Arch foot reinforcement structure and construction method of underground subway station with arch cover method

Abstract

The present invention discloses an arch foot reinforcement structure and construction method for a subway station with an arch cover method. The arch foot reinforcement structure includes two layers of arch cover support, arch foot piles arranged at the arch feet on the left and right sides of the main body of the subway station arch cover, and an arch foot longitudinal beam connected to the arch foot piles. The arch foot piles are arranged along the tangent of the arch foot. The arch foot piles are composed of a steel frame and fine stone concrete poured into the steel frame and the pile hole. The present invention is a reinforcement system combining the arch foot piles with the longitudinal beams. The arch foot piles and the first and second layers of the arch cover support are connected by the longitudinal beams. The structure has good integrity and strong resistance to local stress and deformation. It can effectively reinforce and protect the deep and broken surrounding rock at the arch foot. In addition, the construction method of the arch foot reinforcement structure provided by the present invention has flexible selection of reinforcement scope and implementation object, which is aimed at the broken rock layer of the arch foot of the supporting arch cover, and will not have an overall impact, nor will it affect the advantages of the arch cover method in terms of project cost, construction period, implementation efficiency, mechanized operation, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of rail transit construction, and relates to a subway station arch foot reinforcement structure, and in particular to an arch foot reinforcement structure located near a broken surrounding rock position in the construction of a subway station using an arch cover method, and a construction method. Background Art

[0002] Given my country's vast territory and the obvious differences in soil and rock strata in different regions, with the widespread development of subway projects in my country, the underground excavation method has different implementation methods in different geological conditions, including the "middle tunnel method", "side tunnel method", "PBA tunnel pile method" and "arch cover method".

[0003] The arch capping method is a dark excavation construction method suitable for the surrounding rock conditions of "soft on top and hard on the bottom". It has the advantages of fewer processes, simple support structure, large operating area after the arch cap is formed, high efficiency, and short construction period. At present, the application scope of the arch capping method is mainly in the formations with surrounding rock grades of I to IV, ideal geological conditions, and especially stable bedrock at the arch foot. The upper part of the formation in Qingdao, Chongqing, Dalian and other areas is covered by the Quaternary system, and the underlying Mesozoic bedrock has typical binary stratigraphic structure characteristics, so the application of the arch capping method is quite extensive.

[0004] However, subway stations are usually more than 200 meters high. Due to the influence of local faults and secondary geological structures, they will inevitably face unfavorable conditions such as local weak surrounding rock and broken arch foot rock. If the arch cover method is abandoned in the stratum where the overall surrounding rock condition is good and the local arch foot is broken, it will be unsuitable in terms of construction period and cost. At present, for the situation where the arch foot of the underground excavation subway station with the arch cover method is located in the broken surrounding rock, the main treatment method is to set anchor rods (anchor cables) at the arch foot and local grouting.

[0005] When anchor rods (anchor cables) are used as a flexible reinforcement structure, they stabilize the rock mass mainly by applying tension. Therefore, they can only stabilize the rock mass under the arch foot first, thereby indirectly stabilizing the arch foot. However, the main effect of the arch foot on the surrounding rock is pressure. During the construction process, if the angle of the anchor rods (anchor cables) is too horizontal, the horizontal outward tension generated is too large, which will have an adverse effect on the arch foot. When the local grouting reinforcement method is used, the diffusion range, speed and reinforcement strength of the slurry are all unpredictable. Therefore, the current reinforcement method inevitably has the disadvantages of low structural stiffness, uncontrollable effect and difficulty in effectively covering the deep broken layer in the reinforcement range.

[0006] In summary, designing a more reasonable arch foot reinforcement structure and a new construction method to effectively reinforce the broken surrounding rock of the arch foot of the arch cover method will play an extremely important role in controlling the deformation of the arch cover support system and enabling the entire structural system to fully exert its bearing capacity. At the same time, it also has great practical significance for fully exerting the technical advantages of the arch cover method and promoting its application. Summary of the invention

[0007] The purpose of the present invention is to solve the above problems and to provide an arch foot reinforcement structure and a construction method for a dark-cut subway station using an arch cover method, which is suitable for effectively reinforcing the broken surrounding rock at the arch foot of a dark-cut subway station using an arch cover method.

[0008] In order to solve the above technical problems, the present invention is implemented by the following technical solutions.

[0009] The arch foot reinforcement structure of a subway station excavated by an arch cover method provided by the present invention comprises a first-layer arch cover support, a second-layer arch cover support, arch foot piles arranged at the arch feet on the left and right sides of the second-layer arch cover support, and an arch foot longitudinal beam connected to the arch foot piles in one piece; the arch foot pile bodies are arranged along the tangent of the arch foot; the arch foot piles are composed of a steel frame and fine stone concrete cast in the steel wall of the steel frame and in the pile holes; the arch foot longitudinal beams are arranged on the left and right sides of the second-layer arch cover support along the longitudinal direction of the subway station.

[0010] In order to improve the reinforcement effect of the arch foot of the subway station in the above-mentioned arch cover method, the arch foot pile passes through the arch foot broken rock layer, which improves the reliability of the reinforcement effect and enhances the ability to control the deformation of the arch foot. In a preferred embodiment, the length of the arch foot pile is not less than 5m, and the diameter of the arch foot pile hole is generally 180-250mm.

[0011] For the arch foot reinforcement structure of the above-mentioned arch cover method for underground excavation of subway stations, when the number of arch foot piles arranged at the same fixed position is two or more, the axes of the two adjacent arch foot piles form a fixed angle of 10° to 20°, which can better resist the local force at the broken rock layer of the arch foot.

[0012] In the arch foot reinforcement structure of the above-mentioned arch cover method concealed excavation subway station, the top of the arch foot pile steel frame extends into the arch foot and is cast in the longitudinal beam. The arch foot piles are connected into a whole within the reinforcement range of the subway station through the longitudinal beam, thereby improving the rigidity of the reinforcement system itself.

[0013] The arch foot reinforcement structure of the underground subway station using the arch cover method is mainly composed of a plurality of longitudinal beam reinforcements arranged along the longitudinal direction of the subway station and concrete that casts the longitudinal beam reinforcements into one piece in order to provide the longitudinal beam with its own rigidity.

[0014] In the arch foot reinforcement structure of the above-mentioned arch cover method, the longitudinal beam is located on the inner side of the arch foot of the first-layer arch cover support of the subway station, and a second-layer arch cover grid steel frame joint is reserved in the longitudinal beam to connect the longitudinal beam and the second-layer arch cover support.

[0015] The arch foot reinforcement structure of a subway station excavated by an arch cover method provided by the present invention adopts arch foot piles arranged in the second-layer arch cover support of the subway station to support and reinforce the broken rock strata at the arch foot. Several arch foot piles are connected as a whole by longitudinal beams to form a pile-beam combined reinforcement system.

[0016] The present invention further provides a construction method for the arch foot reinforcement structure of the underground subway station by the arch cover method, comprising the following steps:

[0017] (1) Determine the size of the pilot hole space required for the construction of the arch foot piles;

[0018] (2) Excavate the upper section of the subway station and construct the first layer of arch support;

[0019] According to the size of the pilot tunnel space, the upper section of the station is excavated; while the pilot tunnel is being excavated, the construction of the first layer of arch cover support is completed;

[0020] (3) Determine the reinforcement location based on the crushing conditions and scope of the surrounding rock at the arch foot;

[0021] (4) Determine the arch foot pile parameters, longitudinal beam dimensions and reinforcement according to the arch cap stress;

[0022] (5) Construction of arch foot piles;

[0023] After the reinforcement position is determined, a hole is drilled obliquely along the designed pile axis to obtain the arch foot pile hole, and then a steel frame (8) is hoisted into the arch foot pile hole, and fine stone concrete (9) is poured into the steel wall of the steel frame and the arch foot pile hole to complete the construction of the arch foot pile;

[0024] (6) Construction of longitudinal beams;

[0025] (7) Construction of the second layer of arch support;

[0026] (8) Repeat steps (1) to (7) until all arch cover supports in the station and arch foot reinforcement at the broken surrounding rock locations are completed.

[0027] In the above-mentioned construction method of arch foot reinforcement structure of underground subway station by arch cover method, in step (1), the spatial dimensions of the pilot tunnel excavated in the upper section of the subway station and the position of the temporary vertical support are determined according to the engineering geological and hydrological conditions, the stress of the arch cover support structure and the space requirements of the construction machinery. The spatial dimensions of the pilot tunnel are generally not less than 5m in net width and not less than 7m in net height, which can meet the requirements of mechanical construction. The position of the temporary vertical support should meet the structural stress before the second layer of arch cover support is applied, and care should be taken to prevent the core soil under the temporary vertical support from encroaching on the mechanical construction space.

[0028] In the construction method of the arch foot reinforcement structure of the underground subway station by the arch cover method, in step (2), the upper section of the station is excavated according to the spatial size of the pilot tunnel. While the pilot tunnel is being excavated, the grid steel frame of the first layer of arch cover support and the steel section as a temporary vertical support are erected, and then the steel mesh is tied to the grid steel frame of the first layer of arch cover support and concrete is sprayed to complete the construction of the first layer of arch cover support.

[0029] In the construction method of the arch foot reinforcement structure of the underground subway station by the arch cover method, in step (3), the reinforcement position can be accurately determined according to the surrounding rock crushing conditions and range at the arch foot position revealed after the pilot tunnel is excavated. Generally, when the rock mass integrity under the arch foot is less than 0.45 and the thickness of the crushed rock layer is greater than 1m, reinforcement measures such as arch foot piles and longitudinal beams are required.

[0030] In the construction method of the arch foot reinforcement structure of the above-mentioned arch cover method, in step (4), the arch foot pile and longitudinal beam structural parameters, the arch foot pile parameters (including the length of the arch foot pile body, the specifications of the steel frame, the pile hole diameter, etc.) and the longitudinal beam size and reinforcement can be calculated and determined according to the internal force of the arch cover (such as the arch foot axial force, etc.), wherein the arch foot pile length should pass through the revealed broken rock layer and is generally not less than 5m, and the arch foot pile hole diameter is generally 180-250mm, so that a small drilling machine can be used for mechanical construction. When the number of arch foot piles arranged at the same reinforcement position is more than two, the axes of the two adjacent arch foot piles form a fixed angle of 10°-20°, which can better resist the local force of the broken rock layer of the arch foot.

[0031] In the construction method of the arch foot reinforcement structure of the above-mentioned arch cover method, in step (5), during the construction of the arch foot pile, the hole is first drilled and cleaned, and then the steel frame is suspended, and finally C30 and above fine stone concrete is poured into the arch foot pile hole and the steel wall of the steel frame to complete the construction of the arch foot pile. The selected drilling rig should be suitable for the drilling depth and hole diameter requirements, the drilling process should be smooth and flexible, and the operation can be carried out in a space with a net width of 5m and a net height of 7m. The drill rod can be tilted within a range of 360° to make full use of the pilot hole space after the pile body is tilted. The present invention uses a small tunnel drilling rig. During the drilling process, attention should be paid to using an inclinometer to measure the drilling inclination and strictly control the driving direction. The coarse aggregate gradation and slump of the concrete should ensure that the arch foot pile body is cast densely and continuously.

[0032] In the construction method of the arch foot reinforcement structure of the above-mentioned arch cover method, in step (6), the longitudinal beam is constructed by first tying a number of arch foot longitudinal beam steel bars, and then casting them as a whole using C30 or above concrete. The longitudinal beam is located on the inner side of the arch foot of the first-layer arch cover support of the subway station. The top of the arch foot pile steel frame extends into the arch foot and is cast in the longitudinal beam. A second-layer arch cover grid steel frame joint is reserved in the longitudinal beam to connect the longitudinal beam and the second-layer arch cover support. The position of the steel bars should be appropriately adjusted at the place where the beam steel bars and the arch foot pile heads conflict.

[0033] In the above-mentioned construction method of the arch foot reinforcement structure of the underground subway station by the arch cover method, in step (7), the second layer of arch cover support grid is erected, the steel mesh is tied, and concrete is sprayed to complete the construction of the second layer of arch cover support.

[0034] In the above-mentioned arch cover method for the construction method of the arch foot reinforcement structure of the subway station, the arch foot piles and longitudinal beams are arranged on the left and right sides of the arch cover support. The construction of the above-mentioned structure has no overlapping process with the secondary lining casting. The construction steps are simple, easy to implement, the construction period is short, the workload is small, and the construction quality is easier to ensure.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The arch foot reinforcement structure of the underground subway station provided by the arch cover method can improve the stiffness of the reinforcement system itself, enhance the reinforcement capacity of the broken surrounding rock at the arch foot, and enhance the control of the deformation capacity of the arch foot through the reinforcement system combining the arch foot piles with the longitudinal beams.

[0037] 2. The arch foot reinforcement structure of the underground subway station provided by the arch cover method, the arch foot piles are composed of a steel frame and concrete, which can effectively penetrate deep and broken surrounding rocks, further improving the reinforcement effect and reliability of the broken surrounding rocks at the arch foot.

[0038] 3. The arch foot reinforcement structure of the underground subway station provided by the arch cover method has a steel frame constituting the arch foot pile inserted into the longitudinal beam concrete, thereby enhancing the bonding ability of the arch foot pile and the longitudinal beam, and ensuring that the reinforcement system composed of the two has greater rigidity.

[0039] 4. The arch foot reinforcement structure of the underground subway station using the arch cover method provided by the present invention has longitudinal beams connecting the arch foot piles and the first layer of arch cover support and the second layer of arch cover support. It has good integrity, strong ability to resist local force and deformation, and a wide coverage range. It can effectively protect the broken surrounding rock of the arch foot and can control the overall deformation of the arch cover support system, so that the entire arch cover main structure can give full play to its bearing capacity.

[0040] 5. The arch-covering method provided by the present invention is a construction method for reinforcing the arch foot of a dark-cut subway station. The reinforcement scope and implementation objects are flexibly selected, and are all aimed at the broken rock strata at the arch foot supporting the arch cover. Its implementation will not have an overall impact on the construction of the entire station, and will not affect the advantages of the arch-covering method in terms of project cost, construction period, implementation efficiency, and mechanized operation.

[0041] 6. In the arch cover method for the construction of the arch foot reinforcement structure of a subway station provided by the present invention, the arch foot piles are all bored by a small tunnel drilling rig, and the drill rod can be tilted at any angle, which can fully utilize the guide hole space after the pile body is tilted, avoiding the size limitation of large pile foundations in the tunnel and the engineering risks of artificial drilling.

[0042] 7. The invention provides a construction method for the arch foot reinforcement structure of a dark-cut subway station using the arch cover method. The arch foot piles and longitudinal beams are arranged on the left and right sides of the arch cover support and are separated from the secondary lining structure. The construction process has no overlapping with the secondary lining pouring process, thereby avoiding engineering risks such as arch foot disturbance during the pouring of the secondary lining excavator and removal of temporary supports. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the main structure of a dark-excavated subway station using the arch cover method of the present invention.

[0044] Figure 2 The present invention is a construction sequence diagram of the main structure of a subway station with an arch cover method; wherein, a is excavating the upper step of the left pilot tunnel, constructing the first layer of arch cover support and temporary vertical bracing on the left; b is excavating the lower step of the left pilot tunnel, extending the first layer of arch cover support and temporary vertical bracing on the left; c is sequentially excavating the upper and lower step pilot tunnels on the right, constructing the first layer of arch cover support and temporary vertical bracing on the right; d is sequentially excavating the upper and lower steps of the middle pilot tunnel, connecting the first layer of arch cover support on the left and the first layer of arch cover support on the right; e is constructing arch foot piles, longitudinal beams and the second layer of arch cover support; f is excavating the lower part of the station under the protection of the arch cover and arch foot reinforcement structure, and pouring the secondary lining.

[0045] Figure 3 It is a schematic diagram of the construction site of the arch foot piles and longitudinal beams in the arch foot reinforcement structure of the underground subway station using the arch cover method of the present invention.

[0046] Figure 4 It is a schematic diagram of the arch foot pile structure in the arch foot reinforcement structure of a dark-cut subway station using the arch cover method of the present invention.

[0047] Figure 5 This is a connection diagram of the arch foot piles, longitudinal beams and the second-layer arch cover grid steel frame joints in the arch foot reinforcement structure of the underground excavation subway station using the arch cover method of the present invention.

[0048] Figure 6 This is a schematic diagram of the main structure of a subway station built using the comparative arch cover method.

[0049] Figure 7 It is a schematic diagram for comparing the surface settlement in the application example and the application comparison example. The surface settlement displacement is obtained by monitoring along the width direction of the surface after the application example and the application comparison example are completed.

[0050] Figure 8 It is a schematic diagram for comparing the vault settlement in the application example and the application comparison example; the vault settlement displacement is obtained by real-time monitoring of the vault during the construction of the application example and the application comparison example.

[0051] The names corresponding to the reference numerals are:

[0052] 1-longitudinal beam, 2-arch foot piles, 3-first layer arch cover support, 4-second layer arch cover support, 5-station secondary lining, 6-small tunnel drilling rig, 7-temporary vertical support, 8-steel frame, 9-fine stone concrete, 10-second layer arch cover grid steel frame joint, 11-anchor rod, 12-grouting flower pipe. DETAILED DESCRIPTION

[0053] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments:

[0054] Example

[0055] like Figures 1 to 5 As shown, this embodiment provides an arch foot reinforcement structure and construction method for a dark-cut subway station using an arch cover method.

[0056] The arch cover method is used to reinforce the arch foot of the subway station. Figure 1 As shown, it includes a first-layer arch cover support 3 and a second-layer arch cover support 4 which are arranged in sequence just above the secondary lining of the subway station, arch foot piles 2 arranged at the arch feet on the left and right sides of the second-layer arch cover support, and an arch foot longitudinal beam 1 which is connected to the arch foot piles.

[0057] The on-site construction method of the arch foot reinforcement structure of the underground subway station by the arch cover method comprises the following steps:

[0058] (1) Determine the size of the pilot hole space required for the construction of the arch foot piles.

[0059] According to the engineering geological and hydrological conditions, the stress of the arch cover support structure and the space requirements of the construction machinery, the spatial dimensions of the pilot tunnel excavated in the upper section of the subway station and the position of the temporary vertical support 7 are determined. The spatial dimensions of the pilot tunnel are generally not less than 5m in net width and not less than 7m in net height, which can meet the requirements of mechanical construction. The position of the temporary vertical support 7 should meet the structural stress before the second layer of arch cover support is applied, and attention should be paid to prevent the core soil under the temporary vertical support from encroaching on the mechanical construction space.

[0060] (2) Excavate the upper part of the subway station and construct the first layer of arch support.

[0061] According to the size of the pilot tunnel space, excavate the upper section of the station. Figure 2As shown in (a)-(d), first, the upper step of the left guide tunnel is excavated, and the grid steel frame of the left first layer arch cover support and the steel section as temporary vertical support are erected at the same time. Then, the steel mesh is tied to the grid steel frame of the first layer arch cover support and concrete is sprayed to complete the construction of the left first layer arch cover support and temporary vertical support; then, the lower step of the left guide tunnel is excavated, and the same method is used to extend the left first layer arch cover support and temporary vertical support; then, the upper and lower steps of the right guide tunnel are excavated in turn, and the same method is used to construct the right first layer arch cover support and temporary vertical support; finally, the upper and lower steps of the middle guide tunnel are excavated in turn, and the left first layer arch cover support and the right first layer arch cover support are connected to complete the construction of the first layer arch cover support and temporary vertical support.

[0062] (3) Determine the reinforcement location based on the extent and crushing range of the surrounding rock at the arch foot.

[0063] According to the surrounding rock crushing conditions and range at the arch foot position revealed after the pilot tunnel excavation, the arch foot pile reinforcement position can be accurately determined. Generally, when the rock mass integrity coefficient under the arch foot is less than 0.45 and the thickness of the crushed rock layer is greater than 1m, reinforcement measures such as arch foot piles and longitudinal beams are required.

[0064] (4) Determine the arch foot pile parameters, longitudinal beam dimensions and reinforcement according to the stress on the arch cover.

[0065] The parameters of the arch foot pile (including the length of the arch foot pile body, the specifications of the steel frame, the diameter of the pile hole, etc.) and the size of the longitudinal beam and the reinforcement can be determined based on the calculation of the internal force of the arch cover. The length of the arch foot pile should pass through the revealed broken rock layer and generally not be less than 5m. The diameter of the arch foot pile hole is generally 180-250mm so that a small drilling machine can be used for mechanical construction.

[0066] In this embodiment, the internal forces of the arch foot pile and the longitudinal beam (including axial force, shear force and bending moment) can be calculated through the finite element stratum-structure model of the surrounding rock-support; the required single pile bearing capacity is then calculated through the axial force of the arch foot and the basic bearing capacity of the broken rock layer, and then the length and diameter of the arch foot pile are calculated; according to the calculation method of reinforced concrete structure, the size and wall thickness of the steel frame are obtained through the axial force, shear force and bending moment of the arch foot pile, and the size and reinforcement (main reinforcement and stirrups) of the longitudinal beam are obtained through the axial force, shear force and bending moment of the longitudinal beam.

[0067] In order to better resist the local stress of the broken rock strata at the arch foot, two arch foot piles are set at each reinforcement position on the basis that the axis of the arch foot pile is roughly arranged along the tangent of the arch cover and arch foot, and the axes of the two arch foot piles form an angle of 10 to 20 degrees.

[0068] (5) Construct arch foot piles.

[0069] During the construction of the arch foot pile, the hole is first formed and cleaned, and then the steel frame 8 is hoisted and placed, and finally C30 or above fine stone concrete is poured into the arch foot pile hole and the steel wall of the steel frame. The small-diameter steel concrete pile with a pile hole diameter of 180 to 250 mm, which is composed of the steel frame 8 and the fine stone concrete 9 poured into the steel wall of the steel frame and the pile hole, is the arch foot pile.

[0070] Specifically, Figure 3 As shown, the small tunnel boring machine 6 is adjusted to the reinforcement position determined in step (3), and the hole is drilled along the designed pile body axis to obtain the arch foot pile hole. The selected drilling machine should be suitable for the drilling depth and hole diameter requirements, and the hole forming process should be smooth and flexible. It can be operated in a space with a net width of 5m and a net height of 7m. Its drill rod can be tilted within a range of 360° to make full use of the pilot hole space after the pile body is tilted. During the drilling process, attention should be paid to using an inclinometer to measure the drilling inclination and strictly control the drilling direction.

[0071] After the small tunnel boring machine 6 drills to the final hole position, the residue in the hole is cleared, and then the steel frame 8 is hoisted into the arch foot pile hole, and C30 and above fine stone concrete 9 is poured into the arch foot pile hole and the steel wall of the steel frame to complete the construction of the arch foot pile. The coarse aggregate gradation and slump of the concrete should ensure that the arch foot pile body is poured densely and continuously.

[0072] (6) Construct longitudinal beams.

[0073] Tie up the longitudinal beam reinforcement of the arch foot and pour C30 or above concrete. Several longitudinal beam reinforcements arranged along the longitudinal direction of the subway station and the concrete that casts the longitudinal beam reinforcements together form the longitudinal beam. The second-layer arch cover grid steel frame joint 10 is reserved in the longitudinal beam to connect the longitudinal beam and the second-layer arch cover support 4 (such as Figure 5 The position of the reinforcement should be properly adjusted at the point where the beam reinforcement and the arch foot pile head conflict.

[0074] The top of the steel frame 8 of the arch foot pile extends out of the arch foot pile to 0.5m of the arch foot (that is, 0.5m deep into the longitudinal beam), and is cast in the longitudinal beam of the arch foot (such as Figure 4 The longitudinal beam 1 is located at the inner side of the arch foot of the first-floor arch cover support 3 of the subway station.

[0075] (7) Construct the second layer of arch support.

[0076] The second-layer arch cover support grid is erected, the steel mesh is tied, and concrete is sprayed to complete the construction of the second-layer arch cover support 4. After the arch cover support reaches the designed strength, the temporary vertical support 7 is removed in sections of 5 to 8 meters along the longitudinal direction of the tunnel.

[0077] After the construction of the arch foot piles, longitudinal beams and the second layer of arch cover support is completed, Figure 2 (e) as shown.

[0078] (8) Repeat steps (1) to (7) until all arch cover supports in the station and arch foot reinforcement at the broken surrounding rock locations are completed.

[0079] After the construction of the first layer of arch cover support, arch foot piles, longitudinal beams and the second layer of arch cover support is completed, Figure 2 As shown in (f), the lower part of the station is excavated and the secondary lining is poured under the protection of the station arch cover and arch foot reinforcement structure system in the broken surrounding rock.

[0080] The advantages of the arch foot reinforcement structure of the above-mentioned arch cover method are that it adopts a reinforcement system combining small-diameter steel concrete piles and longitudinal beams, and uses a small tunnel drilling rig for construction, avoiding the size restrictions of large pile foundations in the tunnel and the engineering risks of artificial drilling, and can effectively penetrate deep and broken surrounding rocks. The structural system is easy to construct, the reinforcement position is flexible, and the implementation efficiency is high. The details are as follows:

[0081] (1) After the upper section pilot tunnel is excavated, the structural parameters such as the reinforcement range, arch foot pile length, longitudinal beam size and reinforcement can be accurately determined. On this basis, the degree and range of the surrounding rock fragmentation of the arch foot can be accurately determined.

[0082] (2) The scope of reinforcement and the objects to be implemented are flexible to select. They are all aimed at the broken rock strata at the arch foot of the supporting arch cover. Its implementation will not have an overall impact on the construction of the entire station, and will not affect the advantages of the arch cover method in terms of project cost, construction period, implementation efficiency, mechanized operation, etc.

[0083] (3) The arch foot piles are drilled with a small tunnel drilling rig, and the drill rod can be tilted at any angle, which can fully utilize the pilot hole space after the pile body is tilted, avoiding the size limitations of large pile foundations in the tunnel and the engineering risks of manual drilling.

[0084] Application Examples

[0085] This application takes a section of Qingdao Metro Line 4 project (tunnel length 83m) as an example. The on-site construction of the arch foot reinforcement structure of the underground subway station using the arch cover method includes the following steps:

[0086] (1) Determine the size of the pilot hole space required for the construction of the arch foot piles.

[0087] As the excavation span of the subway station is about 21.4m, according to the engineering geological and hydrological conditions, the stress of the arch cover support structure and the space requirements of the construction machinery, it is determined that the spatial dimensions of the excavation of the pilot tunnel in the upper section of the subway station are about 6.8m in net width and 7.3m in net height, and the temporary vertical support 7 on the inside of the pilot tunnel is about 6.8m away from the wall of the pilot tunnel.

[0088] (2) Excavate the upper part of the subway station and construct the first layer of arch support.

[0089] According to the size of the pilot tunnel space, excavate the upper section of the station. Figure 2 As shown in (a)-(d), firstly, the upper step of the left pilot tunnel is excavated, and at the same time, the grid steel frame (spacing of 0.5m) and the steel section (25b I-beam) as temporary vertical support for the first layer of arch cover support are erected, and then the steel mesh (diameter 250mm) is tied to the grid steel frame for the first layer of arch cover support. Spacing 200mm×200mm), spray C25 and P6 concrete 300mm thick on the grid steel frame and the temporary vertical support steel to complete the construction of the first layer of arch cover support and temporary vertical support on the left; then excavate the lower step of the left guide tunnel, and use the same method to extend the first layer of arch cover support and temporary vertical support on the left; then excavate the upper and lower steps of the right guide tunnel in turn, and use the same method to construct the first layer of arch cover support and temporary vertical support on the right; finally, excavate the upper and lower steps of the middle guide tunnel in turn, connect the first layer of arch cover support on the left and the first layer of arch cover support on the right, and complete the construction of the first layer of arch cover support and temporary vertical support.

[0090] (3) Determine the reinforcement location based on the extent and crushing range of the surrounding rock at the arch foot.

[0091] According to the surrounding rock crushing conditions and scope at the arch foot position revealed after the pilot tunnel excavation, it was determined that the scope that needed to be reinforced at the arch foot was the V and VI grade surrounding rock sections with a rock integrity coefficient less than 0.45 and a crushed rock layer thickness greater than 1m.

[0092] (4) Determine the arch foot pile parameters, longitudinal beam dimensions and reinforcement according to the stress on the arch cover.

[0093] The driving angle of the arch foot piles determined in this application example is 30° away from the vertical direction, and the pile spacing along the longitudinal direction of the tunnel is 1.5m.

[0094] The diameter of the arch pile steel skeleton determined in this application example is The steel pipe has a length of L=7m and a thickness of t=8mm; the diameter of the arch foot pile hole is 220mm, and the pile body is poured with C30 fine stone concrete.

[0095] The upper width of the longitudinal beam determined in this application example is 1050mm, the lower width is 1645mm, and the main reinforcement of the upper end surface is 5 The main reinforcement of the lower end surface is 8 Stirrups are made of For steel bars, the spacing between adjacent stirrups is 250mm.

[0096] In order to better resist the local stress of the broken rock strata at the arch foot, two arch foot piles are set at each reinforcement position on the basis that the axis of the arch foot pile is roughly arranged along the tangent of the arch cover and arch foot, and the axes of the two arch foot piles form an angle of 15°.

[0097] (5) Construct arch foot piles.

[0098] The small tunnel boring machine 6 is adjusted to the reinforcement position determined in step (3), and the hole is drilled obliquely along the designed pile axis to obtain the arch foot pile hole. After the small tunnel boring machine 6 drills to the final hole position, the residue in the hole is removed, and then the steel frame 8 is hoisted into the arch foot pile hole, and C30 fine stone concrete 9 is poured into the arch foot pile hole and the steel wall of the steel frame to complete the construction of the arch foot pile.

[0099] (6) Construct longitudinal beams.

[0100] The arch foot longitudinal beam reinforcement (main reinforcement and stirrups) are tied, and C30 fine stone concrete is poured. Several longitudinal beam reinforcements arranged along the longitudinal direction of the subway station and the concrete in which the longitudinal beam reinforcements are poured together constitute the longitudinal beam.

[0101] The top of the steel frame 8 of the arch foot extends out of the arch foot pile to 0.5m of the arch foot (that is, 0.5m deep into the longitudinal beam), and is cast in the longitudinal beam of the arch foot (such as Figure 4 The longitudinal beam 1 is located at the inner side of the arch foot of the first-floor arch cover support 3 of the subway station.

[0102] (7) Construct the second layer of arch support.

[0103] Set up the second-layer arch cover support steel frame (spacing 0.5m), tie up the single-layer steel mesh (diameter Spacing 200mm×200mm), spray C25 and P6 concrete (arch top 350mm, arch foot 1645mm thick) onto the grid steel frame and temporary vertical support steel to complete the construction of the second layer arch cover support 4.

[0104] After the arch cover support reaches the designed strength, the temporary vertical support 7 is removed in sections of 5 to 8 m along the longitudinal direction of the tunnel.

[0105] After the construction of the arch foot piles, longitudinal beams and the second layer of arch cover support is completed, Figure 2 (e) as shown.

[0106] (8) Repeat steps (1) to (7) until the arch cover support in the station section and the arch foot reinforcement at the broken surrounding rock are completed.

[0107] After the construction of the first arch cover support, arch foot piles, longitudinal beams and the second arch cover support is completed, Figure 2 As shown in (f), the lower part of the station is excavated and the secondary lining is poured under the protection of the station arch cover and arch foot reinforcement structure system in the broken surrounding rock.

[0108] Application comparison

[0109] This application comparison takes a section of Qingdao Metro Line 4 project (the length of the tunnel is 116m) as an example. Figure 6 As shown in the figure, the on-site construction of the arch foot reinforcement structure of the underground subway station using the arch cover method in this application includes the following steps:

[0110] (1) Determine the size of the tunnel space above the station.

[0111] As the excavation span of the subway station is about 21.4m, according to the engineering geological and hydrological conditions, the stress of the arch cover support structure and the space requirements of the construction machinery, it is determined that the spatial dimensions of the excavation of the pilot tunnel in the upper section of the subway station are about 6.8m in net width and 7.3m in net height, and the temporary vertical support 7 on the inside of the pilot tunnel is about 6.8m away from the wall of the pilot tunnel.

[0112] (2) Excavate the upper part of the subway station and construct the first layer of arch support.

[0113] According to the size of the pilot tunnel space, the upper section of the station was excavated. First, the upper steps of the left pilot tunnel were excavated, and at the same time, the grid steel frame (spacing of 0.5m) and the steel (25b I-beam) as temporary vertical support were set up for the first layer of arch cover support on the left side. Then, a single-layer steel mesh (diameter 2.0mm) was tied to the grid steel frame of the first layer of arch cover support. Spacing 200mm×200mm), spray C25 and P6 concrete 300mm thick on the grid steel frame and the temporary vertical support steel to complete the construction of the first layer of arch cover support and temporary vertical support on the left; then excavate the lower step of the left guide tunnel, and use the same method to extend the first layer of arch cover support and temporary vertical support on the left; then excavate the upper and lower steps of the right guide tunnel in turn, and use the same method to construct the first layer of arch cover support and temporary vertical support on the right; finally, excavate the upper and lower steps of the middle guide tunnel in turn, connect the first layer of arch cover support on the left and the first layer of arch cover support on the right, and complete the construction of the first layer of arch cover support and temporary vertical support.

[0114] (3) Grouting and anchor rods are used to reinforce the broken rock around the arch foot.

[0115] Two diameters The hollow grouting flower tube 12 is used to grout the rock mass under the arch foot. The length of the grouting pipe is 3.5m. The grouting liquid is cement slurry. The direction of the flower tube is 30° away from the vertical direction. The spacing between adjacent reinforcement positions along the tunnel direction is 0.5m. The axes of the two grouting flower tubes form an angle of 15°.

[0116] When excavating the rock mass under the arch foot, a diameter The hollow grouting anchor rod 11 has a length of 3.5 m and is arranged in a plum blossom shape of 1 m × 1 m.

[0117] (4) Construct the second layer of arch support.

[0118] Set up the second-layer arch cover support steel frame (spacing 0.5m), tie up the single-layer steel mesh (diameter Spacing 200mm×200mm), spray C25 and P6 concrete (350mm thick for arch top and 1645mm thick for arch foot) on the grid steel frame and temporary vertical support steel to complete the construction of the second layer of arch cover support.

[0119] After the arch cover support reaches the designed strength, the temporary vertical supports will be removed in sections of 5 to 8 meters along the longitudinal direction of the tunnel.

[0120] (5) Repeat steps (1) to (4) until the arch cover support in the station section and the arch foot reinforcement at the broken surrounding rock are completed.

[0121] After the first layer of arch cover support, arch foot grouting, anchor rods and the second layer of arch cover support are completed, the lower part of the station is excavated and the secondary lining is poured under the protection of the station arch cover and arch foot reinforcement structure system in the broken surrounding rock.

[0122] The above-mentioned application example and application comparison example of underground excavation subway stations are both constructed using the arch cover method, with an excavation span of 21.4m and the same excavation sequence. The only difference is the different arch foot reinforcement methods at the broken surrounding rock. The surface settlement and arch crown settlement monitoring of both are carried out, and the results are as follows: Figure 7 and Figure 8 As shown in the figure, it can be seen that the surface settlement and arch settlement of the reinforcement system using arch foot piles and longitudinal beams are smaller than those of the reinforcement system using anchor rods. Therefore, the arch foot reinforcement structure and construction method of the underground excavation subway station provided by the arch cover method of the present invention have a better reinforcement effect on the arch foot in the broken surrounding rock.

[0123] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A construction method for the arch foot reinforcement structure of a subway station by using the arch cover method. It is characterized in that The arch foot reinforcement structure of a subway station using the arch cover method comprises a first layer of arch cover support (3) and a second layer of arch cover support (4) arranged in sequence above the secondary lining of the subway station, and is characterized in that it also comprises arch foot piles (2) arranged at the arch feet on both sides of the second layer of arch cover support and an arch foot longitudinal beam (1) connected to the arch foot piles; the arch foot piles are arranged along the tangent line of the arch foot; the arch foot piles are composed of a steel frame (8) and fine stone concrete cast in the steel wall of the steel frame and in the pile hole; the arch foot longitudinal beam is arranged on both sides of the second layer of arch cover support along the longitudinal direction of the subway station; The construction method of the arch-covering method for the underground excavation subway station arch foot reinforcement structure comprises the following steps: (1) Determine the size of the pilot hole space required for the construction of the arch foot piles; (2) Excavate the upper part of the subway station and construct the first layer of arch support; According to the size of the pilot tunnel space, the upper section of the station is excavated; while the pilot tunnel is being excavated, the first layer of arch cover support is completed; specifically: First, excavate the upper steps of the left pilot tunnel, and at the same time, set up the grid steel frame of the left first-layer arch cover support and the steel section as a temporary vertical support. Then, tie the steel mesh and spray concrete on the grid steel frame of the first-layer arch cover support to complete the construction of the left first-layer arch cover support and temporary vertical support. Then, excavate the lower steps of the left pilot tunnel, and use the same method to extend the left first-layer arch cover support and temporary vertical support. Then, excavate the upper and lower steps of the right pilot tunnel in turn, and use the same method to construct the right first-layer arch cover support and temporary vertical support. Finally, excavate the upper and lower steps of the middle pilot tunnel in turn, connect the left first-layer arch cover support and the right first-layer arch cover support, and complete the construction of the first-layer arch cover support and temporary vertical support. (3) Determine the reinforcement location based on the crushing conditions and scope of the surrounding rock at the arch foot; When the rock mass integrity coefficient under the arch foot is less than 0.45 and the thickness of the broken rock layer is greater than 1m, it is necessary to adopt arch foot piles and longitudinal beam reinforcement measures; (4) Determine the diameter of the arch foot pile, the specifications of the steel frame, the size of the longitudinal beam and the reinforcement according to the stress of the arch cover; the length of the arch foot pile should pass through the revealed broken rock layer and be no less than 5m, and the diameter of the arch foot pile hole should be 180-250mm; (5) Construction of arch foot piles; After the reinforcement position is determined, a small tunnel boring machine is used to drill holes obliquely along the designed pile axis to obtain the arch foot pile holes, and then a steel frame (8) is hoisted into the arch foot pile holes, and fine stone concrete (9) is poured into the steel wall of the steel frame and the arch foot pile holes to complete the construction of the arch foot piles; (6) Construction of longitudinal beams; First, several longitudinal beam steel bars of the arch foot are tied, and then the steel bars are cast into one piece by concrete; the top of the arch foot pile steel frame extends into the arch foot and is cast into the longitudinal beam; (7) Construction of the second layer of arch support; The second-layer arch cover support grid is erected, the steel mesh is tied, and concrete is sprayed to complete the construction of the second-layer arch cover support 4; after the arch cover support reaches the designed strength, the temporary vertical support is removed in sections of 5 to 8 meters along the longitudinal direction of the tunnel; (8) Repeat steps (1) to (7) until all arch cover supports in the station and arch foot reinforcement at the broken surrounding rock locations are completed.

2. The construction method of the arch foot reinforcement structure of a subway station by the arch cover method according to claim 1, Features The net width of the guide tunnel space shall not be less than 5m, and the net height shall not be less than 7m.

3. According to the construction method of the arch cover method for the arch foot reinforcement structure of the underground subway station, Features The arch foot pile passes through the broken rock layer at the arch foot; and the length of the arch foot pile body is not less than 5m.

4. The construction method of the arch foot reinforcement structure of a subway station by the arch cover method according to claim 3, Features When there are two or more arch foot piles arranged at the same reinforcement position, the axes of the two adjacent arch foot piles form a fixed angle of 10° to 20°.

5. According to the construction method of the arch cover method for the arch foot reinforcement structure of the underground subway station, Features In step (6), the longitudinal beam is constructed by first tying a number of arch foot longitudinal beam steel bars, and then using concrete to cast them as a whole; the top of the arch foot pile steel frame extends into the arch foot and is cast in the longitudinal beam.

6. The construction method of the arch foot reinforcement structure of a subway station by the arch cover method according to claim 1, Features The longitudinal beam is located at the inner side of the arch foot of the first-floor arch cover support (3) of the subway station.

7. The construction method of the arch foot reinforcement structure of a subway station by the arch cover method according to claim 6, Features A second layer of arch cover grid steel frame joint (10) is reserved in the longitudinal beam.

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