Tunnel portal section structure suitable for steep terrain and construction method thereof

Abstract

The invention relates to the technical field of tunnels, and provides a tunnel portal section structure suitable for steep terrains and a construction method thereof.A steep rock-soil body is vertically excavated through an upward slope step by step, a soil nailing wall is adopted to support the upward slope while the upward slope is excavated from top to bottom, a box culvert main body, a stand column assembly and a joist assembly are constructed, and the tunnel portal section structure suitable for the steep terrains is constructed. And constructing portal walls and cover arches on the two sides of the tunnel by using the constructed adjacent span bridge, the box culvert main body and the joist assembly as a construction platform, constructing a pipe shed on the basis of the cover arches, backfilling in the second backfilling space to form a second backfilling layer, constructing a shed tunnel assembly, constructing a tunnel hidden hole, and completing the construction of the tunnel portal section structure. According to the double-layer frame structure, the foundation of an upper shed tunnel assembly can be provided, a channel is provided for an existing low-grade road on the lower portion, the double-layer frame structure is used for an adjacent bridge and a bridge abutment, meanwhile, the upper portion of the box culvert is backfilled to the top face of the joist, a construction platform can be provided for tunnel entering, the lateral soil pressure of a mountain can be resisted, and the construction safety is high.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnels, and particularly to a tunnel portal section structure applicable to steep terrains and a construction method thereof. Background Art

[0002] With the continuous improvement of the transportation network, newly built expressways in mountainous and hilly regions will inevitably pass through steep mountains. At the same time, due to terrain and cost limitations, local low-grade roads often follow river valleys, resulting in newly built expressways passing through both steep mountains and crossing existing low-grade roads. The rock mass in steep terrains is exposed to natural wind, sun, and rain, and the rock mass is continuously weathered, easily forming dangerous rocks and falling stones, seriously threatening the driving safety of newly built expressways. At the same time, steep terrains often have bridges and tunnels connected, presenting technical problems such as difficulty in the foundation of bridge abutments reaching the bottom and lack of construction platforms for tunnel entrance. In addition, the foundation of the bridge on the mountain side of the newly built expressway reaching the bottom will encroach on the driving area of the existing low-grade road, resulting in the diversion of the existing low-grade road.

[0003] In response to the above situation, the existing technology mainly adopts the scheme of using bridge abutments to enter the tunnel + building shed tunnels with foundations on the outside of the bridge + local diversion of the existing low-grade road. However, in this scheme, the tunnel entrance often can only be picked out from the other side of the tunnel or through auxiliary chambers, and the construction risk is high at the tunnel portal. At the same time, to avoid dangerous rocks and falling stones, the method of building shed tunnels with foundations on the outside of the bridge will further occupy the existing low-grade road, possibly leading to the interruption of the existing low-grade road or large-scale diversion.

[0004] In view of this, it is necessary to propose a tunnel portal section structure applicable to steep terrains and a construction method thereof to solve or at least alleviate the above defects. Summary of the Invention

[0005] The main purpose of the present invention is to provide a tunnel portal section structure applicable to steep terrains and a construction method thereof, so as to solve the technical problems of high construction risk and encroachment on the existing low-grade road in the scheme of using bridge abutments to enter the tunnel + building shed tunnels with foundations on the outside of the bridge + local diversion of the existing low-grade road for the tunnel portal section in steep terrains.

[0006] To achieve the above object, the present invention provides a tunnel portal section structure applicable to steep terrains, including a portal component and a double-layer frame structure. The portal component and the double-layer frame structure are adjacent. The double-layer frame structure includes a shed tunnel component, a box culvert main body, a column component, and a supporting beam component. The shed tunnel component is connected to the top of the supporting beam component; Wherein, the supporting beam component includes an upper supporting beam and a lower supporting beam. Both the upper supporting beam and the lower supporting beam extend along the extension direction of the tunnel portal section. The shed tunnel component is connected to the top of the upper supporting beam. The portal component is adjacently arranged on the mountain side of the shed tunnel component; The upper joist and the top plate of the box culvert body are cast as one piece, 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 cast as one piece. The column assembly and the side wall of the box culvert body are cast as one piece, and the column assembly is connected between the upper joist and the lower joist. The box culvert body has a vehicle passage that matches the existing low-grade road. The extension direction of the vehicle passage and the extension direction of the tunnel entrance section are arranged crosswise. The box culvert body has a step formed on the top of the side wall away from the end of the mountain, and the step is installed with a support for supporting the adjacent span bridge.

[0007] Preferably, the shed hole assembly includes a shed hole rigid frame body, a T-beam assembly, an end retaining wall, a side retaining wall and a first backfill layer; wherein the shed hole rigid frame body is connected to the top of the upper support beam; The T-beam assembly includes a plurality of T-beams arranged in sequence along the extension direction of the shed hole rigid frame body, and each T-beam is connected to the shed hole rigid frame body; The end retaining wall and the side retaining wall are both arranged on the top of the T-beam, the end retaining wall is located at the end of the T-beam assembly away from the portal assembly, and the side retaining walls are provided on both sides of the T-beam assembly. The T-beam assembly, the end retaining wall and the side retaining wall together form a first backfill space, and the first backfill space is backfilled with a first backfill layer.

[0008] Preferably, the portal assembly includes a casing arch, a portal wall and a second backfill layer, wherein a concave space for the casing arch to be set is formed on the top of the portal wall, the casing arch is set in the concave space and is located on the top of the tunnel lining structure, the two ends of the casing arch are respectively connected to the corresponding portal walls, the inner wall of the portal wall, the top surface of the casing arch and the back slope together form a second backfill space, and the second backfill space is backfilled with a second backfill layer; wherein the inner contour line of the shed tunnel of the shed tunnel rigid frame body and the inner contour line of the portal wall are matched, an asphalt plate is backfilled between the shed tunnel assembly and the portal wall, and the second backfill layer extends along the extension direction of the tunnel to the natural slope above the tunnel.

[0009] Preferably, the thickness of the asphalt sheet is 20 mm.

[0010] Preferably, it further comprises a first water guide assembly and a second water guide assembly, wherein the first water guide assembly comprises a plurality of first cast iron pipes arranged at intervals laterally along the rigid frame body of the shed tunnel, the first cast iron pipes comprising a first end and a second end oppositely arranged along their own extension direction, the first end being pre-buried in the end retaining wall, and the second end extending outward from the first end and being cantilevered; The second water-guiding component includes a plurality of second cast iron pipes arranged at intervals along the extension direction of the shed tunnel rigid frame body, and the second cast iron pipe includes a third end and a fourth end arranged opposite to each other along its own extension direction, the third end is pre-buried in the side retaining wall, and the fourth end extends outward from the third end and is cantilevered.

[0011] Preferably, the length of each T-beam is set between 5 and 8 meters.

[0012] The present invention also provides a construction method for a tunnel portal section structure suitable for steep terrain, which is applied to the above-mentioned tunnel portal section structure suitable for steep terrain, comprising the following steps: S1: Temporary diversion of existing low-grade roads to create construction conditions for backslope excavation. The steep rock and soil mass on the backslope is excavated vertically in steps, and soil nail walls are used to support the backslope from top to bottom while excavating. S2, constructing the box culvert body, column assembly, and joist assembly, and constructing the pavement of the new road using the height difference between the upper joist and the top plate of the box culvert body; S3: Using the existing adjacent span bridge, box culvert body, and joist assembly as a tunnel entry construction platform, the tunnel is constructed using a wall-to-wall approach. Portal walls and casing arches are constructed on both sides of the tunnel. A pipe shed is constructed over the casing arches, and backfill is then performed within the second backfill space to form a second backfill layer. S4, constructing the shed hole assembly; S5, construct the tunnel blind hole and complete the construction of the tunnel portal section structure.

[0013] Preferably, the construction of the box culvert body, column assembly and joist assembly in step S2 specifically includes the following steps: S21: First, excavate the existing low-grade road to the designed ground surface and verify the bearing capacity of the foundation. If the bearing capacity of the foundation meets the bearing capacity requirements, proceed to step S22. If not, perform foundation treatment or construct pile foundations on the designed ground surface before proceeding to step S22. S22, constructing a cushion layer, laying a bottom plate waterproofing board of the box culvert body, constructing the bottom plate and lower joist of the box culvert body, and then tying steel bars, erecting formwork, and pouring concrete to cast the bottom plate and lower joist of the box culvert body into one piece; S23, after the concrete strength of the bottom plate and the lower joist of the box culvert body reaches the first design strength, laying the waterproof layer of the side wall of the box culvert body, constructing the side wall and column assembly of the box culvert body, tying steel bars, erecting formwork, and pouring concrete to cast the side wall and column assembly of the box culvert body into one piece; S24. After the concrete strength of the side walls and column assemblies of the box culvert main body reaches the second design strength, lay the waterproof layer on the top slab of the box culvert main body, construct the top slab of the box culvert main body and the upper supporting beam, and then bind the steel bars, set up the formwork, and pour the concrete to integrate the top slab of the box culvert main body and the upper supporting beam. At the same time, install the bearings at the steps and reserve the connecting steel bars for connecting with the shed tunnel rigid frame main body.

[0014] Preferably, the step S4 specifically includes the following steps: S41. Bind the steel bars of the shed tunnel rigid frame main body, connect them with the connecting steel bars, set up the formwork, and pour the concrete of the shed tunnel rigid frame main body. S42. After the concrete strength of the shed tunnel rigid frame main body reaches the third design strength, erect the T-beam assembly and pour the end retaining wall and side retaining wall. S43. Backfill the first backfill space to form the first backfill layer.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The upper layer of the double-layer frame structure of this application is the shed tunnel assembly, and the shed tunnel assembly can act as a sunshade while facing the steep terrain and falling rocks; the lower layer of the double-layer frame structure includes the box culvert main body, column assemblies and supporting beam assemblies. The upper supporting beam + column assembly + lower supporting beam can provide support for the upper shed tunnel assembly, solve the foundation of the upper shed tunnel assembly, and at the same time the self-weight of the double-layer frame structure can effectively resist the earth pressure against the mountain; the box culvert main body can provide a vehicle passage for the existing low-grade road below, avoiding the realignment and detour of the existing low-grade road; the box culvert main body can also be used as a bridge abutment adjacent to the bridge, support the adjacent span bridge through the embedded bearing, realize the bridge-tunnel connection between the tunnel structure and the bridge structure, and provide conditions for bridge construction; at the same time, the upper backfill of the box culvert main body to the top surface of the supporting beam can provide a construction platform for the tunnel to enter the hole, create conditions for the tunnel to enter the hole, play the role of a disaster prevention and rescue turning lane during the later operation stage, and can resist the lateral earth pressure of the mountain; the building limits of the shed tunnel assembly and the portal assembly are smoothly connected, and the shed tunnel assembly and the portal wall are separately arranged, avoiding structural cracking caused by differential settlement, and the construction safety of this application is high. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0017] Figure 1 It is a schematic diagram after the completion of step S1 in an embodiment of the present invention. Figure 2 Schematic diagram after completion of construction step S2 in an embodiment of the present invention; Figure 3 Schematic diagram after completion of the portal wall and arch ring in construction step S3 in an embodiment of the present invention; Figure 4 Schematic diagram after completion of construction step S4 in an embodiment of the present invention; Figure 5 Schematic diagram after completion of construction step S5 in an embodiment of the present invention; Figure 6 Application scenario diagram of the overall structure in an embodiment of the present invention; Figure 7 Planar schematic diagram of the double - layer frame structure in an embodiment of the present invention; Figure 8 Schematic diagram of the structure of the box culvert main body in an embodiment of the present invention; Figure 9 Schematic diagram of the structure of the double - layer frame structure in an embodiment of the present invention; 3] Figure 10 Schematic diagram of the structure of the portal component in an embodiment of the present invention; Figure 11 Flow schematic diagram of the construction method in an embodiment of the present invention; Figure 12 Flow schematic diagram of the specific steps included in constructing the box culvert main body, column component, and supporting beam component in step S2 in an embodiment of the present invention.

[0018] The realization of the object, functional characteristics, and advantages of the present invention will be further described with reference to the embodiments and the accompanying drawings.

[0019] Explanation of the reference numerals in the drawings: 10. Double - layer frame structure; 110. Box culvert main body; 111. Top plate of the box culvert main body; 112. Bottom plate of the box culvert main body; 113. Side wall of the box culvert main body; 114. Vehicle passage; 115. Step; 116. Support; 120. Column component; 130. Supporting beam component; 131. Upper supporting beam; 132. Lower supporting beam; 140. Shed - type tunnel component; 141. Main body of the shed - type tunnel rigid frame; 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 component; 210. Arch ring; 220. Portal wall; 230. Second backfill layer; 30. Existing low - grade road; 40. Soil nail; 50. Adjacent cross - bridge; 60. Falling rock; 70. Blind tunnel. Detailed implementation manners

[0020] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0022] In the present invention, the descriptions involving "first", "second", etc. are only for descriptive purposes, and cannot be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0023] Please refer to the attached Figures 1 to 12 , a tunnel portal section structure applicable to steep terrain provided by an embodiment of the present invention 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 to each other. The double-layer frame structure 10 includes a shed tunnel assembly 140, a box culvert main body 110, a column assembly 120, and a supporting beam assembly 130. The shed tunnel assembly 140 is connected to the top of the supporting beam assembly 130; Among them, the supporting beam assembly 130 includes an upper supporting beam 131 and a lower supporting beam 132. Both the upper supporting beam 131 and the lower supporting beam 132 extend along the extension direction of the tunnel portal section. The shed tunnel assembly 140 is connected to the top of the upper supporting beam 131. The portal assembly 20 is adjacently arranged on the mountainside side of the shed tunnel assembly 140; The upper supporting beam 131 and the top plate 111 of the box culvert main body are cast as a whole, and the top surface of the upper supporting beam 131 is higher than the top surface of the top plate 111 of the box culvert main body. The lower supporting beam 132 and the bottom plate 112 of the box culvert main body are cast as a whole. The column assembly 120 and the side wall 113 of the box culvert main body are cast as a whole. The column assembly 120 is connected between the upper supporting beam 131 and the lower supporting beam 132; The box culvert main body 110 has a vehicle passage 114 that matches the existing low-grade road 30. The extension direction of the vehicle passage 114 and the extension direction of the tunnel portal section are arranged crosswise. A step 115 is formed at the top of the side wall at the end of the box culvert main body 110 away from the mountain body. A support 116 for supporting the adjacent bridge 50 is installed on the step 115.

[0024] It should be noted that when a new expressway is built in a mountainous and hilly area, it is inevitable to cross steep mountains. At the same time, due to terrain and cost limitations, local low-grade roads often follow river valleys. Therefore, the new expressway not only crosses steep mountains but also spans existing low-grade roads 30. As a result, the extension direction of the tunnel entrance section and the existing low-grade road 30 (such as national roads, county roads, etc.) are vertically crossed in space. 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 entrance section of the new expressway and the extension direction of the vehicle passage 114 are vertically crossed in space.

[0025] The upper layer of the double-layer frame structure 10 of the present application is a shed tunnel component 140, and the shed tunnel component 140 can function as a sunshade while facing the dangerous rocks 60 on the steep terrain; the lower layer of the double-layer frame structure 10 includes a box culvert main body 110, a column component 120, and a supporting beam component 130. The upper supporting beam 131 + column component 120 + lower supporting beam 132 can provide support for the upper shed tunnel component 140, solve the foundation of the upper shed tunnel component 140, and at the same time, the self-weight of the double-layer frame structure 10 can effectively resist the earth pressure against the mountain; the box culvert main body 110 can provide a vehicle passage 114 for the lower existing low-grade road 30, avoiding the realignment and detour of the existing low-grade road 30; the box culvert main body 110 can also be used as a bridge abutment adjacent to the bridge, support the adjacent-span bridge 50 through the embedded bearing 116, realize the bridge-tunnel connection between the tunnel structure and the bridge structure, and provide conditions for bridge construction; at the same time, the upper backfill of the box culvert main body 110 to the top surface of the supporting beam can provide a construction platform for the tunnel to enter the hole, create conditions for the tunnel to enter the hole, play the role of a disaster prevention and rescue turning lane during the later operation stage, and can resist the lateral earth pressure of the mountain; the building limits of the shed tunnel component 140 and the portal component 20 are smoothly connected, and the shed tunnel component 140 and the portal wall 220 are separately arranged to avoid structural cracking caused by differential settlement.

[0026] As a preferred embodiment, the shed tunnel component 140 includes a shed tunnel rigid frame main body 141, a T-beam component (not shown in the figure), an end retaining wall 143, a side retaining wall 144, and a first backfill layer 145; wherein, the shed tunnel rigid frame main body 141 is connected to the top of the upper supporting beam 131; the T-beam component includes a plurality of T-beams 142 arranged in sequence along the extension direction of the shed tunnel rigid frame main body 141, and each T-beam 142 is connected to the shed tunnel rigid frame main body 141; The end retaining wall 143 and the side retaining walls 144 are both 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. The side retaining walls 144 are provided on both sides of the T-beam assembly. The T-beam assembly, the end retaining wall 143, and the side retaining walls 144 enclose a first backfill space, and a first backfill layer 145 is backfilled in the first backfill space.

[0027] In this embodiment, the shed tunnel rigid frame main body 141 serves as the core load-bearing member and forms a basic framework through connection with the upper supporting beam 131. The upper supporting beam 131 provides a construction bearing foundation for the shed tunnel rigid frame main body 141, and can transfer the upper load to the foundation through the upper supporting beam 131 finally; the T-beam assemblies are distributed along the extension direction of the shed tunnel to improve the overall flexural stiffness and avoid local stress concentration; the end retaining wall 143 is located at the end of the shed tunnel rigid frame main body 141 to form a longitudinal limiting structure, and the side retaining walls 144 are connected to the top of the T-beam 142 to form a transverse limit. The first backfill layer 145 can effectively resist the impact force of the falling rock 60. Preferably, the first backfill layer 145 is, from bottom to top, a waterproof layer, a mortar protection layer, a soil and stone layer, and a water isolation layer. In other embodiments, the first backfill layer 145 can also adopt other forms of backfill, and those skilled in the art can choose according to actual needs.

[0028] Specifically, when the falling rock 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 falling rock 60 generally does not fall onto the formed area adjacent to the bridge and tunnel. Since the first backfill layer 145 can be further provided with a transverse slope to guide the falling rock 60 to slide from both sides of the shed tunnel assembly 140.

[0029] Preferably, the length of each T-beam 142 is set between 5 and 8 m. The T-shaped structure has the advantages of light self-weight and large flexural stiffness. Preferably, the length of each T-beam 142 is 5 to 8 m. In other embodiments, those skilled in the art can also adopt a beam body in the form of reinforced concrete.

[0030] As a preferred embodiment, the portal assembly 20 includes an arch ring 210, a portal wall 220, and a second backfill layer 230. Among them, a concave space for arranging the arch ring 210 is formed at the top of the portal wall 220. That is, the two portal walls 220 adopt the double-ear wall portal type, which can ensure the smooth transition of the top of the shed tunnel assembly 140 and the filling on the top of the portal wall 220 and the smooth connection of the structural contour. The arch ring 210 is arranged in the concave space and located at the top of the tunnel lining structure. The two ends of the arch ring 210 are respectively connected to the corresponding portal walls 220. A second backfill space is formed by enclosing the inner wall of the portal wall 220, the top surface of the arch ring 210, and the cut slope. The second backfill layer 230 is filled in the second backfill space. Among them, the inner contour line of the shed tunnel of the rigid frame body 141 of the shed tunnel is matched with the inner contour line of the portal wall 220, that is, they are smoothly connected and corresponding. An asphalt board (not shown in the figure) is filled between the shed tunnel assembly 140 and the portal wall 220. The second backfill layer 230 extends along the tunnel extension direction to the natural slope above the tunnel.

[0031] Preferably, the thickness of the asphalt board is 20 mm.

[0032] In this embodiment, the arch ring 210, as a transverse connecting member at the top of the tunnel entrance, connects the two portal walls 220 into a whole, significantly improving the overall stiffness and stability of the tunnel entrance structure, effectively resisting the lateral pressure of the mountain body and the earth-rock pressure, and reducing the possibility of deformation, cracking, and even collapse of the tunnel entrance. The concave space at the top of the portal wall 220 provides a positioning basis for the accurate installation of the arch ring 210, with clear force and reliable connection. The second backfill layer 230 provides a strong lateral support for the cut slope, reducing the threat to the tunnel entrance structure caused by the instability and sliding of the cut slope. Preferably, the second backfill layer 230 is, from bottom to top, a waterproof layer, a mortar protection layer, a soil-rock layer, and a water isolation layer. In other embodiments, the second backfill layer 230 can also adopt other forms of backfill, and those skilled in the art can select according to actual needs.

[0033] Furthermore, it further includes a pipe shed. The arch ring 210 is provided with a plurality of pipe shed guiding pipes (not shown in the figure) arranged at intervals along its circumferential direction. The pipe shed includes a plurality of grouting steel pipes (not shown in the figure) corresponding to the pipe shed guiding pipes one by one. Each grouting steel pipe includes a connection end (not shown in the figure) and an anchoring end (not shown in the figure) arranged oppositely along its extending direction. The connection end is connected to the arch ring 210, and the anchoring end is anchored into the surrounding rock.

[0034] In this embodiment, the pipe shed is constructed before the excavation of the blind tunnel 70. The grouting steel pipes are driven into the surrounding rock through the guiding pipes of the pipe shed, forming an umbrella-shaped (or shed-shaped) rigid support framework above and around the tunnel excavation contour line. Through the dual effects of advanced physical support and grouting reinforcement, the disturbance, relaxation, and deformation of the surrounding rock caused by tunnel excavation are greatly reduced, providing safe conditions for the subsequent excavation operation of the blind tunnel 70.

[0035] As another preferred embodiment, it further includes a first water guide component and a second water guide component. The first water guide component includes a plurality of first cast iron pipes 146 arranged at intervals in the transverse direction of the rigid frame body 141 of the shed tunnel. The first cast iron pipe 146 includes a first end (not shown in the figure) and a second end (not shown in the figure) arranged opposite to each other along its own extending direction. The first end is embedded in the end retaining wall 143, and the second end extends outward from the first end and is cantilevered. The second water guide component includes a plurality of second cast iron pipes 147 arranged at intervals along the extending direction of the rigid frame body 141 of the shed tunnel. The second cast iron pipe 147 includes a third end (not shown in the figure) and a fourth end (not shown in the figure) arranged opposite to each other along its own extending direction. The third end is embedded in the side retaining wall 144, and the fourth end extends outward from the third end and is cantilevered.

[0036] The first cast iron pipe 146 and the second cast iron pipe 147 of this embodiment can timely drain the accumulated water in the first backfill layer 145 and the second backfill layer 230, 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, and the fourth end extends outward from the third end and is cantilevered. The first cast iron pipe 146 and the second cast iron pipe 147 are inclined, which can achieve the purpose of drainage.

[0037] The present invention also provides a construction method for the tunnel portal section structure suitable for steep terrains, which is applied to the tunnel portal section structure suitable for steep terrains as described above, and includes the following steps: S1, temporarily divert the existing low-grade road 30 to create construction conditions for the excavation of the cut slope. The cut slope is vertically excavated in steps 115 for the steep rock and soil mass, and the soil nail wall 40 is used to support the cut slope while excavating from top to bottom. S2, construct the box culvert main body 110, the column assembly 120, and the supporting beam assembly 130, and construct the road surface of the new road by using the height difference between the upper supporting beam 131 and the top plate 111 of the box culvert main body. S3. Use the adjacent constructed bridge 50, the box culvert main body 110, and the bearing beam assembly 130 as the tunnel entrance construction platform. The tunnel adopts the method of entering the hole by attaching to the wall. Construct the portal wall 220 and the arch ring 210 on both sides of the tunnel, then construct the pipe shed based on the arch ring 210, and then backfill in the second backfill space to form the second backfill layer 230. It should be noted that generally, before tunnel excavation, it is necessary to first construct the arch ring, the advanced pipe shed, and then after excavation, it is necessary to assemble the formwork trolley (the minimum length requirement is 9 - 12m). In such steep rock masses, it is generally excavated from inside the tunnel to the outside of the hole, and the construction risk at the tunnel entrance is high. The tunnel entrance construction platform of the present application can be used as a tunnel construction platform, and in the later operation stage, the upper part of the box culvert can be used as a turning lane for disaster prevention and rescue.

[0038] S4. Construct the shed tunnel assembly 140. S5. Construct the hidden part 70 of the tunnel to complete the construction of the tunnel entrance section structure.

[0039] Specifically, the cut slope is vertically excavated in steps 115 and supported by the soil nail wall 40 to form a cut slope stability scheme of layered unloading + immediate restraint, changing the traditional large - scale slope cutting to precise controlled excavation, reducing the disturbance to the original stratum. The box culvert main body 110 can be used as a support for the adjacent bridge and bearing 116. In addition, the upper bearing beam 131 + the column assembly 120 + the lower bearing beam 132 can provide support for the upper shed tunnel assembly 140. At the same time, the self - weight of the double - layer frame structure 10 can effectively resist the earth pressure against the mountain. The top of the box culvert main body 110 can be paved with a road surface, which can buffer the impact of the road surface load on the box culvert main body 110 and at the same time solve the waterproof problem on the top surface of the box culvert main body 110. It can provide an assembly site for the secondary lining formwork trolley of the hidden part 70 of the tunnel. Constructing the shed tunnel assembly 140 can effectively avoid the falling rocks 60 on the cut slope and provide site conditions for the construction of the hidden part 70 of the tunnel. Adopting the method of entering the hole by attaching to the wall can connect with the shed tunnel assembly 140 smoothly and provide a support point for the advanced support of the hidden part 70 of the tunnel, creating conditions for the tunnel to enter the hole.

[0040] As a preferred embodiment, the step S2 specifically includes the following steps: S21. First, excavate the existing low - grade road 30 to the designed ground surface, and verify the bearing capacity of the foundation. If the bearing capacity of the foundation meets the requirements, enter step S22. If it does not meet the requirements, conduct foundation treatment or construct pile foundations on the designed ground surface, and then enter step S22. S22. Construct the cushion layer, lay the waterproof board on the bottom plate of the box culvert main body, construct the bottom plate 112 of the box culvert main body and the lower bearing beam 132, and then bind the steel bars, set up the formwork, and pour concrete to pour the bottom plate 112 of the box culvert main body and the lower bearing beam 132 into one body. S23. After the concrete strength of the bottom slab 112 of the box culvert main body and the lower supporting beam 132 reaches the first design strength, lay the waterproof layer on the side wall of the box culvert main body, construct the side wall 113 of the box culvert main body and the column assembly 120, and then bind steel bars, set up forms, and pour concrete to pour the side wall 113 of the box culvert main body and the column assembly 120 into one body; among them, the first design strength is preferably that the concrete strength reaches 70%.

[0041] S24. After the concrete strength of the side wall 113 of the box culvert main body and the column assembly 120 reaches the second design strength, lay the waterproof layer on the top slab of the box culvert main body, construct the top slab 111 of the box culvert main body and the upper supporting beam 131, and then bind steel bars, set up forms, and pour concrete to pour the top slab 111 of the box culvert main body and the upper supporting beam 131 into one body; at the same time, install the bearing 116 at the step 115, and reserve the connecting steel bars for connecting with the shed tunnel rigid frame main body 141. Among them, the second design strength is preferably that the concrete strength reaches 70%.

[0042] Specifically, excavate the existing road to the design elevation, conduct bearing capacity verification to ensure the foundation stability. If the bearing capacity is insufficient, adopt foundation reinforcement (such as replacement and compaction) or pile foundation reinforcement to provide strong support for the subsequent structure. The cushion construction levels the base and disperses the load, and the bottom waterproof board of the box culvert forms the first anti-seepage barrier. The bottom slab 112 of the box culvert main body and the lower supporting beam 132 are poured synchronously and work together. After the strength of the bottom slab 112 of the box culvert main body meets the standard, the side wall 113 of the box culvert main body and the column assembly 120 are constructed synchronously. The side wall 113 of the box culvert main body and the column assembly 120 are poured into a whole to form a wall-column frame structure, significantly improving the lateral anti-pushing stiffness. The top slab 111 of the box culvert main body and the upper supporting beam 131 are poured synchronously, and the rigid connection with the shed tunnel rigid frame main body 141 is realized through the reserved connecting steel bars.

[0043] As a preferred embodiment, the step S4 specifically includes the following steps: S41. Bind the steel bars of the shed tunnel rigid frame main body 141, connect them with the connecting steel bars, set up forms, and pour the concrete of the shed tunnel rigid frame main body 141; S42. After the concrete strength of the shed tunnel rigid frame main body 141 reaches the third design strength, erect the T-beam assembly and pour the end retaining wall 143 and the side retaining wall 144; S43. Backfill the first backfill space to form the first backfill layer 145.

[0044] Specifically, the box culvert main body 110 and the shed tunnel rigid frame main body 141 are connected into a whole by the reinforcement bars of the shed tunnel rigid frame main body 141 and the connecting reinforcement bars. After the concrete is poured, it needs to be cured until the third design strength. For example, the concrete ensures that the main structure has sufficient compressive and shear resistance capabilities, providing a stable base for the subsequent erection of the T-beam 142 and the construction of the retaining wall. After the main body concrete reaches the third design strength, for example, when the concrete strength reaches 70%, the T-beam assembly is erected to avoid concrete cracking caused by premature loading. The T-beam 142, as a key force-transferring member, is connected to the shed tunnel rigid frame main body 141 by bolts or welding to form a space truss system. The end retaining wall 143 and the side retaining wall 144 are poured synchronously with the T-beam assembly. The weight and stiffness of the concrete retaining wall are used to resist the impact of the falling rocks 60, and at the same time, they form an integral force with the shed tunnel rigid frame main body 141 to enhance the anti-overturning ability of the structure. The first backfill layer 145 can effectively resist the impact force of the falling rocks 60.

[0045] Preferably, the step of using the soil nail 40 wall to support the cut slope from top to bottom while excavating in the step S1 specifically includes the following steps: using a Φ48 soil nail 40 wall to support the cut slope from top to bottom while excavating; wherein, the length of each soil nail 40 is 3 m, and the spacing distance between two adjacent soil nails 40 is 1 m.

[0046] The above are only the preferred embodiments of the present invention, and thus do not limit the protection scope of the present invention. Any equivalent structural or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be similarly included in the patent protection scope of the present invention.

Claims

1. A tunnel entrance section structure applicable to steep terrains, characterized in that, It includes a portal component and a double-layer frame structure. The portal component and the double-layer frame structure are adjacent. The double-layer frame structure includes a shed tunnel component, a box culvert main body, a column component, and a supporting beam component. The shed tunnel component is connected to the top of the supporting beam component. Among them, the supporting beam component includes an upper supporting beam and a lower supporting beam. Both the upper supporting beam and the lower supporting beam extend along the extension direction of the tunnel portal section. The shed tunnel component is connected to the top of the upper supporting beam. The portal component is adjacently arranged on the mountainside side of the shed tunnel component. The upper supporting beam and the top plate of the box culvert main body are cast integrally, and the top surface of the upper supporting beam is higher than the top surface of the top plate of the box culvert main body. The lower supporting beam and the bottom plate of the box culvert main body are cast integrally. The column component and the side wall of the box culvert main body are cast integrally. The column component is connected between the upper supporting beam and the lower supporting beam. The box culvert main 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 arranged crosswise. A step is formed at the top of the side wall of the box culvert main body at the end far from the mountain body. A bearing for supporting the adjacent bridge is installed on the step.

2. The structure of the tunnel entrance section applicable to steep terrain according to claim 1, characterized in that The shed tunnel component includes a shed tunnel rigid frame main body, a T-beam component, an end retaining wall, a side retaining wall, and a first backfill layer. Among them, the shed tunnel rigid frame main body is connected to the top of the upper supporting beam. The T-beam component includes multiple T-beams arranged in sequence along the extension direction of the shed tunnel rigid frame main body. Each T-beam is connected to the shed tunnel rigid frame main body. Both the end retaining wall and the side retaining wall are arranged on the top of the T-beams. The end retaining wall is located at one end of the T-beam component far from the portal component. Side retaining walls are provided on both sides of the T-beam component. The T-beam component, the end retaining wall, and the side retaining wall enclose a first backfill space, and the first backfill space is filled with a first backfill layer.

3. The tunnel entrance section structure applicable to steep terrains according to claim 2, characterized in that, The portal component includes an arch ring, a portal wall, and a second backfill layer. Among them, a concave space for setting the arch ring is formed at the top of the portal wall. The arch ring is arranged in the concave space and is located at the top of the tunnel lining structure. Both ends of the arch ring are respectively connected to the corresponding portal wall. A second backfill space is enclosed among the inner wall of the portal wall, the top surface of the arch ring, and the slope. The second backfill space is filled with a second backfill layer. Among them, the inner contour line of the shed tunnel of the shed tunnel rigid frame main body and the inner contour line of the portal wall are matched. An asphalt board is backfilled between the shed tunnel component and the portal wall. The second backfill layer extends along the tunnel extension direction to the natural slope above the tunnel.

4. The structure of the tunnel portal section applicable to steep terrain according to claim 3, characterized in that, The thickness of the asphalt board is 20 mm.

5. The tunnel portal section structure applicable to steep terrain according to claim 2, characterized in that, It also includes a first water guiding component and a second water guiding component. The first water guiding component includes multiple first cast iron pipes arranged at intervals transversely along the shed tunnel rigid frame main body. The first cast iron pipe includes a first end and a second end arranged oppositely along its own extension direction. 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-guiding component includes a plurality of second cast iron pipes arranged at intervals along the extension direction of the shed tunnel rigid frame body, and the second cast iron pipe includes a third end and a fourth end arranged opposite to each other along its own extension direction, the third end is pre-buried in the side retaining wall, and the fourth end extends outward from the third end and is cantilevered.

6. The structure of the tunnel portal section applicable to steep terrains according to claim 2, characterized in that, The length of each T-beam is set between 5 and 8 meters.

7. A construction method for the structure of the tunnel portal section applicable to steep terrain, which is applied to the structure of the tunnel portal section applicable to steep terrain as described in any one of claims 3-6, characterized in that, The following steps are involved: S1: Temporary diversion of existing low-grade roads to create construction conditions for backslope excavation. The steep rock and soil mass on the backslope is excavated vertically in steps, and soil nail walls are used to support the backslope from top to bottom while excavating. S2, constructing the box culvert body, column assembly, and joist assembly, and constructing the pavement of the new road using the height difference between the upper joist and the top plate of the box culvert body; S3: Using the existing adjacent span bridge, box culvert body, and joist assembly as a tunnel entry construction platform, the tunnel is constructed using a wall-to-wall approach. Portal walls and casing arches are constructed on both sides of the tunnel. A pipe shed is constructed over the casing arches, and backfill is then performed within the second backfill space to form a second backfill layer. S4, constructing the shed hole assembly; S5, construct the tunnel blind hole and complete the construction of the tunnel portal section structure.

8. The construction method of the tunnel portal section structure applicable to steep terrain according to claim 7, characterized in that, The step S2 of constructing the box culvert body, column assembly and joist assembly specifically includes the following steps: S21: First, excavate the existing low-grade road to the designed ground surface and verify the bearing capacity of the foundation. If the bearing capacity of the foundation meets the bearing capacity requirements, proceed to step S22. If not, perform foundation treatment or construct pile foundations on the designed ground surface before proceeding to step S22. S22, constructing a cushion layer, laying a bottom plate waterproofing board of the box culvert body, constructing the bottom plate and lower joist of the box culvert body, and then tying steel bars, erecting formwork, and pouring concrete to cast the bottom plate and lower joist of the box culvert body into one piece; S23, after the concrete strength of the bottom plate and the lower joist of the box culvert body reaches the first design strength, laying the waterproof layer of the side wall of the box culvert body, constructing the side wall and column assembly of the box culvert body, tying steel bars, erecting formwork, and pouring concrete to cast the side wall and column assembly of the box culvert body into one piece; S24, after the concrete strength of the side walls and column assemblies of the box culvert main body reaches the second design strength, lay the top plate waterproof layer of the box culvert main body, construct the top plate and upper supporting beam of the box culvert main body, then tie the steel bars, erect the formwork, and pour the concrete to cast the top plate and upper supporting beam of the box culvert main body into one; at the same time, install the support at the step, and reserve the connecting steel bars connected to the rigid frame main body of the shed.

9. The construction method of the tunnel entrance section structure applicable to steep terrain according to claim 8, characterized in that, The step S4 specifically includes the following steps: S41: Tie the steel bars of the main rigid frame of the shed tunnel and connect them with the connecting steel bars, erect the formwork, and pour the concrete of the main rigid frame of the shed tunnel; S42: When the concrete strength of the main rigid frame of the shed tunnel reaches the third design strength, erect the T-beam assembly and cast the end retaining wall and side retaining wall; S43, backfilling the first backfill space to form a first backfill layer.

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