Construction methods for shallow-buried biased tunnels

Abstract

This invention discloses a method for constructing shallow-buried, biased-pressure tunnels, relating to slope engineering and tunnel engineering, aiming to improve construction safety and operability while saving project investment. The technical solution adopted in this invention is as follows: The method for constructing shallow-buried, biased-pressure tunnels divides the tunnel into biased-pressure and non-biased-pressure sections based on the thickness of the tunnel excavation outline from the ground surface. The biased-pressure section is further divided into open-cut, semi-open / semi-underground, and closed sections. First, slope support is provided for the biased-pressure section, including shallow and deep support for both the open-cut and closed sections. Then, support and excavation are carried out for the semi-open / semi-underground section, including external and internal support, as well as excavation of the tunnel arch where excavation is required. Finally, support and construction are carried out for the closed section. This invention employs a zero-excavation slope method, maximizing slope protection and modifying its mechanical properties; excavation is carried out only after balancing the biased pressure on the slope, reducing the safety risks of excavation construction. This invention is applicable to the design and construction of shallow-buried, biased-pressure tunnels.

Description

Technical Field

[0001] This invention relates to slope engineering and tunnel engineering, specifically a method for constructing shallow-buried bias-pressure tunnels under steep rock. Background Technology

[0002] The geological conditions at the tunnel entrance connecting the new highway to the existing road are as follows: the existing road passes along a river or stream, intersecting at a small angle with a steeply dipping slate bedrock. The upper part of the bedrock contains toppled deformed bodies or thick layers of colluvium. The rock mass is under strong unloading, with a very deep unloading depth exceeding 30 meters. In some areas, the tunnel excavation outline is less than 5 meters below the surface. There is a shallowly buried bias-pressure section at the tunnel entrance for at least 50 meters. The connection between the new highway and the existing road needs to meet connection requirements such as the 3-second safety distance for the exposed roadway at the tunnel entrance. Under these circumstances, a long section at the tunnel entrance will have the problem of shallowly buried bias-pressure.

[0003] There are four main existing methods for tunnel construction: First, excavating part of the slope and using large pipe roofs or pre-grouting small pipes for pre-support to support the tunnel entrance slope, resulting in a semi-open and semi-closed tunnel; Second, not excavating the slope and using large pipe roofs or pre-grouting small pipes for pre-support to support the tunnel entrance slope, resulting in a semi-open and semi-closed tunnel; Third, designing the tunnel according to the Class V surrounding rock bias pressure tunnel design; Fourth, excavating according to conventional methods such as the CRD method and CD method.

[0004] For the tunneling methods described above, regardless of whether slopes are excavated or not, the design and construction methods all have limitations and unreasonable aspects. Local slope excavation damages the ecological environment and may lead to localized landslides, posing a high safety risk. Insufficient support at the tunnel entrance, unreasonable support parameters, and improper tunnel excavation methods can cause greater eccentric pressure problems, resulting in excessive unloading and relaxation of the surrounding rock, inducing landslides. If conventional methods are used, the pressure to maintain traffic flow is high, the construction period is long, and major safety accidents such as tunnel collapses, roof falls, and landslides may occur. Summary of the Invention

[0005] This invention provides a method for constructing shallow-buried biased tunnels, aiming to improve construction safety and operability, and save on project investment.

[0006] The technical solution adopted in this invention is: a method for constructing shallow-buried biased-pressure tunnels. Based on the thickness of the tunnel excavation outline from the ground surface, the tunnel is divided into biased-pressure sections and non-biased-pressure sections. The biased-pressure sections are further divided into open-cut sections, semi-open / semi-closed sections, and closed sections. The construction includes the following steps:

[0007] Step 1: Slope protection for the biased tunnel section, including shallow and deep support for both open and closed tunnel sections.

[0008] Shallow support involves installing slope anchors on slopes above the tunnel arch elevation, laying steel mesh, and then spraying concrete. Deep support involves arranging anchor bundles on slopes above the tunnel arch elevation but below the maximum elevation of the shallow support, laying steel bars along the slope to form a frame, fixing the exposed ends of the anchor bundles to the frame, and then spraying concrete.

[0009] To facilitate construction, shallow and deep supports are installed simultaneously. First, slope anchors and anchor bundles are installed, followed by the frame structure, then the steel mesh, and finally shotcrete. Generally, the maximum elevation of shallow support is 15m to 20m above the tunnel pavement elevation, and the maximum elevation of deep support is 7m to 11m above the tunnel arch elevation.

[0010] To ensure safety during construction, a further step is taken: after the shallow and deep support in step one, a slope toe retaining wall is constructed on the outside of the entire or partial tunnel section. To ensure effective connection between the slope toe retaining wall and the slope anchors, an additional step is taken: exposed sections of the slope anchors located in the slope toe retaining wall area are reserved, with hooks installed on the exposed sections and cast into the slope toe retaining wall.

[0011] Step 2: Support and excavate the semi-open and semi-closed tunnel section.

[0012] S1. External Support: Measure the tunnel entrance section, construct the open-cut tunnel arch frame along the slope, pour balanced eccentric pressure concrete on the slope outside the open-cut tunnel arch frame and close to the tunnel roof, and then support the slope above the tunnel arch in the semi-open / semi-closed tunnel section. For example, the slope above the tunnel arch in the semi-open / semi-closed tunnel section can be supported using the shallow and deep support methods described in Step 1.

[0013] To ensure effective connection between the eccentrically balanced concrete and the slope anchor, the slope anchor located in the eccentrically balanced concrete area has an exposed section, which is equipped with a hook and cast into the eccentrically balanced concrete.

[0014] S2. Tunnel Support: Advance support is provided for the sections of the tunnel arch requiring excavation, and systematic support is provided on the mountain-side. An internal tunnel arch frame is erected, corresponding to the open-cut tunnel arch frame. Advance support utilizes advanced cement mortar anchors or advanced grouting pipes. Systematic support involves constructing systematic anchors on the mountain-side, installing steel mesh, and spraying concrete. Both the internal tunnel arch frame and the open-cut tunnel arch frame in S1 are steel arch frames.

[0015] S3. Excavate the sections of the tunnel arch that require excavation. The excavation method may be either stepped or unstepped. To ensure construction safety, the excavation cycle advance shall not exceed 200cm. To minimize disturbance to the already constructed concrete and reduce the impact on slope stability, blasting shall employ a method of drilling multiple holes and using fewer explosive charges.

[0016] Step 3: Support and construction of the dark tunnel section.

[0017] S1. Advance support is provided for the tunnel arch area. Support frames are erected across the entire cross section of the tunnel arch, sidewalls, and invert. Steel mesh is laid within the tunnel arch wall area. System support is provided within the tunnel arch wall area using anchor bolts, and shotcrete is applied across the entire cross section before secondary lining is constructed.

[0018] S2. Excavation of the tunnel section. The tunnel section is a biased-pressure tunnel. To minimize disturbance to the external slope during excavation and ensure the stability of the tunnel and the external slope, a balanced biased-pressure excavation method with pre-reserved deformation is adopted. This includes the following steps:

[0019] S2.1 divides the excavation section into five areas: the upper part of the mountain side, the lower part of the mountain side, the upper part of the ditch side, the lower part of the ditch side, and the invert section. The following provides a method for dividing these five areas: the boundary between "the upper part of the mountain side - the upper part of the ditch side" and "the lower part of the mountain side - the lower part of the ditch side" is the line connecting the tunnel's arching line; the boundary between "the upper part of the mountain side - the lower part of the mountain side" and "the upper part of the ditch side - the lower part of the ditch side" is a straight line formed by rotating the tunnel's vertical centerline 15° to 30° towards the ditch side around the intersection of this line and the aforementioned line.

[0020] S2.2 Excavate the upper part of the mountain side and provide initial support; excavate the lower part of the mountain side and provide initial support; excavate the upper part of the ditch side and provide initial support; excavate the lower part of the ditch side and provide initial support; excavate the invert arch and provide initial support.

[0021] S3. Carry out tunnel waterproofing and drainage construction.

[0022] S4. Secondary lining construction.

[0023] To shorten the construction period and speed up the construction progress, the present invention can further construct a temporary branch tunnel at the end of the biased tunnel section. The temporary branch tunnel is connected to the position of the non-biased positive tunnel at the end of the biased tunnel section. The construction of the temporary branch tunnel is carried out simultaneously with step one and step two (S1).

[0024] The beneficial effects of this invention are: It fully understands the geological conditions of this type of project and makes full use of the rock, employing a zero-excavation slope method. First, slope support is provided for the biased tunnel section. Shallow and deep support are used to protect the slope as much as possible and modify its mechanical properties, providing a safe environment for subsequent construction in an economical manner. Before excavating the semi-open / semi-closed tunnel section, and before excavating the closed tunnel section, the biased slope pressure is balanced to reduce construction safety risks. This invention utilizes anchorless deep support and large-pipe roof pre-support, saving investment and offering strong operability. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the slope support in this invention.

[0026] Figure 2 This is a schematic diagram of the support structure for the semi-open, semi-closed tunnel section in this invention.

[0027] Figure 3 This is a schematic diagram of the support structure for the dark tunnel section in this invention.

[0028] Figure 4 This is a partition diagram of the excavation section in the balanced bias excavation method of this invention.

[0029] Attached reference numerals: 1. Slope anchor bolt; 2. Anchor bar bundle; 3. Frame skeleton; 4. Balanced eccentric pressure concrete; 5. Slope toe retaining wall; 6. Advanced support; 7. System anchor bolt; 8. Upper part of the mountain side; 9. Lower part of the mountain side; 10. Upper part of the ditch side; 11. Lower part of the ditch side; 12. Inverted arch; 13. Original ground line. Detailed Implementation

[0030] A section of a mountain road was blocked and could not be repaired. After comprehensive assessment, it was decided to build a new tunnel to connect the existing road. The newly constructed tunnel is shallow, with the excavation outline in some areas less than 5 meters below the surface, and a shallow buried bias pressure section of no less than 50 meters long at the tunnel entrance. The invention will be further explained below in conjunction with this project.

[0031] The present invention provides a method for constructing shallow-buried biased tunnels. First, based on the thickness of the tunnel excavation outline from the ground surface, the tunnel is divided into biased tunnel sections and non-biased tunnel sections. For example, sections where the thickness of the tunnel excavation outline from the ground surface is less than 5m are classified as biased tunnel sections. In addition, biased tunnel sections are further divided into open tunnel sections, semi-open and semi-closed tunnel sections, and closed tunnel sections before subsequent construction.

[0032] Step 1: Slope protection for the biased tunnel section, including shallow and deep support for both open and closed tunnel sections.

[0033] Shallow support involves constructing slope anchors 1 on slopes above the tunnel arch elevation, followed by laying steel mesh and then shotcreting. Deep support involves arranging anchor bundles 2 on slopes above the tunnel arch elevation but below the maximum elevation of the shallow support, laying steel bars along the slope to form a frame skeleton 3, and fixing the exposed ends of the anchor bundles 2 to the frame skeleton 3 before shotcreting. The main difference between shallow and deep support lies in the support depth; the length of the anchor bundles 2 is greater than the length of the slope anchors 1. For ease of construction, shallow and deep support are constructed simultaneously: first, slope anchors 1 and anchor bundles 2 are constructed, then the frame skeleton 3 is constructed, followed by laying the steel mesh, and finally shotcreting.

[0034] For both open and closed sections of a biased tunnel, the shallow support elevation range is above the tunnel crown elevation and covers the entire slope area affecting safe construction, for example, 15-20m above the tunnel crown elevation. A specific example of shallow support is provided below; see [link to example]. Figure 1 and Figure 3The shallow support slope anchor 1 uses model number [model number missing]. Cement mortar anchors with a length L = 4.0m / anchor, slope anchors arranged in a staggered pattern with a row spacing of 2m; a single layer of Φ6 steel mesh with a grid spacing of 25cm is hung; C25 concrete is sprayed with a thickness of 12cm.

[0035] For both open and closed sections of the tunnel under eccentric pressure, the elevation range of deep support is above the tunnel crown elevation and below the maximum elevation of shallow support, for example, 6-10 meters above the tunnel crown elevation. A specific example of deep support is provided below; see [link / reference]. Figure 1 and Figure 3 The anchor bundle 2 of the shallow support is of the following type: The length L = 9m / bar, L = 12m / bar, or L = 15m / bar. Anchor bar bundles 2 are arranged in 3-4 rows in a square pattern with a 3m spacing. Corresponding to the position of each anchor bar bundle 2, two anchor bars are installed horizontally and vertically along the slope. The steel bars are reinforced to form a frame skeleton 3. The frame skeleton 3 is firmly welded to the exposed ends of the anchor bar bundle 2 and then wrapped with shotcrete.

[0036] In the semi-open and semi-closed tunnel section of the biased tunnel section, only shallow support is provided for the slope above the tunnel arch, while the slope below the tunnel arch is constructed according to the actual needs of the site.

[0037] To ensure safety during construction, after shallow and deep support, a slope toe retaining wall 5 is constructed on the outer side of the entire or partial section of the tunnel. For example, see... Figure 1 and Figure 3 On the outer side of the severely biased culvert (adjacent to the ditch side), a retaining wall 5 with a height of 5-8m and an average thickness of not less than 1.5m is constructed against the slope. The retaining wall 5 is made of C20 concrete and is poured tightly against the existing rock slope surface. The outer slope ratio is determined according to the actual situation. When the retaining wall 5 is installed, to ensure effective connection between the retaining wall 5 and the corresponding slope anchor 1, an exposed section is reserved for the slope anchor 1 located in the area of ​​the retaining wall 5. The exposed section has a hook and is poured inside the retaining wall 5. For example, a 50cm exposed section is reserved for the slope anchor 1 located in the area of ​​the retaining wall 5, and a 10cm hook is set in the exposed section and poured inside the retaining wall 5. Figure 3 As shown.

[0038] Step 2: Support and excavate the semi-open and semi-closed tunnel section.

[0039] S1. External support: Measure the tunnel entrance section, construct the open tunnel arch frame along the slope, pour balanced eccentric concrete 4 on the slope outside the open tunnel arch frame and close to the top of the tunnel, and then support the slope above the tunnel arch in the semi-open and semi-closed tunnel section.

[0040] Before construction, the opening section is measured, and then the tunnel arch frame is constructed along the slope. The tunnel arch frame is generally a steel arch frame, and the model and spacing of the steel arch frame are selected according to needs. For example, the longitudinal spacing of the tunnel arch frame is 1m, and the circumferential spacing is 50cm. The tunnel arch frames are connected using... For longitudinal reinforcement connections, a single-layer steel mesh with a grid spacing of 25cm and a diameter of Φ6 is laid on the outer side of the tunnel arch frame. Formwork is hung on the inner side of the tunnel arch frame, and C25 concrete is sprayed from bottom to top, with a thickness of 25cm. After constructing the tunnel arch frame, using the arch formed by the tunnel arch frame and the sprayed concrete as the inner formwork, a balanced eccentric pressure concrete 4 is poured on the slope outside the tunnel steel arch, close to the tunnel top. The balanced eccentric pressure concrete 4 sits on a stable foundation at least 50cm below the existing road surface, with a bearing capacity of at least 0.5MPa. The pouring thickness of the balanced eccentric pressure concrete 4 is at least 100cm, and the balanced eccentric pressure concrete 4 is C25 concrete. To ensure effective connection between the balanced eccentric pressure concrete 4 and the corresponding slope anchor rods 1, exposed sections of the slope anchor rods 1 located in the area of ​​the balanced eccentric pressure concrete 4 are reserved. These exposed sections are equipped with hooks and poured into the balanced eccentric pressure concrete 4. For example, in the area of ​​the balanced eccentric pressure concrete 4, the slope anchor 1 has a 50cm exposed section, and the exposed section is equipped with a 10cm hook and poured into the balanced eccentric pressure concrete 4. Figure 2 As shown. After the balanced eccentric pressure concrete 4 is poured, the slope above the tunnel arch in the semi-open and semi-closed tunnel section is supported, and the slope around the upper part of the balanced eccentric pressure concrete 4 is also supported, for example, according to the shallow support and deep support methods in step one.

[0041] S2. In-tunnel support: Advance support is provided for the parts of the tunnel arch that need to be excavated 6, and systematic support is provided for the mountain-adjacent side. In-tunnel arch frames are erected, and the in-tunnel arch frames correspond to the open-cut arch frames.

[0042] Advanced support 6 was constructed at the section of the tunnel arch on the mountainside that required excavation. See also... Figure 2 The advanced support 6 uses advanced cement mortar anchors or advanced grouting small guide pipes. For example, the advanced cement mortar anchor model is... The length L = 4.0m / piece, and the model of the pre-grouting small guide pipe is Φ42x4, with a length L = 4.0m / piece. Specifically, the circumferential spacing of the pre-support 6 is 40cm, and the longitudinal spacing is 200cm. The system support consists of constructing system anchors 7 on the mountain-side, hanging steel mesh, and spraying concrete. For example, the model of system anchor 7 is... The length L = 4.0m / unit; the system anchor bolts are arranged in a staggered pattern with 7 anchor bolts spaced 100cm circumferentially and 100cm longitudinally; a single layer of Φ6 steel mesh with a grid spacing of 25cm is laid, and C25 concrete is sprayed to a thickness of 25cm. The arch frame inside the tunnel is generally a steel arch frame, and the arch frame inside the tunnel is set up in correspondence with the arch frame of the open tunnel in S1.

[0043] S3. Excavate the parts of the tunnel arch that need to be excavated.

[0044] The excavation method is selected rationally based on the engineering geological conditions. When the surrounding rock is poor, excavation is carried out in upper and lower steps; when the surrounding rock is good, no steps are used. To minimize disturbance to the already constructed concrete and reduce the impact on slope stability, blasting is carried out using a method of drilling more holes and using less explosives.

[0045] Step 3: Support and construct the dark tunnel section.

[0046] Based on the actual engineering geological conditions, highway grade and span, determine the support method and construction method for the tunnel section. The following example is a two-lane highway tunnel of Class IV mining highway with a double road width of 7.5m and a tunnel clearance height of 5.5m, designed according to the Class IV deviation surrounding rock bias pressure composite lining design.

[0047] S1. Advance support is provided for the tunnel arch area. Support frames are erected across the entire cross section of the tunnel arch, sidewalls, and invert. Steel mesh is laid within the tunnel arch wall area. System support is provided within the tunnel arch wall area using anchor bolts, and shotcrete is applied across the entire cross section before secondary lining is constructed.

[0048] For advanced support, within a 120° range of the tunnel arch, pre-grouting guide pipes of model Φ42x4 with a length L=450cm / piece are installed at a circumferential spacing of 30cm and a longitudinal spacing of 240cm, or model... Advanced cement mortar anchor bolts with a length L = 4.0m / bolt.

[0049] The support frames are typically made of steel, such as I18 steel frames. These steel frames are arranged along the entire cross-section of the tunnel arch, sidewalls, and invert. The longitudinal spacing of the steel frames is 60cm, and they are spaced circumferentially at 100cm intervals along the entire cross-section. Longitudinal connecting bars are staggered on both the inner and outer sides of the steel frame. Each steel frame has 8 bars of the specified type. Cement mortar anchor bolts with a length of L = 3.5m / bolt are installed near the upper part of the steel frame joint near the tunnel arching line and near the steel frame joint at the bottom of the sidewall. Two bolts are installed at each location, one on each side of the steel frame. The cement mortar anchor bolts are welded to the steel frame using U-shaped steel bars.

[0050] For the steel mesh, a single layer of Φ6 steel mesh is laid within the tunnel arch wall area, with a mesh spacing of 20cm.

[0051] For system support, within the tunnel arch wall area, the following models are installed at circumferential intervals of 100cm and longitudinal intervals of [model number missing]. Cement mortar anchor rods with a length L = 3.5m / rod are used, and C25 concrete is sprayed across the entire section of the tunnel arch and invert arch, with a thickness of 25cm.

[0052] For the secondary lining, the tunnel arch and invert are lined with C35 reinforced concrete with a thickness of 55cm.

[0053] S2. Excavation of the tunnel section. The tunnel section is a biased tunnel. In order to reduce the disturbance of the external slope of the tunnel during excavation and ensure the stability of the tunnel and the external slope, this invention adopts a balanced biased excavation method, which is different from the existing excavation methods. The balanced biased excavation method reserves deformation, for example, a deformation of 12cm. Specifically, it includes the following steps S2.1 to S2.2.

[0054] S2.1 divides the excavation section into five areas: upper part A on the mountain side, lower part B on the mountain side, upper part C on the ditch side, lower part D on the ditch side, and invert section E. See also... Figure 4 The boundary between "Upper part A on the mountain side - Upper part C on the ditch side" and "Lower part B on the mountain side - Lower part D on the ditch side" is the line connecting the tunnel arching line. This boundary is located between the steel frame joints above the tunnel arching line. The boundary between "Upper part A on the mountain side - Lower part B on the mountain side" and "Upper part C on the ditch side - Lower part D on the ditch side" is a straight line formed by rotating the upper section of the tunnel's vertical centerline around the intersection of this line and the aforementioned line, with the upper section rotating 15° to 30° towards the ditch side. The angle formed by the lower section of this boundary and the horizontal line is 60° to 75°.

[0055] S2.2 Excavation and timely support shall be carried out in the following order: excavate the upper part A on the mountain side and provide initial support; excavate the lower part B on the mountain side and provide initial support; excavate the upper part C on the ditch side and provide initial support; excavate the lower part D on the ditch side and provide initial support; excavate the inverted arch E and provide initial support.

[0056] Each section should implement initial support promptly after excavation. Excavation of the next section can only proceed after the initial support is completed. A slight step may be left between the upper part A and the lower part B on the mountain-side, or it may not be left; the decision depends on the stability of the surrounding rock. The excavation advance should be controlled at a spacing of two steel frames, with a maximum excavation advance not exceeding 150cm. A slight step may be left between the upper part C and the lower part D on the ditch-side, or it may not be left; the decision depends on the stability of the surrounding rock. The excavation advance should be controlled at a spacing of one steel frame, with a maximum excavation advance not exceeding 100cm. The lower part D on the ditch-side should be excavated in its entirety, with an excavation advance not exceeding 3m. Excavation should employ a method of multiple drilling, minimal explosive charge, and smooth blasting to minimize disturbance to the surrounding rock.

[0057] S3. Carry out the construction of tunnel waterproofing and drainage. Specifically, construct the tunnel's waterproofing and drainage structures in accordance with the highway tunnel design specifications and design drawings.

[0058] S4. Construction of secondary lining. For example, construction of secondary lining with C35 reinforced concrete.

[0059] The construction period for shallow-buried, biased-pressure tunnels is relatively long. To alleviate the pressure on the construction schedule, temporary adits can be constructed at the end of the biased-pressure section, depending on the actual situation. These adits are located at a greater horizontal depth and in relatively good surrounding rock conditions at the end of the biased-pressure section. The temporary adits connect to the biased-pressure section, allowing for earlier access to the main tunnel for construction. This increases the working face, enabling simultaneous construction of the main tunnel and its entrance. After completing steps one and two (S1), there is a considerable distance between the main tunnel face and the biased-pressure section. Simultaneous construction using temporary adits reduces the impact of excavating the biased-pressure section and accelerates the overall construction progress.

Claims

1. A method for constructing a shallow-buried, biased-pressure tunnel, characterized in that: Based on the thickness of the tunnel excavation outline from the ground surface, the tunnel is divided into biased pressure tunnel sections and non-biased pressure tunnel sections. The biased pressure tunnel sections are further divided into open tunnel sections, semi-open / semi-closed tunnel sections, and closed tunnel sections. The construction includes the following steps: Step 1: Slope protection for the biased tunnel section, including shallow and deep support for both open and closed tunnel sections. Shallow support is as follows: slope anchors (1) are installed on the slope above the tunnel arch elevation, steel mesh is laid, and then concrete is sprayed. Deep support is as follows: anchor bundles (2) are arranged on the slope above the tunnel arch elevation and below the maximum elevation of the shallow support, steel bars are laid along the slope surface, the steel bars form a frame skeleton (3), the exposed end of the anchor bundle (2) is fixedly connected to the frame skeleton (3), and then concrete is sprayed. Shallow and deep support are constructed simultaneously. First, slope anchors (1) and anchor bundles (2) are constructed, then the frame skeleton (3) is constructed, then the steel mesh is laid, and finally the concrete is sprayed. After shallow and deep support, a slope toe retaining wall (5) is constructed on the outside of the entire or partial dark tunnel section. The slope anchor (1) located in the slope toe retaining wall (5) area is reserved with an exposed section. The exposed section is equipped with hooks and poured into the slope toe retaining wall (5). Step 2: Support and excavate the semi-open, semi-closed tunnel section; S1. External support: The tunnel entrance section is measured, and the open tunnel arch frame is constructed along the slope. Balanced eccentric concrete (4) is poured on the slope outside the open tunnel arch frame and close to the top of the tunnel. The slope above the tunnel arch in the semi-open and semi-dark tunnel section is supported according to the shallow support and deep support methods in step one. Among them, the slope anchor (1) located in the area of ​​balanced eccentric concrete (4) has an exposed section. The exposed section is equipped with hooks and poured into the balanced eccentric concrete (4). S2. In-tunnel support: Advance support is provided for the parts of the tunnel arch that need to be excavated, and systematic support is provided for the mountain-adjacent side. In-tunnel arch frames are erected, and the in-tunnel arch frames correspond to the open-cut arch frames. S3. Excavate the parts of the tunnel arch that need to be excavated; Step 3: Support and construction of the dark tunnel section; S1. Advance support is provided for the tunnel arch area. Support frames are erected across the entire cross section of the tunnel arch, sidewalls, and invert. Steel mesh is laid within the tunnel arch wall area. System support is provided within the tunnel arch wall area using anchor bolts, and shotcrete is applied across the entire cross section before secondary lining is constructed. S2. Excavate the section with the dark cave. S3. Carry out tunnel waterproofing and drainage construction; S4. Secondary lining construction.

2. The tunneling method for shallow-buried biased tunnels as described in claim 1, characterized in that: Step 2 S2 must meet at least one of the following conditions: First, the advanced support (6) adopts advanced cement mortar anchor rods or advanced grouting small pipes; Second, the system support is to construct system anchor rods (7) on the mountain side, hang steel mesh and spray concrete; Third, the arch frame inside the tunnel and the open tunnel arch frame in S1 are both steel arch frames.

3. The tunneling method for shallow-buried biased tunnels as described in claim 1 or 2, characterized in that: Step 3, S2, is excavated using the balanced bias excavation method with reserved deformation, specifically including the following steps: S2.1 divides the excavation section into five areas: upper part of the mountain side (A), lower part of the mountain side (B), upper part of the ditch side (C), lower part of the ditch side (D), and inverted arch (E). S2.2 Excavate the upper part (A) of the mountain side and carry out initial support, excavate the lower part (B) of the mountain side and carry out initial support, excavate the upper part (C) of the ditch side and carry out initial support, excavate the lower part (D) of the ditch side and carry out initial support, and excavate the invert arch (E) and carry out initial support.

4. The tunneling method for shallow-buried biased tunnels as described in claim 3, characterized in that: In the balanced bias excavation method, the boundary between "upper part of the mountain side (A) - upper part of the ditch side (C)" and "lower part of the mountain side (B) - lower part of the ditch side (D)" is the line connecting the tunnel arching line. The boundary between "upper part of the mountain side (A) - lower part of the mountain side (B)" and "upper part of the ditch side (C) - lower part of the ditch side (D)" is the straight line of the tunnel vertical centerline around the intersection of the above-mentioned line, with the upper section rotated 15° to 30° towards the ditch side.

5. The method for forming a shallow-buried biased tunnel as described in claim 1 or 2, characterized in that: At the end of the biased tunnel section, a temporary adit is constructed. The temporary adit connects to the position of the non-biased main tunnel at the end of the biased tunnel section. The construction of the temporary adit is carried out simultaneously with S1 in steps one and two.

Images