A tunnel support structure without a central pilot hole and its construction method

Abstract

The present invention is a tunnel support structure without a central pilot tunnel. Its primary support consists of the primary support of the leading tunnel, the primary support of the trailing tunnel, and a cast-in-place special-shaped central partition wall in the middle. To ensure the stability of the primary support system during construction, the special-shaped central partition wall structure is constructed by cast-in-place, and the primary support steel of the cavern is then supported on the special-shaped central partition wall and fixed by a pre-buried support system. The left and right caverns successively form a secondary lining structure according to conventional mountain tunnel excavation technology. The characteristic of the support method of the present invention is that, while excavating without a central pilot tunnel, the method of the special-shaped central partition wall is improved, thereby increasing the lateral stiffness and stability of the special-shaped central partition wall. The support method of the present invention is more reliable and reasonable in terms of force mechanism, and is particularly suitable for the construction of continuous arch tunnels with large cross-sections and poor geological environments.

Description

Technical Field

[0001] The present invention relates to an excavation and support method in mountain tunnel design, and in particular to a tunnel support structure without a central pilot hole and a construction method thereof. Background Art

[0002] In tunnel engineering design, multi-arch tunnels are widely used due to their ease of connection, minimal footprint, minimal environmental impact, and ability to separate uplink and downlink lines. Multi-arch tunnels typically have large cross-sections and spans, resulting in complex structures. Currently, there are two main types of multi-arch tunnels, depending on whether they have a central pilot tunnel or not.

[0003] Construction methods with a central pilot tunnel present challenges such as multiple construction steps, high construction difficulty, and low efficiency. Furthermore, repeated excavation and blasting significantly disturb the surrounding rock, leading to significant drainage issues at the central pilot tunnel wall. A few construction methods without a central pilot tunnel suffer from insufficient central wall stiffness and stability when tunnel sections are large and geological conditions are complex. The sequential excavation of the leading and trailing tunnels can cause eccentric stress on the central wall, leading to cracking or deformation. A novel excavation and support method for large cross-sections and complex geological conditions is urgently needed.

[0004] Patent and literature searches reveal that construction methods without a central guide hole or with an implicit central wall are currently commonly used for this type of project. Patent publication numbers include CN106761836A, CN204152527U, and CN108266191A. These comparative documents include technologies using central guide holes or implicit central walls, but these walls utilize steel frames, which are weak and pose stringent construction requirements. Summary of the Invention

[0005] The purpose of this invention is to provide a tunnel support structure without a central pilot tunnel, which, while ensuring stress resistance and safety, simplifies construction procedures, reduces construction difficulty, and improves efficiency. Compared to primary support structures constructed with a central pilot tunnel, this invention simplifies construction procedures while overcoming challenges such as the quality of drainage and waterproofing of the central wall of a multi-arch tunnel, as well as absolute and relatively uneven settlement of the central wall, arch, and side walls.

[0006] In order to achieve the above-mentioned purpose, the technical solution of the present invention is as follows: a tunnel support structure without a central guide tunnel, including a leading tunnel and a trailing tunnel, the leading tunnel is provided with a primary support steel arch frame, which is characterized in that a cast-in-place special-shaped middle partition wall is arranged on the inner side of the primary support steel arch frame of the leading tunnel close to the side of the trailing tunnel, and a pre-embedded support system is embedded in the special-shaped middle partition wall, the primary support steel arch frame of the trailing tunnel is supported on the special-shaped middle partition wall, and is fixed by the pre-embedded support system.

[0007] Furthermore, the outline of the special-shaped central partition wall consists of four parts: a first special-shaped area outline, a second special-shaped area outline, a third special-shaped area outline and a fourth special-shaped area outline, which are connected in sequence, wherein the first special-shaped area outline is the outer contour line of the tunnel; the second special-shaped area outline is a first arc with a radius of R1, and the first arc is tangent to the reserved deformed outer contour line of the tunnel, wherein the reserved deformed outer contour line of the tunnel is 50 to 100 mm outside the outer contour line of the tunnel; the third special-shaped area outline is a horizontal straight line with a length of s; the fourth special-shaped area outline is a second arc with a radius of R2, the second arc is tangent to the reserved deformed outer contour line of the tunnel, and intersects with the third special-shaped area outline.

[0008] Furthermore, based on the position of the primary steel arch frame for the rear tunnel, a pre-embedded support system is installed along the contour line of the second special-shaped area. The pre-embedded support system includes a steel pre-reserved joint formed by welding an anchor plate to a steel formwork. Anchor bolts are reserved within the anchor plate. The bottom of the anchor plate is welded to the primary steel arch frame for the first tunnel. The pre-embedded support system is bolted to the special-shaped partition wall. The end of the steel arch frame for the rear tunnel is welded to the upper part of the anchor plate. The anchor bolt anchorage length is no less than 1m. The pre-embedded support system is bolted to the special-shaped partition wall, providing a reliable support for the erection of the steel arch frame for the rear tunnel.

[0009] The reinforcement area of ​​cast-in-place special-shaped partition walls must meet the following requirements: 0.25m≤t h ≤1.2m, t v ≤0.25m;

[0010] t h - the lateral horizontal distance between the contour line of the second special-shaped area and the tunnel edge line;

[0011] t v ——The vertical distance between the fourth special-shaped area outline and the bottom of the special-shaped area outline 1.

[0012] Another object of the present invention is to provide a construction method for a tunnel without a central guide tunnel support structure, which can simplify the construction process, reduce the construction difficulty and improve the construction efficiency while ensuring stress and safety.

[0013] The technical solution of the present invention is as follows: a construction method for a tunnel without a central pilot tunnel support structure, characterized in that the support method includes the following steps: A. excavation of the first tunnel and implementation of the initial support; B. formwork construction of the special-shaped central partition wall structure and pre-embedded right tunnel support system; C. excavation of the subsequent tunnel and implementation of the initial support; D. formwork construction of the tunnel secondary lining to complete the main structure of the tunnel.

[0014] Furthermore, a construction method for a tunnel without a central pilot tunnel support structure comprises the following specific steps:

[0015] Excavate the steps on the first tunnel and build the initial steel arch frame for the first tunnel arch;

[0016] Excavate the steps in the leading tunnel, build the initial steel arch frame for the steps in the leading tunnel, weld the steel reserved joints on the initial steel arch frame for the steps in the leading tunnel on the side of the trailing tunnel, and reserve anchor bolts on the steel reserved joints;

[0017] Excavate the steps under the tunnel first, and initially support the steel arch frame under the tunnel first;

[0018] Cast and construct the middle partition wall in batches, and cast the reserved anchor bolts on the reserved joints of the steel sections into the middle partition wall;

[0019] Construct the reinforced concrete structure of the tunnel side wall and inverted arch first;

[0020] The secondary lining of the arch wall is constructed using a formwork trolley;

[0021] The steps on the rear tunnel are excavated, and the arch of the rear tunnel is initially supported by steel arch frame;

[0022] The steps in the rear tunnel are excavated, and the initial steel arch frame is used to support the steps in the rear tunnel. One end of the initial steel arch frame is welded to the reserved joint of the steel;

[0023] The steps under the rear tunnel are excavated and the steel arch frame is initially supported under the steps under the rear tunnel;

[0024] Fill the area above the primary steel arch frame at the lower step of the rear tunnel near the leading tunnel with plain concrete to match the reinforced concrete structure of the rear tunnel inverted arch;

[0025] After the construction, the side walls of the tunnel and the reinforced concrete structure of the inverted arch are constructed;

[0026] The secondary lining of the rear arch wall is constructed using a formwork trolley.

[0027] Compared with the support method without a central guide tunnel in the comparative documents, the present invention enhances the integrity of the central wall and meets the stress and deformation requirements of the first and second tunnel excavation support. In order to ensure the stability of the primary support system during construction, the special-shaped central partition wall structure is constructed with cast-in-place reinforced concrete, which has large lateral rigidity. The primary support steel sections of the cavern are then supported on the special-shaped central partition wall and fixed by a pre-buried support system. The left and right caverns successively form the secondary lining structure according to the conventional mountain tunnel excavation process. The characteristic of the support method of the present invention is that, while there is no central guide tunnel excavation, the method of the special-shaped central partition wall is improved, and the lateral rigidity and stability of the special-shaped central partition wall are increased. The support method of the present invention is more reliable and reasonable in terms of stress mechanism, and is particularly suitable for the construction of continuous arch tunnels with large cross-sections and poor geological environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a cross-sectional view of the working method of the present invention.

[0029] Figure 2It is a cross-sectional view of the primary branch system of the present invention.

[0030] Figure 3 This is a cross-sectional view of the cast-in-situ special-shaped partition wall structure of the present invention.

[0031] Figure 4 This is a structural requirement diagram of the cast-in-situ special-shaped partition wall structure of the present invention.

[0032] Figure 5 This is a schematic diagram of the embedded support system of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0034] A tunnel support structure without a central guide tunnel includes a leading tunnel and a trailing tunnel. The leading tunnel is provided with a primary support. The structure is characterized in that a cast-in-place special-shaped central partition wall is arranged on the inner side of the primary support of the leading tunnel, close to the side of the trailing tunnel. A pre-embedded support system is embedded in the special-shaped central partition wall. The primary support steel of the trailing tunnel is supported on the special-shaped central partition wall and fixed by the pre-embedded support system.

[0035] In one embodiment, the present invention is applied to the excavation and support design of a geologically complex multi-arch tunnel. The characteristics of this type of project are:

[0036] 1) The tunnel project is located in an area with general or poor geology.

[0037] 2) Tunnel engineering requires a large structural cross-section.

[0038] 3) Tunnel engineering has certain requirements on the construction period.

[0039] For such projects, the present invention recommends the use of a tunnel without a central pilot tunnel initial support method, as follows:

[0040] The steps on the pilot tunnel are excavated 1, and the initial steel arch frame of the pilot tunnel arch is supported 2.

[0041] Excavate the steps in the advance tunnel 3, initially support the steel arch frame 4 in the advance tunnel, weld the steel reserved joints on the initial steel arch frame of the steps in the advance tunnel on the side of the rear tunnel, and reserve anchor bolts on the steel reserved joints.

[0042] The steps under the pilot tunnel are excavated 5, and the initial steel arch frame 6 is supported under the steps under the pilot tunnel.

[0043] The special-shaped partition walls of scope 7 are cast in stages and implemented.

[0044] Construct the tunnel side wall and inverted arch reinforced concrete structure first 8.

[0045] The secondary lining of the first arch wall is constructed using a formwork trolley 9.

[0046] The steps on the rear tunnel are excavated 10, and the arch part of the rear tunnel is initially supported by a steel arch frame 11.

[0047] The steps in the rear tunnel are excavated 12, and the initial steel arch frame 13 is used to support the steps in the rear tunnel.

[0048] The steps under the rear tunnel are excavated 14, and the initial steel arch frame 15 is provided for the steps under the rear tunnel.

[0049] The area 16 is filled with plain concrete.

[0050] After construction, the side walls of the tunnel and the reinforced concrete structure of the inverted arch are 17.

[0051] The secondary lining of the rear arch wall is constructed using a formwork trolley 18.

[0052] like Figure 2 As shown, a special-shaped central partition wall 102 is installed within the primary steel arch frame 101 of the leading tunnel, on the side facing the rear tunnel. A pre-buried connecting steel plate 103 is installed at the lower portion of the primary steel arch frame 101 of the leading tunnel, on the side facing the rear tunnel. A pre-buried support system 104 is installed in the middle of the primary steel arch frame 101 of the leading tunnel, on the side facing the rear tunnel. One end of the primary steel arch frame 105 of the rear tunnel is welded to the pre-buried support system 104, and the other end is welded to the pre-buried connecting steel plate 103, providing a reliable support for the erection of the steel arch frame of the rear tunnel. Locking foot steel pipes 106, slanting downward and facing the outer soil, are installed on both the primary steel arch frame of the leading tunnel and the primary steel arch frame of the rear tunnel. The locking foot steel pipes are 4.5 meters long, 50 mm in diameter, and 5 mm thick.

[0053] like Figure 3 As shown, the pre-embedded support system 104 is welded to the side of the rear tunnel of the initial support steel arch frame 101 of the advance tunnel, and then the main steel bars of the special-shaped middle partition wall 102 are tied, and concrete is poured to form a cast-in-place middle wall 108. A mesh is hung and concrete is sprayed 107 in the area above the cast-in-place middle wall 108.

[0054] In order to ensure the overall stiffness, construction operability and construction quality of the cast-in-place middle wall, the contour line of the special-shaped area, the embedded support system and the reinforcement area must meet certain structural requirements. Among them, the contour line of the special-shaped area is mainly composed of four parts: the first special-shaped area contour line A is the outer contour line of the tunnel; the second special-shaped area contour line B is an arc with a radius of R1, and the second special-shaped area contour line B is tangent to the reserved deformation outer contour line of the tunnel; the third special-shaped area contour line C is a horizontal straight line with a length of s; the fourth special-shaped area contour line E is an arc with a radius of R2, and the fourth special-shaped area contour line E is tangent to the reserved deformation outer contour line of the tunnel and intersects with the third special-shaped area contour line C. The embedded support system is set above the second special-shaped area contour line B according to the position of the rear tunnel steel arch frame. The reserved joint of the steel section is formed by welding 16mm thick steel formwork and anchor plate, and the anchor bolt anchoring length is not less than 1m. The reinforcement area of ​​the cast-in-place special-shaped middle partition wall must meet the following requirements: 0.25m≤t h≤1.2m, t v ≤0.25m. The reserved deformation outer contour line of the tunnel is L = 50 ~ 100mm relative to the outer contour line of the tunnel. In this example, the reserved deformation is 80mm. Figure 4 .

[0055] Some size expressions and their meanings are as follows:

[0056] R1=S+s

[0057] R2=R 仰拱 +a

[0058] s=DH

[0059] R1——Radius of contour line 2 of special-shaped area;

[0060] R2——Radius of contour line 4 of special-shaped area;

[0061] S——the distance from the tunnel edge to the tunnel centerline;

[0062] s——the length of the contour line C of the third special-shaped area;

[0063] R 仰拱 —The radius of the invert profile at the bottom of the tunnel;

[0064] a——tunnel reserved deformation;

[0065] D - tunnel clearance;

[0066] H - height of steel arch;

[0067] t h - the lateral horizontal distance between the contour line B of the second special-shaped area and the tunnel edge;

[0068] t v ——The vertical distance between the bottom of the fourth profiled area outline E and the bottom of the first profiled area outline A.

[0069] In the preliminary steel arch frame 4 of the step in the advance tunnel of the present invention, the embedded support system is formed by a combination of an anchor plate 109 with anchor bolts and a steel formwork 110. The anchor plate 109 is a rectangular structure with steel formwork 110 welded to each of its three sides: a rectangular steel formwork welded to the middle side and a triangular steel formwork welded to the other two corresponding sides. A cavity is formed between the anchor plate 109 and the steel formwork 110. The embedded anchor bolts 111 are preferably four 25mm HRB400 steel bars with a preferred anchoring length of 1000mm, connected to the special-shaped middle partition wall. The anchor plate and steel formwork are preferably 16mm thick steel plates. The anchor plate and the three welded steel formworks have reserved joints to form a reliable support for the steel arch frame of the subsequent tunnel. During construction, the anchor plate of the reserved joint of the steel section is first welded to the initial support steel arch frame of the leading hole. Anchor bolts are reserved on the anchor plate, and the anchor bolts extend into the range of the cast-in-place middle wall 108. The cast-in-place middle wall is cast, that is, the reserved joint of the steel section is anchored on the special-shaped middle partition wall. When constructing the steel arch frame of the rear hole, its end is inserted into the cavity formed between the anchor plate 109 and the steel formwork 110, and its end is welded to the anchor plate, so as to form a reliable support for the steel arch frame of the rear hole.

[0070] The special-shaped middle partition wall of the scope 7 of the present invention is cast in batches to ensure sufficient lateral rigidity and stability. The special-shaped area is surrounded by four contour lines. Taking into account factors such as the tunnel clearance, the cast-in-place special-shaped middle partition wall in the area is preferably 2.76m, t h Preferably 1.2m, t v The preferred depth is 0.25m. In areas where cast-in-place is difficult, mesh sprayed concrete 107 is used to enhance the initial support bearing capacity.

[0071] The present invention can overcome the problems of low tunnel construction efficiency, poor quality of drainage construction, and insufficient overall stability of the middle wall while ensuring stress and safety. It is a mountain tunnel support method with a wide range of applications and good economic benefits.

Claims

1. A tunnel support structure without a central pilot tunnel, comprising a leading tunnel and a trailing tunnel, wherein the leading tunnel is provided with a primary support steel arch frame, characterized in that A cast-in-place special-shaped middle partition wall is set on the inner side of the primary steel arch frame of the leading tunnel near the side of the rear tunnel, and a pre-buried support system is embedded in the special-shaped middle partition wall. The primary steel arch frame of the rear tunnel is supported on the special-shaped middle partition wall and fixed by the pre-buried support system; the contour line of the special-shaped middle partition wall consists of four parts: the contour line of the first special-shaped area, the contour line of the second special-shaped area, the contour line of the third special-shaped area and the contour line of the fourth special-shaped area connected in sequence, wherein the contour line of the first special-shaped area is the outer contour line of the tunnel; the contour line of the second special-shaped area is a first arc with a radius of R1, and the first arc is tangent to the outer contour line of the reserved deformation of the tunnel, wherein the outer contour line of the reserved deformation of the tunnel is 50~outward relative to the outer contour line of the tunnel. 100mm; the contour line of the third special-shaped area is a horizontal straight line with a length of s; the contour line of the fourth special-shaped area is a second arc with a radius of R2, the second arc is tangent to the reserved deformation outer contour line of the tunnel, and intersects with the contour line of the third special-shaped area; according to the position of the primary support steel arch frame of the rear tunnel, the embedded support system is arranged on the contour line of the second special-shaped area, the embedded support system includes a steel reserved joint, the steel reserved joint is welded by an anchor plate and a steel formwork, the anchor plate is a rectangular structure, and steel formworks are welded on the three sides of the anchor plate, wherein a rectangular steel formwork is welded on the middle side, and a triangular steel formwork is welded on the other two corresponding sides, a cavity is formed between the anchor plate and the steel formwork, an anchor bolt is reserved in the anchor plate, the bottom of the anchor plate is welded to the primary support steel arch frame of the leading tunnel, the embedded support system is anchored in the special-shaped middle partition wall by bolts, and the end of the primary support steel arch frame of the rear tunnel is welded to the upper part of the anchor plate.

2. The tunnel support structure without a central pilot tunnel according to claim 1, characterized in that: The reinforcement area of ​​cast-in-place special-shaped partition walls must meet the following requirements: 0.25m≤t h ≤1.2m, t v ≤0.25m; t h - the lateral horizontal distance between the contour line of the second special-shaped area and the tunnel edge line; t v ——The vertical distance between the bottom of the outline of the fourth special-shaped area and the outline of the first special-shaped area.

3. The construction method of a tunnel without a central pilot tunnel support structure according to claim 1, characterized in that The construction method includes the following steps: A. excavation of the preliminary tunnel and implementation of the initial support; B. formwork construction of the special-shaped middle partition wall structure and pre-embedded support system of the subsequent tunnel; C. excavation of the subsequent tunnel and implementation of the initial support; D. formwork construction of the tunnel secondary lining to complete the main structure of the tunnel.

4. The construction method according to claim 3, wherein The specific steps are as follows: Excavate the steps on the first tunnel and construct the initial steel arch frame of the first tunnel arch; Excavate the steps in the leading tunnel, initially support the steel arch frame of the steps in the leading tunnel, weld the steel reserved joints on the initial steel arch frame of the steps in the leading tunnel on the side of the trailing tunnel, and reserve anchor bolts on the steel reserved joints; Excavate the steps under the tunnel first, and initially support the steel arch frame under the tunnel first; Cast and construct the middle partition wall in batches, and cast the reserved anchor bolts on the reserved joints of the steel sections into the middle partition wall; Construct the reinforced concrete structure of the tunnel side wall and inverted arch first; The secondary lining of the arch wall is constructed using a formwork trolley; The steps on the rear tunnel are excavated, and the arch of the rear tunnel is initially supported by steel arch frame; The steps in the rear tunnel are excavated, and the initial steel arch frame is used to support the steps in the rear tunnel. One end of the initial steel arch frame is welded to the reserved joint of the steel; The steps under the rear tunnel are excavated and the steel arch frame is initially supported under the steps under the rear tunnel; Fill the area above the primary steel arch frame at the lower step of the rear tunnel near the leading tunnel with plain concrete to match the reinforced concrete structure of the rear tunnel inverted arch; After the construction, the side walls of the tunnel and the reinforced concrete structure of the inverted arch are constructed; The secondary lining of the rear arch wall is constructed using a formwork trolley.

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