A single-side wall pilot tunnel construction method for ultra-large span soft surrounding rock tunnels

Abstract

The invention relates to a single-side wall pilot pit construction method for a super-large span soft surrounding rock tunnel, belonging to the technical field of tunnel construction. The method comprises the following steps: performing a first single-side wall pilot pit excavation with a step distance of L, constructing an advance guide pipe at the tunnel arch top position, sequentially blasting and excavating a side wall pilot pit, excavating an upper step and excavating a lower step with a step distance of L, setting a safety area with a depth of X, spraying concrete toward an area with a depth of L-X along a tunnel opening toward a heading, defining a tunnel arch surface corresponding to a height of H-h with an arc side length of m, defining an area with an arc side length of m on the tunnel arch surface as a first stress concentration area, and defining an area with two arc side lengths of (M-m) / 2 on the remaining part of the tunnel arch surface as a second stress concentration area. A plurality of channels and gaps designed in different stress concentration areas enable stress to be dispersed in time during blasting, thereby solving the problem of more easily generating stress concentration during blasting.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel construction, and in particular relates to a single-side wall pilot pit construction method for an ultra-large span soft surrounding rock tunnel. Background Art

[0002] At present, in the construction of ultra-large span soft rock tunnels, in order to effectively control surface settlement and improve construction safety, most of them adopt the single side wall pilot method. When constructing the single side wall pilot of the tunnel, generally, an advance guide pipe is first constructed at the top arch of the tunnel to enhance construction safety, and then the side wall pilot is excavated by blasting. After the side wall pilot is excavated, initial support is immediately carried out. After the initial support of the side wall pilot is completed, the upper step is blasted to carry out initial support of the arch, and then the lower step is blasted to carry out initial support of the other side wall. After the initial support of the upper and lower steps is completed, the initial support of the empty part of the pilot is removed to complete the construction of a single side wall pilot of one step. In the construction of the single side wall pilot, after completing the construction of a single side wall pilot of one step, it is necessary to carry out construction treatment on the excavated area of ​​this step to form a complete concrete area, and then carry out the next single side wall pilot with the same step. In this way, step-by-step construction is carried out until the entire tunnel construction is completed.

[0003] However, there are some problems with the current single-side wall pilot pit construction method for tunnels: when a complete concrete area is formed in an area of ​​step excavation, when the next single-side wall pilot pit is constructed, blasting may cause damage to the concrete area of ​​the excavated area, especially when facing ultra-large span soft surrounding rock tunnels, the concrete area of ​​the excavated area is large and the surrounding rock is weak. This large area of ​​concrete structure is more likely to produce stress concentration during blasting, resulting in the stress in the local area exceeding the bearing capacity of the material, thereby generating cracks under the blasting vibration. In this regard, a single-side wall pilot pit construction method for ultra-large span soft surrounding rock tunnels is proposed. Summary of the invention

[0004] In order to solve the above-mentioned problems existing in the prior art, the present invention provides a single-side wall pilot pit construction method for an ultra-large span soft surrounding rock tunnel, which solves the problem that blasting in the prior art may cause damage to the concrete area of ​​the excavated area, especially when facing an ultra-large span soft surrounding rock tunnel. This large area of ​​concrete structure is more likely to produce stress concentration during blasting, causing the stress in the local area to exceed the bearing capacity of the material, thereby generating cracks under the blasting vibration.

[0005] The purpose of the present invention can be achieved by the following technical solution: A single-side wall pilot pit construction method for a super-large span soft surrounding rock tunnel comprises the following steps:

[0006] S1: The first single sidewall pilot pit is excavated with a step distance of L. An advance guide pipe is constructed at the top arch of the tunnel. The sidewall pilot pit, upper step and lower step are excavated by blasting in sequence with a step distance of L. At the same time, initial support is provided for the excavated sidewall pilot pit, upper step and lower step. During the initial support, a safety area with a depth of X is set according to the damage caused by blasting. Concrete is sprayed in an area with a depth of L-X along the tunnel opening toward the heading, completing the first single sidewall pilot pit excavation;

[0007] S2: Select the total length of the arc side along the tunnel arch surface as M, the height from the arch top to the ground as H, take the arch top as the starting point and the point with a height of h from the ground as the end point, define the arc side length of the tunnel arch surface corresponding to the height H-h as m, then the lengths of the two arc sides of the remaining part of the tunnel arch surface are both (M-m) / 2, define the area with the arc side length of the tunnel arch surface as m as the first stress concentration area, and the area with the two arc side lengths of the remaining part of the tunnel arch surface as (M-m) / 2 as the second stress concentration area, from top to bottom with spacing d as the tolerance, the first channel, two second channels to two n-th channels are opened in sequence on the concrete area on the first stress concentration area for dispersing the stress concentration caused by blasting according to an arithmetic progression, then take the distance between the n-1-th channel and the n-th channel as the initial spacing, from top to bottom with spacing -b as the tolerance, and open two first gaps, two second gaps to two k-th gaps on the second stress concentration area for dispersing the stress concentration caused by blasting according to an arithmetic progression;

[0008] S3: using the same supporting device to support both sides of the first channel, the two second channels to the two n-th channels and the two first gaps, and the two second gaps to the two k-th gaps;

[0009] S4: Shotcrete the safe area with a depth of X in S1 to complete the initial support, and then carry out the next single side wall pilot pit construction at the tunnel face with a step distance of L;

[0010] S5: Repeat S1-S4 until the entire tunnel construction is completed step by step.

[0011] As a further solution of the present invention, the initial support of the excavated side wall guide pit, upper step and lower step in S1 includes installing steel arch frames, hanging steel mesh and spraying concrete.

[0012] As a further solution of the present invention, a steel arch frame is installed and a steel mesh is hung in the safety area with a depth of X in S1.

[0013] As a further solution of the present invention, the first channel in S2 is arranged at the center of the arch, and the two k-th gaps in S2 are respectively arranged at two ends of the bottom of the tunnel.

[0014] As a further solution of the present invention, the first channel, the two second channels to the two nth channels, the two first gaps, and the two second gaps to the two kth gaps in S2 are opened after the concrete in the area with a depth of L-X is completely solidified.

[0015] As a further solution of the present invention, when spraying concrete on the safety area with a depth of X in S4, a concrete spraying mechanism with a spraying width of A is used for spraying, and the safety area with a depth of X is divided into a first area with a width of A, a second area with a width of A to an nth area with a width of A, and the spraying mechanism is used to spray the first area with a width of A, the second area with a width of A to the nth area with a width of A and the odd-numbered areas with a width of A in sequence, and then the first area with a width of A, the second area with a width of A to the nth area with a width of A and the even-numbered areas with a width of A in sequence.

[0016] As a further solution of the present invention, the supporting device in S3 includes a supporting plate and a plurality of supporting rods, one end of each of the supporting rods is provided with an elastic pad, and the other ends of each of the supporting rods are hinged to the same supporting plate, and the supporting plate, the plurality of supporting rods and the elastic pad cooperate with each other to form an inner wall of the tunnel separated by the first channel, two second channels to two nth channels and two first gaps, and two second gaps to two kth gaps into a whole.

[0017] As a further solution of the present invention, the elastic pad is an arc-shaped structure, and the arc-shaped structure of the elastic pad is adapted to the arc of the inner wall of the tunnel.

[0018] As a further solution of the present invention, the hinge between the support rod and the support plate is a detachable structure.

[0019] The beneficial effects of the present invention are:

[0020] The first single side wall pilot pit is excavated with a step distance of L, an advance guide pipe is constructed at the top arch of the tunnel, and the side wall pilot pit, upper step and lower step are excavated in sequence with a step distance of L. According to the damage caused by the blasting, a safe area with a depth of X is set, and concrete is sprayed in an area with a depth of L-X along the tunnel opening toward the heading. The total length of the arc side along the tunnel arch surface is M, and the height from the arch top to the ground is H. The arch top is used as the starting point and the point with a height of h from the ground is used as the end point. The length of the arc side of the tunnel arch surface corresponding to the height of H-h is defined as m, and the lengths of the two arc sides of the remaining part of the tunnel arch surface are both (M-m) / 2. The area with an arc side length of m on the tunnel arch surface is defined as the first stress concentration area, and the two arc sides of the remaining part of the tunnel arch surface are defined as (M-m) / 2. The area where the length of each arc side is (M-m) / 2 is the second stress concentration area. According to an arithmetic progression, a first channel, two second channels to two n-th channels are opened in sequence on the concrete area on the first stress concentration area for dispersing the stress concentration caused by blasting. Then, with the distance between the n-1-th channel and the n-th channel as the initial spacing, two first gaps, two second gaps to two k-th gaps are opened on the second stress concentration area for dispersing the stress concentration caused by blasting according to an arithmetic progression. By designing a number of channels and gaps in different stress concentration areas, stress can be dispersed in time during blasting, thereby solving the problem that stress concentration is more likely to occur during blasting, resulting in the stress in the local area exceeding the bearing capacity of the material, thereby generating cracks under the blasting vibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0022] Figure 1 It is a schematic diagram of the single side wall pilot pit construction method of the present invention;

[0023] Figure 2 It is a schematic diagram of the structure of the supporting device of the present invention.

[0024] Description of main component symbols:

[0025] In the figure: 1. support plate; 2. support rod; 3. elastic pad. DETAILED DESCRIPTION

[0026] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0027] See also Figure 1 - Figure 2 This embodiment provides a single-side wall pilot pit construction method for a super-large span soft surrounding rock tunnel, comprising the following steps:

[0028] S1: The first single side wall pilot pit is excavated with a step distance of L, an advance guide pipe is constructed at the top arch of the tunnel, and the side wall pilot pit, upper step and lower step are excavated in sequence by blasting with a step distance of L. At the same time, the excavated side wall pilot pit, upper step and lower step are respectively provided with initial support. During the initial support, a safety area with a depth of X is set according to the damage caused by blasting, and concrete is sprayed in an area with a depth of L-X along the tunnel opening toward the face of the heading to complete the first single side wall pilot pit excavation. The purpose of setting a safety area with a depth of X here is that since blasting is likely to affect the excavated area, the design of this safety area with a depth of X can relatively reduce the impact of blasting, and the setting of the safety area with a depth of X here needs to be designed according to the impact range of the explosives used for blasting. In addition, when excavating the side wall pilot pit, initial support needs to be carried out immediately after the side wall pilot pit is excavated;

[0029] S2: Select the total length of the arc side along the tunnel arch surface as M, the height from the arch top to the ground as H, take the arch top as the starting point and the point with a height of h from the ground as the end point, define the arc side length of the tunnel arch surface corresponding to the height H-h as m, then the lengths of the two arc sides of the remaining part of the tunnel arch surface are both (M-m) / 2, define the area with the arc side length of the tunnel arch surface as m as the first stress concentration area, and the area with the two arc side lengths of the remaining part of the tunnel arch surface as (M-m) / 2 as the second stress concentration area, from top to bottom with spacing d as the tolerance, the first channel, two second channels to two n-th channels are opened in sequence on the concrete area on the first stress concentration area for dispersing the stress concentration caused by blasting according to an arithmetic progression, then take the distance between the n-1-th channel and the n-th channel as the initial spacing, from top to bottom with spacing -b as the tolerance, and open two first gaps, two second gaps to two k-th gaps on the second stress concentration area for dispersing the stress concentration caused by blasting according to an arithmetic progression;Since the present application is aimed at ultra-long span soft rock tunnels, the size of h is designed to be one third of H, because ultra-long span soft rock tunnels are usually elliptical, and this shape forms a natural stress concentration area at one third of the top. This is because at this position, the radius of curvature of the tunnel is the smallest, so the load per unit area is the largest, and the weight of the rock and soil covering the tunnel will exert pressure downward, and this pressure is most significant at one third of the top of the tunnel. Since gravity is vertically downward, the pressure of the rock and soil in the area near the top of the tunnel will be transmitted through a smaller area, resulting in stress concentration. Therefore, the stress at this one third of the height from the top of the tunnel is easy to concentrate, that is, the first stress In the stress concentration area, the first channel, two second channels, and two nth channels are opened in sequence on the concrete area on the first stress concentration area with a spacing d as the tolerance from top to bottom according to an arithmetic progression. By opening multiple channels on the concrete area at the top and bottom of the tunnel, the stress generated by the blasting can be effectively dispersed to each channel, thereby avoiding local damage caused by stress concentration. Especially in the soft surrounding rock environment, the stability of the surrounding rock is poor. The use of arithmetic progression division can better control the risks in the construction process. The equal spacing of the channels can ensure the orderliness and safety of the construction and prevent the instability of the surrounding rock caused by improper construction. -b is the tolerance, and two first gaps, two second gaps to two kth gaps are opened in the second stress concentration area according to an arithmetic progression to disperse the stress concentration caused by blasting. The purpose of this design is that the bottom of the tunnel is prone to stress concentration because it needs to bear the load transmitted from above. It is also an area where stress is easily concentrated. The weak surrounding rock itself has low strength and small deformation modulus, and is more likely to deform under stress and form stress concentration. At the bottom of the tunnel, this weak characteristic is more likely to cause local stress concentration and is also easily damaged during blasting. Therefore, from top to bottom, with a spacing of -b as the tolerance, two first gaps, two second gaps to two kth gaps are opened in the second stress concentration area according to an arithmetic progression to disperse the stress concentration caused by blasting. From the second gap to the two kth gaps, the middle part of the tunnel is a relatively uniform circular or nearly circular straight wall structure, and its stress distribution is relatively uniform. In addition, the middle part is not directly affected by the gravity of the top rock mass, nor does it directly bear the bottom reaction force. Therefore, the stress concentration phenomenon is not as obvious as the top and bottom. Therefore, the above design is adopted. The spacing d here is the tolerance, which represents the increase, and the spacing -b is the tolerance, which represents the decrease. The size of d and b is considered according to the actual size of the tunnel and the force. The size of the channel on the first stress concentration area and the gap on the second stress concentration area is designed according to the actual size of the ultra-large span soft surrounding rock tunnel, and needs to be designed according to the specific conditions of the soft surrounding rock.

[0030] In addition, the design of channels and gaps will reduce the stability of the tunnel. In order to avoid the reduction of stability, the initial support of the excavated sidewall pilot pit, upper step and lower step in S1 includes the installation of steel arches, hanging steel mesh and shotcrete. Although the safety area with a depth of X in S1 is not sprayed with concrete, steel arches and steel mesh are installed. The steel arches and steel mesh can further improve the stability of the tunnel.

[0031] S3: The same supporting device is used to support both sides of the first channel, the two second channels to the two nth channels, the two first gaps, and the two second gaps to the two kth gaps. Here, the excavated areas are connected as one by the supporting device, which further reduces the effect of the channels and gaps on reducing the stability of the tunnel, ensuring the stability of the ultra-large span soft rock tunnel;

[0032] S4: Shotcrete the safe area with a depth of X in S1 to complete the initial support, and then carry out the next single side wall pilot pit construction at the tunnel face with a step distance of L;

[0033] S5: Repeat S1-S4 until the entire tunnel construction is completed step by step;

[0034] The design of the above steps S1-S5 is based on the problems existing in the current tunnel single-side wall pilot pit construction method. The problems existing in the current tunnel single-side wall pilot pit construction method are: after a complete concrete area is formed in an area of ​​step excavation, when the next single-side wall pilot pit construction is carried out, blasting may cause damage to the concrete area of ​​the excavated area, especially when facing an ultra-large span soft surrounding rock tunnel, the concrete area of ​​the excavated area is large and the surrounding rock is weak. This large area of ​​concrete structure is more likely to produce stress concentration during blasting, resulting in the stress in the local area exceeding the bearing capacity of the material, thereby generating cracks under the blasting vibration.

[0035] In order to solve the above problem, in this embodiment, the first single side wall pilot pit is excavated with a step distance of L, an advance guide pipe is constructed at the top arch of the tunnel, and the side wall pilot pit, the upper step and the lower step are excavated in sequence with a step distance of L. According to the damage caused by the blasting, a safe area with a depth of X is set, and concrete is sprayed along the tunnel mouth toward the heading to the area with a depth of L-X. The total length of the arc side along the tunnel arch surface is M, and the height H from the arch top to the ground is selected. The arch top is used as the starting point to the point with a height of h from the ground. The length of the arc side of the tunnel arch surface corresponding to the height of H-h is defined as m, and the lengths of the two arc sides of the remaining part of the tunnel arch surface are both (M-m) / 2. The area with an arc side length of m on the tunnel arch surface is defined as the first stress concentration area, and the remaining part The area where the lengths of the two arc sides of the divided tunnel arch surface are both (M-m) / 2 is the second stress concentration area. According to an arithmetic progression, a first channel, two second channels to two n-th channels are opened in sequence on the concrete area on the first stress concentration area for dispersing the stress concentration caused by blasting. Then, with the distance between the n-1-th channel and the n-th channel as the initial spacing, two first gaps, two second gaps to two k-th gaps are opened on the second stress concentration area for dispersing the stress concentration caused by blasting according to an arithmetic progression. By designing a number of channels and gaps in different stress concentration areas, stress can be dispersed in time during blasting, thereby solving the problem that stress concentration is more likely to occur during blasting, resulting in the stress in the local area exceeding the bearing capacity of the material, thereby generating cracks under the blasting vibration.

[0036] It should be noted that the above steps S1-S5 are only part of the steps in the construction of ultra-large span soft rock tunnels using the single side wall pilot method, and do not include all the steps. When the ultra-large span soft rock tunnel is constructed using the single side wall pilot method, the main steps are divided into the following stages:

[0037] (1) Conduct a detailed geological survey of the construction site to understand the characteristics of the surrounding rock, design a tunnel construction plan, including the shape, size, and construction steps of the single-sidewall pilot pit, and prepare the equipment and materials required for construction;

[0038] (2) Construction of advanced conduit at the top arch of the tunnel: construct an advanced conduit at the top arch of the tunnel to enhance construction safety and reduce the risk of surrounding rock collapse;

[0039] (3) Excavation of side wall pilot pit. The excavation of side wall pilot pit is usually divided into two parts: the upper section and the lower section. The excavation is carried out quickly by drilling holes with hand pneumatic drills and loading explosives for detonation.

[0040] (4) During the excavation process, attention should be paid to maintaining the stability of the pilot pit shape and the initial support of the side wall pilot pit. Anchor support, steel mesh, arch support, and concrete spraying should be carried out in the side wall pilot pit to form an initial support system;

[0041] (5) Excavation of the upper section of the main tunnel. After the initial support of the side wall pilot pit is completed, the excavation of the upper section of the main tunnel is carried out. The same excavation method as the side wall pilot pit is adopted, and the connection part with the side wall pilot pit is ensured to be stable. The initial support of the upper section of the main tunnel is carried out;

[0042] (6) Carry out anchor support, steel mesh hanging and concrete spraying on the upper section of the main tunnel, excavate the lower section of the main tunnel, and carry out initial support on the lower section of the main tunnel in the same way as the upper section. Carry out initial support on the side walls and inverts of the tunnel to ensure the stability of the entire section, and construct geotextiles and waterproof boards;

[0043] (7) After the initial support is completed, geotextiles and waterproof sheets are laid to prevent water penetration, and steel bars and formwork are installed and concrete is poured. Steel bars and formwork are installed according to design requirements, and concrete is poured to form the inner lining;

[0044] (8) Monitoring, measurement and adjustment: During the construction process, monitoring and measurement are carried out to timely understand the stability of the surrounding rock and support structure, and the construction plan is adjusted according to the monitoring data to ensure construction safety;

[0045] (9) Remove temporary support. When the initial support of the entire section is closed into a ring and the stability meets the requirements, remove the temporary support and finish the construction.

[0046] In addition, when blasting a super-large span soft rock tunnel, the mechanical properties of the soft rock are relatively poor, and its shear, compression and tensile strength are low.

[0047] Blasting operations will generate stress waves in the surrounding rock. During the propagation process, these stress waves will be reflected and refracted at geometric mutation locations such as the center and bottom of the arch, causing stress to increase at these locations. The center of the tunnel arch is the highest point of the arch structure, and the bottom of the tunnel is the foundation supporting the entire arch structure. In the arch structure, the highest point and the supporting point are subject to the greatest force, so stress concentration is easily generated in these areas. In order to solve this problem, in one embodiment, the first channel in S2 is set at the center of the arch, and the two k-th gaps in S2 are respectively set at the two ends of the bottom of the tunnel. Through the design of the first channel and the two k-th gaps, the stress is dispersed, thereby reducing the stress caused by reflection and refraction at geometric mutation locations such as the center and bottom of the arch.

[0048] One point that needs to be noted is that when opening channels and gaps on the inner wall of the tunnel, how to open them and when to open them in order to minimize the impact on the stability of the tunnel is particularly important, especially for ultra-large span soft rock tunnels, this issue needs to be considered more during construction. In this regard, in one embodiment, the opening of the first channel, two second channels to two n-th channels, two first gaps, and two second gaps to two k-th gaps in S2 is carried out after the concrete in the area with a depth of L-X is completely solidified. After the concrete in the area with a depth of L-X is completely solidified, the excavated tunnel forms a relatively stable whole. At this time, opening channels and gaps on the inner wall of the tunnel will reduce the impact on the overall stability.

[0049] When spraying concrete, in order to prevent the blasting in the next step of tunnel excavation from damaging the connection between the solidified concrete in the previous step and the excavation face, a safety area with a depth of X is designed. However, after the next step of excavation, when spraying concrete in the previous safety area with a depth of X, the vibration of the blasting may cause unevenness on the inner wall of the tunnel. At this time, if a conventional spraying method is used when spraying concrete, it is easy to cause uneven spraying. In order to deal with this problem, in one embodiment, when spraying concrete in the safety area with a depth of X in S4, a concrete spraying mechanism with a spraying width of A is used for spraying, and the safety area with a depth of X is divided into the first The area with width A, the second area with width A to the nth area with width A, the first area with width A, the second area with width A to the odd-numbered areas with width A in the nth area with width A are sprayed in sequence through the spraying mechanism, and then the first area with width A, the second area with width A to the even-numbered areas with width A in the nth area with width A are sprayed in sequence. The spraying mechanism here is an existing concrete spraying machine, and considering that large machinery cannot enter during the construction of a single-side wall pilot pit of a super-large span soft surrounding rock tunnel, the concrete spraying machine here is small and specially used to deal with local areas such as safety areas.

[0050] It is worth mentioning that when constructing a single-side wall pilot tunnel, generally, after the side wall pilot tunnel is excavated, a supporting structure is used to support it. After the upper and lower steps are excavated, the supporting structure is taken out, and then the heading face is blasted to excavate the next step. However, for ultra-large span soft surrounding rock tunnels, the cross-sectional size of the tunnel itself is large and the self-stabilizing ability of the soft surrounding rock is poor. Even if steel arch frames are installed, steel meshes are hung and shotcrete is sprayed, surrounding rock deformation may still occur during the blasting process, affecting its stability. In order to solve this problem, in one embodiment, the supporting device in S3 includes a supporting plate 1 and a plurality of supporting rods 2, one end of each of the supporting rods 2 is provided with an elastic pad 3, and the other ends of each of the supporting rods 2 are hinged to the same supporting plate 1, and the supporting plate 1, the plurality of supporting rods 2 and the elastic pad 3 are hinged to each other. By cooperating with each other, the inner wall of the tunnel separated by the first channel, the two second channels to the two nth channels and the two first gaps, and the two second gaps to the two kth gaps form a whole. Through the design of the support plate 1 and the plurality of support rods 2, there is a support rod 2 at each channel and gap to connect the outside of the channel and the gap, which is equivalent to connecting the inner wall of the tunnel into a whole while providing support for the entire inner wall of the tunnel. There can be several support devices here, which are placed at different positions in the tunnel. The more support positions, the better the stability. The number of this support device needs to be determined according to the size of the area affected by the blasting explosives used, and an elastic pad 3 is provided at one end of the support rod 2. The purpose is to ensure that when the vibration generated by the blasting causes the inner wall of the tunnel to tend to sink, the existence of the support rod 2 will not cause damage to the inner wall of the tunnel.

[0051] In addition, in order to ensure that the supporting device can press the inner wall of the tunnel without leaving any gaps, the elastic pad 3 is designed to be an arc-shaped structure, and the arc-shaped structure of the elastic pad 3 is adapted to the arc of the inner wall of the tunnel. In addition, after the first excavation with a step distance L, the supporting device is used for support. After the second excavation with a step distance L, the supporting device at the first excavation needs to be removed. Therefore, the hinge between the support rod 2 and the support plate 1 is a detachable structure. The detachable structure here is connected by a rotating shaft. The rotating shaft can make the support rod 2 and the support plate 1 hinged, and the rotating shaft is fixed to the support plate 1 by fastening bolts. The rotating shaft and the fastening bolts are rotatably connected.

[0052] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A single-side wall pilot pit construction method for a super-large span soft surrounding rock tunnel, characterized in that: The following steps are involved: S1: The first single sidewall pilot pit is excavated with a step distance of L. An advance guide pipe is constructed at the top arch of the tunnel. The sidewall pilot pit, upper step and lower step are excavated by blasting in sequence with a step distance of L. At the same time, initial support is provided for the excavated sidewall pilot pit, upper step and lower step. During the initial support, a safety area with a depth of X is set according to the damage caused by blasting. Concrete is sprayed in an area with a depth of L-X along the tunnel opening toward the heading, completing the first single sidewall pilot pit excavation; S2: Select the total length of the arc side along the tunnel arch surface as M, the height from the arch top to the ground as H, take the arch top as the starting point and the point with a height of h from the ground as the end point, define the arc side length of the tunnel arch surface corresponding to the height H-h as m, then the lengths of the two arc sides of the remaining part of the tunnel arch surface are both (M-m) / 2, define the area with the arc side length of the tunnel arch surface as m as the first stress concentration area, and the area with the two arc side lengths of the remaining part of the tunnel arch surface as (M-m) / 2 as the second stress concentration area, from top to bottom with spacing d as the tolerance, the first channel, two second channels to two n-th channels are opened in sequence on the concrete area on the first stress concentration area for dispersing the stress concentration caused by blasting according to an arithmetic progression, then take the distance between the n-1-th channel and the n-th channel as the initial spacing, from top to bottom with spacing -b as the tolerance, and open two first gaps, two second gaps to two k-th gaps on the second stress concentration area for dispersing the stress concentration caused by blasting according to an arithmetic progression; S3: using the same supporting device to support both sides of the first channel, the two second channels to the two n-th channels and the two first gaps, and the two second gaps to the two k-th gaps; S4: Shotcrete the safe area with a depth of X in S1 to complete the initial support, and then carry out the next single side wall pilot pit construction at the tunnel face with a step distance of L; S5: Repeat S1-S4 until the entire tunnel construction is completed step by step; The opening of the first channel, the two second channels to the two nth channels, the two first gaps, and the two second gaps to the two kth gaps in S2 is carried out after the concrete in the area with a depth of L-X is completely solidified; When spraying concrete on the safety area with a depth of X in S4, a concrete spraying mechanism with a spraying width of A is used for spraying, and the safety area with a depth of X is divided into a first area with a width of A, a second area with a width of A to an nth area with a width of A, and the spraying mechanism is used to spray the odd-numbered areas with a width of A in the first area with a width of A, the second area with a width of A to the nth area with a width of A in sequence, and then the even-numbered areas with a width of A in the first area with a width of A, the second area with a width of A to the nth area with a width of A in sequence.

2. The single-side wall pilot pit construction method for a super-large span soft surrounding rock tunnel according to claim 1 is characterized in that: The initial support of the excavated sidewall guide pit, upper step and lower step in S1 includes installing steel arch frames, hanging steel mesh and spraying concrete.

3. The single-side wall pilot pit construction method for a super-large span soft surrounding rock tunnel according to claim 2 is characterized in that: A steel arch frame and a steel mesh are installed in the safety area with a depth of X in S1.

4. The single-side wall pilot pit construction method for a super-large span soft rock tunnel according to claim 1 is characterized in that: The first channel in S2 is arranged at the center of the vault, and the two k-th gaps in S2 are arranged at the two ends of the bottom of the tunnel respectively.

5. The single-side wall pilot pit construction method for a super-large span soft surrounding rock tunnel according to claim 1 is characterized in that: The support device in S3 includes a support plate and a plurality of support rods, one end of each of the support rods is provided with an elastic pad, and the other ends of each of the support rods are hinged to the same support plate, and the support plate, the plurality of support rods and the elastic pad cooperate with each other to form an inner wall of the tunnel separated by the first channel, the two second channels to the two nth channels and the two first gaps, and the two second gaps to the two kth gaps into a whole.

6. The single-side wall pilot tunnel construction method for a super-large span soft surrounding rock tunnel according to claim 5 is characterized in that: The elastic pad is an arc-shaped structure, and the arc-shaped structure of the elastic pad is adapted to the arc shape of the inner wall of the tunnel.

7. The method for constructing a single-side wall pilot pit for a super-large-span soft rock tunnel according to claim 5, characterized in that: The hinge between the support rod and the support plate is a detachable structure.

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