Large-section metro underground excavation station initial support arch cover method construction technology

Abstract

The invention belongs to the field of metro construction, particularly relates to an initial support arch cover method construction technology for a large-section metro underground excavation station, and aims to solve the problems of high construction difficulty, long construction period, high cost and the like when a traditional underground excavation construction method faces a large-span shallow-buried station. The problem that the construction difficulty in the weathered rock stratum is large is effectively solved by introducing a double-layer initial supporting arch structure, gradually changing supporting and expanding arch springing design, automatic monitoring, three-dimensional modeling analysis and other innovative means. According to the technology, the construction efficiency is remarkably improved, the construction period is shortened, the cost is reduced, disturbance of construction to the surrounding environment is remarkably reduced, and the safety and stability of the structure are enhanced. The flexible adaptability and the wide application prospect are achieved, an efficient, economical and environment-friendly construction solution is provided for the field of subway construction, and rapid development of subway construction is promoted.

Description

Technical Field

[0001] The invention belongs to the field of subway construction, and in particular relates to a construction technology of an initial support arch cover method for a large-section subway dark excavation station. Background Art

[0002] In subway construction, the construction of underground excavation stations is a complex and critical task, especially in areas with complex geological conditions and soft strata on the upper part and hard strata on the lower part. Traditional underground excavation methods such as CRD method, glasses method, side hole method, etc., often face problems such as difficult construction, long construction period, and high cost when facing large-span shallow buried stations. Especially in weathered rock strata, due to the high strength of the rock and the difficulty of excavation, traditional construction methods are often difficult to deal with effectively.

[0003] In recent years, with the rapid development of subway construction, the requirements for underground excavation station construction technology have become increasingly higher. Based on the design and construction experience of the PBA construction method in soft soil strata, the Dalian Metro Line 1 project innovatively adopted a new underground excavation station construction method - the arch cover method, in view of the high strength of weathered rock strata. This method makes full use of the high strength of weathered rock and protects the excavation of the lower soil by forming a stable arch cover structure, effectively solving the construction difficulties caused by the soft upper strata and the hard lower strata.

[0004] The core of the arch cover construction technology is to use the large arch foot scheme to replace the side piles in the traditional PBA method, form a stable arch cover structure by buckling the arch in advance, and then use the reverse construction method or the forward construction method to complete the construction of the main structure under the protection of the arch cover. This method has the advantages of fewer guide holes, fewer processes, less disturbance, less ground settlement, simple support, less abandoned engineering, low cost, high efficiency, and short construction period. However, the arch cover method also has higher requirements for the strength of the surrounding rock, and is mainly suitable for weathered rock formations, especially soil-rock composite formations with soft upper and hard lower parts.

[0005] Although the arch capping method has been successfully applied in many projects such as Dalian Metro, it still faces some technical challenges in its actual application, such as the stability of the large arch foot, the support of the surrounding rock of the high side wall, and the bidirectional stability of the steel pipe column. Therefore, further optimizing and improving the construction technology of the arch capping method and improving its adaptability and reliability under different geological conditions are of great significance to promoting the rapid development of subway construction. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a large-section subway underground excavation station initial support arch cover construction technology, to solve the shortcomings of the traditional construction technology of large-section underground excavation stations, to optimize the underground excavation technology, to speed up the construction progress, to improve safety, to reduce the disturbance to the urban environment and buildings, and to improve economy.

[0007] To achieve the above object, the present invention provides the following technical solution: a large-section subway dark excavation station initial support arch cover method construction technology, comprising the following steps:

[0008] S1, small-section passage access to the main system conversion of large-section station;

[0009] S11, during the construction process of accessing the main body of the large-section station through the small-section auxiliary passage, a double-layer primary support arch structure is adopted, including the top section portal frame and the large-section tunnel main body primary support;

[0010] S12, the bottom of the cantilever channel is set with corresponding longitudinal slope according to the cantilever angle and the arch height of the large-section chamber to ensure the applicability of the primary support trolley without modification;

[0011] S13, after the cantilevered passage is connected to the other side of the large-section chamber, the lower steps and side wall supports are excavated to complete the construction of the cantilevered passage;

[0012] S14, after the portal frame support of the cantilevered passage is completed, the primary support structure of the large-section chamber is constructed to form a double-layer primary support arch;

[0013] S2, construction of the main body of the large-section station using the initial support arch cover method;

[0014] S21, the arch adopts a gradient support structure to form an enlarged arch foot to stabilize the arch cap;

[0015] S22, the main body of the station is excavated in three steps, and three pilot tunnels are set up on the upper step. The left and right pilot tunnels are excavated first and the arch foot is expanded;

[0016] S23, temporary vertical supports are set up on both sides of the middle rock mass, and the middle guide tunnel is excavated and the vault is supported after the monitoring data is stable;

[0017] S24, after the initial support of the arch reaches the required strength, the temporary support is removed to form a stable arch cover structure;

[0018] S3, middle rock column release step optimization;

[0019] S31, using an automated monitoring system to monitor surrounding rock pressure and initial support stress in real time;

[0020] S32, determine the spacing between the middle rock pillars through three-dimensional fast Lagrangian modeling and analysis;

[0021] S33, the distance between the middle rock columns should not be greater than 110m to ensure safe and stable construction;

[0022] S4, construction organization of excavation support of the middle and lower steps of the station and the secondary lining of the invert;

[0023] S41, organize construction according to the spacing of medium rock pillars not exceeding 110m;

[0024] S42, retain part of the middle rock pillars to support the surrounding rock of the arch, and excavate the rest of the middle rock pillars and complete the support;

[0025] S43, excavation of pilot tunnels for the middle and lower steps, and secondary lining construction after the backfill of the invert reaches sufficient strength.

[0026] Optionally, three closely spaced steel frames are connected to the starting position of the cantilevered gantry section of the large-section dark-excavation station with a small-section auxiliary passageway. Vertical I-beam supports are arranged on the upper part of the steel frames, crossbeams are arranged on the I-beams, and steel plates for the main primary support steel frames are welded on the crossbeams.

[0027] Optionally, the spacing between the portal steel frames of the cantilevered passage is 0.75m, and the top excavation contour line is raised from the top of the auxiliary passage at an angle of 15° to the designed main arch position of the station.

[0028] Optionally, the main body of the large-section station is excavated in three steps and eleven guide tunnels. The construction sequence is as follows: construction of the cross-channel of the cantilevered section gantry, excavation and support of the guide tunnels on both sides and the expansion of the arch feet, excavation of the middle guide tunnel and initial support of the arch top, excavation and support of the branch guide tunnels of the middle and lower steps, construction of the invert arch, and construction of the secondary lining.

[0029] The beneficial effects of the present invention are:

[0030] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0032] Figure 1 It is a schematic diagram of the top channel of the present invention;

[0033] Figure 2 This is a construction process flow chart of the large-section dark excavation station enlargement arch foot step method of the present invention, wherein 1 to 9 represent guide tunnels respectively;

[0034] Figure 3 This is a schematic diagram of the installation points of the automated monitoring equipment of the present invention;

[0035] Figure 4 This is a cross-sectional view of the steel frame connection of the tunnel portal of the present invention;

[0036] Figure 5 It is a longitudinal section view of the interface section of the cantilever channel of the present invention. DETAILED DESCRIPTION

[0037] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0038] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0039] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0040] See also Figure 1 to Figure 5 , which is a construction technology of initial support arch covering method for large-section subway underground excavation stations, including the following main steps:

[0041] S1: small-section passageway connected to the main system conversion of large-section station;

[0042] S11: During the construction process of connecting the small-section auxiliary passage to the main body of the large-section station, a double-layer primary support arch structure is used; this structure includes the top section portal frame and the large-section tunnel main body primary support, making full use of the channel primary support structure and reducing the arch replacement construction; the top section portal frame is used to support and stabilize the top passage to ensure safety during construction; the large-section tunnel main body primary support is the initial support for the main structure of the station, providing a foundation for subsequent construction;

[0043] S12: The bottom of the cantilever channel is provided with a corresponding longitudinal slope (i.e., a step down) according to the cantilever angle and the arch height of the large-section chamber; this design ensures the applicability of the primary support trolley without modification, thus improving the construction efficiency;

[0044] S13: After the cantilevered passage is connected to the other side of the large-section chamber, the lower steps and side wall supports are excavated; this step completes the construction of the cantilevered passage and provides a passage for the subsequent main station construction.

[0045] S14: After the portal frame support of the cantilevered passage is completed, the initial support structure of the large-section chamber is constructed; this step forms a double-layer initial support arch, reduces arch replacement construction, reduces over-excavation and backfilling, and further enhances the stability of the station body.

[0046] S2: The main body of the large-section station is constructed using the initial support arch method;

[0047] S21: The arch adopts a gradual support structure to form an expanded arch foot to stabilize the arch cover; this design allows the arch surrounding rock pressure to be transmitted to the surrounding rocks on both sides through the expanded arch foot, forming a stable arch cover structure;

[0048] S22: The main body of the station is excavated in three steps; three guide tunnels are set up on the upper step (arch), and the left and right side guide tunnels are excavated first and the arch foot is expanded; this step provides the basis for the subsequent excavation of the middle guide tunnel and arch support.

[0049] S23: Temporary vertical supports are set up on both sides of the middle rock mass; after the monitoring data is stable, the middle guide tunnel is excavated and the vault is supported; this step ensures safety and stability during the construction process;

[0050] S24: After the initial support of the arch reaches the required strength, the temporary support is removed. After the removal, the surrounding rock pressure is transferred to the surrounding rocks on both sides below the station arch through the expanded arch foot, forming a complete and stable arch structure (arch cover) with expanded arch foot. The station body below the arch is constructed using the step method under the protection of the arch cover, achieving the purpose of high efficiency, safety and stability.

[0051] S3: middle rock column release step optimization;

[0052] The excavation of the No. 3 pilot tunnel of the main station and the removal of temporary supports are key links in the construction of the station main body by the arch foot step method. It is also a key process for the force system to change from a small pilot tunnel to a large-section arch cover. The timing of excavation and removal of temporary supports must be strictly controlled. At the same time, the early removal of the middle rock column and the length of the removal directly affect the excavation of the middle and lower steps and the construction of the second lining of the invert. Accelerating the excavation of the No. 3 pilot tunnel and the removal of temporary supports under the premise of ensuring safe and stable force is the key to quickly organize construction. The spacing of the middle rock columns is determined as follows:

[0053] S31: Strengthen monitoring;

[0054] The method of automatic monitoring system + manual monitoring is adopted to avoid many disadvantages of manual monitoring, such as the inaccuracy of monitoring in a high dust environment and the low real-time nature of monitoring data. Conventional construction monitoring includes conventional monitoring methods such as arch settlement, surface settlement, peripheral displacement, and arch foot settlement. This method will not be described in detail. The automatic monitoring system uses vibrating string sensors, including vibrating string earth pressure boxes and vibrating string steel stress gauges. The earth pressure box is a vibrating string sensor. The sensitive element of the vibrating string sensor is a metal steel string, which is connected and fixed to the force-bearing component of the sensor. Various physical quantities are measured using the relationship between the natural frequency of the steel string and the external tension applied to the steel string. The structure of the steel stress gauge is to connect steel bars at both ends of the special instrument. The middle instrument section contains a group of miniature vibrating string strain gauges and an induction coil. The coil connection cable is led out from the center of the strain gauge and connected to the vibrating string reader or data collector (the above two structures are both existing mature technologies, not the core construction technology of this application, so they are not described here).

[0055] After the pilot tunnel is excavated, during the support process, automatic steel bar stress and soil pressure monitoring equipment is installed in time to monitor the surrounding rock pressure and initial support stress in real time. At the same time, the monitoring data is integrated and analyzed as data support for the excavation of the middle rock column and the removal of the temporary steel support.

[0056] S32: Numerical modeling analysis;

[0057] The three-dimensional fast Lagrangian method is used for modeling and analysis. The three-dimensional fast Lagrangian method is a numerical analysis method based on the three-dimensional explicit finite difference method. It can simulate the three-dimensional mechanical properties of rock, soil or other materials. The three-dimensional fast Lagrangian analysis uses an explicit finite difference format to solve the governing differential equations of the field, and applies a mixed unit discrete model. It can accurately simulate the yielding, plastic flow, softening and even large deformation of the material. It has unique advantages in the fields of elastic-plastic analysis, large deformation analysis and simulation of construction processes. The use of FLAC3D in this study can better simulate the mechanical properties of the destruction or plastic flow of geological materials when they reach the strength limit or yield limit. It is particularly suitable for analyzing progressive failure instability and simulating large deformations.

[0058] In this embodiment, according to the analysis of numerical simulation and on-site monitoring data, after all the middle rock pillars were excavated, the construction displacement and stress of the station main support structure did not exceed the standard recommended values. In order to ensure the safety and stability of the construction, some middle rock pillars were retained at appropriate locations in combination with the construction process and schedule. The spacing between the middle rock pillars should not be greater than 110m.

[0059] S4: Excavation support of the middle and lower steps of the station and construction organization of the secondary lining of the invert arch;

[0060] S41: Organize the construction according to the spacing of medium rock columns not more than 110m. This step ensures the continuity and stability of the construction process.

[0061] S42: retain some middle rock columns to support the surrounding rock of the arch, and excavate and support the remaining middle rock columns. This step provides conditions for the excavation of the middle and lower steps.

[0062] S43: Excavation of the pilot tunnels for the middle and lower steps, and construction of the secondary lining after the backfill of the invert reaches the required strength. This step completes the construction of the main body of the station and ensures the stability and safety of the station.

[0063] In this embodiment, the small-section auxiliary passageway can be connected to the starting position of the large-section dark-excavation station cantilevered portal section by closely arranging three steel frames, with vertical I-beams on the upper part of the steel frames, crossbeams on the I-beams, and steel plates for the main primary support steel frames welded on the crossbeams. This design enhances the stability of the cantilevered passageway.

[0064] In this embodiment, the spacing between the portal steel frames of the cantilevered channel can be 0.75m, and the top excavation contour line is raised from the top of the auxiliary channel at an inclination angle of 15° to the designed top of the station main arch, and then expanded by 320mm according to the outer contour line of the station main arch excavation. The rectangular channel within the station section is excavated in sections according to the step method. During the construction process, it is necessary to erect portal steel frames according to the height changes. The portal steel frames are assembled according to the construction conditions, and the overall installation or step-by-step installation is selected, and the hollow grouting anchor rods are used for the initial support of the main tunnel.

[0065] In this embodiment, the main body of the large-section station can be excavated in three steps and eleven guide tunnels, and the main construction sequence is as follows:

[0066] ① Enter the station main body from the construction channel, carry out the initial support of the portal cross channel of the construction section and the main tunnel arch in the inner ring of the station cross channel, and complete the construction of the construction channel to the station main body;

[0067] ②Measure and stake out the outlines of the three guide holes on the upper steps on both sides of the construction passageway entering the top section of the station body, remove the temporary support of the guide holes on both sides of the station arch, and carry out excavation and support construction of the guide holes on both sides and the expansion of the arch foot;

[0068] ③ When the monitoring data is stable, excavate the No. ③ pilot tunnel (middle rock column), carry out the initial support of the arch, complete the initial support structure of the main arch of the large-section station and close it into an arch cover. The initial support strength meets the design requirements. After the monitoring data is stable, remove the temporary support, so that the upper surrounding rock pressure is transmitted to the surrounding rocks on both sides of the station through the arch cover and the expanded arch foot, forming a stable force system;

[0069] ④ Excavate the middle and lower steps of the station by the step method under the arch cover, and slope the pilot tunnels from the upper step to the middle and lower steps, and excavate and support the pilot tunnels of the middle and lower steps of the station in sequence;

[0070] ⑤ After the lower step is excavated to the bottom of the tunnel and the working surface for the invert construction is available, the invert construction will begin. After the invert length reaches the conditions for the assembly of the secondary lining trolley and the secondary lining construction, the trolley assembly and the secondary lining construction will be carried out, forming a construction organization mode of excavation of the upper, middle and lower steps of the station body, and synchronous construction of the invert and the secondary lining.

[0071] In this embodiment, the large-section subway underground excavation station initial support arch cover construction technology of the present invention can better adapt to the soft upper and hard lower geological conditions, and compared with the traditional construction method, it is improved in construction efficiency, working space, economy, etc. This technology can not only enrich the practical experience of design and construction of subway projects under different conditions, but also provide a set of scientific, efficient and practical construction models for the future basic technology field of subway projects.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. The construction technology of the initial support arch cover method for large-section subway underground excavation stations is characterized by: The following steps are involved: S1, small-section passage access to the main system conversion of large-section station; S11, during the construction process of accessing the main body of the large-section station through the small-section auxiliary passage, a double-layer primary support arch structure is adopted, including the top section portal frame and the large-section tunnel main body primary support; S12, the bottom of the cantilever channel is set with corresponding longitudinal slope according to the cantilever angle and the arch height of the large-section chamber to ensure the applicability of the primary support trolley without modification; S13, after the cantilevered passage is connected to the other side of the large-section chamber, the lower steps and side wall supports are excavated to complete the construction of the cantilevered passage; S14, after the portal frame support of the cantilevered passage is completed, the primary support structure of the large-section chamber is constructed to form a double-layer primary support arch; S2, construction of the main body of the large-section station using the initial support arch cover method; S21, the arch adopts a gradient support structure to form an enlarged arch foot to stabilize the arch cap; S22, the main body of the station is excavated in three steps, and three pilot tunnels are set up on the upper step. The left and right pilot tunnels are excavated first and the arch foot is expanded; S23, temporary vertical supports are set up on both sides of the middle rock mass, and the middle guide tunnel is excavated and the vault is supported after the monitoring data is stable; S24, after the initial support of the arch reaches the required strength, the temporary support is removed to form a stable arch cover structure; S3, middle rock column release step optimization; S31, using an automated monitoring system to monitor surrounding rock pressure and initial support stress in real time; S32, determine the spacing between the middle rock pillars through three-dimensional fast Lagrangian modeling and analysis; S33, the distance between the middle rock columns should not be greater than 110m to ensure safe and stable construction; S4, construction organization of excavation support of the middle and lower steps of the station and the secondary lining of the invert; S41, organize construction according to the spacing of medium rock pillars not exceeding 110m; S42, retain part of the middle rock pillars to support the surrounding rock of the arch, and excavate the rest of the middle rock pillars and complete the support; S43, excavation of pilot tunnels for the middle and lower steps, and secondary lining construction after the backfill of the invert reaches sufficient strength.

2. The construction technology of large-section subway underground excavation station initial support arch cover method according to claim 1 is characterized by: Three steel frames are closely arranged at the starting position of the cantilevered gantry section where the small-section auxiliary passage is connected to the large-section dark-excavated station. Vertical I-beam supports are arranged on the upper part of the steel frames, cross beams are arranged on the I-beams, and steel plates for the main primary support steel frame are welded on the cross beams.

3. The construction technology of large-section subway underground excavation station initial support arch cover method according to claim 1 is characterized by: The spacing between the portal steel frames of the cantilevered passage is 0.75m, and the top excavation contour line is raised from the top of the auxiliary passage at an angle of 15° to the designed arch top of the station.

4. The construction technology of large-section subway underground excavation station initial support arch cover method according to claim 1 is characterized by: The main body of the large-section station is excavated in three steps and eleven guide tunnels. The construction sequence is as follows: construction of the cross-channel of the portal frame of the cantilevered section, excavation and support of the guide tunnels on both sides and the expansion of the arch feet, excavation of the middle guide tunnel and initial support of the arch top, excavation and support of the branch guide tunnels of the middle and lower steps, construction of the invert arch, and construction of the secondary lining.

Images