A tunnel portal section structure suitable for steep terrain and a construction method thereof

Abstract

The present application relates to the technical field of tunnel, and provides a tunnel portal section structure suitable for steep terrain and a construction method thereof, wherein the steep rock-soil body is vertically excavated in steps through the upward slope, the upward slope is supported from top to bottom by the soil nailing wall while being excavated, the box culvert main body, the column assembly and the joist assembly are constructed, the adjacent bridge, the box culvert main body and the joist assembly which have been constructed are used as the construction platform, the portal wall and the arch on both sides of the tunnel are constructed, the pipe shed is constructed based on the arch, the second backfill space is backfilled to form the second backfill layer, the shed-hole assembly is constructed, the tunnel underground is constructed, and the construction of the tunnel portal section structure is completed. The double-layer frame structure can solve the foundation of the upper shed-hole assembly, provide a passage for the lower existing low-grade road, be used for the adjacent bridge and abutment, the upper backfill of the box culvert to the top surface of the joist can provide a construction platform for the tunnel portal, can resist the lateral earth pressure of the mountain, and has high construction safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tunnels, in particular to a tunnel portal section structure suitable for steep terrain and a construction method thereof. BACKGROUND

[0002] With the continuous improvement of the transportation network, it is inevitable that the newly built expressway in the mountainous area will pass through steep mountains. At the same time, due to the limitation of terrain and cost, the local low-grade road often follows the valley section, so that the newly built expressway not only passes through steep mountains but also crosses the existing low-grade road. The steep terrain rock mass is constantly weathered by natural wind and sunlight, and it is easy to form dangerous rockfall, which seriously threatens the driving safety of the newly built expressway. At the same time, the steep terrain is often connected by bridges and tunnels, and there are technical problems such as the difficulty of the bridge abutment to fall to the bottom and the lack of construction platform for the tunnel portal. In addition, the foundation of the newly built expressway on the mountain side will encroach on the driving area of the existing low-grade road, resulting in the rerouting of the existing low-grade road.

[0003] In view of the above situation, the existing technology mainly adopts the scheme of bridge abutment portal + bridge outside vertical foundation shed tunnel + local rerouting of the existing low-grade road for the newly built expressway. However, the tunnel portal of this scheme can only be from the other side of the tunnel portal or through the auxiliary chamber to counter-pull out of the hole, and the construction risk is high at the tunnel portal. At the same time, in order to avoid dangerous rockfall, the way of bridge outside vertical foundation shed tunnel will further occupy the existing low-grade road, which may lead to the interruption of the existing low-grade road or large-scale rerouting.

[0004] Therefore, it is necessary to provide a tunnel portal section structure suitable for steep terrain and a construction method thereof to solve or at least alleviate the above-mentioned defects. SUMMARY

[0005] The main purpose of the present application is to provide a tunnel portal section structure suitable for steep terrain and a construction method thereof, so as to solve the technical problems of high construction risk and encroachment on the existing low-grade road for the scheme of bridge abutment portal + bridge outside vertical foundation shed tunnel + local rerouting of the existing low-grade road for the tunnel portal section of steep terrain.

[0006] In order to achieve the above-mentioned purpose, the present application provides a tunnel portal section structure suitable for steep terrain, which comprises a portal assembly and a double-layer frame structure, the portal assembly and the double-layer frame structure are adjacent, the double-layer frame structure comprises a shed tunnel assembly, a box culvert main body, a column assembly and a joist assembly, and the shed tunnel assembly is connected at the top of the joist assembly;

[0007] Wherein, the joist assembly comprises an upper joist and a lower joist, the upper joist and the lower joist extend along the extension direction of the tunnel portal section, the shed tunnel assembly is connected at the top of the upper joist, and the portal assembly is arranged adjacent to the mountain side of the shed tunnel assembly.

[0008] The upper lintel and the top plate of the box culvert body are integrally cast, and the top surface of the upper lintel is higher than the top surface of the top plate of the box culvert body; the lower lintel and the bottom plate of the box culvert body are integrally cast, the column assembly and the side wall of the box culvert body are integrally cast, and the column assembly is connected between the upper lintel and the lower lintel;

[0009] The box culvert body has a vehicle passage matching the existing low-grade road, the extension direction of the vehicle passage and the extension direction of the tunnel portal section are crossly arranged, and a step is formed at the top of the side wall of the box culvert body away from the mountain, and a support for supporting the adjacent bridge is installed on the step.

[0010] Preferably, the shed tunnel assembly comprises a shed tunnel rigid body, a T-beam assembly, an end retaining wall, a side retaining wall and a first backfill layer; wherein the shed tunnel rigid body is connected at the top of the upper lintel;

[0011] The T-beam assembly comprises a plurality of T-beams arranged in sequence along the extension direction of the shed tunnel rigid body, each T-beam being connected with the shed tunnel rigid body;

[0012] The end retaining wall and the side retaining wall are both arranged at the top of the T-beam, the end retaining wall is located at one end of the T-beam assembly away from the portal assembly, the side retaining walls are arranged on both sides of the T-beam assembly, the T-beam assembly, the end retaining wall and the side retaining wall form a first backfill space, and the first backfill layer is backfilled in the first backfill space.

[0013] Preferably, the portal assembly comprises a sleeve arch, a portal wall and a second backfill layer, wherein the top of the portal wall forms a concave space for arranging the sleeve arch, the sleeve arch is arranged in the concave space and located at the top of the tunnel lining structure, the two ends of the sleeve arch are connected with the corresponding portal walls respectively, the inner wall of the portal wall, the top surface of the sleeve arch and the slope form a second backfill space, and the second backfill layer is backfilled in the second backfill space; wherein the shed tunnel inner contour line of the shed tunnel rigid body and the inner contour line of the portal wall are matched, asphalt plates are backfilled between the shed tunnel assembly and the portal wall, and the second backfill layer extends to the natural slope surface above the tunnel along the extension direction of the tunnel.

[0014] Preferably, the thickness of the asphalt plate is 20mm.

[0015] Preferably, the first water guide assembly comprises a plurality of first cast iron pipes arranged in a transverse direction of the shed-hole rigid body, the first cast iron pipes comprising first ends and second ends oppositely arranged along a direction of extension of the first cast iron pipes, the first ends being embedded in the end retaining wall, and the second ends extending outwardly from the first ends and being cantilevered.

[0016] The second water guide assembly comprises a plurality of second cast iron pipes arranged in a direction of extension of the shed-hole rigid body, the second cast iron pipes comprising third ends and fourth ends oppositely arranged along a direction of extension of the second cast iron pipes, the third ends being embedded in the side retaining wall, and the fourth ends extending outwardly from the third ends and being cantilevered.

[0017] Preferably, the length of each T-beam is arranged to be between 5m and 8m.

[0018] The application further provides a construction method of a tunnel portal section structure suitable for steep terrain, which is applied to the tunnel portal section structure suitable for steep terrain as described above, and comprises the following steps.

[0019] S1, temporarily adjusting flow of an existing low-grade road to create construction conditions for excavation of the upward slope, excavating the steep rock-soil body in a step-by-step and vertical manner, and supporting the upward slope from top to bottom by using a soil nailing wall;

[0020] S2, constructing the box culvert body, the column assembly and the joist assembly, and constructing a pavement of a newly-built road by using a height difference between the upper joist and a top plate of the box culvert body;

[0021] S3, using the adjacent bridge, the box culvert body and the joist assembly that have been constructed as a tunnel portal construction platform, excavating the tunnel in a wall-adhering manner, constructing portal walls and a sleeve arch on both sides of the tunnel, constructing a pipe shed based on the sleeve arch, and performing backfilling in the second backfilling space to form a second backfilling layer;

[0022] S4, constructing the shed-hole assembly;

[0023] S5, constructing a tunnel portal section structure.

[0024] Preferably, the step S2 of constructing the box culvert body, the column assembly and the joist assembly specifically comprises the following steps.

[0025] S21, excavating the existing low-grade road to a design ground surface, and verifying a bearing capacity of a foundation, if the bearing capacity of the foundation meets a bearing capacity requirement, proceeding to step S22, or if the bearing capacity requirement is not met, performing foundation treatment or constructing a pile foundation on the design ground surface, and then proceeding to step S22;

[0026] S22, construct the subbase, lay the waterproof slab for the bottom plate of the box culvert body, construct the bottom plate and lower support beam of the box culvert body, then tie the reinforcing steel, erect the formwork, and pour concrete to cast the bottom plate and lower support beam of the box culvert body into one piece.

[0027] S23. After the concrete strength of the bottom slab and lower support beam of the box culvert body reaches the first design strength, the waterproof layer of the side wall of the box culvert body is laid, the side wall and column components of the box culvert body are constructed, and then the steel bars are tied, the formwork is erected, and the concrete is poured to cast the side wall and column components of the box culvert body into one piece.

[0028] S24. After the concrete strength of the side walls and column components of the box culvert body reaches the second design strength, the waterproof layer of the top slab of the box culvert body is laid, the top slab and upper support beam of the box culvert body are constructed, and then the steel bars are tied, the formwork is erected, and the concrete is poured to cast the top slab and upper support beam of the box culvert body into one piece; at the same time, the support is installed at the step, and the connecting steel bars for connection with the rigid structure of the shed are reserved.

[0029] Preferably, step S4 specifically includes the following steps:

[0030] S41, tying the steel bars of the main rigid structure of the shed and connecting them with the connecting steel bars, erecting the formwork, and pouring the concrete of the main rigid structure of the shed;

[0031] S42, once the concrete strength of the main rigid structure of the tunnel reaches the third design strength, erect the T-beam assembly and pour the end retaining wall and side retaining wall;

[0032] S43, backfill the first backfill space to form the first backfill layer.

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

[0034] The upper layer of the double-layer frame structure of the application is a shed tunnel assembly, which can face the dangerous rock falling of steep terrain and simultaneously play the role of a sunshade shed; the lower layer of the double-layer frame structure comprises a box culvert main body, a column assembly and a joist assembly, and the upper shed tunnel assembly is supported by the upper joist + column assembly + lower joist, thereby solving the foundation of the upper shed tunnel assembly, and the self-weight of the double-layer frame structure can effectively resist the earth pressure of the mountain body; the box culvert main body can provide a vehicle passage for the existing low-grade road below, thereby avoiding the rerouting and detouring of the existing low-grade road; the box culvert main body can also be used for a nearby bridge and abutment, supports the nearby bridge through pre-embedded supports, realizes the bridge-tunnel connection between the tunnel structure and the bridge structure, and provides conditions for the bridge construction; meanwhile, the upper part of the box culvert main body is backfilled to the top surface of the joist to provide a construction platform for the tunnel entrance, create conditions for the tunnel entrance, and play the role of a disaster prevention and rescue turning lane in the later operation stage, and can resist the lateral earth pressure of the mountain body; the building limits of the shed tunnel assembly and the tunnel portal assembly are connected in sequence, and the shed tunnel assembly and the tunnel portal wall are separately arranged to avoid structural cracking caused by differential settlement, and the construction safety of the application is high. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only show some embodiments of the application, and other drawings can be obtained by those skilled in the art without any creative effort based on the drawings shown.

[0036] Figure 1 It is a schematic diagram after step S1 of the construction in an embodiment of the application;

[0037] Figure 2 It is a schematic diagram after step S2 of the construction in an embodiment of the application;

[0038] Figure 3 It is a schematic diagram after the tunnel portal wall and the sleeve arch in step S3 of the construction in an embodiment of the application;

[0039] Figure 4 It is a schematic diagram after step S4 of the construction in an embodiment of the application;

[0040] Figure 5 It is a schematic diagram after step S5 of the construction in an embodiment of the application;

[0041] Figure 6 It is an application scenario diagram of the overall structure in an embodiment of the application;

[0042] Figure 7 It is a plane schematic diagram of the double-layer frame structure in an embodiment of the application;

[0043] Figure 8 Fig. 1 is a structural schematic diagram of a box culvert body in an embodiment of the present application;

[0044] Figure 9 Fig. 2 is a structural schematic diagram of a double-layer frame structure in an embodiment of the present application;

[0045] Figure 10 Fig. 3 is a structural schematic diagram of a portal assembly in an embodiment of the present application;

[0046] Figure 11 Fig. 4 is a flow schematic diagram of a construction method in an embodiment of the present application;

[0047] Figure 12 Fig. 5 is a flow schematic diagram of steps included in the construction of the box culvert body, the column assembly and the joist assembly in step S2 in an embodiment of the present application.

[0048] The purposes, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings.

[0049] Explanation of reference numerals:

[0050] 10, double-layer frame structure; 110, box culvert body; 111, top plate of the box culvert body; 112, bottom plate of the box culvert body; 113, side wall of the box culvert body; 114, vehicle passage; 115, step; 116, support; 120, column assembly; 130, joist assembly; 131, upper joist; 132, lower joist; 140, shed tunnel assembly; 141, shed tunnel rigid body; 142, T-beam; 143, end retaining wall; 144, side retaining wall; 145, first backfill layer; 146, first cast iron pipe; 147, second cast iron pipe; 20, portal assembly; 210, sleeve arch; 220, portal wall; 230, second backfill layer; 30, existing low-grade road; 40, soil nail; 50, adjacent bridge; 60, falling rock; 70, underground tunnel. DETAILED DESCRIPTION

[0051] It should be understood that the specific embodiments described herein merely exemplify the present application and do not limit the present application.

[0052] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0053] The description herein involving "first", "second", etc. is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implying the number of the indicated technical features. Therefore, the features defined as "first", "second" can explicitly or implicitly include at least one of the features. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the realization of a person skilled in the art, and when the combination of technical solutions contradicts each other or cannot be realized, it should be considered that the combination of technical solutions does not exist and is not within the protection scope required by the present application.

[0054] Please refer to the accompanying Figures 1 to 12 In an embodiment of the present application, a tunnel portal section structure suitable for steep terrain includes a portal assembly 20 and a double-layer frame structure 10, the portal assembly 20 and the double-layer frame structure 10 are adjacent, the double-layer frame structure 10 includes a shed tunnel assembly 140, a box culvert body 110, a column assembly 120 and a joist assembly 130, the shed tunnel assembly 140 is connected to the top of the joist assembly 130;

[0055] The joist assembly 130 includes an upper joist 131 and a lower joist 132, the upper joist 131 and the lower joist 132 extend along the extension direction of the tunnel portal section, the shed tunnel assembly 140 is connected to the top of the upper joist 131, and the portal assembly 20 is arranged adjacent to the mountain side of the shed tunnel assembly 140;

[0056] The upper joist 131 and the top plate 111 of the box culvert body are integrally poured, and the top surface of the upper joist 131 is higher than the top surface of the top plate 111 of the box culvert body, the lower joist 132 and the bottom plate 112 of the box culvert body are integrally poured, the column assembly 120 and the side wall 113 of the box culvert body are integrally poured, and the column assembly 120 is connected between the upper joist 131 and the lower joist 132;

[0057] The box culvert body 110 has a vehicle passage 114 matching the existing low-grade road 30, the extension direction of the vehicle passage 114 and the extension direction of the tunnel portal section are cross arranged, the box culvert body 110 forms a step 115 on the top of the side wall away from the mountain, and a support 116 for supporting the adjacent bridge 50 is installed on the step 115.

[0058] It should be noted that the newly built expressway in the mountainous area will inevitably pass through steep mountains, and the low-grade road is often along the valley section due to the limitation of the terrain and cost, so that the newly built expressway passes through steep mountains and crosses the existing low-grade road 30. Therefore, the extension direction of the tunnel portal section and the existing low-grade road 30 (such as national road, county road, etc.) are vertically crossed in space, and the extension direction of the vehicle passage 114 of the present application can be adaptively set according to the existing low-grade road 30, such as Figures 2 to 6 As shown, as an example, the extension direction of the tunnel portal section of the newly built expressway and the extension direction of the vehicle passage 114 are vertically crossed in space.

[0059] The upper layer of the double-layer frame structure 10 is the shed tunnel assembly 140, which can face the steep terrain and rockfall 60 while playing the role of a sunshade shed; the lower layer of the double-layer frame structure 10 includes the box culvert body 110, the column assembly 120 and the joist assembly 130, which can provide support for the upper shed tunnel assembly 140 through the upper joist 131 + column assembly 120 + lower joist 132, solve the foundation of the upper shed tunnel assembly 140, and the self-weight of the double-layer frame structure 10 can effectively resist the earth pressure of the mountain body; the box culvert body 110 can provide the vehicle passage 114 for the lower existing low-grade road 30, avoiding the rerouting and detour of the existing low-grade road 30; the box culvert body 110 can also be used for the adjacent bridge and abutment, supporting the adjacent bridge 50 through the pre-embedded support 116, realizing the bridge-tunnel connection between the tunnel structure and the bridge structure, and providing conditions for bridge construction; at the same time, the upper part of the box culvert body 110 backfilled to the top surface of the joist can provide a construction platform for the tunnel portal, create conditions for the tunnel portal, and have the function of the disaster prevention and rescue turning lane in the later operation stage, and can resist the lateral earth pressure of the mountain body; the building limit of the shed tunnel assembly 140 and the portal assembly 20 is connected in sequence, and the shed tunnel assembly 140 and the portal wall 220 are separately arranged to avoid structural cracking caused by differential settlement.

[0060] As a preferred embodiment, the shed tunnel assembly 140 includes a shed tunnel rigid body 141, a T-beam assembly (not marked in the figure), an end retaining wall 143, a side retaining wall 144 and a first backfill layer 145; wherein the shed tunnel rigid body 141 is connected to the top of the upper joist 131; the T-beam assembly includes a plurality of T-beams 142 arranged in sequence along the extension direction of the shed tunnel rigid body 141, and each T-beam 142 is connected with the shed tunnel rigid body 141;

[0061] The end retaining wall 143 and the side retaining wall 144 are arranged on the top of the T-beam 142, the end retaining wall 143 is located at one end of the T-beam assembly away from the portal assembly 20, and the side retaining wall 144 is arranged on both sides of the T-beam assembly. The T-beam assembly, the end retaining wall 143 and the side retaining wall 144 form a first backfill space, and the first backfill layer 145 is backfilled in the first backfill space.

[0062] In the embodiment, the shed tunnel rigid body 141 is used as a core load-bearing component, and a foundation frame is formed by connecting the shed tunnel rigid body 141 with the upper lintel 131. The upper lintel 131 provides a construction load-bearing foundation for the shed tunnel rigid body 141, and the upper load can be finally transmitted to the foundation through the upper lintel 131. The T-beam assembly is distributed along the extension direction of the shed tunnel, which improves the overall bending stiffness and avoids local stress concentration. The end retaining wall 143 is located at the end of the shed tunnel rigid body 141, forming a longitudinal limiting structure. The side retaining wall 144 is connected with the top of the T-beam 142, forming a transverse limiting structure. The first backfill layer 145 can effectively resist the impact force of the rockfall 60. Preferably, the first backfill layer 145 is sequentially composed of a waterproof layer, a mortar protective layer, a soil and rock layer and a water-resistant layer from bottom to top. In other embodiments, the first backfill layer 145 can also adopt other forms of backfilling, which can be selected by those skilled in the art according to actual needs.

[0063] Specifically, when the rockfall 60 falls from the top, due to the buffering effect of the first backfill layer 145 and the relatively long length of the shed tunnel assembly 140 along the longitudinal direction of the tunnel, the rockfall 60 usually does not fall into the adjacent formation area of the bridge and tunnel. The first backfill layer 145 can be further provided with a transverse slope to guide the rockfall 60 to slide from both sides of the shed tunnel assembly 140.

[0064] Preferably, the length of each T-beam 142 is arranged between 5-8m. The T-shaped structure has the advantages of light self-weight and large bending stiffness, and the length of each T-beam 142 is preferably 5-8m. In other embodiments, those skilled in the art can also use a reinforced concrete beam body.

[0065] As a preferred embodiment, the portal assembly 20 comprises a sleeve arch 210, portal walls 220, and a second backfill layer 230. The top of the portal walls 220 is formed with a concave space for the sleeve arch 210, i.e. the two portal walls 220 adopt a double-ear wall portal type, which can ensure the continuity of the top of the portal assembly 140 and the top of the portal walls 220 and the continuity of the structural contour. The sleeve arch 210 is arranged in the concave space and at the top of the tunnel lining structure. The two ends of the sleeve arch 210 are connected with the corresponding portal walls 220, respectively. The inner wall of the portal walls 220, the top surface of the sleeve arch 210, and the slope form a second backfill space, which is backfilled with the second backfill layer 230. The inner contour line of the portal assembly 140 and the inner contour line of the portal walls 220 are matched, i.e. continuous. The asphalt board (not shown in the figure) is backfilled between the portal assembly 140 and the portal walls 220. The second backfill layer 230 extends to the natural slope surface above the tunnel along the tunnel extension direction.

[0066] Preferably, the thickness of the asphalt board is 20 mm.

[0067] In this embodiment, the sleeve arch 210 serves as a transverse connecting member at the top of the portal, connecting the two portal walls 220 into a whole, significantly improving the overall stiffness and stability of the portal structure, effectively resisting the mountain bias pressure and the earth pressure, and reducing the possibility of deformation, cracking, and even collapse of the portal. The concave space at the top of the portal walls 220 provides a positioning basis for accurate installation of the sleeve arch 210, with clear stress and reliable connection. The second backfill layer 230 provides strong lateral support for the slope, reducing the threat of slope instability and sliding to the portal structure. Preferably, the second backfill layer 230 comprises, from bottom to top, a waterproof layer, a mortar protection layer, an earth layer, and a water-resistant layer. In other embodiments, the second backfill layer 230 can also adopt other forms of backfilling, which can be selected by those skilled in the art according to actual needs.

[0068] Further, a pipe roof is also included. The sleeve arch 210 is provided with a plurality of pipe roof guide pipes (not shown in the figure) arranged along the circumferential direction of the sleeve arch 210. The pipe roof comprises a plurality of grouting steel pipes (not shown in the figure) corresponding to the pipe roof guide pipes. Each grouting steel pipe comprises a connecting end (not shown in the figure) and an anchoring end (not shown in the figure) arranged oppositely along the extension direction of the grouting steel pipe. The connecting end is connected with the sleeve arch 210, and the anchoring end is anchored into the surrounding rock.

[0069] In the embodiment, the pipe shed is constructed before the excavation of the tunnel 70, the grouting steel pipe is punched into the surrounding rock by the pipe shed guide pipe, an umbrella-shaped (or shed-shaped) rigid support framework is formed above and around the tunnel excavation contour line, the disturbance, relaxation and deformation of the surrounding rock caused by the tunnel excavation are greatly reduced through the double effects of advanced physical support and grouting reinforcement, and the safety conditions are provided for the subsequent tunnel 70 excavation operation.

[0070] As another preferable embodiment, the first water guide assembly and the second water guide assembly are further included, the first water guide assembly includes a plurality of first cast iron pipes 146 arranged in the lateral direction of the shed tunnel rigid body 141, the first cast iron pipe 146 includes a first end (not marked in the figure) and a second end (not marked in the figure) oppositely arranged along the extension direction of the first cast iron pipe 146, the first end is embedded in the end retaining wall 143, and the second end extends outward from the first end and is cantilevered.

[0071] The second water guide assembly includes a plurality of second cast iron pipes 147 arranged in the extension direction of the shed tunnel rigid body 141, the second cast iron pipe 147 includes a third end (not marked in the figure) and a fourth end (not marked in the figure) oppositely arranged along the extension direction of the second cast iron pipe 147, the third end is embedded in the side retaining wall 144, and the fourth end extends outward from the third end and is cantilevered.

[0072] The first cast iron pipe 146 and the second cast iron pipe 147 of the embodiment can timely drain the accumulated water in the first backfill layer 145 and the second backfill layer 230, and relieve the water pressure, the first end is embedded in the end retaining wall 143, the second end extends outward from the first end and is cantilevered, the third end is embedded in the side retaining wall 144, the fourth end extends outward from the third end and is cantilevered, and the first cast iron pipe 146 and the second cast iron pipe 147 are inclined to achieve the drainage purpose.

[0073] The application further provides a construction method of a tunnel portal section structure suitable for steep terrain, which is applied to the tunnel portal section structure suitable for steep terrain as described above and includes the following steps.

[0074] S1, the existing low-grade road 30 is temporarily adjusted to create construction conditions for the excavation of the inclined slope, the inclined slope is vertically excavated into steep rock-soil bodies in steps 115, and the soil nail 40 wall is used to support the inclined slope from top to bottom while excavating;

[0075] S2, the box culvert body 110, the column assembly 120 and the joist assembly 130 are constructed, and the pavement of the newly-built road is constructed by using the height difference between the upper joist 131 and the top plate 111 of the box culvert body.

[0076] S3, using the constructed adjacent bridge 50, box culvert body 110 and joist assembly 130 as a tunnel entrance construction platform, the tunnel adopts a wall-adhering entrance method, hole door walls 220 and a sleeve arch 210 are constructed on both sides of the tunnel, a pipe shed is then constructed based on the sleeve arch 210, and a second backfill layer 230 is formed by backfilling in the second backfill space;

[0077] Notably, generally, a sleeve arch, a leading pipe shed, and post-excavation are required before tunnel excavation, a formwork trolley needs to be assembled (the minimum length requirement is 9-12 m), and in such steep rock mass, the hole is generally inverted from the inside, and the construction risk is high at the tunnel portal. The tunnel entrance construction platform of the present application can be used as a tunnel construction platform, and the upper part of the box culvert can be used as a rotary lane for disaster prevention and rescue during the later operation stage.

[0078] S4, the shed hole assembly 140 is constructed;

[0079] S5, the tunnel underground hole 70 is constructed, and the construction of the tunnel portal section structure is completed.

[0080] Specifically, the bench slope 115 is vertically excavated with a soil nail 40 wall support, forming a layered unloading + immediate restraint bench slope stability scheme, which changes the traditional large-scale slope cutting to precise controlled excavation, reducing disturbance to the original stratum. The box culvert body 110 can be used for the adjacent bridge and support 116, and the upper shed hole assembly 140 can be supported by the upper joist 131 + column assembly 120 + lower joist 132, while the self-weight of the double-layer frame structure 10 can effectively resist the earth pressure of the abutment body; the top of the box culvert body 110 can be paved with a road surface, which can buffer the impact of the road surface load on the box culvert body 110, and can solve the waterproof problem of the top surface of the box culvert body 110; the shed hole assembly 140 can provide a site for the second lining formwork trolley of the tunnel underground hole 70; the shed hole assembly 140 can effectively avoid the rockfall 60 of the bench slope and provide site conditions for the construction of the tunnel underground hole 70, and the wall-adhering entrance method can connect the shed hole assembly 140 and provide support points for the advance support of the underground hole 70, creating conditions for the tunnel entrance.

[0081] As a preferred embodiment, the step S2 specifically comprises the following steps:

[0082] S21, the existing low-grade road 30 is excavated to the design ground surface, and the foundation bearing capacity is verified, if the foundation bearing capacity meets the bearing capacity requirement, step S22 is entered, if the foundation bearing capacity does not meet the bearing capacity requirement, the foundation is treated or a pile foundation is constructed on the design ground surface, and then step S22 is entered;

[0083] S22, a cushion layer is applied, a bottom plate waterproof layer of the box culvert body is laid, the bottom plate 112 and the lower joist 132 of the box culvert body are applied, and then the reinforcement is bound, the formwork is erected, and the concrete is poured to pour the bottom plate 112 and the lower joist 132 of the box culvert body into one body;

[0084] S23, after the concrete strength of the bottom plate 112 and the lower joist 132 of the box culvert body reaches a first design strength, a side wall waterproof layer of the box culvert body is laid, the side wall 113 and the column assembly 120 of the box culvert body are applied, and then the reinforcement is bound, the formwork is erected, and the concrete is poured to pour the side wall 113 and the column assembly 120 of the box culvert body into one body; preferably, the first design strength is that the concrete strength reaches 70%.

[0085] S24, after the concrete strength of the side wall 113 and the column assembly 120 of the box culvert body reaches a second design strength, a top plate waterproof layer of the box culvert body is laid, the top plate 111 and the upper joist 131 of the box culvert body are applied, and then the reinforcement is bound, the formwork is erected, and the concrete is poured to pour the top plate 111 and the upper joist 131 of the box culvert body into one body; meanwhile, the support 116 is installed at the step 115, and the connecting reinforcement for connecting the shed cave rigid frame body 141 is reserved. Preferably, the second design strength is that the concrete strength reaches 70%.

[0086] Specifically, the existing road is excavated to the design elevation, the bearing capacity is verified, and the foundation stability is ensured. If the bearing capacity is insufficient, the foundation is reinforced (such as replacement and compaction) or the pile foundation is supplemented to provide strong support for the subsequent structure. The cushion layer construction levels the base and disperses the load, and the bottom plate waterproof layer forms the first anti-seepage barrier. The bottom plate 112 and the lower joist 132 of the box culvert body are poured synchronously, and the side wall 113 and the column assembly 120 of the box culvert body are constructed synchronously after the strength of the bottom plate 112 of the box culvert body reaches the standard. The side wall 113 and the column assembly 120 of the box culvert body are poured into one body to form a wall-column frame structure, which significantly improves the lateral anti-push stiffness. The top plate 111 and the upper joist 131 of the box culvert body are poured synchronously, and the rigid connection with the shed cave rigid frame body 141 is realized through the reserved connecting reinforcement.

[0087] As a preferred embodiment, the step S4 specifically includes the following steps:

[0088] S41, the reinforcement of the shed cave rigid frame body 141 is bound and connected with the connecting reinforcement, the formwork is erected, and the concrete of the shed cave rigid frame body 141 is poured;

[0089] S42, after the concrete strength of the shed cave rigid frame body 141 reaches a third design strength, the T-beam assembly is erected, and the end retaining wall 143 and the side retaining wall 144 are poured;

[0090] S43, the first backfill space is backfilled to form the first backfill layer 145.

[0091] Specifically, the box culvert body 110 and the shed tunnel rigid body 141 are connected as a whole by connecting the reinforcing bars of the shed tunnel rigid body 141, and the concrete needs to be cured to the third design strength after pouring. For example, the concrete ensures that the main structure has sufficient compressive and shear resistance to provide a stable base for subsequent T-beam 142 erection and retaining wall construction. After the main concrete reaches the third design strength, for example, the concrete strength reaches 70%, the T-beam assembly is erected again to avoid premature loading that may cause concrete cracking. The T-beam 142, as a key force transmission component, is connected to the shed tunnel rigid body 141 by bolts or welding to form a spatial truss system. The end retaining wall 143 and the side retaining wall 144 are poured synchronously with the T-beam assembly, and the weight and stiffness of the concrete retaining wall are used to resist rockfall 60 impact, while forming a whole force with the shed tunnel rigid body 141 to improve the structure's overturning resistance. The first backfill layer 145 can effectively resist the impact force of the rockfall 60.

[0092] Preferably, the step S1 of supporting the upward slope by the soil nail 40 wall from top to bottom while excavating from side to side specifically comprises the following steps: supporting the upward slope by the Φ48 soil nail 40 wall from top to bottom while excavating from side to side; wherein the length of each soil nail 40 is 3m, and the interval distance between adjacent two soil nails 40 is 1m.

[0093] The above is only the preferred embodiment of the present application, and does not limit the protection scope of the present application. Any equivalent structure or equivalent process transformation, or direct or indirect application in other related technical fields based on the content of the specification and drawings, is also included in the patent protection scope of the present application.

Claims

1. A tunnel portal section structure suitable for steep terrain, characterized by, The tunnel portal assembly and the double-layer frame structure are adjacent, the double-layer frame structure comprises a shed tunnel assembly, a box culvert body, a column assembly and a joist assembly, and the shed tunnel assembly is connected at the top of the joist assembly; The joist assembly comprises an upper joist and a lower joist, both of which extend along the extension direction of the tunnel portal section, the shed tunnel assembly is connected at the top of the upper joist, and the tunnel portal assembly is arranged adjacent to the mountain side of the shed tunnel assembly. The upper joist and the top plate of the box culvert body are integrally cast, and the top surface of the upper joist is higher than the top surface of the top plate of the box culvert body; the lower joist and the bottom plate of the box culvert body are integrally cast, the column assembly and the side wall of the box culvert body are integrally cast, and the column assembly is connected between the upper joist and the lower joist. The box culvert body has a vehicle passage matching the existing low-grade road, the extension direction of the vehicle passage and the extension direction of the tunnel portal section are cross arranged, a step is formed at the top of the side wall of the box culvert body away from the mountain, and a support for supporting the adjacent bridge is installed on the step.

2. The tunnel portal section structure suitable for steep terrain according to claim 1, wherein The shed tunnel assembly comprises a shed tunnel rigid body, a T-beam assembly, an end retaining wall, a side retaining wall and a first backfill layer; wherein the shed tunnel rigid body is connected at the top of the upper joist; The T-beam assembly comprises a plurality of T-beams arranged in sequence along the extension direction of the shed tunnel rigid body, each T-beam is connected with the shed tunnel rigid body; The end retaining wall and the side retaining wall are arranged at the top of the T-beam, the end retaining wall is located at the end of the T-beam assembly away from the tunnel portal assembly, the side retaining walls are arranged on both sides of the T-beam assembly, and the T-beam assembly, the end retaining wall and the side retaining wall form a first backfill space, and the first backfill layer is backfilled in the first backfill space.

3. The tunnel portal section structure suitable for steep terrain according to claim 2, wherein The tunnel portal assembly comprises a sleeve arch, a tunnel portal wall and a second backfill layer, wherein a concave space for arranging the sleeve arch is formed at the top of the tunnel portal wall, the sleeve arch is arranged in the concave space and located at the top of the tunnel lining structure, both ends of the sleeve arch are connected with the corresponding tunnel portal wall, and the second backfill layer is backfilled in the second backfill space formed between the inner wall of the tunnel portal wall, the top surface of the sleeve arch and the slope.

4. The tunnel portal section structure suitable for steep terrain according to claim 3, wherein The shed tunnel inner contour line of the shed tunnel rigid body and the inner contour line of the tunnel portal wall are matched, asphalt plates are backfilled between the shed tunnel assembly and the tunnel portal wall, and the second backfill layer extends to the natural slope surface above the tunnel along the extension direction of the tunnel.

5. The tunnel portal section structure suitable for steep terrain according to claim 3, wherein The thickness of the asphalt plate is 20mm. Further comprising a first water guide assembly and a second water guide assembly, the first water guide assembly comprises a plurality of first cast iron pipes arranged at intervals in the transverse direction of the shed tunnel rigid body, the first cast iron pipe comprises a first end and a second end arranged oppositely along the extension direction thereof, the first end is embedded in the end retaining wall, and the second end extends outward from the first end and is cantilevered. The second water guide assembly comprises a plurality of second cast iron pipes arranged at intervals along the extension direction of the shed tunnel rigid body, the second cast iron pipe comprises a third end and a fourth end arranged oppositely along the extension direction of the second cast iron pipe, the third end is embedded in the side retaining wall, and the fourth end extends outward from the third end and is cantilevered.

6. The tunnel portal section structure suitable for steep terrain according to claim 3, wherein The length of each T beam is arranged between 5-8m.

7. A method for constructing a tunnel portal section structure suitable for a steep terrain, applied to the tunnel portal section structure suitable for a steep terrain according to any one of claims 3 to 6, characterized in that, The method comprises the following steps: S1, the existing low-grade road is temporarily adjusted to create construction conditions for the excavation of the upward slope, the upward slope is excavated in steps and vertically, and a soil nailing wall is used to support the upward slope while excavating from top to bottom; S2, the box culvert body, column assembly and joist assembly are constructed, and the difference in height between the upper joist and the top plate of the box culvert body is used to construct the pavement of the newly-built road; S3, the adjacent bridge, box culvert body and joist assembly that have been constructed are used as a tunnel portal construction platform, the tunnel is constructed in a wall-adhering manner, the portal walls and arches on both sides of the tunnel are constructed, the pipe shed is constructed based on the arches, and the second backfill space is backfilled to form a second backfill layer; S4, the shed tunnel assembly is constructed; S5, the tunnel is constructed, and the construction of the tunnel portal section structure is completed.

8. The construction method of a tunnel portal section structure suitable for a steep terrain according to claim 7, characterized in that, The step S2 of constructing the box culvert body, column assembly and joist assembly comprises the following steps: S21, the existing low-grade road is excavated to the design ground level, and the bearing capacity of the foundation is verified, if the bearing capacity of the foundation meets the bearing capacity requirement, step S22 is entered, if the bearing capacity requirement is not met, the foundation is treated or a pile foundation is constructed at the design ground level, and then step S22 is entered; S22, a cushion layer is constructed, a waterproof layer of the bottom plate of the box culvert body is laid, the bottom plate of the box culvert body and the lower joist are constructed, and then the steel bars are bound, the formwork is erected, and the concrete is poured to integrate the bottom plate of the box culvert body and the lower joist; S23, after the concrete strength of the bottom plate of the box culvert body and the lower joist reaches a first design strength, a waterproof layer of the side wall of the box culvert body is laid, the side wall of the box culvert body and the column assembly are constructed, and then the steel bars are bound, the formwork is erected, and the concrete is poured to integrate the side wall of the box culvert body and the column assembly; S24, after the concrete strength of the side wall of the box culvert body and the column assembly reaches a second design strength, a waterproof layer of the top plate of the box culvert body is laid, the top plate of the box culvert body and the upper joist are constructed, and then the steel bars are bound, the formwork is erected, and the concrete is poured to integrate the top plate of the box culvert body and the upper joist; meanwhile, the abutment is installed at the step, and the connecting steel bars connected with the shed tunnel rigid body are reserved.

9. The construction method of a tunnel portal section structure suitable for a steep terrain according to Claim 8, wherein The step S4 comprises the following steps: S41, the steel bars of the shed tunnel rigid body are bound and connected with the connecting steel bars, the formwork is erected, and the concrete of the shed tunnel rigid body is poured; S42, after the concrete strength of the shed tunnel rigid body reaches a third design strength, the T beam assembly is erected, and the end retaining wall and the side retaining wall are poured; S43, the first backfill space is backfilled to form a first backfill layer.

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