A construction method for a shallow-buried extra-large cross-section tunnel

Abstract

The present invention discloses a construction method for a shallow-buried extra-large cross-section tunnel. The method comprises the following steps: on the ground surface, along the tunnel central axis direction, pile holes are vertically formed at intervals in sequence; steel sleeves are lowered into a plurality of holes, and both the upper and lower ends of the steel sleeves are located outside the tunnel excavation contour line; steel reinforcement cages are placed into the steel sleeves, and concrete is poured to form steel pipe piles; the upper bench of the pilot tunnel on any one side of the steel pipe piles is excavated and supported; the lower bench of the pilot tunnel on the same side is excavated and supported; the upper bench of the pilot tunnel on the other side of the steel pipe piles is excavated and supported; the lower bench of the pilot tunnel on the other side is excavated and supported; the inverted arch is excavated and poured; after pouring is completed, the tunnel section of the steel pipe piles is truncated; and finally, the secondary lining is poured. By adopting this solution, the problem of complicated construction procedures of the traditional double-side drift method or cross-middle diaphragm method for shallow-buried extra-large cross-section tunnels can be solved, thereby achieving fast and safe construction.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and particularly relates to a construction method for a shallow-buried extra-large cross-section tunnel. Background Art

[0002] Conventional extra-large cross-section tunnels adopt a flat horseshoe-shaped cross-section, drill and blast tunneling, and New Austrian Tunneling Method for support. Due to the large excavation cross-section, generally over 150, and the single-tunnel four-lane highway tunnel can reach over 260. For example, Figure 1 as shown in the bench cut method of construction, among which, the extra-large cross-section tunnels in grade Ⅳ and Ⅴ surrounding rocks all adopt the partial excavation method, such as Figure 2 the ring excavation with core soil retention method shown in Figure 3 the middle diaphragm method shown in Figure 4 the cross middle diaphragm method shown in Figure 5 and the double-side drift method shown in

[0003] As shown in the following table, the suitable excavation methods for different surrounding rock conditions and excavation end faces are as follows:

[0004]

[0005] The above-mentioned various excavation methods can select different construction methods according to different cross-sections. However, among the above-mentioned excavation methods, especially for the double-side drift method or the cross middle diaphragm method of shallow-buried extra-large cross-section tunnels, their construction procedures are complicated, there are many excavation procedures, the construction progress is slow, and at the same time, the construction unit is very uncooperative due to benefit considerations. Summary of the Invention

[0006] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a construction method for a shallow-buried extra-large cross-section tunnel. By adopting this solution, the problem of complicated construction procedures of the traditional double-side drift method or cross middle diaphragm method for shallow-buried extra-large cross-section tunnels can be solved, so as to achieve fast and safe construction.

[0007] The present invention is achieved through the following technical solutions:

[0008] A construction method for a shallow-buried extra-large cross-section tunnel, the method comprising the following steps:

[0009] Step 1: On the ground surface, along the tunnel central axis direction, successively form vertical holes for pile foundations at intervals.

[0010] Step 2: Lower steel sleeves into several holes, and both the upper and lower ends of the steel sleeves are located outside the tunnel excavation contour line.

[0011] Step 3: Lower steel reinforcement cages into the steel sleeves and pour concrete to form steel pipe piles.

[0012] Step 4: Excavate the upper bench of the drift on either side of the steel pipe pile and carry out support.

[0013] Step 5: Excavate the lower bench of the pilot tunnel on the same side and carry out support.

[0014] Step 6: Excavate the upper bench of the pilot tunnel on the other side of the steel pipe piles and carry out support.

[0015] Step 7: Excavate the lower bench of the pilot tunnel on the other side and carry out support.

[0016] Step 8: Excavate the inverted arch and carry out pouring.

[0017] Step 9: After pouring is completed, cut off the tunnel section of the steel pipe piles.

[0018] Step 10: Finally, pour the secondary lining.

[0019] Compared with the existing technologies, among various excavation methods, especially for the double-side drift method or the cross-middle diaphragm method of shallow-buried extra-large-section tunnels, which have the problems of complicated construction procedures, many excavation procedures, and slow construction progress, this solution provides a construction method for shallow-buried extra-large-section tunnels. By adopting this solution, the steel pipe piles constructed by surface pre-embedding are used to replace the steel section sprayed with concrete middle diaphragm constructed in the conventional tunnel, significantly improving the support effect of the middle diaphragm on the surrounding rock of the subsequent pilot tunnel of the tunnel, and the pilot tunnel can be optimized from the conventional three-bench excavation to two-bench excavation; in the specific steps, before the tunnel excavation, it is necessary to construct on the surface, and the pile foundation is formed by using the rotary drilling method or the impact hole forming method, etc. A number of formed holes are arranged at intervals along the tunnel axis direction, that is, there is a spacing between adjacent two holes, the holes vertically penetrate the pre-excavated tunnel and are located below the tunnel excavation contour line;

[0020] Subsequently, a steel casing and a steel reinforcement cage of the same length are lowered into the holes. The lower end of the steel casing extends out of the tunnel excavation contour line and extends 3m outwards, while the upper end of the steel casing extends out of the tunnel excavation contour line and extends 3m outwards; subsequently, reinforced concrete is poured to form reinforced concrete steel pipe piles. By using the steel casing, it is possible to form high-strength and high-rigidity reinforced concrete steel pipe piles while facilitating the welding with the steel section of the pilot tunnel.

[0021] Subsequently, the steel pipe piles divide the tunnel excavation end face into left and right pilot tunnels, and the front and back construction sequences of the left and right pilot tunnels are the same as those of the conventional middle diaphragm method. The pilot tunnels themselves are excavated by the upper and lower benches. Because the steel pipe piles replace the steel section sprayed with concrete support of the traditional method to ensure the stability of the surrounding rock on the side of the subsequent pilot tunnel, there is no need to construct the middle diaphragm steel section during the excavation of the first pilot tunnel, and the surrounding rock between the piles is sealed with sprayed concrete;

[0022] In the specific excavation process, for each excavated bench, a steel section of the pilot tunnel is set up for support. After the support is completed, the inverted arch is excavated and poured. After the pouring is completed, the tunnel section of the steel pipe piles is cut off, and finally the secondary lining is poured to complete the construction.

[0023] The above solution aims to achieve the following: replacing the steel arch shotcrete middle wall constructed in the tunnel conventionally with steel pipe piles embedded in the ground surface, significantly improving the support effect of the middle wall on the surrounding rock of the subsequent pilot tunnels of the tunnel, creating conditions for simplifying the construction procedures of the two side pilot tunnels, and optimizing the excavation of the pilot tunnels from the conventional three - step excavation to two - step excavation. Since the construction of the steel pipe piles on the ground surface and the in - tunnel construction are two separate and non - interfering construction lines, the steel pipe piles can be constructed in advance at an opportune time, reducing the in - tunnel construction process time and significantly improving the construction progress of the shallow - buried section of the main tunnel.

[0024] For further optimization, the steel pipe pile is a middle wall structure. The steel pipe pile section is filled with reinforced concrete, and the hole part above the steel pipe pile is filled with lean concrete; during the specific construction process, according to the different functional roles and materials of the holes from bottom to top, it is divided into upper and lower ends. The lower end is set as a reinforced concrete steel pipe pile, and the upper end, that is, between 3m from the tunnel roof to the ground surface, is filled and backfilled with lean concrete, such as C15 rubble concrete.

[0025] For further optimization, the diameter of the steel pipe pile is 1 - 1.2m.

[0026] For further optimization, the spacing between two adjacent steel pipe piles is an integer multiple of the longitudinal spacing of the tunnel - designed steel frames and is not less than 2 times the pile diameter.

[0027] For further optimization, it also includes a pilot - tunnel steel arch frame. The pilot - tunnel steel arch frame includes a pile - installed section and a non - pile - installed section. The top of the non - pile - installed section includes several A units connected in sequence along the tunnel contour line; the top of the pile - installed section includes an A1 unit at the center, and several A2 units are connected in sequence along the tunnel contour line on both sides of the A1 unit; the chord length of the A1 unit is not less than the diameter of the steel pipe pile; among them, the pilot - tunnel steel arch frame used for support is divided into two layout forms: the pile - installed section and the non - pile - installed section. The non - pile - installed section of the pilot - tunnel steel arch frame is designed by connecting several A2 units in sequence along the tunnel contour line, that is, using the conventional steel frame segments of the same length for design; while for the pile - installed section, a shorter - length A1 unit is used in the middle, but its chord length should not be less than the diameter of the steel pipe pile to facilitate the insertion and connection of the steel pipe pile. Subsequently, conventional A2 units are set at both ends of the A1 unit and connected in sequence, where the A1 unit only represents the reserved length and no steel frame is set.

[0028] For further optimization, the A2 steel frame units on both sides of the steel pipe pile are welded to the outer wall of the steel pipe pile through connectors; during the specific connection process, adjacent two A2 units and between the A2 unit and the steel pipe pile are all connected through connectors, thus forming a stable connection support structure.

[0029] For further optimization, the connecting member includes a back plate. An I-shaped joint is also provided at the end of the A2 unit close to the steel pipe pile. One end of the I-shaped joint is fixed to the middle of the back plate, and the other end of the I-shaped joint is welded to the side wall of the steel pipe pile. To achieve a stable connection with the steel pipe pile, the connecting member includes a back plate which is fixedly connected to the A2 unit. An I-shaped joint is also provided in the back plates of the connecting members on both sides of the steel pipe pile. The A2 unit is stably connected to the steel pipe pile by welding the I-shaped joint to the steel pipe pile. The entire guide tunnel steel frame is made of I-shaped steel, and the part of the steel pipe pile extending into the guide tunnel steel frame is similar to cutting off the A1 unit. During the specific installation process, the position of the steel pipe pile can also be directly reserved, and the positions of the connecting members on both sides of the steel pipe pile can be directly adjusted so that the connecting members are arranged adjacent to the pile.

[0030] For further optimization, a back plate is also provided at the end of the A2 unit. The back plate of the connecting member is in mutual contact with the back plate at the end of the A2 unit and is connected by a plurality of bolts. Adjacent steel frame units are connected by a back plate. A plurality of threaded holes are provided in the back plate, and they are connected by a plurality of bolts, thereby realizing a detachable connection method.

[0031] For further optimization, the steps for cutting off the hole section of the steel pipe pile are as follows: Cut off all the parts of the steel pipe pile inside the tunnel excavation contour line. After cutting off, remove the connecting members on both sides of the steel pipe pile, and then add a steel frame with the length of the A1 unit between the two A2 units and connect them through the connecting members.

[0032] For further optimization, the steps for cutting off the hole section of the steel pipe pile are as follows: Cut off the steel pipe pile along the contour of the primary support surface.

[0033] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0034] The present invention provides a construction method for a shallow-buried extra-large cross-section tunnel. By adopting this solution, the steel pipe piles constructed by surface pre-burial are used to replace the conventional steel section sprayed concrete middle wall constructed inside the tunnel, which significantly improves the support effect of the middle wall on the surrounding rock of the subsequent pilot tunnel of the tunnel, creates conditions for simplifying the construction procedures of the two side pilot tunnels, and the pilot tunnels can be optimized from the conventional three-step excavation to two-step excavation. Since the surface steel pipe pile construction and the in-tunnel construction are two separate and non-interfering construction lines, the steel pipe piles can be constructed in advance at an opportune time, reducing the in-tunnel construction procedure time and significantly improving the construction progress of the shallow-buried section of the main tunnel of the tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts. In the drawings:

[0036] Figure 1 It is a construction schematic diagram of the bench method provided by the prior art;

[0037] Figure 2 It is a construction schematic diagram of the ring excavation with core soil method provided by the prior art;

[0038] Figure 3 It is a construction schematic diagram of the middle diaphragm method provided by the prior art;

[0039] Figure 4 It is a construction schematic diagram of the cross middle diaphragm method provided by the prior art;

[0040] Figure 5 It is a construction schematic diagram of the double side drift method provided by the prior art;

[0041] Figure 6 It is a construction schematic diagram provided by the present invention;

[0042] Figure 7 It is a schematic diagram of the longitudinal arrangement of the pre-embedded steel pipe piles provided by the present invention;

[0043] Figure 8 It is a partial top view between the pile and the steel frame provided by the present invention;

[0044] Figure 9 It is a schematic diagram of the connection structure of the non-piled section provided by the present invention;

[0045] Figure 10 It is a partial schematic diagram A provided by the present invention;

[0046] Figure 11 It is a schematic diagram of the connection structure of the piled section provided by the present invention;

[0047] Figure 12 It is a partial schematic diagram B provided by the present invention;

[0048] Figure 13 It is a schematic diagram of the first truncation method provided by the present invention;

[0049] Figure 14 It is a schematic diagram of the second truncation method provided by the present invention;

[0050] Figure 15 It is a connection schematic diagram of the connecting piece and the steel casing provided by the present invention;

[0051] Figure 16 Front view of the connecting piece provided by the present invention;

[0052] Figure 17 Top view of the connection between the connecting piece and the steel casing provided by the present invention.

[0053] Markings in the drawings and corresponding component names:

[0054] 1 - Steel pipe pile, 2 - Guide hole steel rigid frame, 3 - Connecting piece, 31 - Back plate, 32 - I-shaped joint. Detailed implementation manners

[0055] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in combination with embodiments and drawings. The illustrative implementation manners of the present invention and their descriptions are only used to explain the present invention and do not limit the present invention.

[0056] Embodiment: This embodiment provides a new method for excavating the middle wall based on the pre-embedded steel pipe pile 1. As shown in the figure, the method includes the following specific steps: Figures 6 to 17 As shown in the figure, the method includes the following specific steps:

[0057] S1: Before tunnel excavation, construction needs to be carried out on the ground surface. The pile holes are formed by using the rotary drilling method or impact hole forming method. A number of formed holes are arranged at intervals along the tunnel central axis direction, that is, there is a spacing between adjacent two holes. The holes vertically penetrate the pre-excavated tunnel and are located below the tunnel excavation contour line.

[0058] S2: Lower the steel casing and the steel reinforcement cage of the same length into the holes. The lower end of the steel casing extends out of the tunnel excavation contour line and extends 3m outward, and the upper end of the steel casing extends out of the tunnel excavation contour line and extends 3m outward; then pour the reinforced concrete to form the reinforced concrete steel pipe pile 1. By using the steel casing, while forming the reinforced concrete steel pipe pile 1 with high strength and high stiffness, it is also convenient to weld with the guide hole steel rigid frame 2; during the specific pouring process, according to the functional roles and different materials of the holes from bottom to top, it is divided into upper and lower ends. The lower end is set as the reinforced concrete steel pipe pile 1, and the upper end, that is, between 3m above the tunnel roof and the ground surface, is backfilled with lean concrete, such as C15 crushed stone concrete.

[0059] S3: As shown in [figure reference], excavate the upper bench of the left pilot tunnel of the steel pipe pile 1, and then support the upper bench of the left pilot tunnel; Figure 6 as shown in [figure reference], excavate the upper bench of the left pilot tunnel of the steel pipe pile 1, and then support the upper bench of the left pilot tunnel;

[0060] S4: Excavate the lower bench of the left pilot tunnel of the steel pipe pile 1, and then support the lower bench of the left pilot tunnel;

[0061] S5: Excavate the upper bench of the right pilot tunnel of the steel pipe pile 1 and support the upper bench of the right pilot tunnel;

[0062] S6: Excavate the lower bench of the right pilot tunnel of the steel pipe pile 1 and support the lower bench of the right pilot tunnel. The front - to - back sequence of the left - and - right pilot tunnel construction from S3 to S6 is the same as that of the conventional middle diaphragm method. The pilot tunnel itself is excavated in upper and lower benches. Since the steel pipe pile 1 replaces the steel - shaped sprayed concrete support in the traditional method to ensure the stability of the surrounding rock on the side of the subsequent pilot tunnel, there is no need to construct the middle diaphragm steel shape during the excavation of the previous pilot tunnel, and the surrounding rock between the piles can be closed with sprayed concrete.

[0063] S7: Excavate and pour the inverted arch.

[0064] S8: After pouring is completed, truncate the tunnel section of the steel pipe pile 1. In this embodiment, when constructing the secondary lining, there are two ways to truncate the steel pipe pile 1 one by one. Truncation method one: Truncate all the parts of the steel pipe pile 1 inside the tunnel excavation contour line. After truncation, remove the connecting pieces on both sides of the steel pipe pile, and then add a steel frame with the length of the A1 unit between the two A2 units on both sides and connect them through the connecting pieces, as Figure 13 shown; Truncation method two: The steps for truncating the tunnel section of the steel pipe pile 1 include: Just truncate the steel pipe pile 1 along the contour of the primary support surface, and there is no need to add the A1 unit, as Figure 14 shown; This embodiment recommends using the second truncation method.

[0065] S9: Finally, pour the secondary lining.

[0066] In this embodiment, the pile diameter of the steel pipe pile 1 is 1 - 1.2 m.

[0067] In this embodiment, the distance between two adjacent steel pipe piles 1 is an integer multiple of the longitudinal spacing of the tunnel - designed steel frame and is not less than 2 times the pile diameter.

[0068] Please refer to Figure 9 , in this embodiment, it further includes a pilot - tunnel steel - shaped steel frame 2. The pilot - tunnel steel - shaped steel frame 2 includes a pile - installed section and a non - pile - installed section. The top of the non - pile - installed section includes several sections of A units connected in sequence along the tunnel contour line; the top of the pile - installed section includes an A1 unit at the center, and several sections of A2 units are sequentially connected along the tunnel contour line on both sides of the A1 unit; the chord length of the A1 unit is not less than the pipe diameter of the steel pipe pile 1; Among them, the pilot - tunnel steel - shaped steel frame 2 used for support is divided into two layout forms: the pile - installed section and the non - pile - installed section. The non - pile - installed section of the pilot - tunnel steel - shaped steel frame is designed by connecting several sections of A units in sequence along the tunnel contour line, that is, using the conventional steel - frame segmented design with the same length, or as Figure 9 and Figure 10As shown, at the top, three A units with the same length are connected, and the remaining parts can be set with B units / C units / D units / E units, etc. with other lengths according to the actual situation; for the pile - setting section, among the three units at the top, two A2 units and one A1 unit are adopted, and the remaining parts can also be set with B units / C units / D units / E units, etc. with other lengths according to the actual situation, such as Figure 11 and Figure 12 As shown, among them, an A1 unit with a shorter length is adopted in the middle, which is convenient for the insertion and connection of the steel pipe pile 1. Subsequently, conventional A2 units are arranged at both ends of the A1 unit and connected in sequence.

[0069] Please refer to Figures 15 - 17 . In this embodiment, the A2 units on both sides of the steel pipe pile are welded to the outer side wall of the steel pipe pile through connecting pieces; during the specific connection process, the A2 units and the steel pipe pile 1 are all connected through the connecting piece 3, so as to form a stable connection and support structure.

[0070] Please refer to Figures 15 - 17 . In this embodiment, the connecting piece 3 includes a back plate 31. At the end of the A2 unit close to the steel pipe pile 1, a profiled joint 32 is also provided. One end of the profiled joint 32 is fixed to the middle of the back plate 31, and the other end of the profiled joint 32 is welded to the side wall of the steel pipe pile 1; to achieve a stable connection with the steel pipe pile 1, the connecting piece 3 includes a back plate 31. The back plate 31 is fixedly connected to the A2 unit. In the back plates 31 of the connecting pieces 3 on both sides of the steel pipe pile 1, profiled joints 32 are also provided. Through welding the profiled joints 32 to the steel pipe pile 1, the A2 unit and the steel pipe pile 1 are stably connected; among them, the guide - hole steel - framed support 2 is entirely made of I - shaped steel, and the part of the steel pipe pile 1 extending into the guide - hole steel - framed support 2 is similar to cutting off the A1 unit. During the specific installation process, the position of the steel pipe pile 1 can also be directly reserved, and the positions of the connecting pieces 3 on both sides of the steel pipe pile 1 can be directly adjusted, so that the connecting pieces 3 are arranged closely adjacent to the pile.

[0071] In this embodiment, the end of the A2 unit is also provided with a back plate 31. The back plate 31 of the connecting piece 3 and the back plate 31 at the end of the A2 unit are mutually attached and connected by a number of bolts; the adjacent steel - framed units are connected by the back plate 31. A number of threaded holes are opened on the back plate 31, and through a number of bolts, a detachable connection method is realized.

[0072] In addition, please refer to Figure 17 . In this embodiment, Figure 17 is a top view. At the position where the profiled joint 32 is connected to the end of the steel pipe pile 1, in order to match the arc outside the steel pipe pile, before welding, the end of the profiled joint 32 needs to be subjected to arc treatment.

[0073] The above solution aims to achieve the following: using the steel pipe piles 1 constructed by surface pre-burial to replace the steel section shotcrete middle wall constructed by conventional in-tunnel construction, significantly improving the support effect of the middle wall on the surrounding rock of the subsequent pilot tunnel of the tunnel, creating conditions for simplifying the construction procedures of the two side pilot tunnels, and the pilot tunnels can be optimized from the conventional three-step excavation to two-step excavation. Since the construction of the surface steel pipe piles 1 and the in-tunnel construction are two separate and non-interfering construction lines, the steel pipe piles 1 can be constructed in advance at an opportune time, reducing the in-tunnel construction procedure time and significantly improving the construction progress of the shallow-buried section of the main tunnel of the tunnel.

[0074] The specific implementation manners described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only the specific implementation manners of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A construction method for a shallow-buried super-large cross-section tunnel, characterized in that The method includes the following steps: Step 1: On the ground surface, along the tunnel central axis direction, vertical piles are formed at intervals in sequence; Step 2: Steel casings are lowered into several holes, and both the upper and lower ends of the steel casings are located outside the tunnel excavation contour line; Step 3: Reinforcement cages are placed into the steel casings, and concrete is poured to form steel pipe piles (1); Step 4: The upper bench of the pilot tunnel on any one side of the steel pipe pile (1) is excavated and supported; Step 5: The lower bench of the same side of the pilot tunnel is excavated and supported; Step 6: The upper bench of the pilot tunnel on the other side of the steel pipe pile (1) is excavated and supported; Step 7: The lower bench of the other side of the pilot tunnel is excavated and supported; Step 8: The invert is excavated and poured; Step 9: After pouring is completed, the tunnel section of the steel pipe pile (1) is truncated; Step 10: Finally, the secondary lining is poured.

2. The construction method of a shallow-buried extra-large cross-section tunnel according to claim 1, wherein The steel pipe pile (1) is a middle wall structure. The steel pipe pile section is filled with reinforced concrete, and the hole part above the steel pipe pile (1) is filled with lean concrete.

3. A construction method for a shallow-buried extra-large cross-section tunnel according to claim 1, characterized in that The pile diameter of the steel pipe pile (1) is 1 - 1.2 m.

4. A construction method for a shallow-buried extra-large cross-section tunnel according to claim 1, characterized in that, The distance between two adjacent steel pipe piles (1) is an integer multiple of the longitudinal spacing of the tunnel design steel frame and is not less than 2 times the pile diameter.

5. A construction method for a shallow-buried extra-large cross-section tunnel according to claim 1, characterized in that, It also includes a pilot tunnel steel frame (2). The pilot tunnel steel frame (2) includes a pile - installed section and a non - pile - installed section. The top of the non - pile - installed section includes several A units connected in sequence along the tunnel contour line. The top of the pile - installed section includes an A1 unit at the center, and several A2 units are connected in sequence along the tunnel contour line on both sides of the A1 unit. The chord length of the A1 unit is not less than the pipe diameter of the steel pipe pile (1).

6. The construction method of a shallow-buried extra-large cross-section tunnel according to claim 5, characterized in that, The A2 units on both sides of the steel pipe pile (1) are welded to the outer side wall of the steel pipe pile (1) through connectors (3).

7. A construction method for a shallow-buried extra-large cross-section tunnel according to claim 6, characterized in that, The connector (3) includes a back plate (31). An I - shaped joint (32) is also provided on the end back plate (31) of the A2 unit close to the steel pipe pile (1). One end of the I - shaped joint (32) is fixed to the middle of the back plate (31), and the other end of the I - shaped joint (32) is welded to the side wall of the steel pipe pile (1).

8. A construction method for a shallow-buried extra-large cross-section tunnel according to claim 7, characterized in that, The end of the A2 unit is also provided with a back plate (31). The back plates (31) of the connector (3) and the back plates (31) at the end of the top pilot tunnel steel frame (2) are mutually attached and connected by several bolts.

9. A construction method for a shallow-buried super-large cross-section tunnel according to claim 6, characterized in that, Truncating the tunnel section of the steel pipe pile (1) includes the following steps: All parts of the steel pipe pile (1) within the tunnel excavation contour line are truncated. After truncation, the connectors (3) on both sides of the steel pipe pile (1) are removed, and then a steel frame with the length of the A1 unit is added between the two side A2 units and connected through the connectors (3).

10. A construction method for a shallow-buried extra-large cross-section tunnel according to claim 6, characterized in that, Truncating the tunnel section of the steel pipe pile (1) includes the following steps: The steel pipe pile (1) is truncated along the surface contour of the primary support.

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