integers, steps or components mentioned, but does not exclude the presence or addition of one or more other features, integers, steps or components and groups thereof. Therefore, the expression "a device comprising means A and B" should not be limited to a device consisting of components A and B only.

[0163] References to "one embodiment" or "an embodiment" in this specification mean that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present application. Therefore, the phrases "in one embodiment" or "in an embodiment" appearing in various places in this specification do not necessarily refer to the same embodiment, but may refer to the same embodiment. In addition, in one or more embodiments, the particular features, structures, or characteristics can be combined in any appropriate manner, as would be apparent to one of ordinary skill in the art from this disclosure.

[0164] Note that the above are only preferred embodiments of the present application and the technical principles used. Those skilled in the art will understand that the present application is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present application. Therefore, although the present application is described in more detail through the above embodiments, the present application is not limited to the above embodiments, and may also include more other equivalent embodiments without departing from the concept of the present application, all of which belong to the scope of protection of the present application.

Claims

1. A three-pilot-tunnel shallow buried dark excavation subway station construction method, characterized in that: The method comprises excavating and constructing a central guide hole and two side guide holes located on both sides of the central guide hole, wherein the cross section of the central guide hole is divided into two parts by a central partition wall, corresponding to the first central guide hole and the second central guide hole; the method comprises the following steps: S1: Provide advance support for the middle and side guide tunnels; S2: using a small conduit to reinforce the stratum at the middle partition wall of the middle guide tunnel; S3: excavating the middle guide tunnel and the side guide tunnel by adopting the step method, and excavating the guide tunnels at intervals and staggered progress; wherein, during the excavation process, the initial support construction of the side walls and the vaults of the middle guide tunnel and the side guide tunnel is carried out simultaneously; S4: constructing the middle pile in the middle guide tunnel and the side pile in the side guide tunnel, constructing the pile top crown beam on the upper end of the side pile; and constructing the buckle arch in the side guide tunnel above the pile top crown beam; S5: Casting the column top longitudinal beam of the middle pile, and waterproofing and concrete pouring the vault of the middle guide tunnel; S6: using a small guide tube to perform advance support on the buckle arch between the middle guide tunnel and the side guide tunnel; using the step method to dig the buckle arch between the middle guide tunnel and the side guide tunnel; and performing initial support construction and backfilling of the buckle arch between the middle guide tunnel and the side guide tunnel; S7: Cutting off the side walls of the guide tunnel in sections, and performing waterproofing and concrete pouring on the buckle arches in the side guide tunnels and the buckle arches between the middle guide tunnel and the side guide tunnels; S8: Carry out earth excavation, floor slab construction, side wall waterproofing and structure construction at each level of the subway station.

2. The method according to claim 1, characterized in that The middle partition wall is located in the middle of the middle guide hole and has an arc-shaped side convex cross section.

3. The method according to claim 1, characterized in that The net size of the middle guide tunnel is 8.6*5.650m, and the initial support thickness of the middle guide tunnel is 350mm; the size of the side guide tunnel is 4.0m*5.0m, and the initial support thickness of the side guide tunnel is 300mm.

4. The method according to claim 1, characterized in that: The S3 step includes: The middle guide tunnel and the side guide tunnel have two stages of earth excavation, upper and lower steps. The upper step is excavated first to reserve core soil, and then a steel grid is set up on the arch of the middle guide tunnel and concrete is sprayed. Wooden formwork is fixed on the side wall of the middle guide tunnel and the side guide tunnel and concrete is sprayed. Then the lower steps are excavated, wooden formwork is set up on the side walls of the pilot hole, and concrete is sprayed; Grouting is carried out on the outside of the primary support consisting of steel grid and shotcrete or wooden formwork and shotcrete; The pilot tunnels are excavated at staggered progress, and the progress of adjacent pilot tunnel faces is staggered by no less than 10m; the length of the upper step is 3-5m, the length of the core soil retention is 2-3m, and the height and width of the core soil are not less than 1 / 2 of the excavation section.

5. The method according to claim 4, characterized in that The shotcrete is C25 shotcrete, and the steel grating is a steel mesh with a spacing of 0.5m and a diameter of 8mm. The size of each steel mesh is 150mm*150mm.

6. The method according to claim 1, characterized in that The construction of the buckle arch in the side guide tunnel above the pile top crown beam includes: along the extension direction of the guide tunnel, from inside to outside, above the pile top crown beam of the side pile, using steel grids and C25 shotcrete as the initial support of the buckle arch; Use C20 pumped concrete on the outside of the buckle arch in the side guide tunnel to backfill from the inside to the outside along the extension direction of the guide tunnel; The back of the buckle arch in the side guide hole is grouted and backfilled with cement mortar.

7. The method according to claim 1, characterized in that The advanced support described in step S1 includes: According to the predetermined positions of the middle guide tunnel and the side guide tunnels on both sides of the middle guide tunnel, a large pipe shed is set up and grouting is performed to provide advance support for the primary lining buckle arch at the arch top position of the middle guide tunnel and the side guide tunnel; According to the predetermined positions of the middle guide tunnel and the side guide tunnels on both sides of the middle guide tunnel, deep hole grouting is used to perform advance support on the excavation section positions of the middle guide tunnel and the side guide tunnels.

8. The method according to claim 7, characterized in that The large pipe shed adopts the pipe drilling construction method; wherein, the steel pipe of the large pipe shed adopts a seamless steel pipe with a diameter of 108@400mm and a wall thickness of 6mm, and the steel pipe joints adopt threaded threads with a setting angle of 1°, and the number of joints in each section is less than 50%; The range of the deep hole grouting is from 0.5m inside the excavation surface to 1.5m outside the excavation surface. Forward grouting or backward grouting is adopted. The depth of each ring of deep hole grouting is 10m, and the overlap of two adjacent grouting sections is 2m; the deep hole grouting pressure control value is 0.5~0.8MPa, and the grouting slurry adopts cement-water glass double liquid slurry with a diffusion radius of 0.5m; the unconfined compressive strength of the soil after grouting reinforcement is 0.5~0.8MPa, and the permeability coefficient is not greater than 1×10-6cm / s.

9. The method according to claim 1, characterized in that: The middle pile adopts a steel tube concrete column with a diameter of 900mm; the pile foundation under the middle pile is 1800mm in diameter and 19.5-20.5m in length, and is made of C35, 1.2MPa concrete poured underwater; The side piles are bored cast-in-place columns with a diameter of 1000mm and an interval of 1600-1650mm.

10. The method according to claim 1, characterized in that The middle partition wall of the middle guide tunnel and the horse head gate of the side guide tunnel are supported in advance by small guide tubes; The small conduit is a DN32, t=2.75mm welded steel pipe, with holes drilled alternately on the pipe wall every 200mm, the hole diameter is 6mm, and the circumferential spacing is 0.3m; The small conduit used at the middle partition wall is 2m long and has an external insertion angle of 20-25°; The small ducts used at the horse head gate of the side guide tunnel are double-row small ducts with a single length of 4.5m, which are laid horizontally.

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