Tunnel combined supporting structure suitable for high ground stress condition and construction method of tunnel combined supporting structure

Abstract

The invention relates to the technical field of tunnel supporting, in particular to a tunnel combined supporting structure suitable for high ground stress conditions and a construction method of the tunnel combined supporting structure. A plurality of rectangular steel pipes are vertically arranged between a tunnel and surrounding rock, an anchor rod is arranged between every two rectangular steel pipes, and V-shaped grooves are formed in the ends, close to the surrounding rock, of the rectangular steel pipes; a reinforcing mesh is welded to the periphery of the V-shaped groove, common concrete is filled between the surrounding rock and the rectangular steel pipe part, and steel fiber concrete is filled between the remaining part of the rectangular steel pipe and the tunnel. The construction method is carried out in stages, after a tunnel is excavated, common sprayed concrete is primarily sprayed until the section is smooth, rectangular steel pipes and reinforcing meshes are erected, anchor rods are constructed, and the common concrete is re-sprayed to the designed thickness of the stage 1; and when the yielding deformation reaches the designed value of the stage 1, spraying the steel fiber reinforced concrete to the designed thickness of the stage 2. The stress state of an original supporting structure is changed, the steel pipe is pulled, concrete is pressed, and tension cracks are avoided.

Description

Technical Field

[0001] This invention relates to the field of tunnel support technology, and in particular to a combined support structure and construction method suitable for tunnels under high ground stress conditions. Background Technology

[0002] During tunnel excavation, high-stress surrounding rock conditions are frequently encountered. For these challenging areas, traditional tunnel initial support structures typically use I-beams, which only consider bending resistance and have poor torsional resistance. Under high stress conditions, these steel frames often suffer torsional failure. The deformation of the steel frame and shotcrete is not coordinated, easily leading to circumferential cracks at the steel frame location. Furthermore, traditional initial support structures lack pressure relief capacity, and the design of pressure relief joints cannot meet the coordination deformation issues between the outer surrounding rock and the initial support. The overall initial support has poor toughness, often resulting in cracking and torsional failure of the initial support after the tunnel invert is closed in high-stress sections. In addition, the current widespread use of large-scale mechanized construction leads to over-excavation of the tunnel. The over-excavated portion requires backfilling with shotcrete, causing further cost overruns. Moreover, the over-excavated backfill portion is not considered in the support stress system, resulting in significant waste. Summary of the Invention

[0003] The purpose of this invention is to provide a combined support structure and its construction method suitable for tunnels under high ground stress conditions, in order to solve the problem that traditional initial support structures have virtually no tensile strength, uneven stress distribution, and localized tensile cracking under high ground stress conditions.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A composite support structure suitable for tunnels under high ground stress conditions is provided, in which several rectangular steel pipes are vertically installed between the tunnel and the surrounding rock, and an anchor rod is installed between every two rectangular steel pipes. A V-shaped groove is opened at the end of the rectangular steel pipe near the surrounding rock, and a steel mesh is welded around the V-shaped groove. Ordinary concrete is filled between the surrounding rock and the rectangular steel pipe, and steel fiber reinforced concrete is filled between the remaining part of the rectangular steel pipe and the tunnel.

[0006] Furthermore, the individual opening size of the V-groove is 2~4cm, and the spacing is 30~60cm.

[0007] Furthermore, the ratio of the filling thickness of the ordinary concrete to that of the steel fiber concrete is 0.6 to 1.5.

[0008] Furthermore, the length of the rectangular steel pipe is 14cm to 25cm.

[0009] A construction method for composite support structures in tunnels under high ground stress conditions includes the following steps:

[0010] Step 1. After tunnel excavation, spray ordinary shotcrete until the cross-section is smooth, erect rectangular steel pipes and steel mesh, construct anchor bolts, and spray ordinary concrete again to the design thickness to allow for pressure deformation.

[0011] Step 2. Once the compressive deformation reaches the design thickness one, spray steel fiber reinforced concrete to the design thickness two.

[0012] The beneficial effects of this invention are as follows:

[0013] 1. This invention, through a combined support structure, alters the stress state of the original support system, dividing the construction process into two stages. In stage 1, the outer steel pipe is under tension and the inner concrete is under compression, with a V-groove on the outer side of the steel pipe, enabling stage 1 to also release pressure. In stage 2, the outer steel fiber shotcrete is under tension and the inner concrete is under compression. The overall design achieves balanced stress on the initial support structure, essentially avoiding cracking and torsional failure of the initial support.

[0014] 2. This invention replaces the inner sprayed steel fiber concrete with ordinary concrete, reducing the amount of steel fiber concrete used due to over-excavation, etc., and at the same time, it replaces part of the concrete with hollow steel pipes, thus reducing costs overall. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the longitudinal section of the combined support structure in the construction stage 1 of the present invention.

[0016] Figure 2 This is a schematic diagram of the longitudinal section of the combined support structure during the construction stage of the present invention.

[0017] Figure 3 This is a schematic diagram of the V-groove structure at the edge of a circumferential steel pipe.

[0018] In the diagram, 1-rectangular steel pipe; 2-anchor bolt; 3-steel mesh; 4-ordinary concrete; 5-V-groove; 6-steel fiber reinforced concrete. Detailed Implementation

[0019] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0020] This invention discloses a combined support structure and its construction method suitable for tunnels under high ground stress conditions. The combined support structure for tunnels under high ground stress conditions includes a rectangular steel pipe 1, anchor bolts 2, steel mesh 3, ordinary concrete 4, and steel fiber concrete 6, which are assembled together to form a combined support structure.

[0021] Specifically, the present invention uses a rectangular steel pipe 1 to replace the original I-beam, and sets a V-groove 5 on the outside of the rectangular steel pipe 1.

[0022] Several rectangular steel pipes 1 are vertically installed between the tunnel and the surrounding rock. Anchor bolts 2 are installed parallel to the rectangular steel pipes 1 between two rectangular steel pipes 1. Part of the anchor bolt 2 extends into the surrounding rock, and part is submerged in ordinary concrete 4. The filling thickness of the ordinary concrete 4 is consistent with the length of the anchor bolt 2 exposed outside the surrounding rock. Part of the rectangular steel pipe 1 is located in the ordinary concrete 4, and part is located in steel fiber reinforced concrete 6. The steel fiber reinforced concrete 6 fills the space between the tunnel and the ordinary concrete 4. Reinforcing mesh 3 is placed in the ordinary concrete 4 and laid perpendicular to the rectangular steel pipe 1 at one end of the rectangular steel pipe 1 located in the ordinary concrete 4.

[0023] Steel mesh 3 can be replaced with energy dissipation mesh.

[0024] The construction method for composite support structures in tunnels under high ground stress conditions includes the following steps:

[0025] like Figure 1 As shown, after the tunnel excavation, ordinary shotcrete 4 is initially sprayed until the cross-section is smooth, rectangular steel pipe 1 and steel mesh 3 are erected, construction anchor bolt 2 is installed, and ordinary shotcrete 4 is sprayed again to the design thickness of stage 1.

[0026] like Figure 2 As shown, when the compressive deformation reaches the design value of stage 1, the sprayed steel fiber concrete thickness is 6 to the design thickness of stage 2.

[0027] The design thickness for Stage 1 depends on the deformation and stress conditions; in this embodiment, it is 10-16cm. The greater the ground stress, the larger the thickness. It mainly bears the pressure. The design thickness for Stage 2 is 11-16cm, calculated as steel pipe size + 7cm - Stage 1 design thickness. The steel pipe size is 14cm-25cm (refer to I14-I25 steel frame for replacement).

[0028] The V-shaped groove on the edge of the rectangular steel pipe 1 is as follows: Figure 3 As shown, the purpose of the V-groove design is to reduce the rigidity of the steel pipe, allowing for partial compression deformation. This enables the deformation of the steel pipe to develop in tandem with the surrounding ordinary concrete, solving the problem of instability caused by insufficient initial concrete strength and the steel pipe bearing the load alone. The depth of the V-groove is approximately 0.8 times the thickness of the ordinary concrete, with a single opening size of 2-4 cm and a spacing of 30-60 cm.

[0029] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite support structure suitable for tunnels under high ground stress conditions, characterized in that: Several rectangular steel pipes (1) are vertically installed between the tunnel and the surrounding rock. An anchor rod (2) is installed between every two rectangular steel pipes (1). A V-shaped groove (5) is opened at the end of the rectangular steel pipe (1) near the surrounding rock. A steel mesh (3) is welded around the V-shaped groove (5). Ordinary concrete (4) is filled between the surrounding rock and the rectangular steel pipe (1). Steel fiber concrete (6) is filled between the remaining part of the rectangular steel pipe (1) and the tunnel.

2. The combined support structure for tunnels under high ground stress conditions according to claim 1, characterized in that: The V-groove (5) has a single opening size of 2~4cm and a spacing of 30~60cm.

3. A combined support structure for tunnels under high ground stress conditions according to claim 1, characterized in that: The ratio of the filling thickness of the ordinary concrete (4) to that of the steel fiber concrete (6) is 0.6 to 1.

5.

4. A combined support structure for tunnels under high ground stress conditions according to claim 1, characterized in that: The length of the rectangular steel pipe (1) is 14cm~25cm.

5. The construction method for combined support structures for tunnels under high ground stress conditions according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1. After tunnel excavation, spray ordinary shotcrete (4) until the cross-section is smooth, erect rectangular steel pipe (1) and steel mesh (3), construct anchor bolts (2), and spray ordinary shotcrete (4) to the design thickness to allow for pressure deformation; Step 2. When the compression deformation reaches the design thickness one, spray steel fiber concrete (6) to the design thickness two.

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