Construction device and method for reducing rebound rate of tunnel shotcrete

Abstract

This invention discloses a construction device and method for reducing the rebound rate of shotcrete in tunnels. The construction device includes an initial tunnel support structure, a rebound reduction mechanism, and a concrete spraying device. The construction method includes the following steps: 1. Constructing the initial tunnel support structure and the rebound reduction mechanism; 2. Preparing concrete and starting the spraying operation using the concrete spraying device; 3. Real-time netting of the rebound material in the shotcrete; 4. Gradually increasing the thickness of the shotcrete spraying; 5. Repeating steps 1 to 4 multiple times, installing the initial tunnel support structure and the rebound reduction mechanism as a whole or in sections along the tunnel length and completing the spraying operation until the construction is finished. The rebound reduction mechanism of this invention can form an elastic net on the concrete surface, significantly reducing the rebound rate of shotcrete in tunnels. At the same time, the elastic net generates rebound shrinkage stress on the microcracks in the concrete, realizing the closure and repair of microcracks, improving the crack resistance of concrete, and thus improving concrete quality.

Description

Technical Field

[0001] This invention belongs to the field of shotcrete construction technology, specifically relating to a construction device and method for reducing the rebound rate of shotcrete in tunnels. Background Technology

[0002] Shotcrete has advantages such as fast construction speed, high early strength, and no need for vibration, and is widely used in tunnel (road) support, slope protection, water conservancy projects, rail transit and other projects. In the field of tunnel construction, the initial support of surrounding rock structures of Class III and IV and above generally adopts a combined support form of anchor bolts + steel arch frame + steel mesh + shotcrete.

[0003] Shotcrete, as a core material for initial support in engineering projects, has a rebound rate that is a key indicator affecting construction quality and cost. The rebound rate of shotcrete refers to the ratio of rebound material not adhering to the sprayed surface to the total mass of shotcrete. In traditional tunnel construction, the rebound rate of shotcrete (such as C20 and C25) generally exceeds 25%. Especially under adverse conditions such as poor surrounding rock stability (Class IV or above), large deformation of soft rock, or water-rich areas, the rebound rate can even reach 50%. Surveys show that the main component of the rebound material is coarse aggregate (generally 5-10mm), which, due to its large mass and high kinetic energy, is most prone to rebound upon impact with the sprayed surface. It also contains a small amount of fine aggregate (sand) and cement paste. A high rebound rate of shotcrete leads to significant material waste, reduced construction efficiency, increased slag removal costs, and negatively impacts construction results. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a construction device and method for reducing the rebound rate of shotcrete in tunnels, addressing the shortcomings of the prior art.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a construction device for reducing the rebound rate of shotcrete in tunnels, characterized in that: it includes an initial support mechanism for the tunnel and a rebound reduction mechanism. The initial support mechanism for the tunnel includes multiple anchor rods that are spaced apart and inserted into the rock wall according to design requirements, and a steel mesh arranged close to the rock wall and wrapping around the multiple anchor rods. Multiple steel arch frames are arranged on the outside of the steel mesh. A rebound reduction mechanism is arranged between two adjacent steel arch frames. The rebound reduction mechanism includes an elastic net arranged between two adjacent steel arch frames. A concrete spraying device is arranged on the outside of the steel arch frames.

[0006] The above-mentioned construction device for reducing the rebound rate of shotcrete in tunnels is characterized in that: the inner end of the steel arch frame is tightly attached to the steel mesh.

[0007] The above-mentioned construction device for reducing the rebound rate of shotcrete in tunnels is characterized in that: the steel arch frame is an H-beam or an I-beam.

[0008] The above-mentioned construction device for reducing the rebound rate of shotcrete in tunnels is characterized in that: a fixing connector is fixedly installed on the inner side of the outer wing plate of the H-beam or I-beam steel arch frame, and the two ends of the elastic net are respectively fixedly connected to the corresponding fixing connectors on both sides.

[0009] The above-mentioned construction device for reducing the rebound rate of shotcrete in tunnels is characterized in that: the elastic net is woven from several elastic lines into a mesh structure, the mesh shape of the elastic net includes square or triangular, and the side length of the mesh is 2mm to 5mm.

[0010] The above-mentioned construction device for reducing the rebound rate of shotcrete in tunnels is characterized in that: the elastic wire is a fiber elastic wire, which includes one or more of natural latex filaments, polyurethane fibers and synthetic copolymer fibers, thermoplastic polyurethane elastic fibers, and polyether ester elastic fibers; the cross-sectional shape of the fiber elastic wire is one or more of square, trefoil, Y-shaped, L-shaped, dumbbell-shaped, T-shaped, and threaded ribbed type; the maximum length of the cross-section of the fiber elastic wire is 0.5mm to 1mm.

[0011] Meanwhile, this invention also discloses a construction method for reducing the rebound rate of shotcrete in tunnels, characterized by the following steps: Step 1: Initial support structure and rebound mechanism for the construction tunnel; Step 2: Prepare concrete and start spraying operation using concrete spraying equipment. In the concrete spraying equipment, concrete, quick-setting agent and compressed air are mixed. The spraying force generated by the compressed air carries the concrete to the working area between two adjacent steel arches. Step 3: Real-time netting of shotcrete rebound material: When concrete passes through the elastic mesh, the fine aggregate and cement paste in the concrete pass directly through the mesh and are sprayed directly onto the rock wall because the mesh side length is 2mm to 5mm and the maximum cross-sectional length of the fiber elastic line is 0.5mm to 1mm. The coarse aggregate has a particle size of 5mm to 10mm. When it passes through the elastic mesh, due to the elastic recovery rate of the elastic mesh, the coarse aggregate is squeezed by the spraying force. The mesh on the elastic mesh deforms under the action of external force, making the mesh opening larger. Thus, some of the coarse aggregate in the concrete passes through and is sprayed directly onto the rock surface, thereby forming a support structure with the steel mesh and anchor bolts. When concrete is sprayed onto the work surface, the surface layer separates due to the rebound effect, forming a rebound material mainly composed of coarse aggregate in the concrete. Due to the limited thickness of the sprayed layer, the rebound material falls a short distance and has a small gravitational acceleration, so the impact force generated is insufficient to cause significant deformation of the elastic net. At the same time, the mesh size of the elastic net is smaller than the particle size of the coarse aggregate in the concrete. The elastic net can effectively constrain the rebounded coarse aggregate, keeping it within the sprayed area and preventing it from falling off the sprayed work area. Step 4: Gradually increase the thickness of the sprayed concrete: The thickness of the shotcrete is slightly greater than that of the rigid arch frame. The construction process of step three is repeated, and the thickness of the shotcrete is gradually increased, gradually covering the elastic net and the steel arch frame, forming a concrete protective layer that wraps the steel arch frame. The initial support structure of the tunnel is completely wrapped inside the shotcrete. Since the cross-sectional shape of the fiber elastic cord is one or more of square, trilobal, Y-shaped, L-shaped, dumbbell-shaped, T-shaped, and threaded ribbed type, it can increase the mechanical adhesion between the fiber elastic cord and the concrete, thus bonding it with the concrete as one. When the concrete is subjected to external tensile force, the elastic net composed of fiber elastic cord improves the toughness and impact resistance of the concrete. With the completion of the shotcreting operation in the working area between two adjacent steel arch frames, the tunnel's initial support mechanism and rebound reduction mechanism form a complete support system with the help of shotcrete. Due to the elastic net binding, the rebound rate during the overall shotcrete operation is reduced, and the toughening effect of the fiber elastic cord makes the overall concrete structure more stable, forming a more perfect combined support system. Step 5: Repeat steps 1 to 4 multiple times, install the initial support mechanism and rebound mechanism of the tunnel as a whole or in sections along the tunnel length, and complete the spraying operation until the construction is completed. Compared with the prior art, the present invention has the following advantages: 1. The construction device used in this invention has a simple principle, is flexible and convenient to construct, requires less additional equipment compared to the original process, and is economical and feasible, making it suitable for large-scale application in the field of tunnel construction. The tunnel initial support mechanism adopts the existing tunnel initial support system, with an elastic grid of a certain size laid out on the outside of the spraying operation area. During the spraying process, the concrete uses its own spraying impact force to squeeze the elastic fibers, causing the grid to expand, and the coarse aggregate components can pass through smoothly and adhere to the spraying surface. When the concrete rebounds, the rebound material falls a short distance and cannot generate enough to cause significant deformation of the elastic grid. Since the unexpanded size of the elastic grid is smaller than the coarse aggregate particle size, it can effectively bind the rebound material within the operation area, achieving real-time netting of the rebound material, thereby effectively reducing the overall rebound rate of the spraying operation.

[0012] 2. The elastic fiber contained in the rebound mechanism of the present invention has an irregular cross section that allows it to bond better with the concrete. When the concrete is subjected to external tensile force, the elastic fiber can deform in tandem with the concrete. Through stretching and deformation, it can efficiently absorb and dissipate impact energy, effectively prevent brittle failure of the concrete structure, and improve the toughness and impact resistance of the concrete.

[0013] 3. The elastic mesh in the rebound mechanism of the present invention can form an elastic network on the concrete surface. Due to the addition of fiber elastic lines, the crack resistance of concrete can be significantly improved. In addition, when the concrete cracks and is stretched, the fiber elastic lines generate rebound shrinkage stress on the microcracks, realizing the closure and repair of the microcracks. Furthermore, it can also constrain and limit the further expansion of microcracks, which is beneficial to improving the quality of concrete.

[0014] 4. This invention reduces material waste and saves on personnel and machinery costs for slag removal by lowering the rebound rate during overall shotcrete operations, thereby significantly reducing the overall construction cost. In addition, it can shorten the construction time of shotcrete support, thus improving the overall construction efficiency.

[0015] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structural connection of the construction device used in this invention.

[0017] Figure 2 for Figure 1 A bottom view.

[0018] Figure 3 This is a flowchart of the construction method of the present invention.

[0019] Explanation of reference numerals in the attached figures: 11—Rock wall; 12—Anchor bolt; 13—Reinforcing mesh; 14—Steel arch frame; 15—Outer wing plate of steel arch frame; 21—Fixed connector; 22—Elastic netting; 23—Elastic thread. Detailed Implementation

[0020] like Figure 1 and Figure 2As shown, the construction device for reducing the rebound rate of shotcrete in tunnels according to the present invention includes an initial support mechanism for the tunnel and a rebound reduction mechanism. The initial support mechanism includes multiple anchor bolts 12 that are spaced apart and inserted into the rock wall 11 according to design requirements, and a steel mesh 13 that is arranged close to the rock wall 11 and wraps around the multiple anchor bolts 12. Multiple steel arch frames 14 are arranged on the outside of the steel mesh 13. A rebound reduction mechanism is arranged between two adjacent steel arch frames 14. The rebound reduction mechanism includes an elastic net 22 arranged between two adjacent steel arch frames 14. A concrete spraying device is arranged on the outside of the steel arch frame 14.

[0021] It should be noted that the construction device used is simple in principle, flexible and convenient in construction, requires less additional equipment compared to the original process, and is economical and feasible, making it suitable for large-scale application in the field of tunnel construction. The tunnel initial support mechanism adopts the existing tunnel initial support system, and elastic grids of a certain size are laid on the outside of the shotcrete operation area. During the shotcrete process, the concrete uses its own impact force to squeeze the elastic fibers, causing the grid to expand, and the coarse aggregate components can pass through smoothly and adhere to the shotcrete surface. When the concrete rebounds, the rebound material falls a short distance and cannot generate enough to cause significant deformation of the elastic grid. Since the unexpanded size of the elastic grid is smaller than the particle size of the coarse aggregate, it can effectively bind the rebound material within the operation area, realizing real-time netting of the rebound material, thereby effectively reducing the overall rebound rate of the shotcrete operation.

[0022] In this embodiment, the inner end of the steel arch frame 14 is tightly attached to the steel mesh 13.

[0023] In this embodiment, the steel arch frame 14 is an H-beam or an I-beam.

[0024] In this embodiment, a fixing connector 21 is fixedly installed on the inner side of the outer wing plate 15 of the H-beam or I-beam steel arch frame, and the two ends of the elastic net 22 are fixedly connected to the corresponding fixing connectors 21 on both sides.

[0025] In this embodiment, the elastic net 22 is woven from several elastic threads 23 into a mesh structure. The mesh shape of the elastic net 22 includes squares or triangles, and the side length of the mesh is 2mm to 5mm.

[0026] In this embodiment, the elastic thread 23 is a fiber elastic thread, which includes one or more of natural latex filaments, polyurethane fibers and synthetic copolymer fibers, thermoplastic polyurethane elastic fibers, and polyether ester elastic fibers; the cross-sectional shape of the fiber elastic thread is one or more of square, trefoil, Y-shaped, L-shaped, dumbbell-shaped, T-shaped, and threaded ribbed type; the maximum length of the cross-section of the fiber elastic thread is 0.5mm to 1mm.

[0027] It should be noted that the elastic fiber is a synthetic fiber with a certain elastic recovery rate. It has the characteristics of high elongation and high elastic recovery rate. It can undergo a certain deformation under external impact without breaking. When the external force is small, its small deformation can be ignored. The addition of the elastic net significantly reduces the drop of rebound material during the spraying process, thereby effectively reducing the rebound rate during the overall spraying operation.

[0028] like Figure 3 The construction method shown includes the following steps to reduce the rebound rate of shotcrete in tunnels: Step 1: Initial support structure and rebound mechanism for the construction tunnel; Step 2: Prepare concrete and start spraying operation using concrete spraying equipment. In the concrete spraying equipment, concrete, quick-setting agent and compressed air are mixed. The spraying force generated by the compressed air carries the concrete to the working area between two adjacent steel arch frames 14 to start spraying operation. Step 3: Real-time netting of shotcrete rebound material: When concrete passes through the elastic mesh 22, the fine aggregate and cement paste in the concrete pass directly through the elastic mesh and are sprayed directly onto the rock wall because the mesh side length is 2mm to 5mm and the maximum cross-sectional length of the fiber elastic line is 0.5mm to 1mm. The coarse aggregate has a particle size of 5mm to 10mm. When it passes through the elastic mesh 22, the coarse aggregate is squeezed by the elastic mesh 22 under the action of the spraying force because the elastic mesh has an elastic recovery rate. The mesh on the elastic mesh deforms under the action of external force, making the mesh opening larger. Thus, some of the coarse aggregate in the concrete passes through and is sprayed directly onto the rock surface, thereby forming a support structure with the steel mesh 13 and the anchor rod 12. When concrete is sprayed onto the working surface, the surface layer separates due to the rebound effect, forming a rebound material mainly composed of coarse aggregate in the concrete. Due to the limited thickness of the sprayed layer, the rebound material falls a short distance and has a small gravitational acceleration, so the impact force generated is insufficient to cause significant deformation of the elastic net 22. At the same time, the mesh size of the elastic net 22 is smaller than the particle size of the coarse aggregate in the concrete, and the elastic net can effectively constrain the rebounded coarse aggregate, binding it within the sprayed area and preventing it from falling off the sprayed working area. Step 4: Gradually increase the thickness of the sprayed concrete: The thickness of the shotcrete is slightly greater than that of the rigid arch frame. The construction process of step three is repeated, and the thickness of the shotcrete is gradually increased, gradually covering the elastic net 22 and the steel arch frame 14, forming a concrete protective layer that wraps the steel arch frame 14. The tunnel's initial support structure is completely wrapped inside the shotcrete. Since the cross-sectional shape of the fiber elastic cord is one or more of square, trilobal, Y-shaped, L-shaped, dumbbell-shaped, T-shaped, or threaded ribbed type, it can increase the mechanical adhesion between the fiber elastic cord and the concrete, thus bonding it with the concrete as one. When the concrete is subjected to external tensile force, the elastic net composed of fiber elastic cord improves the toughness and impact resistance of the concrete. With the completion of the shotcreting operation in the working area between the two adjacent steel arch frames 14, the tunnel's initial support mechanism and rebound reduction mechanism form a complete support system with the help of shotcrete. Due to the elastic net binding, the rebound rate during the overall shotcrete operation is reduced, and the toughening effect of the fiber elastic line makes the overall concrete structure more stable, forming a more perfect combined support system. Step 5: Repeat steps 1 to 4 multiple times, install the initial support mechanism and rebound mechanism of the tunnel as a whole or in sections along the tunnel length, and complete the spraying operation until the construction is completed.

[0029] When this invention is used, the elastic fiber lines in the rebound mechanism, due to their irregular cross-section, can better bond with the concrete. When the concrete is subjected to external tensile force, the elastic fiber lines can deform in tandem with the concrete, efficiently absorbing and dissipating impact energy through stretching and deformation, effectively preventing brittle failure of the concrete structure and improving the concrete's toughness and impact resistance. The elastic mesh in the rebound mechanism can form an elastic network on the concrete surface. The addition of the elastic fiber lines can significantly improve the concrete's crack resistance. Furthermore, when the concrete cracks and is stretched, the elastic fiber lines generate rebound shrinkage stress on the micro-cracks, achieving the closure and repair of the micro-cracks. In addition, it can also constrain and limit the further expansion of micro-cracks, which is beneficial to improving concrete quality. By reducing the rebound rate during overall shotcrete operations, material waste is greatly reduced, and personnel and machinery costs for slag removal are saved, significantly reducing the overall construction cost. In addition, it can shorten the construction time of shotcrete support, thereby improving the overall construction efficiency. The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A construction method for reducing the rebound rate of shotcrete in tunnels, comprising using a construction device for reducing the rebound rate of shotcrete in tunnels, characterized in that: The construction device for reducing the rebound rate of shotcrete in tunnels includes an initial support mechanism for tunnels and a rebound reduction mechanism. The initial support mechanism for tunnels includes multiple anchor rods (12) that are spaced out into the rock wall (11) according to design requirements, and a steel mesh (13) that is arranged close to the rock wall (11) and wraps around the multiple anchor rods (12). Multiple steel arch frames (14) are set on the outside of the steel mesh (13). A rebound reduction mechanism is set between two adjacent steel arch frames (14). The rebound reduction mechanism includes an elastic net (22) set between two adjacent steel arch frames (14). A concrete spraying device is set on the outside of the steel arch frame (14). The elastic net (22) is woven from several elastic threads (23) into a mesh structure. The mesh shape of the elastic net (22) includes squares or triangles, and the side length of the mesh is 2mm to 5mm. The elastic thread (23) is a fiber elastic thread, which includes one or more of natural latex filaments, polyurethane fibers and synthetic copolymer fibers, thermoplastic polyurethane elastic fibers, and polyether ester elastic fibers; the cross-sectional shape of the fiber elastic thread is one or more of square, trefoil, Y-shaped, L-shaped, dumbbell-shaped, T-shaped, and spiral ribbed type; the maximum length dimension of the cross-section of the fiber elastic thread is 0.5mm to 1mm; The method includes the following steps: Step 1: Initial support structure and rebound mechanism for the construction tunnel; Step 2: Prepare concrete and start spraying operation using concrete spraying equipment. In the concrete spraying equipment, concrete, quick-setting agent and compressed air are mixed. The spraying force generated by the compressed air carries the concrete to the working area between two adjacent steel arch frames (14) to start spraying operation. Step 3: Real-time netting of shotcrete rebound material: When the concrete passes through the elastic mesh (22), since the side length of the mesh on the elastic mesh is 2mm to 5mm and the maximum cross-sectional length of the fiber elastic line is 0.5mm to 1mm, the fine aggregate and cement paste in the concrete pass directly through the elastic mesh and are directly sprayed onto the rock wall; the coarse aggregate has a particle size of 5mm to 10mm. When it passes through the elastic mesh (22), since the elastic mesh has an elastic recovery rate, the coarse aggregate is squeezed by the spraying force. The mesh on the elastic mesh is deformed under the action of external force, which makes the mesh opening larger. Thus, part of the coarse aggregate in the concrete passes through and is directly sprayed onto the rock surface, thereby forming a support structure with the steel mesh (13) and anchor rods (12). When concrete is sprayed onto the working surface, the surface layer separates due to the rebound effect, forming a rebound material mainly composed of coarse aggregate in the concrete. Due to the limited thickness of the sprayed layer, the rebound material falls a short distance and has a small gravitational acceleration, so the impact force generated is insufficient to cause significant deformation of the elastic net (22). At the same time, the mesh size of the elastic net (22) is smaller than the particle size of the coarse aggregate in the concrete. The elastic net can effectively constrain the rebounded coarse aggregate, keeping it within the sprayed area and preventing it from falling off the sprayed working area. Step 4: Gradually increase the thickness of the sprayed concrete: The thickness of the shotcrete is slightly greater than that of the rigid arch frame. The construction process of step three is repeated. The thickness of the shotcrete is gradually increased and gradually covers the elastic net (22) and the steel arch frame (14), forming a concrete protective layer that wraps the steel arch frame (14). The tunnel initial support structure is completely wrapped inside the shotcrete. Since the cross-sectional shape of the fiber elastic line is one or more of square, trilobal, Y-shaped, L-shaped, dumbbell-shaped, T-shaped, and threaded ribbed type, it can increase the mechanical adhesion between it and the concrete, thus combining with the concrete as one. When the concrete is subjected to external tensile force, the elastic net composed of fiber elastic lines improves the toughness and impact resistance of the concrete. With the completion of the shotcreting operation in the working area between two adjacent steel arch frames (14), the tunnel initial support mechanism and the rebound mechanism form a complete support whole with the help of shotcreting. Due to the elastic net binding, the rebound rate during the overall shotcreting operation is reduced. The toughening effect of the fiber elastic line makes the overall concrete structure more stable, forming a more perfect joint support body. Step 5: Repeat steps 1 to 4 multiple times, install the tunnel initial support mechanism and rebound mechanism as a whole or in sections along the tunnel length, and complete the spraying operation until the construction is completed.

2. A method of reducing the rebound of shotcrete in a tunnel according to claim 1, characterised in that: The inner end of the steel arch frame (14) is tightly attached to the steel mesh (13).

3. A construction method for reducing the rebound rate of shotcrete in tunnels according to claim 1, characterized in that: The steel arch frame (14) is an H-beam or an I-beam.

4. A construction method for reducing the rebound rate of shotcrete in tunnels according to claim 3, characterized in that: The inner side of the outer wing plate (15) of the H-beam or I-beam steel arch frame is fixedly provided with a fixing connector (21), and the two ends of the elastic net (22) are respectively fixedly connected to the corresponding fixing connectors (21) on both sides.

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