Drill-and-blast tunnel cast-in-place porous concrete anti-fault buffer layer structure and construction method

Abstract

This invention provides a cast-in-place porous concrete anti-fault buffer layer structure for drill-and-blast tunnels, comprising a buffer layer disposed between the initial support and the secondary lining. The buffer layer includes several plastic pipes, each distributed sequentially along the tunnel excavation direction and fixed to the initial support. At least a portion of the plastic pipes are filled with porous concrete. This invention also provides a construction method for the cast-in-place porous concrete anti-fault buffer layer structure for drill-and-blast tunnels. This invention allows for rapid and convenient construction without significantly increasing costs or construction time due to the buffer layer construction. Furthermore, the porosity of the buffer layer can be adjusted as needed by varying the pipe diameter and arrangement, thereby achieving effective anti-fault buffering performance.

Description

Technical Field

[0001] This invention relates to the field of tunnels and underground engineering, and in particular to a cast-in-place porous concrete anti-fault buffer layer structure and construction method for drill-and-blast tunnels. Background Technology

[0002] With the increasing number of tunnels being built, the number of tunnels crossing active faults is also increasing. How to address the damage to tunnel structures caused by the displacement of active faults is a major engineering challenge in tunnel construction. Due to the immense shearing force of the strata, reinforcement methods using lining often lead to even more severe damage. More and more scholars and engineering researchers are beginning to consider methods to increase tunnel flexibility to mitigate the direct shearing effect of active faults on the tunnel lining. A common approach is to add a buffer layer between the initial support and the secondary lining. The compression deformation of the buffer layer absorbs the displacement of the active fault, thereby reducing the pressure of the active fault on the lining.

[0003] Materials used for buffer layers typically include organic materials such as rubber and polyurethane, and cement-based inorganic materials such as foamed concrete and polystyrene granular foamed concrete (EPS). While chemical products like rubber and polyethylene do not require on-site preparation, their durability is insufficient to meet the long-life requirements of tunnel structures. When foamed concrete or EPS concrete is used for tunnel buffer layers, traditional cast-in-place concrete structures require formwork erected at the location of the existing secondary lining trolley, or the fabrication of additional formwork trolleys, resulting in high costs. Furthermore, due to the low density of foamed concrete, the durability of the buffer structure in corrosive groundwater environments such as sulfate-contaminated groundwater is difficult to meet requirements. Some projects have constructed foamed concrete buffer structures as prefabricated components encapsulated in plastic pipes for on-site assembly, but this requires assembly using a platform, which presents disadvantages such as high on-site assembly difficulty and poor safety.

[0004] Therefore, it is necessary to design a cast-in-place porous concrete anti-fault buffer layer structure and construction method for drill-and-blast tunnels to overcome the above problems. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a structure and construction method for a cast-in-place porous concrete anti-fault buffer layer in a drill-and-blast tunnel. This invention solves at least some of the problems in the prior art.

[0006] This invention is implemented as follows:

[0007] This invention provides a cast-in-place porous concrete anti-fault buffer layer structure for drill-and-blast tunnels, comprising a buffer layer disposed between the initial support and the secondary lining. The buffer layer includes a plurality of plastic pipes, each of which is distributed sequentially along the tunnel excavation direction. The plastic pipes are fixed to the initial support, and at least a portion of the plastic pipes are filled with porous concrete.

[0008] Furthermore, the plastic pipe includes a first sleeve arranged along the inverted arch and a second sleeve arranged along the arch wall, the first sleeve and the second sleeve forming an annulus, and the first sleeve and the second sleeve being connected and connected.

[0009] Furthermore, both the first sleeve and the second sleeve are provided with openings for pumping porous concrete into the sleeve, and the top of the second sleeve is provided with air holes.

[0010] Furthermore, the plastic pipe is fixed to the initial support by steel bar clamps.

[0011] Furthermore, a leveling isolation plate is provided between the plastic pipe and the secondary lining, and a waterproof layer is laid between the isolation plate and the secondary lining.

[0012] Furthermore, the isolation plate is disposed between two adjacent plastic pipes, and the isolation plate is provided with an arc-shaped support portion that fits against the outer surface of the plastic pipe.

[0013] This invention also provides a construction method for a cast-in-place porous concrete anti-fault buffer layer structure for drill-and-blast tunnels, comprising the following steps:

[0014] S1. Determine the diameter of the plastic pipe: The diameter D of the circular plastic pipe is determined according to the thickness h0 of the buffer layer required for the fracture resistance of the project. The pipe diameter D = the thickness h0 of the buffer layer. The thickness h0 of the buffer layer is determined by the allowable compression deformation Δh of the buffer layer structure and the compression height ratio α of the buffer layer structure. h0 = Δh / (1-α).

[0015] S2. Determine the arrangement spacing S of the plastic pipes along the longitudinal direction of the tunnel: The arrangement spacing S of the plastic pipes along the longitudinal direction of the tunnel is related to the pipe diameter D, the volume change coefficient n after concrete failure, and the compression height ratio α of the buffer layer structure. According to the principle that the remaining space volume after the allowable deformation of the buffer layer Δh is equal to the volume of the porous concrete after failure, the arrangement spacing S of the plastic pipes along the longitudinal direction of the tunnel can be calculated as nπD / 4α.

[0016] S3. Determine the material and model of the plastic pipe; the pipe pressure rating shall not be lower than 0.6MPa.

[0017] S4. Determine the appropriate compressive strength of the buffer layer;

[0018] S5. Determine the method for preparing porous concrete;

[0019] S6. Based on the lining profile and anti-fault buffer layer thickness determined in the design, carry out tunnel excavation and initial support construction to ensure the stability of the surrounding rock.

[0020] S7. Based on the tunnel cross-section shape and the designed diameter of the plastic pipe, process or prefabricate plastic pipes in sections;

[0021] S8. Based on the reasonable compressive strength of the buffer layer, test-mix porous concrete and determine the mix proportion;

[0022] S9. Lay the first sleeve of the invert arch section, pump porous concrete into the first sleeve from the opening until grout comes out at the end, and seal the opening after the porous concrete has set.

[0023] S10. Install the second sleeve at the arch wall. The second sleeve is fixed on the initial support. Pump porous concrete material through the opening on the second sleeve until the grout comes out of the high-level pores. After the concrete has set, seal the opening and pores.

[0024] S11. Lay a leveling isolation plate on the surface of the plastic pipe, lay a waterproof layer on the isolation plate, and then perform secondary lining.

[0025] Furthermore, in step S2, when S > 2D, an empty plastic pipe of the same diameter is placed between the two plastic pipes filled with porous concrete.

[0026] Furthermore, in step S4, the maximum allowable compressive strength of the buffer layer is related to various factors such as the size and shape of the tunnel cross section, the direction of fault faulting, the thickness, strength, and reinforcement of the secondary lining concrete. The minimum strength must meet the bearing requirements during the normal service stage of the structure. The compressive strength of the buffer layer is generally 1 / 10 to 1 / 30 of the compressive strength of the secondary lining concrete.

[0027] Furthermore, in step S10, the second sleeve is fixed to the initial support by steel bar clamps.

[0028] The buffer layer structure of cast-in-place porous concrete inside a plastic tube proposed in this invention ensures that the secondary lining of the tunnel lining structure crossing an active fault does not fail under the action of large displacement active fault faults, thus guaranteeing the structural safety of the tunnel crossing the active fault. Compared with existing tunnel buffer layer structures, it has the following advantages:

[0029] (1) Plastic pipes serve as a component of the buffer structure and also as a casting mold for porous concrete. Compared with the traditional formwork casting method, no formwork trolley is required, which greatly saves construction costs. Compared with precast buffer structures, only plastic pipes need to be erected on site. The pipes are lightweight and easier and safer to install than precast buffer structures.

[0030] (2) The porosity of the buffer layer structure can be adjusted by flexibly adjusting the pipe diameter and the arrangement spacing, thereby achieving the optimized design of the anti-breakage buffer layer structure.

[0031] (3) The porous concrete is enclosed in the plastic pipe and does not come into contact with groundwater, which can prevent groundwater from eroding the porous concrete and improve the structural durability. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic cross-sectional view of the cast-in-place porous concrete anti-fault buffer layer structure for drill-and-blast tunnels provided in an embodiment of the present invention.

[0034] Figure 2 A longitudinal section schematic diagram (S<2D) of a cast-in-place porous concrete anti-fault buffer layer structure for a drill-and-blast tunnel provided in an embodiment of the present invention;

[0035] Figure 3 This is a longitudinal section schematic diagram (S>2D) of a cast-in-place porous concrete anti-fault buffer layer structure for a drill-and-blast tunnel provided in an embodiment of the present invention.

[0036] Figure 4 This is a schematic diagram of the installation of the first sleeve of the plastic tube provided in an embodiment of the present invention;

[0037] Figure 5 This is a schematic diagram of the installation of the second sleeve of the plastic pipe provided in an embodiment of the present invention;

[0038] Figure 6 This is a schematic diagram of the U-shaped steel bar clamp fixing provided in an embodiment of the present invention;

[0039] Figure 7 This is a schematic diagram of the cross-section of the isolation plate provided in an embodiment of the present invention;

[0040] Figure 8 This is a diagram showing the installation location of the isolation plate according to an embodiment of the present invention.

[0041] In the diagram: 1. Initial support; 2. Buffer layer; 3. Secondary lining; 4. Tunnel excavation direction; 5. Plastic pipe; 6. Porous concrete; 7. First sleeve; 8. Sleeve joint; 9. Opening; 10. Second sleeve; 11. Vent hole; 12. Rebar clamp; 13. Expansion bolt; 14. Isolation plate; 15. Waterproof layer (geotextile, waterproof board); 16. Curved support. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0044] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature; in the description of this invention, unless otherwise stated, "several" means two or more.

[0045] like Figures 1-8 This invention provides a cast-in-place porous concrete anti-fault buffer layer structure for drill-and-blast tunnels, comprising a buffer layer 2 disposed between the initial support 1 and the secondary lining 3. The buffer layer 2 includes several plastic pipes 5, each distributed sequentially along the tunnel excavation direction, surrounding the secondary lining 3, and fixed to the initial support 1. At least a portion of the plastic pipes 5 are filled with porous concrete 6. The porous concrete 6 is a high-porosity, low-strength concrete; in this embodiment, it is a porous concrete with saturated water-absorbing beads forming the pores (SAP porous concrete). The plastic pipes 5 are made of flexible polyethylene (PE). This invention provides a fast and convenient structural design and construction method for cast-in-place tunnel buffer layers, which allows for rapid and convenient construction without significantly increasing costs or construction time. Furthermore, the porosity of the buffer layer can be adjusted as needed by varying the pipe diameter and arrangement, thereby achieving effective anti-fault buffering performance.

[0046] like Figures 4-5The plastic pipe 5 includes a first sleeve 7 arranged along the invert arch and a second sleeve 10 arranged along the arch wall. The first sleeve 7 and the second sleeve 10 form an annular structure and are connected to each other. The end of the first sleeve 7 is provided with a sleeve connector 8 that connects with the second sleeve 10. Both the first sleeve 7 and the second sleeve 10 are provided with openings 9 for pumping porous concrete into the sleeves, and the top of the second sleeve 10 is provided with an air hole 11.

[0047] like Figure 6 The plastic pipe 5 is fixed to the initial support 1 by a steel bar clamp 12. The steel bar clamp 12 is fixedly connected to the initial support 1 by expansion bolts 13.

[0048] like Figures 7-8 A leveling partition plate is provided between the plastic pipe 5 and the secondary lining 3, and a waterproof layer 15 is laid between the partition plate and the secondary lining 3. In this embodiment, the waterproof layer 15 is made of geotextile, waterproof board, etc. In this embodiment, the partition plate 14 is made of plastic board. The partition plate is located between two adjacent plastic pipes 5, and the partition plate is provided with an arc-shaped support part 16 that fits against the outer surface of the plastic pipe 5.

[0049] To facilitate safe and rapid construction of the anti-fault buffer layer, this invention provides a buffer layer structure in which concrete is cast in place inside a plastic pipe 5. This buffer layer structure is set between the initial support 1 and the secondary lining 3. The plastic pipe 5 is arranged circumferentially along the inner surface of the initial support 1. Porous, low-strength concrete with high porosity (foamed concrete or SAP porous concrete can be used) is poured in place inside the plastic pipe 5.

[0050] Plastic pipe 5 serves as the template for the porous concrete pouring and is also a component of the anti-fault buffer layer structure. It enhances the ductility of the porous concrete during the failure stage and isolates the porous concrete from groundwater, preventing corrosion damage. The design steps for the anti-fault buffer layer are as follows:

[0051] The first step is to determine the diameter of plastic tube 5. Plastic tube 5 has a circular cross-section (e.g., ...). Figure 2 The pipe diameter D is determined based on the buffer layer thickness h0 required for the engineering fracture resistance (pipe diameter D = buffer layer thickness h0). The buffer layer thickness h0 is determined by the allowable compression deformation Δh of the buffer layer structure and the compression height ratio α of the buffer layer structure, h0 = Δh / (1-α).

[0052] The second step is to determine the spacing of the plastic pipes along the longitudinal direction of the tunnel (the longitudinal direction of the tunnel is the direction of tunnel excavation). The spacing S of the plastic pipes along the longitudinal direction of the tunnel is related to the pipe diameter D, the volume change coefficient n after concrete failure, and the compression height ratio α of the buffer layer structure. Based on the principle that the remaining space volume after the allowable compression deformation Δh of the fracture-resistant buffer layer is equal to the volume of the concrete after failure, the pipe spacing S = nπD / 4α can be calculated. When S > 2D, a hollow pipe of the same diameter can be placed between two concrete pipes (e.g., ...). Figure 3 (As shown).

[0053] The third step is to determine the material and model of the plastic pipes. Commonly used plastic pipes and corrugated pipes include polyvinyl chloride (PVC), polyethylene (PE), and polypropylene (PP), among other materials. Based on the characteristics of the tunnel's anti-fault buffer structure, polyethylene (PE) pipes with good flexibility are selected. Considering the pressure on the pipes during concrete pouring and their own stability as formwork for cast-in-place concrete, the pipe pressure rating should not be lower than 0.6 MPa, and commonly available specifications and models should be selected.

[0054] The fourth step is to determine the reasonable compressive strength of the anti-fault buffer layer structure. Based on the working principle of the anti-fault buffer layer structure, under the allowable ground deformation, the buffer layer structure will deform or fail, but the secondary lining of the tunnel will not be damaged under the same ground deformation. Therefore, the maximum compressive strength of the buffer layer cannot be too high, otherwise it will lead to the failure of the secondary lining. The maximum allowable compressive strength of the buffer layer is related to various factors such as the tunnel cross-section size, cross-sectional shape, fault direction, thickness, strength, and reinforcement of the secondary lining concrete. The minimum strength must meet the load-bearing requirements during the normal service stage of the structure, and the reasonable strength needs to be determined through calculation and analysis based on the specific project. Preliminary research suggests that the reasonable compressive strength of the anti-fault buffer layer structure is generally 1 / 10 to 1 / 30 of the compressive strength of the secondary lining concrete.

[0055] The fifth step is to determine the preparation method for porous concrete. Porous concrete can be prepared using various processes, including foamed concrete, polystyrene particle foamed concrete (EPS), and superabsorbent polymer (SAP) porous concrete. Considering the long concrete transportation time during tunnel construction, superabsorbent polymer (SAP) porous concrete, which has easy-to-control pore stability and a simple process, is the preferred choice.

[0056] To facilitate the implementation of the aforementioned buffer layer structure on the construction site, a corresponding construction method was invented:

[0057] Step 1: Based on the lining outline and anti-fault buffer layer thickness determined by the design, tunnel excavation and initial support 1 are carried out to ensure the stability of the surrounding rock.

[0058] Step 2: Based on the tunnel cross-sectional shape and designed pipe diameter, process or prefabricate polypropylene (PE) plastic pipes in sections.

[0059] Step 3: Based on the reasonable compressive strength of the buffer layer, test-mix porous concrete and determine the mix proportion.

[0060] Step 4: Lay the first sleeve 7 of the invert arch section, pump porous concrete material into the first sleeve 7 from the opening until the grout comes out of the high-level pores. After the concrete has set, use thermoplastic welding to seal the pouring hole and pores.

[0061] Step 5: Install the second sleeve 10 in sections for the arch wall, and fix the second sleeve 10 with steel clamps (e.g., Figure 6 Porous concrete material is pumped through openings on both sides of the second sleeve 10 side wall section until grout comes out of the high-level pores. After the concrete has set, the pouring holes and pores are sealed by thermoplastic welding.

[0062] Step Six: Lay a leveling partition plate (such as...) on the surface of the plastic pipe. Figures 7-8 On the isolation board, geotextile, waterproof board, drainage board and other waterproof and drainage structures are laid, and the secondary lining of the tunnel is constructed in accordance with conventional methods.

[0063] The buffer layer structure of cast-in-place porous concrete inside a plastic tube proposed in this invention ensures that the secondary lining of the tunnel lining structure crossing an active fault does not fail under the action of large displacement active fault faults, thus guaranteeing the structural safety of the tunnel crossing the active fault. Compared with existing tunnel buffer layer structures, it has the following advantages:

[0064] (1) Plastic pipes serve as a component of the buffer structure and also as a casting mold for porous concrete. Compared with the traditional formwork casting method, no formwork trolley is required, which greatly saves construction costs. Compared with precast buffer structures, only plastic pipes need to be erected on site. The pipes are lightweight and easier and safer to install than precast buffer structures.

[0065] (2) The porosity of the buffer layer structure can be adjusted by flexibly adjusting the pipe diameter and the arrangement spacing, thereby achieving the optimized design of the anti-breakage buffer layer structure.

[0066] (3) The porous concrete is enclosed in the plastic pipe and does not come into contact with groundwater, which can prevent groundwater from eroding the porous concrete and improve the structural durability.

[0067] The design methodology will be further explained using specific engineering examples:

[0068] (1) The maximum vertical displacement of a tunnel project crossing an active fault section is predicted to be 0.5m, and the required compression Δh of the buffer layer structure is taken as 0.5m; the secondary lining is made of 60cm thick C50 reinforced concrete.

[0069] (2) The loose volume coefficient of porous concrete after crushing is n = 1.1.

[0070] (3) Assuming the thickness of the buffer layer is 0.8m, that is, the pipe diameter D is 0.8m, the calculated compression height ratio α = 0.375.

[0071] (4) Pipe spacing S = nπD / 4α = 1.84m. The pipe spacing is greater than twice the pipe diameter D, so an empty pipe can be placed in the middle.

[0072] (5) The plastic pipe is a commonly used PE pipe with a nominal diameter of 800mm, a pressure of 0.6MPa, and a wall thickness of 30.6mm.

[0073] (6) Based on the cross-sectional dimensions and shape of the tunnel structure, a model was established for calculation. When the strength of the buffer layer structure is less than 4MPa, the safety factor of the secondary lining structure can meet the requirements. The compressive strength of the porous concrete is 3MPa, and SAP concrete is used.

[0074] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

[0075] 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, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A construction method for a cast-in-place porous concrete anti-fault buffer layer structure in a drill-and-blast tunnel, characterized in that: The drill-and-blast tunnel cast-in-place porous concrete anti-fault buffer layer structure includes a buffer layer located between the initial support and the secondary lining. The buffer layer comprises several plastic pipes, each distributed sequentially along the tunnel excavation direction. The plastic pipes are fixed to the initial support, and at least a portion of the plastic pipes are filled with porous concrete. The construction method includes the following steps: S1. Determine the diameter of the plastic pipe: The diameter D of the plastic pipe is determined according to the thickness h0 of the buffer layer required for the fracture resistance of the project. The pipe diameter D = the thickness h0 of the buffer layer. The thickness h0 of the buffer layer is determined by the allowable compression deformation Δh of the buffer layer structure and the compression height ratio α of the buffer layer structure. h0 = Δh / (1-α). S2. Determine the arrangement spacing S of the plastic pipes along the longitudinal direction of the tunnel: The arrangement spacing S of the plastic pipes along the longitudinal direction of the tunnel is related to the pipe diameter D, the volume change coefficient n after concrete failure, and the compression height ratio α of the buffer layer structure. According to the principle that the remaining space volume after the allowable deformation of the buffer layer △h is equal to the volume of the porous concrete after failure, the arrangement spacing S of the plastic pipes along the longitudinal direction of the tunnel can be calculated as nπD / 4α. S3. Determine the material and model of the plastic pipe; the pipe pressure rating shall not be lower than 0.6MPa. S4. Determine the appropriate compressive strength of the buffer layer; S5. Determine the method for preparing porous concrete; S6. Based on the lining profile and anti-fault buffer layer thickness determined in the design, carry out tunnel excavation and initial support construction to ensure the stability of the surrounding rock. S7. Based on the tunnel cross-section shape and the designed diameter of the plastic pipe, process or prefabricate plastic pipes in sections; S8. Based on the reasonable compressive strength of the buffer layer, test-mix porous concrete and determine the mix proportion; S9. Lay the first sleeve of the invert arch section, pump porous concrete into the first sleeve from the opening until grout comes out at the end, and seal the opening after the porous concrete has set. S10. Install the second sleeve at the arch wall. The second sleeve is fixed on the initial support. Pump porous concrete material through the opening on the second sleeve until the grout comes out of the high-level pores. After the concrete has set, seal the opening and pores. S11. Lay a leveling isolation plate on the surface of the plastic pipe, lay a waterproof layer on the isolation plate, and then perform secondary lining.

2. The construction method of the cast-in-place porous concrete anti-fault buffer layer structure for drill-and-blast tunnels as described in claim 1, characterized in that: The plastic pipe includes a first sleeve arranged along the inverted arch and a second sleeve arranged along the arch wall. The first sleeve and the second sleeve form an annular ring, and the first sleeve and the second sleeve are connected and interlocked.

3. The construction method of the cast-in-place porous concrete anti-fault buffer layer structure for drill-and-blast tunnels as described in claim 2, characterized in that: Both the first sleeve and the second sleeve are provided with openings for pumping porous concrete into the sleeve, and the top of the second sleeve is provided with air holes.

4. The construction method of the cast-in-place porous concrete anti-fault buffer layer structure for drill-and-blast tunnels as described in claim 1, characterized in that: The plastic pipe is fixed to the initial support by steel clamps.

5. The construction method of the cast-in-place porous concrete anti-fault buffer layer structure for drill-and-blast tunnels as described in claim 1, characterized in that: A leveling isolation plate is provided between the plastic pipe and the secondary lining, and a waterproof layer is laid between the isolation plate and the secondary lining.

6. The construction method of the cast-in-place porous concrete anti-fault buffer layer structure for drill-and-blast tunnels as described in claim 5, characterized in that: The isolation plate is disposed between two adjacent plastic pipes, and the isolation plate is provided with an arc-shaped support portion that fits against the outer surface of the plastic pipe.

7. The construction method of the cast-in-place porous concrete anti-fault buffer layer structure for drill-and-blast tunnels as described in claim 1, characterized in that: In step S2, when S > 2D, an empty plastic pipe of the same diameter is placed between two plastic pipes filled with porous concrete.

8. The construction method of the cast-in-place porous concrete anti-fault buffer layer structure for drill-and-blast tunnels as described in claim 1, characterized in that: In step S4, the compressive strength of the buffer layer is taken as 1 / 10 to 1 / 30 of the compressive strength of the secondary lining concrete.

9. The construction method of the cast-in-place porous concrete anti-fault buffer layer structure for drill-and-blast tunnels as described in claim 1, characterized in that: In step S10, the second sleeve is fixed to the initial support by steel bar clamps.

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