Supporting method for large-span earth excavation of airport tunnel

Abstract

The invention relates to the field of earth excavation, and discloses a supporting method for large-span earth excavation of an airport tunnel, which comprises the following steps of: performing zoned progressive three-dimensional excavation: dividing the tunnel into three-dimensional latticed construction units along the longitudinal direction and the vertical direction, and forming a space collaborative stress system by adopting a construction sequence of combining central island type excavation with annular support; a dynamic supporting system composed of a variable-rigidity supporting shell, a stress self-adaptive grouting system and a prestress space grid is synchronously constructed after each layer is excavated; overlapped secondary supporting: after the initial supporting system forms a stable arch effect, a permanent bearing structure composed of a fiber concrete lining, a space truss support and stratum compensation reinforcement is constructed; and controlled soil body replacement is conducted, and a zoning and layering replacement and dynamic back pressure method is adopted. According to the construction method, a space collaborative stress system is formed through partition progressive three-dimensional excavation, combined type primary support, overlapped type secondary support and controlled soil body replacement, and the construction safety is improved.

Description

Technical Field

[0001] The present application relates to the field of earth excavation, and in particular to a support method for large-span earth excavation of airport tunnels. Background Art

[0002] The construction of large-span tunnels at airports is an important part of the underground engineering of airport terminal areas. It mainly includes underground passages connecting the terminal building with the surrounding transportation hub to alleviate the pressure of ground transportation. The comprehensive pipeline corridor project is also part of the underground engineering of the airport terminal area. The comprehensive pipeline corridor project intensively lays underground tunnels for municipal pipelines such as electricity, communications, water supply and drainage, and gas. The two together constitute the airport's underground infrastructure network, which improves passenger travel efficiency while realizing centralized management and maintenance of pipelines.

[0003] Airport tunnel projects, due to their large spans, shallow depths, and sensitive surrounding environments, such as terminal buildings and runways, place extremely high demands on excavation support. Currently, the mainstream approaches employ pile-anchor support, underground diaphragm walls, or internal bracing systems, all of which fall under the technical area of ​​temporary support structures. With the increasing number of airport renovation and expansion projects, achieving safe, efficient, and minimally disruptive construction in soft strata and confined sites has become a pressing challenge for the industry. Summary of the Invention

[0004] This application provides a support method for large-span earth excavation of airport tunnels. Through technical means such as zoned progressive three-dimensional excavation, composite initial support, superimposed secondary support and controlled soil replacement, a spatial coordinated force system is formed to effectively control stratum deformation and improve construction safety.

[0005] The present application provides a support method for large-span earth excavation of an airport tunnel, comprising the following steps: zoned progressive three-dimensional excavation: dividing the tunnel into three-dimensional grid-like construction units along the longitudinal and vertical directions, and adopting a construction sequence of central island excavation combined with annular support to form a spatial coordinated force system; composite initial support: after each layer of excavation, a dynamic support system consisting of a variable stiffness support shell, a stress-adaptive grouting system and a prestressed spatial grid is simultaneously constructed; superimposed secondary support: after the initial support system forms a stable arch effect, a permanent bearing structure consisting of fiber concrete lining, spatial truss support and stratum compensation reinforcement is constructed; controlled soil replacement: adopting a zoned and layered replacement and dynamic counter-pressure method to gradually release soil stress.

[0006] Furthermore, the steps of the zoned progressive excavation include: establishing a spatial excavation matrix, decomposing each construction unit into a central core column, a ring excavation zone and a transition connection area; adopting a construction method of layered excavation combined with ring temporary support; and setting an adjustable temporary support arch to control spatial deformation.

[0007] Furthermore, the composite initial support includes: a variable stiffness support shell, which is composed of mutually embedded curved steel shell units through three-dimensional hinged nodes to form a spatial force system; a stress adaptive grouting system, which uses a gradient pressure grouting process to form a reinforcement zone coordinated with the formation deformation; and a spatial prestressed grid, which forms a spatial force field through bidirectional cross-tensioned steel cables.

[0008] Furthermore, the variable stiffness support shell includes: an outer curved pressure-bearing shell, which adopts a corrugated reinforcement structure; an intermediate damping adjustment layer, which adopts a variable hardness composite material; and an inner stress distribution shell, which is provided with a stress diffusion structure.

[0009] Furthermore, the composite secondary support includes: reinforced concrete lining poured in batches, with construction joints and deformation joints; detachable steel supports to form circumferential and longitudinal support grids; and compensatory grouting reinforcement to fill the lost gaps in the stratum.

[0010] Furthermore, the steps of pouring reinforced concrete lining in stages include: first pouring the inverted arch and the lower part of the side wall to form a bottom stable structure; then pouring the upper part of the side wall and the arch top to form a superimposed force system with the composite initial support; and finally applying circumferential prestressing to enhance the overall bearing capacity of the lining.

[0011] Furthermore, the layered replacement and dynamic back pressure method includes: block replacement: dividing the soil to be replaced into several small blocks and replacing them step by step in sequence; dynamic back pressure: maintaining the balance of the soil through temporary support during the replacement process; stress release control: adopting the method of replacing first and then dismantling to reduce stress mutations.

[0012] One or more technical solutions provided in this application have at least the following technical effects or advantages:

[0013] Due to the adoption of a zoned progressive three-dimensional excavation + composite support system, the core soil column is retained through central island excavation, and circular layered excavation is carried out around the core column. Adjustable support arches are erected simultaneously to maintain the three-dimensional force balance of the soil. Subsequently, composite initial support is applied, followed by overlapping secondary support, and finally controlled soil replacement is used to effectively prevent the excavation face from becoming unstable. It is especially suitable for soft strata. The variable stiffness support shell and gradient grouting system can automatically adjust the force, reduce stratum disturbance, reduce stratum settlement, and extend the life of the structure. It is suitable for sensitive areas such as airport underground projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a flow chart of a method for supporting large-span earth excavation in an airport tunnel according to an embodiment of the present application;

[0015] Figure 2 This is a schematic diagram of the process of composite initial support in an embodiment of the present application. DETAILED DESCRIPTION

[0016] In order to better understand the technical solution of the present application, the technical solution of the present application will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0017] This application proposes a support method for large-span earthwork excavation of airport tunnels, referring to Figure 1 As shown, support methods include:

[0018] Step 1: Gradual three-dimensional excavation in different zones

[0019] First, retain the core soil in the center of the tunnel as a natural support, and then carry out circular layered excavation around the core area. Figure 2 , the specific implementation is:

[0020] 1. Spatial excavation matrix division

[0021] The tunnel is divided into several construction sections along the longitudinal direction, each of which can be 15-20m long. Each construction section is decomposed vertically into a central core column, a circular excavation zone and a transition connection area to form a three-dimensional grid excavation unit.

[0022] 2. Central island excavation combined with ring support

[0023] S21, central core column excavation: first retain the central core soil column, which can be 3-5m wide, as a temporary support structure to maintain ground stability.

[0024] S22, circular layered excavation: Excavation is carried out in steps around the core column, with the excavation height of each layer not exceeding 2m. Adjustable temporary support arches are immediately erected after excavation to form a circular support system.

[0025] S23, transition zone connection: a transition zone is set up between the core column and the annular excavation zone, and a short advance and fast closure cycle operation method is adopted to reduce ground disturbance.

[0026] 3. Deformation control measures

[0027] Use low-vibration machinery for excavation, such as a hydraulic breaker + small excavator combination. After each layer is excavated, a temporary invert arch is immediately constructed to control the base uplift.

[0028] Therefore, zoned progressive three-dimensional excavation employs a construction method combining core soil retention and circular layered excavation. This method divides the tunnel into longitudinal construction sections and three-dimensional grid cells, forming a spatial excavation matrix. During construction, a 3-5m wide central core soil column is retained as a natural support. Circular layered excavation is then carried out around this core column, while adjustable temporary support arches are simultaneously erected. This cycle of short advances and rapid closure maintains three-dimensional stress balance in the soil.

[0029] This excavation method has outstanding advantages: the core soil column provides a stable support benchmark for the excavation surface, effectively preventing the excavation surface from becoming unstable under soft stratum conditions; the circular layered excavation combined with immediate support keeps the soil in a three-dimensional equilibrium state at all times, improving the accuracy of settlement control; the modular construction organization is flexible and efficient, especially suitable for the safe construction of large-span underground projects, and can reduce support costs.

[0030] Step 2: Composite initial support

[0031] After each layer is excavated, a dynamic support system consisting of a variable stiffness support shell, a stress-adaptive grouting system, and a prestressed spatial grid is installed simultaneously. The specific implementation method is as follows:

[0032] 1. Construction of variable stiffness support shell

[0033] Outer curved pressure shell: Made of corrugated steel plates with a thickness of 10-12mm, connected into a continuous support surface by high-strength bolts.

[0034] Intermediate damping adjustment layer: laying variable hardness composite materials, such as polyurethane elastic pads, with a thickness of 20-30mm to absorb stratum deformation.

[0035] Inner stress distribution shell: Made of flat steel plate with a thickness of 6-8mm, with stiffening ribs to increase rigidity.

[0036] 2. Stress adaptive grouting system

[0037] The grouting pipe is pre-buried behind the variable stiffness support shell, and the gradient pressure grouting process is adopted:

[0038] S21, initial grouting: the pressure can be 0.3-0.5MPa, used to fill the gaps.

[0039] S22, secondary compensatory grouting: the pressure can be 0.1-0.2MPa, which is used to adjust the support stress state.

[0040] 3. Spatial prestressed grid tensioning

[0041] Bidirectional cross-steel strands are arranged between the support shells. Steel strands with a diameter of 15.2 mm can be used. Prestress is applied by hydraulic jacks to form a spatial force field.

[0042] Therefore, composite primary support adopts a multi-layered, synergistic design, divided from the outside inward into a load-bearing shell, an adjustment layer, and a stress distribution layer. The outermost layer, a corrugated steel plate, combines high stiffness and deformation adaptability to effectively resist soil pressure. The middle layer utilizes a new composite material that dynamically adjusts its mechanical properties to adapt to ground changes. The inner layer utilizes a stiffening rib system to evenly distribute stress and avoid localized stress concentration. This structure combines stress-adaptive grouting with a prestressed spatial grid to form a dynamically stable support system, ensuring ground stability during excavation. This support structure significantly enhances safety and adaptability: the corrugated steel plate and composite material work together to enhance bearing capacity while allowing for moderate deformation and reducing ground disturbance. The inner layer's stress distribution design avoids localized damage and extends the support life. Furthermore, the grouting system and prestressed grid further optimize the stress state, enabling the support system to dynamically respond to ground changes. This makes it particularly suitable for excavations in weak ground or for large-span excavations, balancing construction efficiency and long-term stability.

[0043] During the composite primary support construction process, an innovative grouting system was employed. This system monitors ground deformation data in real time and dynamically adjusts the grouting pressure (0.3-0.5 MPa for initial grouting, 0.1-0.2 MPa for secondary compensatory grouting) and the slurry ratio to achieve a close, real-time fit between the support structure and the surrounding rock. This synchronized grouting process, combined with the variable-rigidity support shell, enables the entire support system to proactively adapt to ground changes.

[0044] This intelligent grouting system significantly improves the support system's adaptability to the strata: through pressure gradient grouting, it ensures seamless integration of the support and surrounding rock, effectively controlling stratum deformation; the automatic adjustment function enables the support to respond promptly to changes in different geological conditions, improving construction safety; compared with traditional grouting, it reduces material waste and optimizes support effects, making it particularly suitable for large-span underground projects with complex geological conditions.

[0045] Step 3: Superimposed secondary support

[0046] After the initial support system forms a stable arch effect, a permanent load-bearing structure consisting of fiber concrete lining, space truss support and ground compensation reinforcement is constructed to complete the composite secondary support. The specific implementation method is as follows:

[0047] 1. Concrete lining construction

[0048] S11: Casting of the lower part of the inverted arch and side wall: Use steel fiber concrete with a fiber content of 30-40kg / m³ and a thickness of 300-400mm to form a stable bottom structure.

[0049] S21: Casting of the upper part of the side wall and the arch: Leave a gap of 50-100mm with the initial support and fill it tightly with grouting after casting.

[0050] S31: Circumferential prestressing: Unbonded steel strands are embedded in the lining and tensioned to create a circumferential compression state, improving integrity.

[0051] 2. Removable steel support installation

[0052] H-shaped steel is used to form a circumferential + longitudinal support grid, and the nodes are connected with high-strength bolts. After the lining reaches the design strength, the temporary support is gradually removed.

[0053] 3. Compensation grouting reinforcement

[0054] Secondary grouting is carried out behind the lining using ultra-fine cement slurry with a water-cement ratio of 0.8-1.0 to fill the ground loss.

[0055] Therefore, the composite secondary support system utilizes a three-in-one technology system of steel fiber concrete lining, spatial truss support, and compensating grouting. Through a layered, progressive casting process, the invert arch is constructed first, followed by the side walls, and finally the vault. Combined with circumferential prestressing, this creates a monolithic load-bearing structure. During construction, a removable steel support grid is installed simultaneously. Once the lining reaches full strength, it is removed in stages. Compensating grouting is then performed using ultra-fine cement slurry, achieving coordinated deformation between the support structure and the surrounding rock.

[0056] This technical system has multiple advantages: steel fiber concrete significantly improves the structure's crack resistance and impermeability; the detachable support system balances construction convenience and structural safety; compensating grouting effectively fills gaps and controls settlement, making it particularly suitable for deformation-sensitive projects such as airports; the overall solution can reduce maintenance costs, extend the service life of the structure, and has significant economic benefits.

[0057] Step 4: Controlled Soil Replacement

[0058] The method of partitioned and layered replacement and dynamic counter-pressure is used to gradually release soil stress. The specific implementation method is as follows:

[0059] 1. Block replacement process: Divide the soil to be replaced into small blocks of 2m×2m, and replace them in sequence according to the skipping method. After each block is replaced, backfill it with quick-setting concrete immediately.

[0060] 2. Dynamic back pressure control: Temporary steel supports, such as steel pipe diagonal braces, are set up at adjacent locations in the replacement area to maintain soil balance. The replacement speed is adjusted based on monitoring data to ensure that the deformation is ≤3mm / d.

[0061] 3. Stress release management: The principle of replacement before removal is adopted, that is, the old support is removed after the new support structure reaches the required strength. For sensitive areas such as those near the terminal, time-sharing replacement is adopted to avoid construction during peak flight periods.

[0062] Therefore, controlled soil replacement technology employs an innovative process system combining block replacement, dynamic backpressure, and stress release management. Uniform stress release is achieved through 2m×2m modular jump-chamber replacement combined with rapid-setting concrete backfill. During construction, a temporary steel support system is installed for dynamic backpressure. Construction parameters are dynamically adjusted based on real-time deformation monitoring data. The principle of replacement before removal is strictly adhered to. In sensitive areas, a time-sharing construction strategy is employed to avoid peak operating periods, ensuring construction safety and continuity.

[0063] This technical solution has significant advantages: modular jump-bin replacement makes stress release uniform and controllable, and construction efficiency is improved compared with traditional methods; the dynamic backpressure system strictly controls ground deformation within 3mm / d, reducing the settlement of surrounding buildings; the time-sharing construction strategy minimizes interference with airport operations, and is particularly suitable for large-scale soil replacement projects in environmentally sensitive areas, with significant social and economic benefits.

[0064] This application can explain its functional principles through the following operation methods:

[0065] This application adopts the technical solution of zoned progressive three-dimensional excavation + composite support system. The core soil column is retained through central island excavation, and circular layered excavation is carried out around the core column. Adjustable support arches are erected simultaneously to maintain the three-dimensional force balance of the soil. Subsequently, composite initial support, variable stiffness shell + adaptive grouting + prestressed grid, superimposed secondary support, steel fiber concrete lining + detachable steel support + compensating grouting are implemented to form a dynamically stable support system. Finally, controlled soil replacement, block-by-block jump-bin replacement + dynamic back pressure are used to gradually release stress and ensure construction safety.

[0066] This method effectively prevents the excavation face from becoming unstable, and is particularly suitable for soft strata. The variable stiffness support shell and gradient grouting system can automatically adjust the force, reduce stratum disturbance, and the steel fiber concrete lining + prestressed tensioning improves the structural integrity and crack resistance, and reduces subsequent maintenance costs. Thus, it achieves the goal of safe, efficient, and low-interference construction, reduces stratum settlement, and extends the life of the structure. It is suitable for sensitive areas such as airport underground projects.

[0067] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

[0068] The above is only a preferred specific implementation method of the embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes based on the technical solution and concept of the present application within the technical scope disclosed in the present application, and they should be covered by the scope of protection of the present application.

Claims

1. The supporting method for large-span earth excavation of airport tunnel is characterized by: The following steps are involved: Partitioned progressive three-dimensional excavation: The tunnel is divided into three-dimensional grid-like construction units along the longitudinal and vertical directions. A construction sequence of central island excavation combined with ring support is adopted to form a spatial coordinated force system. Composite primary support: A dynamic support system consisting of a variable stiffness support shell, a stress-adaptive grouting system, and a prestressed spatial grid is installed simultaneously after each layer of excavation. Composite secondary support: After the initial support system forms a stable arch effect, a permanent load-bearing structure consisting of fiber concrete lining, space truss support and ground compensation reinforcement is constructed; Controlled soil replacement: using partitioned and layered replacement and dynamic back pressure methods to gradually release soil stress.

2. The method for supporting large-span earth excavation of an airport tunnel according to claim 1, characterized in that: The steps of the zoned progressive excavation include: Establish a spatial excavation matrix and decompose each construction unit into a central core column, a ring excavation zone and a transition connection area; The construction method of layered excavation combined with temporary ring support is adopted; Set up adjustable temporary support arches to control space deformation.

3. The method for supporting large-span earth excavation of an airport tunnel according to claim 2, characterized in that: The composite initial support includes: The variable stiffness support shell is composed of interlocking curved steel shell units connected by three-dimensional hinge nodes to form a spatial force system; Stress adaptive grouting system, which uses gradient pressure grouting technology to form a reinforcement zone coordinated with the ground deformation; The spatial prestressed grid forms a spatial force field through bidirectional cross-tensioned steel cables.

4. The method for supporting large-span earth excavation in an airport tunnel according to claim 3, characterized in that: The variable stiffness support shell comprises: The outer curved pressure shell adopts a corrugated reinforcement structure; The middle damping adjustment layer is made of a composite material with variable hardness; The inner stress distribution shell is equipped with a stress diffusion structure.

5. The method for supporting large-span earth excavation in an airport tunnel according to claim 1, characterized in that: The superimposed secondary support comprises: The reinforced concrete lining is poured in stages, with construction joints and expansion joints; Detachable steel supports to form circumferential and longitudinal support grids; Compensatory grouting reinforcement to fill the lost voids in the stratum.

6. The method for supporting large-span earth excavation in an airport tunnel according to claim 5, characterized in that: The steps of pouring reinforced concrete lining in stages include: First, cast the inverted arch and the lower part of the side wall to form a stable bottom structure; Then cast the upper part of the side wall and the vault to form a superimposed force system with the composite primary support; Finally, hoop prestressing is applied to enhance the overall bearing capacity of the lining.

7. The method for supporting large-span earth excavation in an airport tunnel according to claim 1, characterized in that: The layered replacement and dynamic back pressure method includes: Block replacement: Divide the soil to be replaced into several small blocks and replace them step by step in sequence; Dynamic counterpressure: During the displacement process, soil equilibrium is maintained through temporary support; Stress release control: adopt the method of replacing first and then disassembling to reduce sudden stress changes.

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