Tunnel portal and tunnel body pipe shed construction method

Abstract

The present application relates to the technical field of tunnel construction, and particularly relates to a tunnel portal and tunnel body pipe shed construction method, step S1, portal side slope and portal drainage ditch construction is carried out, step S2, concrete arch is constructed in open cut section and buried section, step S3, step method is used for tunnel excavation, first, upper step arc-shaped guide pit is excavated, step S4, lower step excavation is carried out in staggered manner at a certain distance from the lag upper step working face, step S5, invert and tunnel bottom filling are poured at a certain distance from the lag lower step working face, and secondary lining construction is carried out after initial support, invert and tunnel bottom filling convergence; step S6, steps S4-S5 are repeated until tunnel construction is completed. The concrete arch is set, the concrete arch is used as a guide wall, the arch uses the existing soil layer as a formwork, so that the formwork setting difficulty is reduced, and the construction efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the technical field of tunnel construction, specifically relating to a method for constructing a tunnel entrance and tunnel body pipe roof. Background Technology

[0002] In tunnel construction, although the entire process and construction methods are mature and complete, advanced support is a common measure to ensure the safety of tunnel excavation. It mainly includes advanced pipe roof, advanced small guide pipe, advanced anchor bolt, and advanced grouting. Advanced support for the junction of open and closed tunnels can adopt the advanced pipe roof method. Generally, on-site concrete pouring is used. During the operation, a series of procedures are usually required, such as installing formwork, erecting steel frames, installing orifice pipes, pouring concrete, and curing. It has high requirements for labor, materials, and processing sites. Moreover, for loose surrounding rock, instability is prone to occur during tunnel construction, which can lead to landslides at the tunnel entrance.

[0003] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art. This invention provides a method for constructing tunnel entrances and tunnel body pipe roofs.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for constructing pipe roofs at tunnel entrances and within the tunnel body, comprising: Step S1: Construction of the outer slope of the tunnel entrance and the drainage ditch at the tunnel entrance. The open tunnel section is divided into upper and lower end faces for open excavation. Advanced small guide pipe construction is carried out within a 30° range on both sides of the open tunnel section. Step S2: Concrete arches are constructed in the open and dark tunnel sections. The concrete arches are used as guide walls for the construction of the first circulation pipe roof. Cement slurry is injected into the pipe roof through a high-pressure pump to solidify the surrounding soil and rock of the dark tunnel section. Step S3: The tunnel is excavated using the bench method. First, the upper bench arc-shaped pilot tunnel is excavated. According to the surrounding rock conditions, the tunnel face is sealed with shotcrete. Then, the initial support of the upper bench is carried out. Step S4: At a certain distance from the working face of the lagging upper bench, the lower bench is excavated in a staggered manner, and the initial support of the lower bench is carried out in a way that supports as it is excavated, connecting the initial support of the lower bench and the initial support of the upper bench into one. Step S5: Cast the invert arch and tunnel bottom fill at a certain distance from the lagging lower bench working face. After the initial support, invert arch and tunnel bottom fill converge, carry out the secondary lining construction. Step S6, repeat steps S4-S5 until tunnel construction is completed.

[0006] Preferably, in step S2, after measurement and layout, the pouring trench corresponding to the arch outline is excavated by an excavator, and then after re-measurement, the pouring trench is trimmed by manual excavation. Reinforcing bars are tied in the pouring trench, and positioning rings are welded or tied in the reinforcing bars. After the guide pipe passes through the positioning ring, it is driven into the rock and soil outside the tunnel at a set angle. Install the top formwork and end formwork corresponding to the pouring trough. The end formwork is provided with a through hole for the corresponding guide tube, and the through hole is sealed to the guide tube. After backfilling the soil and rock on both sides of the tunnel, the arch is poured from the top of the casting trench. After the arch has initially set, the top of the arch is backfilled with soil and rock and then the slope protection is constructed.

[0007] Preferably, the first circulation pipe roof is inserted into the rock and soil outside the tunnel from the guide pipe. The end of the pipe roof inserted into the guide pipe is provided with an external thread corresponding to the guide pipe, so as to fix it to the guide pipe through the threaded connection. A grouting valve is provided at the end of the pipe roof. After the pipe roof is numbered, grouting is performed at intervals. First, the "odd" holes are grouted and solidified, and then the "even" holes are grouted.

[0008] Preferably, the bottom of the casting trough and the corresponding external rock and soil of the tunnel are used as the bottom formwork of the arch and the end formwork on one side of the tunnel extension direction, respectively. A steel frame is provided at the bottom of the casting trough, and the steel frame is connected to the internal steel reinforcement skeleton of the arch. After the arch concrete reaches the preset strength, tunneling is carried out. The working face is divided into core soil and outer soil. The outer soil is divided into multiple tunneling areas along the extension direction of the arch. Multiple tunneling areas are excavated in a symmetrical tunneling manner.

[0009] Preferably, after the excavation of each tunneling area is completed, a hydraulic cylinder is installed between the arch and the core soil. Prestress is applied by the hydraulic cylinder before the next tunneling area is excavated. After the excavation is completed, multiple hydraulic cylinders are depressurized simultaneously. After the depressurization is completed, the tunnel body is excavated using the step method.

[0010] Preferably, as the tunnel is excavated, initial support is constructed on the inner wall of the arch, and the steel arch frame of the initial support is fixed to the steel frame by welding.

[0011] Preferably, the initial support inside the tunnel includes steel arch frames, pipe roofs, grouting anchors, and shotcrete. The steel arch frames of the upper and lower bench initial support are spliced ​​together to form the corresponding tunnel arch structure. The steel arch frames are fixed in the rock and soil outside the tunnel by grouting anchors. Corresponding positioning holes are provided on the steel arch frames of the corresponding pipe roofs. The tunnel body is equipped with pipe roofs at least within a 90° range of the corresponding tunnel arch top and a 30° range on each side.

[0012] Preferably, shear-tensioned tie bars are laid between any two steel arch frames, and a steel mesh is laid on the inner side of the initial support after shotcreting, and the steel mesh is fixed by grouting anchors as hanging points.

[0013] Preferably, the waterproof layer is constructed after the initial setting of the shotcrete. First, a single piece of geotextile is fixed to the predetermined position using a work trolley. Then, the geotextile is fixed to the shotcrete using a special hot-melt liner and nails. The waterproof membrane is laid from the bottom of one side wall towards the arch, and then from the arch towards the other side wall. The bottom of the waterproof membrane is wrapped with a longitudinal drainage blind pipe. The overlap of the waterproof membrane is staggered from the longitudinal construction joint by not less than 1.0m.

[0014] Beneficial effects: Setting up a concrete arch and using it as a guide wall, while utilizing the existing soil layer as formwork, reduces the difficulty of formwork erection and improves construction efficiency.

[0015] A steel frame is pre-installed inside the arch, which is connected to the steel arch frame to ensure support strength. Furthermore, hydraulic cylinders are installed to gradually release pressure, preventing the arch from becoming unstable under the action of the surrounding rock and soil, and improving construction safety. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein: Figure 1 This is a schematic diagram of the arch-tunneling process in a specific embodiment of the present invention.

[0017] In the diagram: 1. Core soil; 2. Excavation area; 3. Arch; 4. Guide pipe; 5. Steel frame. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0019] In the description of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. The terms "connected" and "linked" used in this invention should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; they can refer to a direct connection or an indirect connection through intermediate components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0020] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0021] like Figure 1 As shown, a method for constructing a tunnel portal and tunnel body pipe roof includes the following steps: Step S1, constructing the external slope of the tunnel portal and the drainage ditch at the tunnel portal. Before excavation, drainage should be prepared for the external slope and the tunnel portal, and a water interception (drainage) ditch system should be constructed outside the external slope. A water interception ditch should be set 10m outside the excavation line, using C25 reinforced concrete for cast-in-place construction. The water interception ditch should be properly connected to the road cut ditch. The open-cut section is divided into upper and lower end faces for open excavation. Each step of excavation is carried out in steps from top to bottom as needed, with a step height of 2-3 meters.

[0022] After the excavation of the upper section of the open tunnel, the construction of temporary slopes, and the protection of the open and closed vertical excavation faces are completed, the pre-support construction of the large pipe shed for the closed tunnel is carried out to prepare for the excavation of the closed tunnel. Pre-support small pipes are constructed within a 30° range on both sides of the open tunnel section. Grouting of the pre-support small pipes is carried out using a special grouting pump. The grout meets the design requirements. A grout distributor is installed at the front end of the small pipes, and 3 to 5 small pipes are injected at a time.

[0023] After cleaning the hole, proceed with construction from bottom to top, symmetrically from both sides towards the middle, using a grout that is initially thin and then thickens, and with a large grouting volume initially and then a small volume.

[0024] The grouting pressure is controlled by a graded pressure increase method, which is regulated by the oil pressure control of the grouting pump. The grouting pressure gradually increases from low to high, eventually reaching the termination pressure of 1.0 MPa.

[0025] Step S2: Concrete arch 3 is constructed in both the open and closed tunnel sections. Arch 3 is an arch-shaped cast-in-place concrete corresponding to the outer contour of the tunnel. The guide wall is constructed outside the tunnel excavation outline. The guide wall is made of C25 concrete. The concrete arch 3 is used as the guide wall for the construction of the first circulation pipe roof. Cement slurry is injected into the pipe roof through a high-pressure pump to solidify the surrounding soil and rock of the closed tunnel section. The pipe roof at the tunnel entrance should be numbered before construction. Odd-numbered pipes use steel perforated pipes, and even-numbered pipes use steel pipes. During construction, the steel perforated pipes are installed first and grout is injected. Then, the grouting quality of the steel perforated pipes is checked while the steel pipes are installed. The guide wall should be set on a stable foundation with a bearing capacity of not less than 180 kPa. If the bearing capacity of the foundation is insufficient, two φ300 steel pipe piles should be installed side by side on both sides of the guide wall, and C25 concrete should be poured into the piles.

[0026] Step S3 involves tunneling using the bench method. First, an upper bench arc-shaped pilot tunnel is excavated. Depending on the surrounding rock conditions, shotcrete is applied to seal the tunnel face. Then, initial support for the upper bench is implemented, consisting of a 4cm thick shotcrete layer. Steel arch frames (with anchor bolts) are erected, with a temporary cross bracing frame placed between every two initial support steel arch frames. Temporary I-beam supports are installed at the bottom of the pilot tunnel, followed by 18cm thick shotcrete. The construction system includes anchor bolts, reinforcing mesh, and shotcrete applied to the designed thickness before the next cycle of advanced support is implemented.

[0027] Step S4: At a certain distance from the working face of the upper bench, excavate the lower bench using a staggered left-right method. Initially spray 4cm thick concrete, erect steel arch frames (with anchor pipes at the base), construct system anchors, steel mesh, and re-spray concrete to the designed thickness, then perform the next cycle of advanced support. The initial support for the lower bench is carried out using a method of excavation and support simultaneously, connecting the initial support of the lower bench with that of the upper bench as a single unit. The excavation and support advance per cycle for the upper bench should not exceed the spacing of one steel arch frame, and the advance per cycle for the lower bench should not exceed the spacing of two steel arch frames. In sections where the initial support design steel arch frames are not closed, the excavation advance of the invert arch in one go should not exceed 3m. After tunnel excavation, the initial support should be constructed promptly and closed into a ring; for Class V surrounding rock, the closure position should not be more than 35m from the working face.

[0028] The initial support inside the tunnel includes steel arch frames, pipe roofs, grouting anchors, and shotcrete. The steel arch frames of the upper and lower bench initial support are spliced ​​together to form the corresponding tunnel arch structure. The steel arch frames are fixed in the rock and soil outside the tunnel by grouting anchors. Corresponding positioning holes are provided on the steel arch frames of the corresponding pipe roofs. Pipe roofs are installed in the tunnel body at least within a 90° range of the corresponding tunnel arch top and within a 30° range on each side.

[0029] The pipe roof uses φ89mm hot-rolled seamless steel pipes with a wall thickness of 5mm. The pipe joints are threaded, and the number of joints in the same cross-section must not exceed 50% of the total number of pipes. Adjacent pipe joints must be staggered by at least 1m. The circumferential spacing of the pipe roof is 40cm from center to center, and the longitudinal length is generally 10m per ring, with an overlap of at least 3m between two rings. The external insertion angle is ≯12°. Grouting holes with a diameter of 10-16mm are provided on the pipe roof, spaced 15cm apart in a quincunx pattern, with a 150cm un-drilled grout-stopping section reserved at the end.

[0030] Tie bars with shear tension are laid between any two steel arch frames. After shotcreting, a steel mesh is laid inside the initial support, and the mesh is fixed using grouting anchors as anchor points. The steel mesh is laid after the initial shotcreting, following the undulations of the rock surface, with a gap of no more than 3cm between the mesh and the shotcreted surface. It is firmly connected to the anchors, and the protective layer thickness of the steel mesh is greater than 2cm.

[0031] Step S5 involves pouring the invert arch and filling the tunnel bottom at a certain distance from the lower bench working face. Secondary lining construction is carried out after the initial support, invert arch, and tunnel bottom filling have converged. Invert arch formwork and secondary lining trolleys are fabricated according to the division of the pouring sections. The invert arch formwork is divided into a lightweight invert arch perimeter and a standardized combined steel end mold. The invert arch perimeter is made of steel plates combined with angle steel, serving to shape the arch's arc structure during pouring. To ensure the lightweight nature of the invert arch perimeter, small arc-shaped formwork pieces are spliced ​​together to form the overall invert arch perimeter. Each arc-shaped piece is 80cm x 150cm, and adjacent arc-shaped formwork pieces are bolted together to ensure integrity.

[0032] The tunnel invert arch is constructed using C35 and C40 reinforced concrete. The invert arch is poured using an arch-shaped formwork, symmetrically from the center outwards, and is poured as a single unit. The invert arch pouring is carried out in parallel with the tunneling work, using an invert arch trestle for concrete pouring and muck removal to ensure undamaged working space and the newly poured concrete structure. Before excavation, the steel arch frame must be secured, and each excavation cycle should not exceed 3 meters. Initial support must be promptly installed and closed into a ring after tunnel excavation; for Class V surrounding rock, the closure point should be no more than 35 meters from the tunnel face. The invert arch is poured in segments as a single, continuous pour.

[0033] The tunnel invert arch filling uses C20 concrete, which is produced by a centralized mixing plant and transported to the pouring site by concrete trucks. The invert arch and its filling are poured in stages. After the invert arch concrete is poured and reaches the required strength, the end formwork for the invert arch filling and the integral formwork for the central drainage ditch are installed, and then the invert arch filling concrete is poured. The arch wall lining construction must be carried out after the deformation of the surrounding rock and the initial support has stabilized. The arch wall lining concrete is poured in one go using a hydraulic formwork trolley.

[0034] Step S6, repeat steps S4-S5 until tunnel construction is completed.

[0035] In an optional embodiment, in step S2, after measurement and layout, the excavator is used to excavate the casting trench corresponding to the outline of the arch 3. The arch 3 is located at the top of the arch, and its corresponding angle is 120°. The casting trench is stepped, corresponding to the shape of the tunnel. Its side away from the tunnel extension direction and the top are open. The bottom and the side corresponding to the tunnel extension direction are respectively used as the bottom mold and end mold of the casting trench. In order to ensure construction accuracy, the casting trench is trimmed by manual excavation after re-measurement.

[0036] Reinforcing bars are tied inside the pouring trench. The reinforcing bars can be pre-tied. Positioning rings are welded or tied inside the reinforcing bars. The diameter of the positioning ring is slightly larger than that of the guide tube 4. Guided by the positioning ring, the guide tube 4 passes through the positioning ring and is driven into the external rock and soil of the tunnel at a set angle. The driving depth of the guide tube 4 is 1-3m. Then, the top form and end form of the corresponding pouring trench are installed. The end form has a through hole for the guide tube 4. The through hole is used to install the guide tube 4. The through hole is sealed to the guide tube 4 with a sealing ring or expanding foam to prevent grout leakage.

[0037] After backfilling the soil and rock on both sides of the tunnel, the arch 3 is poured from the top of the casting trench. After the arch 3 has initially set, the top of the arch 3 is backfilled with soil and rock before the slope protection is constructed. The slope protection method is a concrete frame slope protection with low shrubs planted inside. The frame should be embedded in the slope surface, and the embedding depth can be adjusted appropriately according to the properties of the slope rock and the thickness of the turf to ensure that the surface of the frame is smooth with the surface of the turf. The slope protection should be completed before the main tunnel construction.

[0038] In this embodiment, to ensure that the guide pipe 4 does not vibrate and shift during the pouring process, it is preferable to carry out the first cycle pipe roof construction before the arch 3 is poured. The first cycle pipe roof is inserted into the rock and soil outside the tunnel from the guide pipe 4. The pipe roof can be driven into the guide hole by an electric hammer, or the guide pipe 4 can be used as a guide to drill a hole and then insert the pipe roof. The end of the pipe roof inserted into the guide pipe 4 is provided with an external thread corresponding to the guide pipe 4, so as to fix it to the guide pipe 4 through the threaded connection. A grouting valve is provided at the end of the pipe roof. After the pipe roof is numbered, grout is injected in alternate holes. First, the "odd" numbered holes are injected and after 1 to 2 days of solidification, the "even" numbered holes are injected, so as to form after the grout solidifies.

[0039] The bottom of the pouring trough and the corresponding external rock and soil of the tunnel are used as the bottom formwork of the arch 3 and the end formwork on one side of the tunnel extension direction, respectively. A steel frame 5 is provided at the bottom of the pouring trough. The steel frame 5 is an arch shape corresponding to the outer contour of the tunnel. The steel frame 5 is connected to the internal steel reinforcement skeleton of the arch 3. The two are formed by welding or binding. The concrete of the arch 3 is poured in one go (to the longitudinal construction joint position) and should not be poured in layers.

[0040] After the concrete of the arch 3 reaches the preset strength (80% of the strength), tunneling will begin. The section corresponding to the arch 3 will be excavated by micro-blasting or excavators. Inside the arch 3, the working face will be divided into core soil 1 and outer soil. The shape of the core soil 1 will match the tunnel outline. The width of the outer soil in the radial direction of the tunnel will be no less than 1.2m. The outer soil will be divided into multiple excavation areas 2 along the extension direction of the arch 3. Multiple excavation areas 2 will be excavated in a symmetrical manner.

[0041] Specifically, the outer soil can be divided into 8-10 excavation zones 2. The excavation depth of each excavation zone 2 is adapted to the thickness of the arch 3 in the tunnel extension direction. Taking the setting of 8 excavation zones 2 as an example, the excavation zones 2 are numbered 1-8 in a clockwise direction, and the excavation sequence is 1, 8, 2, 7, 3, 6, 4, 5.

[0042] In this embodiment, the lower edge of the core soil 1 is located at the bottom of the tunnel invert. After each excavation area 2 is completed, a hydraulic cylinder is installed between the arch 3 and the core soil 1. After the hydraulic cylinder applies prestress, the next excavation area 2 is excavated. After the excavation is completed, multiple hydraulic cylinders are depressurized simultaneously. After the depressurization is completed, the core soil 1 is excavated in one go, and then the tunnel body is excavated using the step method.

[0043] Support plates corresponding to each hydraulic cylinder are installed on the core soil 1. Multiple support plates are spliced ​​to form an arch shape corresponding to the outer wall of the core soil 1. After the working face excavation within the arch 3 is completed, tunnel excavation proceeds. As the tunnel excavation progresses, initial support is constructed on the inner wall of the arch 3. The corresponding initial support within the arch 3 is constructed in one go. There is no need to distinguish between the initial support for the lower and upper steps. The steel arch frame is fixed to the steel arch frame by welding. The steel arch frame can be a double-row I-beam or a truss frame.

[0044] In an optional embodiment, a separate waterproof layer is provided on the arch wall in general sections of the tunnel culvert. The waterproof layer consists of a 1.5mm thick EVA waterproof membrane + 350g / m³ waterproof layer. 2 The waterproofing layer is constructed using non-woven fabric. After the initial setting of the shotcrete, the tunnel cross-section is scanned, and the surface of the initial support shotcrete is treated, removing anchor heads and exposed rebar. First, a single-width geotextile is fixed to the predetermined position using a work trolley. Then, special hot-melt linings and nails are used to fix the geotextile to the shotcrete. The hot-melt linings are arranged in a quincunx pattern, with a spacing of ≤0.5m at the arch and 0.8~1.0m at the sidewalls. The geotextile should be laid with appropriate tightness, ensuring it adheres tightly to the shotcrete surface without tearing due to excessive tightness or accumulating wrinkles to prevent artificial water accumulation.

[0045] The waterproof membrane is laid from the lower part of one side wall towards the arch, and then from the arch towards the other side wall. First, a work trolley is used to fix the waterproof membrane in the predetermined position. Then, a manual electric welding machine is used to heat and weld the waterproof membrane to the special hot-melt lining for fixing the geotextile. The waterproof membrane is laid with appropriate tightness and allowance, and the ratio of the actual laid length to the arc length of the initial support base surface is 10:8 to ensure close contact with the initial support surface after concrete pouring. A longitudinal drainage blind pipe is wrapped around the lower part of the waterproof membrane. A circumferential φ50 HDPE double-wall perforated corrugated pipe wrapped with geotextile is installed behind the waterproof membrane of the secondary tunnel lining as a drainage blind pipe. Longitudinal φ80 double-wall perforated corrugated pipe wrapped with geotextile is installed on the outer side of the side wall footings of both sides of the tunnel, at a distance greater than 30cm from the bottom of the drainage ditch. A continuous drainage ditch is set up on both sides of the tunnel, with the arch wall ring and longitudinal permeable blind pipes directly leading into the side ditch. The outer edge of the ring and longitudinal blind pipes must be at least 30cm from the construction joint. The overlap joints of the waterproof membrane should be staggered from the longitudinal construction joints by at least 1.0m.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A method for constructing pipe roofs at tunnel entrances and within the tunnel body, characterized in that, include: Step S1: Construction of the outer slope of the tunnel entrance and the drainage ditch at the tunnel entrance. The open tunnel section is divided into upper and lower end faces for open excavation. Advanced small guide pipe construction is carried out within a 30° range on both sides of the open tunnel section. Step S2: Concrete arches are constructed in the open and dark tunnel sections. The concrete arches are used as guide walls for the construction of the first circulation pipe roof. Cement slurry is injected into the pipe roof through a high-pressure pump to solidify the surrounding soil and rock of the dark tunnel section. Step S3: The tunnel is excavated using the bench method. First, the upper bench arc-shaped pilot tunnel is excavated. According to the surrounding rock conditions, the tunnel face is sealed with shotcrete. Then, the initial support of the upper bench is carried out. Step S4: At a certain distance from the working face of the lagging upper bench, the lower bench is excavated in a staggered manner, and the initial support of the lower bench is carried out in a way that supports as it is excavated, connecting the initial support of the lower bench and the initial support of the upper bench into one. Step S5: Cast the invert arch and tunnel bottom fill at a certain distance from the lagging lower bench working face. After the initial support, invert arch and tunnel bottom fill converge, carry out the secondary lining construction. Step S6, repeat steps S4-S5 until tunnel construction is completed; In step S2, after measurement and layout, the excavator is used to excavate the corresponding arch contour of the casting trench, and after re-measurement, the casting trench is trimmed by manual excavation. Reinforcing bars are tied in the pouring trench, and positioning rings are welded or tied in the reinforcing bars. After the guide pipe passes through the positioning ring, it is driven into the rock and soil outside the tunnel at a set angle. Install the top formwork and end formwork corresponding to the pouring trough. The end formwork is provided with a through hole for the corresponding guide tube, and the through hole is sealed to the guide tube. After backfilling the soil and rock on both sides of the tunnel, the arch is poured from the top of the casting trench. After the arch has initially set, the top of the arch is backfilled with soil and rock and then the slope protection is constructed. The bottom of the casting trough and the corresponding external rock and soil of the tunnel are used as the bottom formwork of the arch and the end formwork on the side of the tunnel extension direction, respectively. A steel frame is set at the bottom of the casting trough, and the steel frame is connected to the internal steel reinforcement skeleton of the arch. After the arch concrete reaches the preset strength, tunneling is carried out. The working face is divided into core soil and outer soil. The outer soil is divided into multiple tunneling areas along the extension direction of the arch. Multiple tunneling areas are excavated in a symmetrical tunneling manner. After the excavation of each tunneling area is completed, a hydraulic cylinder is installed between the arch and the core soil. Prestress is applied by the hydraulic cylinder before the next tunneling area is excavated. After the excavation is completed, multiple hydraulic cylinders are depressurized simultaneously. After the depressurization is completed, the tunnel body is excavated using the step method.

2. The method for constructing pipe roofs at tunnel entrances and within the tunnel body according to claim 1, characterized in that, The first-cycle pipe roof is inserted into the rock and soil outside the tunnel from the guide pipe. The end of the pipe roof inserted into the guide pipe is provided with an external thread corresponding to the guide pipe. It is fixed to the guide pipe through the threaded connection. A grouting valve is provided at the end of the pipe roof. After the pipe roof is numbered, grouting is performed in alternate holes. First, the "odd" holes are grouted and solidified, and then the "even" holes are grouted.

3. The method for constructing pipe roofs at tunnel entrances and in tunnel body according to claim 1, characterized in that, As the tunnel is excavated, initial support is constructed on the inner wall of the arch. The steel arch frame of the initial support is fixed to the steel frame by welding.

4. The method for constructing pipe roofs at tunnel entrances and in tunnel body according to claim 1, characterized in that, The initial support inside the tunnel includes steel arch frames, pipe roofs, grouting anchors, and shotcrete. The steel arch frames of the upper and lower bench initial support are spliced ​​together to form the corresponding tunnel arch structure. The steel arch frames are fixed in the rock and soil outside the tunnel by grouting anchors. Corresponding positioning holes are provided on the steel arch frames of the corresponding pipe roofs. Pipe roofs are installed in the tunnel body at least within a 90° range of the corresponding tunnel arch top and within a 30° range on each side.

5. The method for constructing pipe roofs at tunnel entrances and in tunnel body according to claim 4, characterized in that, Tie bars with shear tension are laid between any two steel arch frames. After shotcreting, a steel mesh is laid on the inner side of the initial support, and the steel mesh is fixed by grouting anchors as hanging points.

6. The method for constructing pipe roofs at tunnel entrances and in tunnel body according to claim 4, characterized in that, After the initial setting of the shotcrete, the waterproof layer is constructed. First, a single piece of geotextile is fixed to the predetermined position using a work trolley. Then, the geotextile is fixed to the shotcrete using a special hot-melt liner and nails. The waterproof membrane is laid from the bottom of one side wall towards the arch, and then from the arch towards the other side wall. The bottom of the waterproof membrane is wrapped with a longitudinal drainage blind pipe. The overlap of the waterproof membrane and the longitudinal construction joint are staggered by no less than 1.0m.

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