A pilot tunnel excavation method for shallow buried, large-section tunnels in inclined strata

Abstract

This invention discloses a method for pilot tunnel excavation in shallow-buried, large-section tunnels in inclined strata. Several boreholes are arranged along the dip side of the tunnel, and rock-reinforcing anchor cables are driven into these boreholes. The rock-reinforcing anchor cables are perpendicular to the rock strata structure, and their driving depth covers the tunnel to be excavated. The excavation face is divided into three pilot tunnels: left, middle, and right. The right pilot tunnel is a dip-side pilot tunnel, and the widths of the left, middle, and right pilot tunnels decrease sequentially. The excavation line apex between the left and middle pilot tunnels is located at the tunnel apex. The right pilot tunnel is divided into upper and lower excavation faces, while the middle and left pilot tunnels are divided into upper, middle, and lower excavation faces, which are excavated sequentially. A comprehensive rock reinforcement technology is employed, combining surface rock-reinforcing anchor cables with localized rock-reinforcing anchor rods within the tunnel. Before tunnel excavation, the rock strata are integrated into a unified structure to reduce the impact of bias pressure. An eight-step excavation process is used to construct a corresponding support system, and anchor rods are driven into composite beams to further improve the ground bias pressure situation.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, specifically to a method for excavating large-section shallow-buried tunnels with irregular sidewall pilot tunnels in inclined strata. Background Technology

[0002] Inclined rock strata refer to rock strata whose bedding planes intersect the horizontal plane at a certain angle and dip in a generally consistent manner. The vast majority of inclined rock strata are formed from original horizontal rock strata after tectonic deformation, and are components of various tectonic deformations. When excavating tunnels in such rock strata, the layered rock mass will tend to slide or relatively slide along the rock stratum structural planes, generating an eccentric load on the tunnel as a whole and its support structure. The value of this load is related to factors such as rock strata characteristics, rock strata dip angle, groundwater development, and weak rock strata structural planes.

[0003] In recent years, with the increasing number of tunnels being built, the problem of biased pressure on inclined rock strata has become increasingly common. After tunnel excavation, the integrity of the surrounding rock is lacking, and the biased pressure causes excessive local deformation, making it difficult for general construction methods to meet the excavation requirements or resulting in excessive costs. Currently available tunnel excavation methods and technologies are mostly designed for excavation in general geological strata, rarely addressing biased geological conditions, especially for the construction of shallow-buried, large-section tunnels in inclined rock strata. Summary of the Invention

[0004] To address the shortcomings of the existing technology, the technical problem to be solved by the present invention is to provide a method for excavating a large-section shallow-buried tunnel in inclined strata using a method that combines surface rock reinforcement anchor cables with local rock reinforcement anchors inside the tunnel, and involves sequential excavation of eight excavation faces. This method results in a natural arch formation, good stress distribution, and minimal impact from bias pressure.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for excavating a pilot tunnel for a shallow-buried, large-section tunnel in inclined strata, comprising the following steps:

[0006] Step 1: Conduct construction preparation, including making advance predictions of the surrounding rock and strata conditions and conducting surveying and setting out before excavation;

[0007] Step 2: Install rock reinforcement anchors. On the dip side of the excavated tunnel, several parallel boreholes are arranged from far to near, and the rock reinforcement anchors are installed in the boreholes. The rock reinforcement anchors are perpendicular to the rock structure surface, and the nearest rock reinforcement anchor is 2 to 3 meters away from the tunnel outline. The driving depth of the rock reinforcement anchors should ensure that they cover the tunnel to be excavated along the rock stratum.

[0008] Step 3: Prepare for excavation. Divide the excavation face into three pilot tunnels: left, middle, and right. The right pilot tunnel is a dipping side pilot tunnel. The widths of the left, middle, and right pilot tunnels decrease sequentially, and the excavation line apex between the left and middle pilot tunnels is set at the tunnel apex. The right pilot tunnel is divided into upper and lower excavation faces, and the middle and left pilot tunnels are divided into upper, middle, and lower excavation faces. Excavate eight excavation faces sequentially from the right pilot tunnel to the middle pilot tunnel, and then to the left pilot tunnel from top to bottom. During excavation, initial support for the tunnel walls, temporary invert arches, and initial support for the invert arches are carried out. Temporary partition walls are erected between the right and middle pilot tunnels, and between the middle and left pilot tunnels. The temporary invert arches and partition walls divide the large-section tunnel into several small closed support units.

[0009] During the excavation of the right pilot tunnel, rock reinforcement anchors parallel to the rock reinforcement anchor cables were driven into the rock strata on the right side of tunnels 1 and 2, and temporary support partition walls were erected on the left side of tunnels 1 and 2. The temporary support partition walls on the left side of tunnels 1 and 2 arched to the left, making the cross-section of the right pilot tunnel approximately elliptical with a smooth perimeter.

[0010] During the excavation of the central pilot tunnel, rock reinforcement anchors parallel to the rock reinforcement anchor cables were driven into the top rock layer of tunnel No. 3; the temporary support of the partition wall on the left side of tunnels No. 3, No. 4 and No. 5 arched to the left, so that the overall cross-section of the right central pilot tunnel was approximately elliptical and the surrounding contour was smooth.

[0011] When the left pilot tunnel is being excavated, rock reinforcement anchors parallel to the rock reinforcement anchor cables are driven into the top rock layer of tunnel No. 6; once the excavation of this section of the left pilot tunnel is completed, this section of the tunnel is closed.

[0012] Step 4: After the initial support structure strength and tunnel deformation have reached initial stability, remove the temporary invert arches and partition walls of the excavated tunnel section, pour the secondary support for the tunnel walls for the initial support of each tunnel wall, and pour the secondary support for each invert arch for the initial support of each invert arch, thus completing the construction of the tunnel section.

[0013] Preferably, in step two, the rock stratum reinforcement anchor cables are evenly spaced at intervals of 3 to 5 meters.

[0014] Preferably, the rock reinforcement anchor cable is a shear anchor cable, which consists of anchor cable strands, smooth sleeves, shear reinforcement bars and anchor cable heads; after the rock reinforcement anchor cable is driven into the surface of the stratum, it is fixed to the anchor cable hole wall by anchor cable adhesive, which includes cement, sand and water.

[0015] Preferably, in step three, the bottom widths of the left, middle, and right pilot tunnels are 0.4 times, 0.35 times, and 0.25 times the tunnel span, respectively. The smaller cross-sections are excavated first, and after the excavated cross-sections are arched and stabilized, the excavation area is gradually expanded to prevent large-scale collapse of the surrounding rock at the tunnel face.

[0016] Preferably, in step three, after excavating tunnel ① for 3-5 meters, the right guide tunnel ② is excavated; after excavating tunnel ② for 6-10 meters, the middle guide tunnel ③ is excavated; after excavating tunnel ③ for 3-5 meters, the middle guide tunnel ④ is excavated; after excavating tunnel ④ for 3-5 meters, the middle guide tunnel ⑤ is excavated; after excavating tunnel ⑤ for 6-10 meters, the left guide tunnel ⑥ is excavated; after excavating tunnel ⑥ for 3-5 meters, the left guide tunnel ⑦ is excavated; and after excavating tunnel ⑦ for 3-5 meters, the left guide tunnel ⑧ is excavated.

[0017] Preferably, in step three, the initial support of the tunnel wall includes a steel mesh, initial anchor rods, and initial shotcrete. After drilling and installing the rock reinforcement anchor rods, the shotcrete is applied to the designed thickness. The rock reinforcement anchor rods are installed perpendicular to the rock structure surface. The rock reinforcement anchor rods consist of an anchoring end, a smooth sleeve, an anchor rod body, and an anchor head. After the rock reinforcement anchor rods are driven into the rock strata, they are fixed to the anchor hole wall by anchor rod adhesive.

[0018] Preferably, in step three, the initial support of the invert arch consists of initial shotcrete, erection of steel mesh, and re-shotcrete to the designed thickness, until the initial support construction of the invert arch of the left guide tunnel is completed, thus completing the closed loop of the tunnel's initial support.

[0019] Preferably, in step four, the second-stage support construction of the tunnel walls and the second-stage support construction of the invert arch are carried out, and a layer of cast-in-place reinforced concrete is constructed on the initial support of each tunnel wall and the initial support of each invert arch.

[0020] The beneficial effects of this invention are:

[0021] 1) The tunnel cross-section is divided into several sections and further divided into three pilot tunnels (left, middle, and right) along the width direction. Excavation proceeds gradually from the dip side to the other side, with the width of the three pilot tunnels decreasing sequentially. The smaller cross-sections are excavated first, and after the excavated cross-sections have formed an arch and stabilized, the excavation area is gradually expanded. Eight excavation faces are provided while ensuring sufficient excavation space, so that the main sliding surface and the main layer interface are less exposed in the excavation space, which increases the safety of tunnel construction. Furthermore, the support and expansion excavation are carried out by combining permanent and temporary support, which prevents large-scale collapse of the surrounding rock at the tunnel face. The excavation line apex between the left and middle pilot tunnels is set at the tunnel apex, so that the angle between the excavation line and the tunnel outline is small, the tangency is natural and smooth, and the impact of stress concentration is reduced.

[0022] 2) Dividing the pilot tunnel into eight excavation faces with approximately elliptical cross-sections and smooth perimeter contours can make the arch formation more natural, better stress distribution, and less impact from eccentric pressure, thus avoiding stress concentration and helping to control the settlement of the arch crown. Moreover, after each cross-section is excavated, it forms a closed arch with the excavated part, which is more conducive to controlling deformation.

[0023] 3) The surrounding rock reinforcement technology adopts a combination of surface rock reinforcement anchor cables and local rock reinforcement anchor rods inside the tunnel. The rock reinforcement anchor cables are perpendicular to the rock structure surface. At the same time, the driving depth of the rock reinforcement anchor cables should ensure that they cover the tunnel to be excavated along the rock stratum. The rock reinforcement anchor cables will combine the rock stratum into a whole before the tunnel is excavated to reduce the impact of bias pressure.

[0024] 4) During the initial support setup after excavation, rock reinforcement anchors are installed. The rock reinforcement anchors are parallel to the rock reinforcement anchor cables, i.e., the rock reinforcement anchors are perpendicular to the rock strata surface. This can form a composite beam around the tunnel rock strata, reducing the local bias pressure or deformation caused by the influence of the inclined rock strata surface. Moreover, the nearest rock reinforcement anchor cable is 2 to 3 meters away from the tunnel outline. When the rock reinforcement anchors inside the tunnel cannot be driven perpendicular to the rock strata surface, they can act as anchors to reinforce the rock strata. Both anchor cables and anchors help reduce the impact of bedding bias pressure on large-section tunnels.

[0025] 5) Compared with the traditional large-section tunnel excavation method, it has fewer excavation steps, reduces tunnel excavation disturbance, and has a larger tunnel cross-section, which is more conducive to full-section mechanical construction, thereby improving excavation efficiency. Attached Figure Description

[0026] Figure 1 This is a construction diagram of the present invention;

[0027] Figure 2 A schematic diagram of the structure of rock strata reinforcement anchor cables;

[0028] Figure 3 A schematic diagram of the structure of rock strata reinforcement anchors;

[0029] Figure 4 This is a schematic diagram of excavation and support.

[0030] In the diagram, 1: Rock reinforcement anchor cable, 1-1: Anchor cable hole wall, 1-2: Anchor cable adhesive, 1-3: Shear reinforcement, 1-4: Smooth sleeve, 1-5: Anchor cable head, 1-6: Anchor cable strand, 2: Rock reinforcement anchor rod, 2-1 Anchor end, 2-2: Anchor rod hole wall, 2-3: Anchor rod adhesive, 2-4: Smooth sleeve, 2-5: Anchor rod head, 2-6: Anchor rod body, 3: Initial support of tunnel wall, 4: Temporary invert arch, 5: Temporary support of partition wall, 6: Initial support of invert arch. Detailed Implementation

[0031] To better understand the improvements made by the present invention compared to the prior art, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0032] like Figure 1 As shown, a method for excavating a pilot tunnel for a shallow-buried, large-section tunnel in inclined strata is described, with the following steps:

[0033] Step 1: Prepare for construction by making advance predictions of the surrounding rock and strata conditions and conducting surveying and setting out before excavation.

[0034] Step 2: Install rock reinforcement anchor cables 1. On the dip side of the excavated tunnel, several parallel boreholes are arranged from far to near, and the rock reinforcement anchor cables 1 are installed in the boreholes. The rock reinforcement anchor cables 1 are evenly arranged at intervals of 3 to 5 meters.

[0035] like Figure 2 As shown, the rock stratum reinforcement anchor cable 1 is a shear anchor cable, composed of anchor cable strands 1-6, smooth sleeves 1-4, shear reinforcement bars 1-3, and anchor cable heads 1-5. After the rock stratum reinforcement anchor cable 1 is driven into the surface borehole, it is fixed to the anchor cable hole wall 1-1 by anchor cable adhesive 1-2, which is mainly composed of cement, sand, and water. The rock stratum reinforcement anchor cable can reinforce the dip-sloping rock strata and provide shear resistance to prevent the rock strata from sliding along the structural surface. The rock stratum reinforcement anchor cable 1 is perpendicular to the rock stratum structural surface, and the nearest rock stratum reinforcement anchor cable 1 is 2-3 meters away from the tunnel outline. The driving depth of the rock stratum reinforcement anchor cable 1 should ensure that it covers the tunnel to be excavated along the strike of the rock strata, so that the rock strata are assembled into a whole before tunnel excavation to reduce the influence of eccentric pressure.

[0036] Step 3: Prepare for excavation by dividing the excavation face into three pilot tunnels: left, middle, and right. The right pilot tunnel is a dipping side-guided tunnel. The widths of the left, middle, and right pilot tunnels decrease sequentially, ideally with bottom widths of 0.4, 0.35, and 0.25 times the tunnel span, respectively. Excavate the smaller sections first, and gradually expand the excavation area after the excavated sections have formed an arch and stabilized. The excavation line apex between the left and middle pilot tunnels should be located at the tunnel apex to minimize the angle between the excavation line and the tunnel outline, ensuring a smooth and natural tangency and reducing stress concentration.

[0037] The right pilot tunnel is divided into upper and lower excavation faces, while the middle and left pilot tunnels are divided into upper, middle, and lower excavation faces. Excavation proceeds sequentially from the right pilot tunnel to the middle pilot tunnel, then to the left pilot tunnel, and from top to bottom, covering eight excavation faces. Figure 4 As shown, during excavation, initial support 3, temporary invert arch 4, and initial support 6 for the invert arch are constructed simultaneously. The initial support 6 for the invert arch consists of initial shotcrete, installation of steel mesh, and subsequent shotcrete to the designed thickness. Temporary partition walls 5 are erected between the right and middle pilot tunnels, and between the middle and left pilot tunnels. The temporary invert arch 4 and the temporary partition walls 5 divide the large-section tunnel into several small closed support units.

[0038] First, excavation of the right pilot tunnel No. 1 is carried out. Simultaneously with the excavation of No. 1, initial support 3 and temporary invert arch 4 are installed on the tunnel walls. A temporary partition wall 5 is erected on the left side of No. 1, and rock reinforcement anchors 2 are driven into the rock strata on the right side of No. 1. After excavating 3-5 meters from No. 1, excavation of the right pilot tunnel No. 2 begins. Simultaneously with the excavation of No. 2, initial support 3 and initial invert arch 6 are installed on the tunnel walls. A temporary partition wall 5 is erected on the left side of No. 2, and rock reinforcement anchors 2 are driven into the rock strata on the right side of No. 2. The rock reinforcement anchors 2 on the right side of both No. 1 and No. 2 are parallel to the rock reinforcement anchor cables 1. Due to the angle, rock reinforcement anchors 2 cannot be driven into the top of No. 1; instead, the rock strata are reinforced by the pre-driven rock reinforcement anchor cables 1. The temporary support 5 of the partition wall on the left side of tunnels ① and ② arches to the left, making the cross-section of the right guide tunnel approximately elliptical with a smooth outline.

[0039] After excavating 6-10 meters from tunnel ②, the intermediate pilot tunnel ③ will be excavated. Simultaneously, initial support 3 and a temporary invert arch 4 will be constructed on the tunnel wall during tunnel ③ excavation. A temporary partition wall 5 will be erected on the left side of tunnel ③, and rock reinforcement anchors 2 will be driven into the top rock stratum of tunnel ③. After excavating 3-5 meters from tunnel ③, the intermediate pilot tunnel ④ will be excavated. Simultaneously, a temporary invert arch 4 will be constructed on tunnel ④, and a temporary partition wall 5 will be erected on the left side of tunnel ④. After excavating 3-5 meters from tunnel ④, the intermediate pilot tunnel ⑤ will be excavated. Simultaneously, initial support 6 for the invert arch will be constructed on tunnel ⑤, and a temporary partition wall 5 will be erected on the left side of tunnel ⑤. The rock reinforcement anchors 2 driven into the top rock stratum of tunnel ③ will be parallel to the rock reinforcement anchor cables. The temporary support wall on the left side of tunnels ③, ④ and ⑤ arches to the left, making the overall cross-section of the right central tunnel approximately elliptical with a smooth outline.

[0040] After excavating 6-10 meters in tunnel ⑤, the left pilot tunnel ⑥ will be excavated. Simultaneously with the excavation of tunnel ⑥, initial wall support 3 and temporary invert arch 4 will be installed, and rock reinforcement anchors 2 will be driven into the rock strata on the left side of tunnel ⑥. After excavating 3-5 meters in tunnel ⑥, the left pilot tunnel ⑦ will be excavated. Simultaneously with the excavation of tunnel ⑦, initial wall support 3 and temporary invert arch 4 will be installed. After excavating 3-5 meters in tunnel ⑦, the left pilot tunnel ⑧ will be excavated. Simultaneously with the excavation of tunnel ⑧, initial wall support 3 and initial invert arch support 6 will be installed. The rock reinforcement anchors 2 driven into the top rock strata of tunnel ⑥ are parallel to the rock reinforcement anchor cables 1. Because the rock strata will slide to the left side of the tunnel in case of slippage, rock reinforcement anchors 2 are not required on the left side of tunnels ⑦ and ⑧.

[0041] Once the initial support of the left guide tunnel's invert arch is completed, the initial support of the tunnel will be closed, and the excavation of this section of the left guide tunnel will be completed.

[0042] The initial support 3 of the tunnel wall mainly consists of steel mesh, initial anchor bolts, and initial shotcrete. After drilling and installing the rock reinforcement anchor bolts 2, shotcrete is applied to the designed thickness. The rock reinforcement anchor bolts 2 are installed perpendicular to the rock strata surface. In addition to reinforcing the surrounding rock, they also help to integrate the surrounding rock strata into a unified whole, mitigating the impact caused by the structural surface. Figure 3 As shown, the rock reinforcement anchor 2 is mainly composed of anchor end 2-1, smooth sleeve 2-4, anchor body 2-6 and anchor head 2-5. After the rock reinforcement anchor 2 is driven into the rock stratum, it is fixed to the anchor hole wall 2-2 by anchor adhesive 2-3.

[0043] Step 4: After the initial support structure strength and tunnel deformation have reached preliminary stability, remove the temporary invert arches 4 and temporary partition wall supports 5 from the excavated tunnel section. Then, pour the secondary support for the tunnel walls 3 and the secondary support for the invert arches 6, completing the construction of this tunnel section. For the secondary support of the tunnel walls and invert arches, construct another layer of cast-in-place reinforced concrete on top of the initial support for each tunnel wall and invert arch.

[0044] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for excavating a pilot tunnel for a shallow-buried, large-section tunnel in inclined strata, characterized in that, Includes the following steps: Step 1: Conduct construction preparation, including making advance predictions of the surrounding rock and strata conditions and conducting surveying and setting out before excavation; Step 2: Install rock reinforcement anchors (1). On the dip side of the excavated tunnel, several parallel boreholes are arranged from far to near, and the rock reinforcement anchors (1) are installed in the boreholes. The rock reinforcement anchors (1) are perpendicular to the rock structure surface, and the nearest rock reinforcement anchor (1) is 2 to 3 meters away from the tunnel outline. The driving depth of the rock reinforcement anchors (1) should ensure that the tunnel to be excavated is covered along the rock stratum. Step 3: Prepare for excavation. Divide the excavation face into three pilot tunnels: left, middle, and right. The right pilot tunnel is a dipping side pilot tunnel. The widths of the left, middle, and right pilot tunnels decrease sequentially. The excavation line between the left and middle pilot tunnels is set at the tunnel apex. The right pilot tunnel is divided into two excavation faces: upper and lower. The middle and left pilot tunnels are divided into three excavation faces: upper, middle, and lower. Excavate eight excavation faces sequentially from the right pilot tunnel to the middle pilot tunnel, then to the left pilot tunnel, and from top to bottom. At the same time as excavation, perform initial support (3), temporary invert arch (4), and initial support (6) for the tunnel wall. Temporary support (5) of partition walls is erected between the right and middle pilot tunnels and between the middle and left pilot tunnels. The temporary invert arch (4) and temporary support (5) of the partition walls divide the large-section tunnel into several small closed support units. When the right pilot tunnel is excavated, rock reinforcement anchor rods (2) parallel to the rock reinforcement anchor cable (1) are driven into the rock strata on the right side of tunnels 1 and 2, and temporary support walls (5) are erected on the left side of tunnels 1 and 2; the temporary support walls (5) on the left side of tunnels 1 and 2 arch to the left, so that the cross section of the right pilot tunnel is elliptical and the surrounding contour is smooth. When the central tunnel is excavated, rock reinforcement anchor rods (2) parallel to the rock reinforcement anchor cable (1) are driven into the top rock layer of tunnel No. 3; the temporary support (5) of the partition wall on the left side of tunnel No. 3, tunnel No. 4 and tunnel No. 5 arches to the left, so that the overall cross section of the right central tunnel is elliptical and the surrounding contour is smooth. When the left pilot tunnel is excavated, rock reinforcement anchor rods (2) parallel to the rock reinforcement anchor cable (1) are driven into the top rock layer of tunnel No. 6; when the excavation of the left pilot tunnel is completed, the tunnel section is closed. Step 4: After the initial support structure strength and tunnel deformation reach initial stability, remove the temporary invert arches (4) and partition wall temporary supports (5) of the excavated tunnel section, pour the secondary support of the tunnel wall for the initial support (3) of each tunnel wall, and pour the secondary support of the invert arches for the initial support (6) of each invert arch, thus completing the construction of the tunnel section.

2. The method for excavating pilot tunnels for shallow-buried, large-section tunnels in inclined strata according to claim 1, characterized in that: In step two, the rock strata reinforcement anchor cables (1) are evenly installed at intervals of 3 to 5 m.

3. The method for excavating pilot tunnels for shallow-buried, large-section tunnels in inclined strata according to claim 1, characterized in that: The rock reinforcement anchor cable (1) is a shear anchor cable, which is composed of anchor cable strand (1-6), smooth sleeve (1-4), shear reinforcement (1-3) and anchor cable head (1-5). After the rock reinforcement anchor cable (1) is driven into the surface of the stratum, it is fixed to the anchor cable hole wall (1-1) by anchor cable adhesive (1-2). The anchor cable adhesive (1-2) includes cement, sand and water.

4. The method for excavating pilot tunnels for shallow-buried, large-section tunnels in inclined strata according to claim 1, characterized in that: In step three, the bottom widths of the left, middle, and right pilot tunnels are 0.4 times, 0.35 times, and 0.25 times the tunnel span, respectively.

5. The method for excavating pilot tunnels for shallow-buried, large-section tunnels in inclined strata according to claim 1, characterized in that: In step three, after excavating tunnel ① for 3-5 meters, the right pilot tunnel ② is excavated; after excavating tunnel ② for 6-10 meters, the middle pilot tunnel ③ is excavated; after excavating tunnel ③ for 3-5 meters, the middle pilot tunnel ④ is excavated; after excavating tunnel ④ for 3-5 meters, the middle pilot tunnel ⑤ is excavated; after excavating tunnel ⑤ for 6-10 meters, the left pilot tunnel ⑥ is excavated; after excavating tunnel ⑥ for 3-5 meters, the left pilot tunnel ⑦ is excavated; after excavating tunnel ⑦ for 3-5 meters, the left pilot tunnel ⑧ is excavated.

6. The method for excavating pilot tunnels for shallow-buried, large-section tunnels in inclined strata according to claim 1, characterized in that: In step three, the initial support (3) of the tunnel wall includes a steel mesh, initial support anchors and initial shotcrete. After drilling and installing the rock reinforcement anchors (2), the shotcrete is sprayed to the designed thickness. The rock reinforcement anchors (2) are installed perpendicular to the rock structure surface. The rock reinforcement anchors (2) consist of an anchor end (2-1), a smooth sleeve (2-4), an anchor body (2-6), and an anchor head (2-5). After the rock reinforcement anchors (2) are driven into the rock, they are fixed to the anchor hole wall (2-2) by the anchor adhesive (2-3).

7. The method for excavating pilot tunnels for shallow-buried, large-section tunnels in inclined strata according to claim 1, characterized in that: In step three, the initial support (6) of the invert arch consists of initial shotcrete, erection of steel mesh and re-shotcrete to the designed thickness, until the initial support (6) of the invert arch of the left guide tunnel is completed, and the initial support of the tunnel is completed in a closed loop.

8. The method for excavating pilot tunnels for shallow-buried, large-section tunnels in inclined strata according to claim 1, characterized in that: In step four, the second phase of tunnel wall support and invert arch support construction is carried out. An additional layer of cast-in-place reinforced concrete is then constructed on top of the initial support of each tunnel wall and each invert arch.

Images