Initial support structure for rapid support in tunnel excavation and construction method

Abstract

The invention discloses a tunnel excavation rapid support preliminary bracing structure and a construction method, the tunnel excavation rapid support preliminary bracing structure comprises an inner layer, an outer layer and anchor rods, the inner layer is formed by splicing preliminary bracing segments, and the segments are made of steel plates and used for forming a framework of a preliminary bracing system; the pipe pieces also serve as inner formworks for concrete pouring, and the adjacent pipe pieces are welded or bolted; the outer layer is composed of mould bag concrete, geotextile is adopted to manufacture a geotextile mould bag, the concrete is poured into the mould bag through a high-pressure pump, and after solidification, an integral concrete plate is formed and serves as a main supporting structure of primary support. The shape and the size of the geotextile mold bag can be adjusted to cope with different excavation conditions, the primary support inner layer can adopt temporary support or permanent support or combination of the temporary support and the permanent support, the primary support inner layer can be used for placing construction facilities through expansion, and the mold bag can keep certain pressure to actively support surrounding rock before concrete is solidified when concrete is poured. According to the method, the excavation efficiency can be greatly improved, supporting is more timely and effective, the operation safety is improved, the tunnel face environment is improved, convenience is provided for construction operation, construction is convenient and fast, practicability is high, and the method is worthy of popularization.

Description

Technical Field

[0001] The present invention relates to the technical field related to tunnel construction, and in particular to an initial support structure and a construction method for rapid support of tunnel excavation. Background Art

[0002] Currently, mountain tunnel excavation typically utilizes the drill-and-blast method, which primarily involves excavation, primary support, and secondary lining. Primary support primarily consists of steel arches, shotcrete, and anchor bolts. This method has the following disadvantages: ① Because the steel arches are divided into multiple units and need to be assembled and connected within the tunnel, erecting multiple arches requires a long construction time and a high number of personnel, significantly limiting excavation progress. ② The speed of shotcrete construction depends on the spray rate, which is virtually unadjustable. Furthermore, the process requires high concrete material requirements. The operation also generates significant dust, resulting in a harsh tunnel face environment. The time required for primary support construction directly impacts the duration of each excavation cycle. Reducing the time required for erecting the arches and shotcrete spraying can significantly accelerate excavation and improve tunnel construction efficiency. Summary of the Invention

[0003] Therefore, in order to solve the above-mentioned deficiencies, the present invention provides an initial support structure and construction method for rapid support of tunnel excavation; to solve the current problems of slow initial tunnel support construction, serious environmental pollution of shotcrete, and high material requirements, this patent uses prefabricated pipe segments for assembly as the inner layer of initial support and the inner concrete formwork, and a mold bag is set between the inner layer and the surrounding rock excavation contour. Concrete is poured into the mold bag to fill the gap between the inner layer and the surrounding rock to form the outer layer of initial support. After the concrete solidifies, anchor rods are applied to form the initial support system.

[0004] The present invention is achieved in this way: an initial support structure for rapid support of tunnel excavation is constructed, which is characterized by comprising: an inner layer of initial support segments, the inner layer of the initial support being assembled by segments, and joints being arranged between the segments for connection; and a mold bag arranged between the initial support inner layer and the excavation contour, which is made of geotextile, with nylon rope arranged inside to limit its shape after filling, and a filling cuff reserved for pouring concrete; the mold bag lower layer corresponding to the mold bag is fitted with the initial support inner layer, and the mold bag is filled with concrete to form an outer layer, and then anchor rods are applied, and the concrete is poured and formed, and its shape is controlled by the initial support inner layer and the mold bag.

[0005] According to the present invention, an initial support structure for rapid support of tunnel excavation is characterized in that the segments of the inner layer of the initial support are temporary support segments, permanent support segments or a combination of the two; the temporary support segments are removed before the secondary lining is applied, and the permanent support segments are not removed. When the temporary support segments and the permanent support segments are combined, the two layers of segments are connected by fasteners and assembled as a whole at one time.

[0006] According to the present invention, an initial support structure for rapid support of tunnel excavation is characterized in that the initial support inner layer segments are manufactured outside the tunnel and assembled on site. During the manufacturing process, interfaces for docking with detachable hangers can be reserved. After the inner layer is assembled, corresponding detachable hangers are arranged at the reserved interfaces for hanging lighting equipment, ventilation ducts, and cables, thereby solving the problem of facility drainage at the tunnel face. Initial support inner-layer segments typically consist of 5 to 7 segments in a cycle, which can be quickly assembled after excavation, replacing the traditional installation of I-beam steel frames and welding of steel mesh, significantly reducing installation time. Bag concrete replaces the traditional sprayed concrete process, and bag concrete pouring can be performed simultaneously through multiple ports, also saving considerable time. The inner layer of the initial support can withstand a certain amount of pressure and can apply appropriate pressure to the formwork concrete. This pressure will be converted into pressure on the inner formwork and surrounding rock. This pressure can provide a certain support to the surrounding rock. It can support the surrounding rock before the concrete solidifies. The support is more timely and can more effectively control deformation.

[0007] According to the present invention, an initial support structure for rapid support of tunnel excavation is characterized in that the mold bag can adjust its shape according to the excavation situation to fit the surrounding rock.

[0008] According to the present invention, an initial support structure for rapid support of tunnel excavation is characterized in that: the pipe segments are made of steel plates and are used to form the skeleton of the initial support system; the pipe segments are assembled to form a semicircular shell structure, without a head steel plate, and also serve as an internal formwork for concrete pouring, with a certain supporting capacity and can play a protective role; adjacent pipe segments are welded or bolted.

[0009] According to the present invention, a primary support structure for rapid tunnel excavation support is characterized in that: in the aforementioned primary tunnel support structure, the mold bag is connected to the primary support inner layer by fasteners, ensuring that the mold bag is assembled and arranged between the inner layer and the surrounding rock along with the segments; the upper and lower sides of the mold bag have different shapes, and the inner side, after expansion, has the same area as the initial support inner layer, while the outer side has a larger area to adapt to the tunnel excavation contour; Tunnel blasting excavation forms a large over-excavation in some areas. When making the mold bag, the area of ​​the corresponding position on the upper layer of the mold bag is increased to form an expanded mold bag section. The specific increased area depends on the over-excavation situation. Nylon rope should be set inside the expanded section to limit its filling shape to ensure that it fits the over-excavation.

[0010] According to the present invention, an initial support structure for rapid tunnel excavation support is characterized in that: the outer layer is composed of mold bag concrete, the geotextile mold bag is made of geotextile, and concrete is poured into the mold bag by a high-pressure pump. After solidification, an integral concrete slab is formed, which serves as the main supporting structure of the initial support; The shape and size of the geotextile mold bag can be adjusted to cope with different excavation conditions. The inner layer of the primary support can adopt temporary support or permanent support or a combination of the two. It can be used to place construction facilities through expansion. When the mold bag concrete is poured, a certain pressure can be maintained to actively support the surrounding rock before the concrete solidifies.

[0011] According to the present invention, the initial support structure for rapid tunnel excavation support is characterized in that: the initial support adopts bagged concrete, which eliminates the need for sprayed concrete, thereby greatly improving the tunnel face environment; The primary support inner layer can be used as a foundation to build a removable construction platform, replacing the excavation trolley and waterproofing trolley. The expanded functionality of the primary support inner formwork can greatly facilitate construction.

[0012] A construction method of an initial support structure for rapid tunnel excavation support according to the above-mentioned method is characterized in that the implementation process is as follows: (1) Preparation and assembly of the initial support inner layer segments: (1.1) The initial support inner layer segments are manufactured outside the tunnel according to the design requirements. The segments are made of steel plates. The segment composition is determined according to the project requirements. The permanent support inner layer can be constructed alone, the temporary support inner layer can be constructed alone, or the permanent support inner layer and the temporary support inner layer can be combined. When the permanent support segments are combined with the temporary support segments, they are connected into a whole with fasteners before assembly. At the same time, when manufacturing the segments, interfaces for docking with detachable hangers are reserved. (1.2) The prepared segments are transported to the tunnel construction site and assembled into a semicircular shell structure using welding or bolting according to the designed assembly method. This forms the initial support inner layer, which serves as the skeleton of the initial support system and also as the inner formwork for concrete pouring. (2) Mold bag setting: (2.1) A mold bag is prepared based on the tunnel excavation profile and expected overexcavation. The mold bag consists of two layers of geotextile, the lower layer of which, after expansion, has the same shape and area as the initial support inner layer. The area of ​​the upper layer is determined based on the concave and convex conditions of the surrounding rock. If significant overexcavation occurs in a certain area during tunnel blasting excavation, the corresponding area of ​​the upper layer of the mold bag needs to be enlarged to form an expanded mold bag section. Nylon ropes are then installed inside the expanded section to limit its filling shape. (2.2) During the assembly of the primary support inner layer, the mold bag is connected to the inner layer by fasteners, and the mold bag is placed between the inner layer and the excavation contour, ensuring that the lower layer of the mold bag fits the primary support inner layer and the upper layer of the mold bag is in a relaxed state. At the same time, multiple concrete filling cuffs are reserved on the mold bag to facilitate subsequent concrete pouring; (3) Outer concrete pouring: (3.1) After the initial support inner layer segments are assembled and the formwork bags are set up, use a high-pressure pump to pour concrete into the formwork bags through the reserved filling cuffs. During the pouring process, maintain a certain pressure so that the concrete in the formwork bags can closely fit the excavation contour, densely filling the space between the initial support inner layer and the surrounding rock, and providing early support for the surrounding rock. (3.2) After pouring, seal the filling cuffs of the mold bag. After the concrete solidifies, the outer layer of the initial support is formed, which serves as the main supporting structure of the initial support. (4) Anchor bolt construction: After the outer layer of concrete solidifies, anchor bolts are installed in the reserved anchor holes according to the design requirements. For general surrounding rocks, ordinary mortar anchor bolts are used; in areas with broken surrounding rocks, small grouting pipes or self-propelled anchor bolts are used to complete the initial support construction. (5) Installation of auxiliary facilities and construction platform construction: (5.1) After the initial support inner layer is assembled, detachable hangers are arranged at the reserved interfaces to hang lighting equipment, ventilation ducts, cables, etc. to solve the problem of face facility discharge; (5.2) If the inner layer includes temporary support, a detachable construction platform can be built on the inner layer as a foundation to replace the excavation trolley and waterproofing board trolley, providing convenience for subsequent construction.

[0013] The present invention has the following advantages: It provides a primary support structure for rapid tunnel excavation support, comprising an inner layer, an outer layer, and anchor rods. The inner layer is assembled from primary support segments, which are machined from steel plates and serve as the skeleton of the primary support system. The segments also serve as the internal formwork for concrete pouring, with adjacent segments welded or bolted together. The outer layer is composed of bagged concrete, made of geotextile. Concrete is poured into the bags using a high-pressure pump, and after solidification, a monolithic concrete slab forms the primary support structure. The shape and size of the geobags can be adjusted to accommodate different excavation conditions. The primary support inner layer can be used for temporary support, permanent support, or a combination of both, and can be expanded to accommodate construction facilities. During concrete pouring, the bagged concrete maintains a certain pressure to actively support the surrounding rock before the concrete solidifies. This invention can significantly improve excavation efficiency, make support more timely and effective, enhance operational safety, improve the tunnel face environment, and facilitate construction operations. Its convenient construction and high practicality make it worthy of promotion.

[0014] The present invention also has the following beneficial effects: First, excavation efficiency is high. The initial support inner segments are fabricated outside the tunnel, typically consisting of 5 to 7 segments per cycle. These segments can be quickly assembled after excavation, replacing the traditional installation of I-beam steel frames and welding of steel mesh, significantly reducing installation time. Bag concrete replaces the traditional shotcrete process. Bag concrete can be poured simultaneously through multiple ports, also saving significant time.

[0015] Second, support is provided more timely. The inner layer of the initial support can withstand a certain amount of pressure, exerting appropriate pressure on the bagged concrete. This pressure is then converted into pressure on the internal formwork and surrounding rock, providing a certain degree of support for the surrounding rock. This allows for a rapid formation of a support system, providing support for the surrounding rock before the concrete solidifies. This allows for more timely support and more effective deformation control.

[0016] Third, high safety. The initial support formwork segments are assembled using a trolley. After the segments are assembled, the arch is a complete formwork segment, which can effectively prevent falling segments from injuring people.

[0017] Fourth, the initial support thickness is adjustable. When using steel arch frames in traditional processes, the minimum initial support thickness depends on the type of I-beam and cannot be adjusted. With this initial support structure, the initial support thickness can be adjusted according to actual conditions, achieving the goal of saving materials.

[0018] Fifth, it improves the tunnel face environment. Shotcrete is the primary source of tunnel face dust, creating a harsh tunnel face environment during shotcrete application, hindering operations. However, using bagged concrete for initial support eliminates the need for shotcrete, significantly improving the tunnel face environment.

[0019] Sixth, the inner layer of the initial support is expandable. The steel structure of the inner layer allows for convenient placement of various hangers and fasteners, solving the problem of placing various construction equipment on the tunnel face. For example, cables and water pipes can be hung on the side walls using the inner layer hangers. Furthermore, while ensuring safety, a detachable construction platform can be constructed based on the inner layer of the initial support, replacing the excavation trolley and waterproofing board trolley. The expandable formwork of the initial support inner layer greatly facilitates construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the present invention; Figure 2 This is a schematic diagram of the assembly of the inner layer segments of the initial support; Figure 3 This is a schematic diagram of the completion of the assembly of the initial support inner layer segments; Figure 4 This is a schematic diagram of bag concrete pouring; Figure 5 Prepare a schematic diagram for the completion of the initial support; Figure 6 This is a schematic diagram of the initial support inner layer combination of temporary support + permanent support; Figure 7-Figure 8 This is the expanded view of the mold bag.

[0021] Among them: 1 excavation outline, 2 mold bag, 3 inner layer, 4 assembly trolley, 5 concrete pouring equipment, 6 concrete pumping pipe, 7 filling cuff, 8 concrete outer layer, 9 anchor rod, 10 inner layer detachable hanger, 11 permanent support inner layer, 12 temporary support inner layer, 13 mold bag upper layer, 14 mold bag lower layer, 15 nylon rope, 16 mold bag expansion section. DETAILED DESCRIPTION

[0022] The following will be combined with the Figures 1-8 The present invention is described in detail, and the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0023] The present invention provides an initial support structure for rapid support of tunnel excavation, which solves the current problems of slow initial tunnel support construction, serious environmental pollution of shotcrete, and high material requirements; this patent uses prefabricated pipe segments for assembly as the inner layer of initial support and the inner concrete formwork, and a mold bag is set between the inner layer and the surrounding rock excavation contour. Concrete is poured into the mold bag to fill the gap between the inner layer and the surrounding rock to form the outer layer of initial support. After the concrete solidifies, anchor rods are applied to form the initial support system.

[0024] The primary support structure primarily consists of an inner layer 3, an outer layer 8, and anchor rods 9. After tunnel excavation blasting, an excavation profile 1 is formed. The inner layer of the primary support is formed by assembling segments, which are connected or welded using connectors. A mold bag 2 is placed between the inner layer and the excavation profile 1. Before the bag 2 is filled with concrete, its lower layer 14 is in contact with the initial support inner layer, while its upper layer 13 is relaxed. Nylon ropes 15 are placed inside the bag to control the shape of the concrete. After the bag 2 is filled with concrete, a certain pressure is maintained to provide early support for the surrounding rock. After the concrete solidifies, the outer layer 8 is formed, and anchor rods 9 are then installed, completing the primary support construction.

[0025] like Figure 6 As shown, the segments of the initial support inner layer can be composed of a permanent support inner layer 11 and a temporary support inner layer 12, either singly or in combination. The permanent support segments 11 are not removed, while the temporary support segments 12 are removed before the secondary lining is applied. When a combination of permanent and temporary support segments is used, the permanent and temporary support segments are connected with fasteners before assembly, completing the assembly as a whole in one go.

[0026] like Figure 7 As shown, a large over-excavation is formed locally during tunnel blasting excavation. When making the mold bag, the area of ​​the corresponding position of the upper layer 13 of the mold bag is enlarged to form an expanded mold bag section 16. The specific increased area depends on the over-excavation situation. A nylon rope 15 should be set inside the expanded section 16 to limit its filling shape to ensure that it fits the over-excavation area.

[0027] like Figure 5 As shown, the initial support inner layer segments are made outside the tunnel and assembled on site. During the production, interfaces for docking with the detachable hangers 10 can be reserved. After the inner layer 3 is assembled, corresponding detachable hangers 10 are arranged at the reserved interfaces, which can be used to hang lighting equipment, ventilation ducts, cables, etc., to solve the problem of face facility discharge.

[0028] Furthermore, especially when the inner layer includes temporary supports, a detachable construction platform can be built based on the inner layer to replace the excavation trolley and the waterproofing board trolley.

[0029] In summary, this patent provides a tunnel initial support structure, including an inner layer, an outer layer and anchor rods. The inner layer is assembled from steel segments, which are made from steel plates and are used to form the skeleton of the initial support system. The segments are assembled to form a semicircular shell structure without a head steel plate, which also serves as the inner formwork for concrete pouring. It has a certain support capacity and can play a protective role. Adjacent segments are welded or bolted. The outer layer is formed by pouring concrete into a mold bag. The geotextile mold bag is a large-area continuous bag-shaped material made of two layers of geotextile. Concrete is poured into the mold bag with a high-pressure pump. After solidification, an integral concrete slab is formed. The concrete slab has a certain strength and serves as the main supporting structure of the initial support. Ordinary mortar anchor rods are used for anchor rods, and small grouting guide tubes or self-propelled anchor rods are used in the broken surrounding rock. The anchor rods are installed through the reserved anchor rod holes after the outer layer of concrete solidifies.

[0030] The main construction process of the initial support structure of the above-mentioned tunnel is: first, the initial support formwork segments are assembled, and a mold bag is set behind the initial support formwork segments. After the assembly is completed, concrete is poured into the mold bag by using a high-pressure pump and a certain pressure is applied. After the concrete solidifies, anchor rods are installed in the reserved anchor rod holes.

[0031] The initial tunnel support structure described above has an inner layer of permanent steel segment support, which can also be a combination of permanent support and temporary support, or all temporary support. The inner layer of permanent support is not removed, while the inner layer of temporary support is removed before pouring the secondary lining.

[0032] In the above-mentioned initial support structure of the tunnel, the mold bag is connected to the inner layer of the initial support through fasteners to ensure that the mold bag is assembled and arranged between the inner layer and the surrounding rock along with the pipe segments; the upper and lower sides of the mold bag have different shapes, and the inner side has the same area as the inner layer of the initial support after expansion, while the outer area should be larger to adapt to the tunnel excavation contour, and the specific area is determined according to the concave and convex conditions of the surrounding rock; the mold bag has reserved concrete filling cuffs, and multiple places can be reserved to improve the efficiency of concrete pouring. After pouring, the filling cuffs need to be sealed; concrete is poured into the mold bag to form support, which adapts to the excavation contour to the maximum extent and fills the space between the inner layer of the initial support and the surrounding rock densely.

[0033] The beneficial effects of the present invention are: First, high excavation efficiency: The initial support inner layer segments are fabricated outside the tunnel, typically consisting of 5 to 7 segments per cycle. These segments can be quickly assembled after excavation, replacing the traditional installation of I-beam steel frames and welding of steel mesh, significantly reducing installation time. Bag concrete replaces the traditional shotcrete process, and bag concrete can be poured simultaneously through multiple ports, also saving significant time.

[0034] Second, support is more timely: The initial inner support layer can withstand a certain amount of pressure, which can be applied to the bagged concrete. This pressure is converted into pressure on the inner formwork and surrounding rock, which can provide a certain degree of support for the surrounding rock. Therefore, a support system can be quickly established, supporting the surrounding rock before the concrete solidifies, providing more timely support and more effective deformation control.

[0035] Thirdly, high safety: the initial support formwork segments are assembled using a trolley. After the segments are assembled, the arch is a complete formwork pipe section, which can effectively prevent falling segments from injuring people.

[0036] Fourthly, the initial support thickness is adjustable: When steel arch frames are used in traditional processes, the minimum thickness of the initial support depends on the type of I-beam and cannot be adjusted. By adopting this initial support structure, the initial support thickness can be adjusted according to actual conditions to achieve the purpose of saving materials.

[0037] Fifth, it improves the tunnel face environment: Shotcrete is the main source of tunnel face dust. During shotcrete spraying, the tunnel face environment is harsh, affecting operations. However, using bagged concrete for initial support eliminates the need for shotcrete spraying, significantly improving the tunnel face environment.

[0038] Sixth, the inner layer of the initial support is expandable. The steel structure of the inner layer allows for convenient placement of various hangers and fasteners, solving the problem of placing various construction equipment on the tunnel face. For example, cables and water pipes can be hung on the side walls using the inner layer hangers. Furthermore, while ensuring safety, a detachable construction platform can be constructed based on the inner layer of the initial support, replacing the excavation trolley and waterproofing board trolley. The expandable formwork of the initial support inner layer greatly facilitates construction.

[0039] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A rapid support initial support structure for tunnel excavation, characterized by comprising: The primary support segment inner layer (3) is assembled from segments, and joints are provided between the segments for connection; it also includes a mold bag (2) provided between the primary support segment inner layer (3) and the excavation contour (1), which is made of geotextile, and has a nylon rope (15) provided inside to limit its shape after filling, and a filling cuff (7) reserved for pouring concrete; the mold bag lower layer (14) corresponding to the mold bag (2) is fitted with the primary support inner layer (3), and the mold bag (2) is filled with concrete to form an outer layer (8), and then an anchor rod (9) is applied, and the concrete is poured and formed, and its shape is controlled by the primary support inner layer and the mold bag.

2. The initial support structure for rapid tunnel excavation support according to claim 1, characterized in that: The segments of the inner layer (3) of the primary support segments are temporary support segments (12), permanent support segments (11) or a combination of the two; the temporary support segments (12) are removed before the secondary lining is applied, and the permanent support segments (11) are not removed. When the temporary support segments and the permanent support segments are combined, the two layers of segments are connected by fasteners and assembled as a whole at one time.

3. The initial support structure for rapid tunnel excavation support according to claim 1, characterized in that: The initial support inner layer segments are manufactured outside the tunnel and assembled on site. During the manufacturing process, interfaces for docking with detachable hangers (10) can be reserved. After the inner layer (3) is assembled, corresponding detachable hangers (10) are arranged at the reserved interfaces for hanging lighting equipment, ventilation ducts, and cables, thereby solving the problem of tunnel face facility discharge. The initial support inner layer (3) segments usually consist of 5 to 7 segments in a cycle, which can be quickly assembled after excavation, replacing the installation of I-beam steel frames and welding of steel mesh in traditional processes, greatly reducing installation time; bagged concrete is used to replace the traditional sprayed concrete process, and the bagged concrete can be poured through multiple ports simultaneously, which can also save a lot of time; The inner layer of the initial support can withstand a certain amount of pressure and can apply appropriate pressure to the formwork concrete. This pressure is used to convert into pressure on the internal formwork and surrounding rock. At this time, this pressure is used to support the surrounding rock; it supports the surrounding rock before the concrete solidifies, and the support is more timely and can more effectively control deformation.

4. The initial support structure for rapid tunnel excavation support according to claim 1, characterized in that: The mold bag (2) can adjust its shape according to the excavation situation to fit the surrounding rock.

5. The initial support structure for rapid tunnel excavation support according to claim 1, characterized in that: The segments are made of steel plates and are used to form the skeleton of the initial support system. The segments are assembled to form a semicircular shell structure without a head steel plate. It also serves as an internal formwork for concrete pouring, has a certain supporting capacity, and can play a protective role. Adjacent segments are welded or bolted together.

6. The initial support structure for rapid tunnel excavation support according to claim 1, characterized in that: In the above-mentioned tunnel primary support structure, the mold bag is connected to the inner layer of the primary support through fasteners, ensuring that the mold bag is arranged between the inner layer and the surrounding rock along with the segment assembly. The upper and lower sides of the mold bag have different shapes. When the inner side is expanded, the area is the same as the inner layer of the primary support, while the outer area should be larger to adapt to the tunnel excavation contour. When tunnel blasting excavation forms a large over-excavation in a part, when making the mold bag, the area of ​​the corresponding position of the upper layer (13) of the mold bag is enlarged to form an expanded mold bag section (16). The specific enlarged area depends on the over-excavation situation. Nylon rope (15) should be set inside the expanded section (16) to limit its filling shape to ensure that it fits the over-excavation area.

7. The initial support structure for rapid tunnel excavation support according to claim 1, characterized in that: The outer layer is made of bagged concrete. Geotextiles are used to make geobags. Concrete is poured into the bags using a high-pressure pump. After solidification, an integral concrete slab is formed, which serves as the main supporting structure for the initial support. The shape and size of the geotextile mold bag can be adjusted to cope with different excavation conditions. The inner layer of the primary support can adopt temporary support or permanent support or a combination of the two. It can be used to place construction facilities through expansion. When the mold bag concrete is poured, a certain pressure can be maintained to actively support the surrounding rock before the concrete solidifies.

8. The initial support structure for rapid tunnel excavation support according to claim 1, characterized in that: The use of bagged concrete for initial support eliminates the need for shotcrete, thus greatly improving the tunnel face environment. Based on the inner layer of the initial support, a detachable construction platform can be built to replace the excavation trolley and waterproof board trolley; the extended function of the template inside the initial support can bring great convenience to the construction.

9. A construction method of an initial support structure for rapid support of tunnel excavation according to claim 1, characterized in that; The implementation process is as follows: (1) Preparation and assembly of the initial support inner layer segments: (1.1) The initial support inner layer segments are manufactured outside the tunnel according to the design requirements. The segments are made of steel plates. The segment composition is determined according to the project requirements. The permanent support inner layer can be constructed alone, the temporary support inner layer can be constructed alone, or the permanent support inner layer and the temporary support inner layer can be combined. When the permanent support segments are combined with the temporary support segments, they are connected into a whole with fasteners before assembly. At the same time, when manufacturing the segments, interfaces for docking with detachable hangers are reserved. (1.2) The prepared segments are transported to the tunnel construction site and assembled into a semicircular shell structure using welding or bolting according to the designed assembly method. This forms the initial support inner layer, which serves as the skeleton of the initial support system and also as the inner formwork for concrete pouring. (2) Mold bag setting: (2.1) A mold bag is prepared based on the tunnel excavation profile and expected overexcavation. The mold bag consists of two layers of geotextile, the lower layer of which, after expansion, has the same shape and area as the initial support inner layer. The area of ​​the upper layer is determined based on the concave and convex conditions of the surrounding rock. If significant overexcavation occurs in a certain area during tunnel blasting excavation, the corresponding area of ​​the upper layer of the mold bag needs to be enlarged to form an expanded mold bag section. Nylon ropes are then installed inside the expanded section to limit its filling shape. (2.2) During the assembly of the primary support inner layer, the mold bag is connected to the inner layer by fasteners, and the mold bag is placed between the inner layer and the excavation contour, ensuring that the lower layer of the mold bag fits the primary support inner layer and the upper layer of the mold bag is in a relaxed state. At the same time, multiple concrete filling cuffs are reserved on the mold bag to facilitate subsequent concrete pouring; (3) Outer concrete pouring: (3.1) After the assembly of the inner layer segments of the initial support and the setting of the form bags, use a high-pressure pump to pour concrete into the form bags through the reserved filling cuffs. During the pouring process, maintain a certain pressure so that the concrete in the form bags can fit closely to the excavation contour, filling the space between the inner layer of the initial support and the surrounding rock densely, and providing early support to the surrounding rock. (3.2) After the pouring is completed, the filling cuffs of the form bags are sealed. After the concrete solidifies, the outer layer of the initial support is formed, which serves as the main supporting structure of the initial support. (4) Anchor bolt construction: After the outer layer of concrete solidifies, anchor bolts are installed in the reserved anchor holes according to the design requirements. For general surrounding rocks, ordinary mortar anchor bolts are used; in areas with broken surrounding rocks, small grouting pipes or self-propelled anchor bolts are used to complete the initial support construction. (5) Installation of auxiliary facilities and construction platform construction: (5.1) After the initial support inner layer is assembled, detachable hangers are arranged at the reserved interfaces to hang lighting equipment, ventilation ducts, cables, etc. to solve the problem of face facility discharge; (5.2) If the inner layer includes temporary support, a detachable construction platform can be built on the inner layer as a foundation to replace the excavation trolley and waterproofing board trolley, providing convenience for subsequent construction.

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