Construction method of multi-arch tunnel without central pilot tunnel

Abstract

The present invention discloses a method for constructing a multi-arch tunnel without a central pilot tunnel. The method features a three-step circular excavation method for pre-excavating core soil in a Class V surrounding rock section, followed by a three-step temporary inverted arch excavation method for the subsequent tunnel. Tunnel construction begins with a tunnel with poorer geology and a shallower burial depth. This method is suitable for construction environments with complex geotechnical conditions, can accelerate construction progress, ensure construction quality and safety, and offer low cost.

Description

Technical Field

[0001] The present invention relates to the field of building construction, and more particularly to a construction method for a multi-arch tunnel without a central pilot tunnel. Background Art

[0002] At present, the construction scheme of multi-arch tunnels mostly adopts the advance construction of three pilot tunnels or the middle pilot tunnel. A large number of engineering practices have proved that the construction process is safe and reliable.

[0003] The pilot tunnel can be excavated simultaneously from both ends of the tunnel, with the tunnel being broken through in the middle, or from one end and broken through at the other. Depending on the geological conditions, pilot tunnel excavation can be carried out using either full-section or short-step methods. In Class IV rock with good surrounding rock, full-section pilot tunnel excavation can be used to accelerate construction progress. Short steps can also ensure safety in areas with fractured rock, well-developed joints, and at the tunnel entrance. Regardless of the method used, smooth blasting techniques are employed to minimize disturbance of the pilot tunnel to the surrounding rock on both sides of the main tunnel. Each cycle of advance should be controlled below 1 meter, and should not exceed 1.5 meters in good surrounding rock conditions. Support should closely follow the excavation face, preventing prolonged exposure of the surrounding rock to prevent landslides. Even small landslides in the pilot tunnel can significantly impact the main tunnel excavation. The construction sequence of the intermediate partition wall concrete is the opposite of that of the pilot tunnel excavation. Depending on the site conditions, construction can be carried out from the center of the tunnel toward the ends. To mitigate mutual impact, the excavation of the upper and lower tunnels is generally staggered by approximately 40 meters. Single-span tunnels are constructed in stages using the arch-first, wall-later method. An arch excavation height of 3.5 to 4 meters is ideal. Blasting techniques should minimize the impact on the central partition wall, and the central pilot tunnel should never be used as an open-air surface for blasting. Lower excavation begins with slotting the side walls. After initial arch support is installed, care should be taken to minimize excessive excavation depth in the middle section. A maximum excavation length of two arch frames should be excavated, and initial support should be installed as soon as possible. The surrounding rock should be sealed to prevent collapse caused by arch supports remaining suspended in the air for extended periods.

[0004] The three-pilot tunnel construction method involves excavating a pilot tunnel at the center partition wall. A side pilot tunnel is excavated on both sides of the up and down lines. After the middle and side wall concrete is completed, the main tunnels for the up and down lines are excavated. The excavation method for the side pilot tunnel is similar to that for the center pilot tunnel. After the three pilot tunnels are completed, the main tunnels for the up and down lines are excavated. The main tunnel is excavated using the step method for Class II surrounding rock. The sequence is different from that of the center pilot tunnel method, with the wall first and the arch second, not the arch first and the wall second. During the excavation of the side pilot tunnel, the initial support for the main tunnel side walls has already been constructed. During blasting design, the impact of blasting on the center partition wall and side walls must be minimized. Do not arbitrarily increase the charge or advance length just because the initial support has been completed, as this may cause the initial support to collapse.

[0005] The two construction methods described above demonstrate that the central pilot tunnel method offers simple procedures, minimal temporary support and demolition, a short construction period, and low costs. However, complex geological conditions and surrounding rock formations pose challenges for safe construction. While the three-pilot tunnel method offers the advantages of early closure of the main tunnel support and safer construction, it also presents complex procedures and high construction costs. Both the three-pilot tunnel method and the central pilot tunnel advance construction method suffer from numerous construction steps that interfere with each other, extensive temporary support leading to significant demolition work, poor waterproofing of multi-arch tunnels, and long construction periods. These issues have hindered the development of multi-arch tunnels. Pilot-less multi-arch tunnel construction is a development direction for multi-arch tunnel construction. It has been tested in several domestic tunnels, such as the Baiyun Mountain Double-Arch Tunnel and the Yangquangou Tunnel on the Huangyan Expressway, but the construction process is not yet mature. Summary of the Invention

[0006] The purpose of the present invention is to provide a construction method for a multi-arch tunnel without a central pilot tunnel, thereby reducing construction costs and accelerating construction progress.

[0007] The technical solution adopted by the present invention to solve this technical problem is: a construction method for a multi-arch tunnel without a central pilot tunnel, in which a three-step circular excavation method for reserving core soil is adopted for the first tunnel in the V-level surrounding rock section, and a three-step temporary inverted arch excavation method is adopted for the subsequent tunnel. During tunnel construction, a tunnel with poor geology and shallow burial depth should be constructed first.

[0008] Preferably, the following construction steps are included:

[0009] Step 1: Carry out advance support for the first tunnel with poor geology, then excavate the upper bench arc pilot pit and set up the upper bench initial support; continue to excavate the core soil of the upper bench of the first tunnel; stagger the middle bench of the first tunnel to the left and right, and set up the initial support for the middle bench; stagger the lower bench of the first tunnel to the left and right, and set up the initial support for the lower bench; excavate the reserved core soil of the upper, middle and lower benches, excavate the tunnel bottom in sections, set up the initial support, cast the secondary lining of the first tunnel invert arch, the invert arch filling, lay the waterproof layer, and cast the secondary lining of the first tunnel arch wall;

[0010] Step 2: Excavate the arc-shaped pilot pit on the upper step of the second tunnel, and set up the initial support for the upper step; continue to excavate the core soil of the upper step of the second tunnel, and construct a temporary inverted arch on the upper step of the second tunnel; excavate the middle step of the second tunnel in a staggered manner on the left and right, and set up the initial support for the middle step; excavate the lower step of the second tunnel in a staggered manner on the left and right, and set up the initial support for the lower step; excavate the reserved core soil on the upper, middle and lower steps, excavate the tunnel bottom in sections, and construct the initial support; cast the secondary lining and inverted arch filling of the second tunnel; dismantle the temporary inverted arch of the second tunnel in sections, lay the waterproof layer, and cast the secondary lining of the arch wall of the second tunnel.

[0011] Preferably, when excavating the first and second holes, the cross-sectional area of the reserved core soil is 50% of the excavation area.

[0012] Preferably, mechanical excavation is used for the upper step, the cycle advance is controlled, and initial spraying and support are carried out in time to ensure the stability of the excavation surrounding rock surface and the tunnel face surrounding rock;

[0013] The excavation height of the upper step is 3.7m, and the upper height of the reserved core soil is 1.8m (including the initial support height and the reserved settlement amount). The upper step has a reserved core soil height of 1.9m close to the heading face, and the upper opening is 3m wide. The three sides are sloped according to construction needs. The excavation advance is 1 frame / time, and the step length is controlled at 3 to 5m.

[0014] Preferably, the initial support of the upper step is specifically as follows: under the protection of the advance support of the previous cycle, weak blasting is performed to excavate the part, initial concrete is sprayed, steel mesh is laid, steel frames are erected, radial anchors and locking anchor pipes are drilled, and concrete is sprayed again to the designed thickness;

[0015] The construction of the middle step is as follows: mechanical excavation or weak blasting excavation, initial support around the step: initial spraying of concrete, laying of steel mesh, erection of steel frame, drilling of radial anchors, and re-spraying of concrete to the designed thickness; construction of temporary invert: erection of temporary cross braces, laying of steel mesh, and spraying of concrete to seal the temporary invert;

[0016] The construction of the lower step is specifically as follows: mechanical excavation or weak blasting excavation, initial support around the step: initial spraying of concrete, laying of steel mesh, erection of steel frame, drilling of radial anchor rods and locking anchor pipes, and re-spraying of concrete to the designed thickness.

[0017] The specific construction of the tunnel bottom is: weak blasting to open the part, constructing the initial support around the steps: initial spraying of concrete, erecting steel frame, and re-spraying of concrete to the designed thickness.

[0018] Preferably, the excavation length of each step should be controlled between 2m and 3m.

[0019] Preferably, the middle steps and lower steps of the first and second holes are staggered in excavation, with the staggered length being 5 to 10 meters.

[0020] The present invention includes at least the following beneficial effects: the construction method of the multi-arch tunnel without a central guide tunnel is suitable for construction environments with complex address conditions, can speed up the construction progress, ensure construction quality and construction safety, and has low cost, compared with the existing three-guide tunnel and central guide tunnel construction.

[0021] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the construction procedure of the present invention;

[0023] Figure 2 yes Figure 1 Middle AA section;

[0024] Figure 3 It is a process flow chart;

[0025] Figure 4 A schematic structural diagram of the outer surface of a cathode structure according to an embodiment of the invention;

[0026] Figure 5 Invent the actual construction reserved core soil step diagram. DETAILED DESCRIPTION

[0027] The present invention is described in detail and completely below with reference to the accompanying drawings. Those skilled in the art will be able to implement the present invention based on this description. Before describing the present invention with reference to the accompanying drawings, it should be noted that the technical solutions and technical features provided in various parts of the present invention, including those described below, may be combined with each other unless they conflict.

[0028] In addition, the embodiments of the present invention described below are generally only part of the embodiments of the present invention, rather than all of the embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making any creative efforts should fall within the scope of protection of the present invention.

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific implementation process is as follows:

[0030] like Figures 1 to 5 The present invention provides a construction method for a multi-arch tunnel without a central pilot tunnel, which is applied to the civil construction of a highway in Yunnan Province. The total length of the line is 19.264 km. In a certain section of the tunnel, the leading tunnel adopts a three-step circular excavation method to reserve core soil for the surrounding rock section of V grade, and the trailing tunnel adopts a three-step temporary inverted arch excavation method. Figure 1 The Greek letters (I, II, III...) indicate the excavation sequence, and the Arabic numerals (1, 2, 3...) indicate the lining support sequence. During tunnel construction, the section with poorer geology and shallower burial depth should be constructed first.

[0031] This technical solution may also include the following technical details to better achieve the technical effect: including the following construction steps:

[0032] Step 1: For the first hole with poor geology ( Figure 1The first tunnel section is staggered left and right, and the middle step is staggered left and right. The first step is staggered left and right, and the lower step is staggered left and right. The lower step is staggered left and right, and the lower step is staggered left and right. The core soil is reserved for the upper, middle, and lower steps. The tunnel bottom is excavated in sections, and the initial support is provided. The secondary lining and backfill of the inverted arch of the first tunnel are poured. The waterproof layer is laid, and the secondary lining of the arch wall of the first tunnel is poured.

[0033] Step 2: The second hole ( Figure 1 (In the middle right section), the arc-shaped pilot pit on the upper step is excavated, and the initial support for the upper step is set; the core soil of the upper step of the second tunnel is continued to be excavated, and a temporary invert is constructed on the upper step of the second tunnel; the middle step of the second tunnel is staggered to the left and right, and the initial support is set for the middle step; the lower step of the second tunnel is staggered to the left and right, and the initial support is set for the lower step; the core soil is reserved for the upper, middle and lower steps, the tunnel bottom is excavated in sections, and the initial support is constructed; the secondary lining and invert filling of the second tunnel are poured; the temporary invert of the second tunnel is dismantled in sections, the waterproof layer is laid, and the secondary lining of the arch wall of the second tunnel is poured.

[0034] This technical solution may also include the following technical details to better achieve the technical effect: when excavating the first and second holes, the reserved core soil cross-sectional area is 50% of the excavation area.

[0035] This technical solution may also include the following technical details to better achieve the technical effect: mechanical excavation is used for the upper step to reduce the disturbance to the surrounding rock, the cycle advance is strictly controlled, and initial spraying and support are carried out in a timely manner to ensure the stability of the excavation surrounding rock surface and the tunnel face surrounding rock;

[0036] The excavation height of the upper step is 3.7m, and the upper height of the core soil is reserved at 1.8m (including the initial support height and the reserved settlement amount). The core soil height of the upper step is 1.9m near the face, and the upper opening is 3m wide. The three sides are sloped according to construction needs. The excavation advance is 1 frame / time. The step length is controlled at 3-5m. The arch foot of the upper step steel frame falls on the steel longitudinal beam, and the lower part of the longitudinal beam is strictly prohibited from having any loose slag. The small locking foot conduit is constructed strictly according to the design, and the small locking foot conduit is firmly connected to the steel frame (the small locking foot conduit uses φ20L steel bars and is firmly welded to the steel frame).

[0037] This technical solution may also include the following technical details to better achieve the technical effect: The initial support of the upper step is specifically as follows: under the protection of the advance support of the previous cycle, the excavation part is weakly blasted, the initial concrete is sprayed, the steel mesh is laid, the steel frame is erected, the radial anchor rods and the locking foot anchor pipes are drilled, and the concrete is sprayed again to the designed thickness;

[0038] The construction of the middle step is as follows: mechanical excavation or weak blasting excavation, initial support around the step: initial spraying of concrete, laying of steel mesh, erection of steel frame, drilling of radial anchors, and re-spraying of concrete to the designed thickness; construction of temporary invert: erection of temporary cross braces, laying of steel mesh, and spraying of concrete to seal the temporary invert;

[0039] The construction of the lower step is specifically as follows: mechanical excavation or weak blasting excavation, initial support around the step: initial spraying of concrete, laying of steel mesh, erection of steel frame, drilling of radial anchor rods and locking anchor pipes, and re-spraying of concrete to the designed thickness.

[0040] The specific construction of the tunnel bottom is: weak blasting to open the part, constructing the initial support around the steps: initial spraying of concrete, erecting steel frame, and re-spraying of concrete to the designed thickness.

[0041] This technical solution may also include the following technical details to better achieve the technical effect: Figure 4 It is indicated that the excavation length of each step should be controlled between 2m and 3m.

[0042] This technical solution may also include the following technical details to better achieve the technical effect: the middle steps and lower steps of the first and second holes are staggered on both sides of the excavation, and the staggered length is 5 to 10 meters.

[0043] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A construction method for a multi-arch tunnel without a central pilot tunnel, characterized in that: For the V-level surrounding rock section, the first tunnel adopts the three-step circular excavation method to reserve the core soil, and the subsequent tunnel adopts the three-step temporary invert arch excavation method. During tunnel construction, the tunnel with poor geology and shallow burial depth should be constructed first. The construction steps include: Step 1: Carry out advance support for the first tunnel with poor geology, then excavate the upper bench arc pilot pit and set up the upper bench initial support; continue to excavate the core soil of the upper bench of the first tunnel; stagger the middle bench of the first tunnel to the left and right, and set up the initial support for the middle bench; stagger the lower bench of the first tunnel to the left and right, and set up the initial support for the lower bench; excavate the reserved core soil of the upper, middle and lower benches, excavate the tunnel bottom in sections, set up the initial support, cast the secondary lining of the first tunnel invert arch, the invert arch filling, lay the waterproof layer, and cast the secondary lining of the first tunnel arch wall; Step 2: Excavate the arc-shaped pilot pit on the upper step of the second tunnel, and set up the initial support for the upper step; continue to excavate the core soil of the upper step of the second tunnel, and construct a temporary inverted arch on the upper step of the second tunnel; excavate the middle step of the second tunnel in a staggered manner on the left and right, and set up the initial support for the middle step; excavate the lower step of the second tunnel in a staggered manner on the left and right, and set up the initial support for the lower step; excavate the reserved core soil on the upper, middle and lower steps, excavate the tunnel bottom in sections, and construct the initial support; cast the secondary lining and inverted arch filling of the second tunnel; dismantle the temporary inverted arch of the second tunnel in sections, lay the waterproof layer, and cast the secondary lining of the arch wall of the second tunnel.

2. The method for constructing a multi-arch tunnel without a central pilot tunnel according to claim 1, characterized in that: When excavating the first and second tunnels, the reserved core soil cross-sectional area is 50% of the excavation area.

3. The method for constructing a multi-arch tunnel without a central pilot tunnel according to claim 1, wherein: Mechanical excavation is used for the upper steps, and the cycle advance is controlled. Initial spraying and support are carried out in a timely manner to ensure the stability of the excavation surrounding rock surface and the tunnel face. The excavation height of the upper step is 3.7m, and the upper height of the reserved core soil is 1.8m (including the initial support height and the reserved settlement amount). The core soil height of the upper step close to the heading face is 1.9m, the upper opening is 3m wide, and the three sides are sloped according to construction needs. The excavation advance is 1 frame / time, and the step length is controlled at 3 to 5m.

4. The method for constructing a multi-arch tunnel without a central pilot tunnel according to claim 1, wherein: The initial support of the upper step is as follows: under the protection of the previous cycle of advance support, the excavation part is weakly blasted, the initial concrete is sprayed, the steel mesh is laid, the steel frame is erected, the radial anchor rods and the locking anchor pipes are drilled, and the concrete is sprayed again to the designed thickness; The construction of the middle step is as follows: mechanical excavation or weak blasting excavation, initial support around the step: initial spraying of concrete, laying of steel mesh, erection of steel frame, drilling of radial anchors, and re-spraying of concrete to the designed thickness; construction of temporary invert: erection of temporary cross braces, laying of steel mesh, and spraying of concrete to seal the temporary invert; The construction of the lower step is as follows: mechanical excavation or weak blasting excavation, initial support around the step: initial spraying of concrete, laying of steel mesh, erection of steel frame, drilling of radial anchors and locking anchor pipes, and re-spraying of concrete to the designed thickness; The specific construction of the tunnel bottom is: weak blasting to open the part, constructing the initial support around the steps: initial spraying of concrete, erecting steel frame, and re-spraying of concrete to the designed thickness.

5. The method for constructing a multi-arch tunnel without a central pilot tunnel according to claim 1, wherein: The excavation length of each step should be controlled between 2m and 3m.

6. The method for constructing a multi-arch tunnel without a central pilot tunnel according to claim 1, characterized in that: The middle steps and lower steps of the first and second tunnels are staggered on both sides, with a staggered length of 5 to 10 meters.

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