Construction method of tunnel XPS buffer layer

Abstract

The present invention discloses a tunnel XPS buffer layer construction method, which is characterized in that: during construction design, fixing strips made of tunnel waterproof boards are pasted to XPS boards to form buffer layer units, and the buffer layer units are staggered along the longitudinal direction of the tunnel and the seams are sealed with self-adhesive tape to form a buffer layer. By appropriately increasing the back connection of the tunnel waterproof board, the fixing strips of the buffer layer unit are connected and fixed to the tunnel waterproof board by a combination of gluing and hot-melt welding, and the buffer layer is supported by a positioning steel bar structure, effectively preventing the buffer layer from falling off and shifting, forming an overall stable positioning reinforcement system. The present invention has the following advantages: (1) The buffer layer positioning reinforcement system is studied to form a set of tunnel buffer layer installation processes; (2) The selected XPS boards have the advantages of being environmentally friendly, lightweight, high-strength, high-quality, hydrophobic, moisture-proof, and corrosion-resistant, as well as good stability and long service life; (3) The buffer layer units formed by pre-pasting the fixing strips and XPS boards can be mass-produced, with rapid production and convenient installation.

Description

Technical Field

[0001] The present invention relates to the field of tunnel construction, and in particular to a method for constructing an XPS buffer layer in a soft rock large deformation tunnel. Background Art

[0002] Long tunnels on mountainous highways are common and often feature numerous unfavorable geological conditions. For example, the Wuzhishan long tunnel on the Renmu New Expressway features numerous unfavorable geological conditions, including high gas content, fault fracture zones, gypsum strata, water inrush, karst formations, and rockbursts, making construction challenging. Gypsum strata, with their high free expansion rate and strong expansive force, and low surrounding rock strength, can easily lead to cracking, damage, and even collapse of the tunnel support structure, among other safety and quality issues. Summary of the Invention

[0003] To address these shortcomings, the present invention provides a tunnel XPS buffer layer construction method. This method utilizes the adaptive deformation of the buffer layer under the pressure of the expansive surrounding rock to reduce the compressive stress of the surrounding rock on the secondary lining structure, improving the structural resistance to damage and achieving the goals of "combining resistance and yielding, first flexible then rigid, first release then resistance."

[0004] The present invention is realized by constructing a tunnel XPS buffer layer construction method, which is characterized in that: during construction design, a fixing strip (1012) made of a waterproof board is pasted to an XPS board (1011) to form a buffer layer unit (101), the buffer layer unit (101) is arranged along the longitudinal direction of the tunnel with staggered joints and the joints are sealed with an adhesive tape (102) to form a buffer layer (1) overall structure; by appropriately encrypting the back connection of the tunnel waterproof board (2), the buffer layer (1) XPS board (1011) is connected and fixed to the waterproof board (2) with a fixing strip (1012) by a combination of gluing and hot melt welding, and a positioning steel bar structure (3) (longitudinal positioning steel bar (302) + annular positioning steel bar (301)) is used. ) + protective layer pad (303) supports the buffer layer (1), forming an overall stable positioning reinforcement system, effectively preventing the buffer layer (1) from falling off and shifting, and solving the problems of the installation process of the buffer layer (1) and the XPS board (1011); the buffer layer (1) is connected with the waterproof board (2) and the positioning steel bar structure (3), which completely realizes the buffer layer (1) without nails and closely fits with the waterproof layer, avoiding the waterproof board (2) from breaking and failing, and preventing the buffer layer (1) from falling due to its own weight and the lining back from being squeezed during the pouring of the second lining concrete; the concrete protective layer pad (303) set between the positioning steel bar skeleton and the tunnel waterproof board (2) solves the problems of exposed steel bar corrosion and insufficient protective layer thickness; the specific construction is as follows;

[0005] (1) Buffer layer (1) design;

[0006] (2) Construction preparation;

[0007] (3) Installation of waterproof board (2);

[0008] (4) Laying out and laying out; after the waterproof board (2) is laid out and accepted, the buffer layer unit (101) is laid out and laid out on the waterproof board (2);

[0009] (5) Making the buffer layer unit (101): uniformly making the buffer layer unit (101) in the processing plant, installing two fixing strips (1012) on each buffer layer unit (101), and bonding the fixing strips (1012) and the XPS board (1011) with adhesive;

[0010] (6) Installing the buffer layer unit (101): The buffer layer unit (101) is installed layer by layer from both sides to the vault;

[0011] (7) Treatment of plate joints: 100 mm wide double-layer adhesive tape (102) is applied between adjacent buffer layer units (101) to prevent cement slurry from seeping in during concrete pouring;

[0012] (8) Installing the positioning steel bar structure (3): The positioning steel bar structure (3) is connected by tying;

[0013] (9) Acceptance: After the buffer layer (1) is installed, timely acceptance is organized and any defects found during the inspection are rectified. Only after the acceptance is qualified can the secondary lining construction be carried out;

[0014] (10) Construction of secondary lining: tying secondary lining steel bars, installing lining trolley, and pouring secondary lining concrete.

[0015] According to the present invention, a tunnel XPS buffer layer (1) construction method is characterized by: step (1) the buffer layer (1) structure is designed as follows: a 100 mm thick buffer layer (1) is provided; the XPS board (1011) design technical indicators are: water absorption rate ≤ 1.0%, dimensional stability ≤ 1.0%, density of about 38 kg / m, compressive strength ≥ 0.4 MPa;

[0016] Buffer layer (1) construction design:

[0017] 1) Buffer layer (1) Material selection

[0018] ——Buffer layer (1) Main material: Customized XPS board (1011), size 1800mm×600mm×100mm, technical indicators meet the design requirements;

[0019] ——XPS board (1011) fixing strip (1012): Made of tunnel waterproof board, the fixing strip (1012) is 1.2m long and 200mm wide;

[0020] ——Adhesive: all-purpose glue;

[0021] - Seam sealing material: adhesive tape (102);

[0022] —— Positioning steel bar structure (3): HRB400 steel bar;

[0023] ——Concrete protective layer pad (303): customized high-strength concrete pad;

[0024] 2) Buffer layer unit (101) and positioning structure:

[0025] The fixing strip (1012) is glued to the XPS board (1011) and connected to the tunnel waterproof board (2) by heat welding in a cradle-type manner, and the longitudinal board seam of adjacent buffer layer units (101) is controlled to be 2 mm to 4 mm, and the circumferential board seam is controlled to be 1.5 mm to 3 mm;

[0026] 3) Buffer layer (1) positioning steel bar structure (3): concrete protective layer pads (303), circumferential steel bars, and longitudinal steel bars are sequentially arranged from the buffer layer (1) to the clear interface in the tunnel, forming a buffer layer (1) positioning steel bar structure (3). The steel bar specification is φ20 mm, and the thickness of the concrete protective layer pads (303) is 25 mm. Among them, the spacing between the circumferential steel bars is 0.6 m, and the spacing between the longitudinal steel bars is 1.0 m. A concrete protective layer pad (303) is arranged every 300 mm along the circumferential steel bars.

[0027] According to the present invention, a tunnel XPS buffer layer (1) construction method is characterized in that: step (3) the waterproof board (2) is installed as follows: before installing the waterproof board (2), the initial support surface should be checked and processed to meet the flatness requirements before laying the geotextile; because the XPS buffer layer (1) is attached to the surface of the waterproof board (2), in order to reduce the sagging of the waterproof board (2) and prevent it from falling, the number of hot-melt pads is appropriately increased during the installation of the waterproof board (2), preferably 2 to 3 points / ㎡ for the vault and 3 to 4 points / ㎡ for the side wall.

[0028] According to the present invention, a tunnel XPS buffer layer (1) construction method is characterized in that: step (4) laying out and layout are specifically as follows: after the waterproof board (2) is laid and inspected and qualified, the buffer layer unit (101) is laid out and laid out on the waterproof board (2); the size of the buffer layer unit (101) is controlled to be 1803 mm in length and 602 mm in width, and the length direction is parallel to the tunnel axis, and the vertical joints of adjacent units along the tunnel circumference are staggered by 1 / 2 unit length, and the local minimum staggered joint is not less than 600 mm; after the layout is completed, the installation position of the XPS board (1011) is marked on the waterproof board (2) with an ink line.

[0029] According to the present invention, a tunnel XPS buffer layer (1) construction method is characterized in that: step (6) installing the buffer layer unit (101) is specifically as follows: the buffer layer unit (101) is installed layer by layer from both sides toward the arch;

[0030] 1) Before installing the buffer layer unit (101), clean the floating dust, dirt and other debris remaining on the waterproof board (2);

[0031] 2) Apply adhesive to the contact surface between the XPS board (1011) and the waterproof board (2);

[0032] 3) Welding the fixing strip (1012) at the lower end of the XPS board (1011) to the already laid tunnel waterproof board (2) using a heat welding machine according to the layout position, and then immediately pasting it together with the waterproof board (2);

[0033] 4) After the XPS board (1011) is pasted, the fixing strip (1012) at the upper end thereof is thermally welded to the tunnel waterproofing board (2);

[0034] When installing the buffer layer unit (101), the board seam width should be checked and controlled. The misalignment between adjacent units should be less than 1.5 mm. The bonding area between the XPS board (1011) and the waterproof board (2) should be no less than 80%. After installation, the XPS board (1011) can be repeatedly flattened with a ruler to ensure that the XPS board (1011) and the waterproof board (2) are firmly bonded.

[0035] According to the present invention, a tunnel XPS buffer layer (1) construction method is characterized in that: step (8) installing the positioning steel bar structure (3) is specifically: the positioning steel bar structure (3) is all connected by binding, and the steps are as follows:

[0036] 1) After the buffer layer (1) is installed, first install φ20mm circumferential steel bars, with a spacing of 0.6m between the circumferential steel bars; 25mm thick concrete protective layer pads (303) are used between the steel bars and the buffer unit, with a spacing of about 300mm between the pads; when installing the circumferential steel bars, the arch waist and arch crown can be temporarily supported by means such as curved steel pipes to assist in positioning;

[0037] 2) After the installation of the circumferential reinforcement is completed, one longitudinal reinforcement is installed every 1.0m. The longitudinal reinforcement, circumferential reinforcement and concrete cover pad (303) together form a positioning reinforcement structure (3).

[0038] The present invention has the following advantages: The present invention provides a tunnel XPS buffer layer (1) construction method through improvement, and the construction method of the present invention has the following characteristics;

[0039] (1) The XPS board (extruded polystyrene foam board) used in the buffer layer is an environmentally friendly building material. The closed-cell honeycomb structure of the XPS board makes it light, high-strength, and has high-quality water repellency, moisture resistance, and corrosion resistance, as well as good stability and long service life.

[0040] (2) The fixing strips are pre-pasted to the XPS board, and the buffer layer units formed can be mass-produced and cut easily. They can be installed using a waterproof board mounting trolley.

[0041] (3) The positioning reinforcement system designed for the buffer layer solves the installation process problem of the XPS board in the buffer layer. It has the following characteristics: it completely realizes the nail-free laying of the buffer layer, avoiding the damage and failure of the waterproof board; it prevents the buffer layer from falling due to its own weight and the back of the lining from being hollowed out when pouring the secondary lining concrete; the concrete protective layer pads avoid direct contact between the positioning steel frame and the tunnel waterproof board, solving the problem of exposed rust on the positioning steel bars. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Process flow chart;

[0043] Figure 2 Cross-section of gypsum lining;

[0044] Figure 3-Figure 4 Buffer layer unit installation and positioning structure diagram;

[0045] Figure 5 Buffer layer positioning steel bar structure diagram;

[0046] Figure 6 Buffer layer unit installation diagram. DETAILED DESCRIPTION

[0047] The following will be combined with the Figures 1-6 The present invention is described in detail, and the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0048] The present invention provides an improved method for constructing a tunnel XPS buffer layer 1. The construction method of the present invention has the following characteristics:

[0049] (1) The XPS board 1011 (extruded polystyrene foam board) used in the buffer layer 1 is an environmentally friendly building material. The closed-cell honeycomb structure of the XPS board 1011 makes it lightweight, high-strength, and has high-quality water repellency, moisture resistance, and corrosion resistance, as well as good stability and long service life.

[0050] (2) The fixing strips 1012 and the XPS board 1011 are pre-pasted, and the buffer layer unit 101 formed can be mass-produced and cut conveniently, and can be installed using a trolley for installing the waterproof board 2.

[0051] (3) The positioning and reinforcement system designed for the buffer layer 1 solves the installation process problems of the buffer layer 1 and the XPS board 1011. It has the following characteristics:

[0052] The buffer layer 1 is completely laid without nails, avoiding the waterproof board 2 from being damaged and failing; the buffer layer 1 is prevented from falling due to its own weight and the lining back is prevented from being hollowed out when pouring the second lining concrete; the concrete protective layer pad 303 avoids direct contact between the positioning steel bar skeleton and the tunnel waterproof board 2, solving the problem of exposed rust on the positioning steel bars.

[0053] Scope of application: This method is applicable to the construction of soft rock large deformation tunnel projects with a buffer layer 1.

[0054] Process principle: Utilize the adaptive deformation of the buffer layer 1 under the pressure of the expansive surrounding rock to reduce the extrusion stress of the surrounding rock on the secondary lining structure, improve the anti-destruction ability of the structure, and achieve the purpose of "combining resistance and yielding, first soft then hard, first release then resistance".

[0055] During the construction design, fixing strips 1012 made from waterproofing board 2 were bonded to XPS boards 1011 to form buffer layer units 101. These units 101 were staggered along the tunnel's longitudinal axis, and the joints were sealed with adhesive tape 102 to form the overall structure of the buffer layer 1. By appropriately increasing the back connection of the tunnel waterproofing board 2, the XPS boards 1011 of the buffer layer 1 were fixed to the waterproofing board 2 using fixing strips 1012 using a combination of gluing and hot-melt welding. The buffer layer 1 was supported by a positioning steel structure 3 (longitudinal positioning steel bars 302 + circumferential positioning steel bars 301 + protective layer pads 303), creating a stable overall positioning and reinforcement system. This effectively prevented the buffer layer 1 from falling or shifting, and resolved issues related to the installation process of the XPS boards 1011 of the buffer layer 1. The connection between the buffer layer 1 and the waterproofing board 2 and the positioning steel structure 3 ensured a nail-free installation of the buffer layer 1, ensuring a tight fit with the waterproofing layer. This prevented damage and failure of the waterproofing board 2, and prevented the buffer layer 1 from falling due to its own weight and from being squeezed during the pouring of the secondary lining concrete. The concrete protective layer pad 303 provided between the positioning steel bar skeleton and the tunnel waterproofing plate 2 solves the problems of exposed steel bar corrosion and insufficient protective layer thickness.

[0056] The specific construction process of the present invention is as follows: the installation process of the XPS buffer layer 1 is as follows: Figure 1 As shown;

[0057] (1) Buffer layer 1 design:

[0058] Structural design of buffer layer 1: The Wuzhishan super-long tunnel passes through the gypsum stratum, which expands in volume when it encounters water. According to sampling tests, its free expansion rate reaches 60%, the expansion force is 17.6KPa, and the surrounding rock strength is low.

[0059] Design countermeasures: Increase the reserved deformation and set a 100mm thick buffer layer 1.

[0060] Gypsum lining section diagram Figure 2 .

[0061] XPS board 1011 design technical indicators: water absorption ≤1.0%, dimensional stability ≤1.0%, density about 38kg / m3, compressive strength ≥0.4MPa.

[0062] Buffer layer 1 construction design:

[0063] 1) Buffer layer 1 material selection;

[0064] ——Main material of buffer layer 1: customized XPS board 1011, size 1800mm×600mm×100mm, technical indicators meet design requirements;

[0065] ——XPS board 1011 fixing strip 1012: Made of tunnel waterproof board, fixing strip 1012 is 1.2m long and 200mm wide;

[0066] ——Adhesive: all-purpose glue;

[0067] - Seam sealing material: adhesive tape 102;

[0068] ——Positioning steel bar structure 3: HRB400 steel bar;

[0069] ——Concrete protective layer pad 303: customized high-strength concrete pad.

[0070] 2) Buffer layer unit 101 and positioning structure;

[0071] The positioning structure design of the buffer layer unit 101 is as follows: Figure 3 The fixing strip 1012 is glued to the XPS board 1011 and connected to the tunnel waterproof board 2 by heat welding in a scooping manner. The longitudinal board seam of adjacent buffer layer units 101 is controlled at 2mm~4mm, and the circumferential board seam is controlled at 1.5mm~3mm.

[0072] 3) Buffer layer 1 positioning steel bar structure 3;

[0073] like Figure 4 Concrete protective layer pads (303), circumferential steel bars, and longitudinal steel bars are sequentially arranged from the buffer layer 1 to the clear interface in the tunnel, forming a buffer layer 1 positioning steel bar structure 3. The steel bar specification is φ20mm, and the thickness of the concrete protective layer pads (303) is 25mm. Among them, the spacing between the circumferential steel bars is 0.6m, and the spacing between the longitudinal steel bars is 1.0m. A concrete protective layer pad 303 is arranged every 300mm along the circumferential steel bars.

[0074] (2) Construction preparation:

[0075] 1) Prepare a special construction plan for buffer layer 1, familiarize yourself with the design documents, and clarify material requirements, manufacturing and installation methods and process sequence, quality requirements and inspection standards.

[0076] 2) Confirm the manufacturer of XPS board 1011, and customize it according to the design indicators. When XPS board 1011 enters the site, a material list, product certificate, quality assurance certificate, and inspection report should be provided, and samples should be sent to a qualified testing agency for re-inspection. It can only be used after passing the re-inspection.

[0077] 3) Prepare personnel, materials, and construction machinery and equipment according to construction needs. Provide pre-job safety training and construction technology briefings to construction personnel to ensure they understand construction method requirements and quality standards.

[0078] 3) Waterproof Board 2 Installation: Before installing waterproof board 2, inspect and prepare the initial support surface to ensure it meets flatness requirements before laying the geotextile. Because the XPS buffer layer 1 adheres to the surface of waterproof board 2, to minimize sagging and prevent it from falling, increase the number of hot-melt underlayments during installation. A maximum of 2-3 points / ㎡ is recommended for the vault and 3-4 points / ㎡ for the side walls.

[0079] 4) Laying out and laying out: After the waterproof board 2 is laid out and accepted, the buffer layer unit 101 is laid out and laid out on the waterproof board 2. Figure 6 The buffer layer unit 101 is sized to 1803mm long and 602mm wide, with its length parallel to the tunnel axis. Vertical joints between adjacent units along the tunnel circumference are staggered by 1 / 2 the unit length, with a minimum local stagger of no less than 600mm. After layout is complete, use ink to mark the installation location of the XPS board 1011 on the waterproof sheet 2.

[0080] 5) Making the buffer layer unit 101: Making the buffer layer unit 101 uniformly in the processing plant, such as Figure 5 Each buffer layer unit 101 is installed with two fixing strips 1012 , and the fixing strips 1012 are glued to the XPS board 1011 with adhesive.

[0081] 6) Installing the buffer layer unit 101: The buffer layer unit 101 is installed layer by layer from both sides toward the vault.

[0082] Before installing the buffer layer unit 101 , first clean up any dust, dirt, and other debris remaining on the waterproof board 2 .

[0083] Apply adhesive fully on the contact surface between XPS board 1011 and waterproof board 2.

[0084] The fixing strip 1012 at the lower end of the XPS board 1011 is welded to the laid tunnel waterproof board 2 using a heat welding machine according to the layout position, and then immediately pasted together with the waterproof board 2.

[0085] The installation cross-section of the buffer layer unit 101 is shown in FIG. Figure 5 After the XPS board 1011 is pasted, the fixing strip 1012 at the upper end is thermally welded to the tunnel waterproof board 2.

[0086] During installation of buffer layer unit 101, check and control the board seam width. The misalignment between adjacent units should be less than 1.5mm. The bond area between XPS board 1011 and waterproofing board 2 should be at least 80%. After installation, use a ruler to repeatedly flatten the XPS board 1011 and waterproofing board 2 to ensure a secure bond.

[0087] (7) Treatment of plate joints: 100 mm wide double-layer adhesive tape 102 is applied between adjacent buffer layer units 101 to prevent cement slurry from seeping in during concrete pouring.

[0088] (8) Install the positioning steel bar structure 3: The positioning steel bar structure 3 is connected by binding, and the steps are as follows:

[0089] 1) After installing buffer layer 1, install φ20mm circumferential reinforcement first, spacing the reinforcement 0.6m apart. Use 25mm thick concrete protective layer pads 303 between the reinforcement and the buffer unit, spacing the pads approximately 300mm apart. During the installation of the circumferential reinforcement, use curved steel pipes or other temporary supports to assist in positioning the arch haunches and crown.

[0090] 2) After the installation of the circumferential reinforcement is completed, one longitudinal reinforcement is installed every 1.0m. The longitudinal reinforcement, circumferential reinforcement and concrete cover pad 303 together form the positioning reinforcement structure 3.

[0091] (9) Acceptance: After the installation of buffer layer 1 is completed, timely acceptance should be organized and any defects found during the inspection should be rectified. Only after the acceptance is qualified can the second lining construction be carried out.

[0092] (10) Construction of secondary lining: tying secondary lining steel bars, installing lining trolley, and pouring secondary lining concrete.

[0093] The benefit analysis is as follows;

[0094] Economic Benefits: This method provides important technical support for the construction of tunnels with large deformation in expansive soft rock in gypsum strata, generating a significant technological driving effect, ensuring construction quality, accelerating construction progress, and effectively guaranteeing structural safety. During the construction of the Wuzhishan Tunnel Project in the LJ15 section of the Renmu New Expressway, a detailed analysis and comparison was conducted between traditional measures for handling large deformation in soft rock and this method. The cost analysis for a 100-meter construction length is shown below:

[0095] Table 10-1100m double-layer arch support economic benefit analysis (second layer)

[0096]

[0097] Table 10-2 100m buffer layer structural support

[0098]

[0099] By comparing the analysis results in Table 10-1 and Table 10-2, it can be seen that the comprehensive construction cost of the traditional soft rock large deformation double-layer arch support is 2,494,087 yuan, while the comprehensive construction cost of the buffer layer structure support operation scheme is 1,788,240 yuan, a cost reduction of 705,847 yuan, and a cost saving rate of 28%. While ensuring that the construction quality meets the standards, this method has significantly improved the work efficiency time, saved process time, reduced labor input, and greatly reduced management costs.

[0100] Social Benefits: The proposed construction technology enables rapid and effective support for large deformations in expansive soft rock tunnels. This demonstrates the principle of "flexibility first, rigidity later" in treating expansive soft rock tunnel structures. It replaces traditional double-layer primary support measures, significantly reducing the use of steel and concrete, and conserving resources. Through a "resistance-yield combination" approach, the method employs an XPS buffer layer to mitigate the expansion stress of the expansive soft rock. This reduces the lining damage caused by traditional construction methods in expansive soft rock tunnels and reduces maintenance costs during subsequent operations.

[0101] Currently, highway construction is shifting from plains to mountainous areas, a particularly pronounced trend in Sichuan Province's highway network. Mountainous tunnels are often subject to unfavorable geological conditions, such as weak surrounding rock. This method can be directly applied to the integral support construction of tunnels in complex, soft rock formations with large deformations. Because highway tunnels share similar structures with other tunnels, the research results of this project can be widely applied not only to highways but also to railways, water conservancy projects, and other fields. Therefore, the project has a promising future for its promotion and application, and will undoubtedly accumulate important technical experience for the construction of tunnels in complex, soft rock formations with large deformations.

[0102] Application examples:

[0103] The LJ15 contract section of the Renmu New Expressway, part of the Renshou to Pingshan Xinshi Highway Project in Sichuan Province, is located in Zhongdu Town, Pingshan County, Yibin City. The contract section runs from K137+750 to K145+160 (ZK145+150), with a total length of 7.405 km. The Wuzhishan Super Long Tunnel exit is the key project for this contract section. The right tunnel is 4,530 meters long, and the left tunnel is 4,522 meters long. The strata are primarily composed of mudstone, silty mudstone, argillaceous siltstone, fine sandstone, coal seams (lines), limestone, marl, dolomite, breccia, and gypsum. Groundwater types include carbonate karst water, pore water in clastic rocks, bedrock fissure water, and fracture zone water. Large-scale water inrush is possible in fracture zones, igneous intrusion contact zones, non-soluble rock contact zones, and carbonate strata.

[0104] The aforementioned unfavorable geological conditions include a 132-meter-long gypsum stratum section in the left tunnel (ZK138+888 to ZK139+020), and a 137-meter-long gypsum stratum section in the right tunnel (K138+890 to K139+027). The project applicant, in collaboration with all parties involved in the construction, actively conducted research using new materials to address the unfavorable geological conditions in the gypsum section of the tunnel. They developed a tunnel XPS buffer layer construction technology to resist large deformations in expansive soft rock, forming the "XPS Buffer Layer Construction Method for Tunnels with Large Deformations in Soft Rock." Through practical on-site application, this method effectively mitigated the stress compression on the lining caused by surrounding rock expansion. The construction method was safe, reliable, environmentally friendly, and faster than traditional methods, saving time and costs. The project received unanimous recognition from the owner and supervisor, achieving significant socioeconomic benefits.

[0105] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A tunnel XPS buffer layer construction method, characterized in that ； During construction design, a fixing strip (1012) made of a tunnel waterproof board is pasted to an XPS board (1011) to form a buffer layer unit (101). The buffer layer units (101) are arranged in a staggered manner along the longitudinal direction of the tunnel and the joints are sealed with a self-adhesive tape (102) to form a buffer layer (1). By appropriately increasing the back connection of the tunnel waterproofing board, the fixing strip (1012) of the buffer layer unit (101) is connected and fixed to the tunnel waterproofing board (2) by a combination of gluing and hot-melt welding, and the buffer layer (1) is supported by a positioning steel bar structure (3), thereby forming an overall stable positioning reinforcement system, effectively preventing the buffer layer (1) from falling off and shifting, and solving the process problem of installing the buffer layer (1); the specific construction steps and methods are as follows; Step 1: buffer layer construction structure design; 1) Material and specification selection: ——XPS board (1011): refers to extruded polystyrene foam board, with a size of 1800mm×600mm×100mm, and technical indicators meet the design requirements; ——Fixing strip (1012): Made of 1.5mm thick tunnel waterproof board, the fixing strip (1012) is 1.2m long and 200mm wide; ——Adhesive: all-purpose glue; ——Self-adhesive tape (102): width 100 mm; —— Positioning steel bar structure (3): Made of HRB400 steel bar; ——Concrete protective layer pad (303): customized high-strength concrete protective layer pad; 2) Design of the positioning structure of the buffer layer unit (101): the fixing strip (1012) is glued to the XPS board (1011) and connected to the tunnel waterproof board by heat welding in a cradle-type manner. The longitudinal board seams of adjacent buffer layer units (101) are controlled within 2 mm to 4 mm, and the circumferential board seams are controlled within 1.5 mm to 3 mm. The longitudinal board seams and the circumferential board seams are both sealed with self-adhesive tape (102); 3) Design of the buffer layer positioning steel bar structure (3): concrete protective layer pads (303), circumferential steel bars (301), and longitudinal steel bars (302) are sequentially arranged from the buffer layer (1) to the clear interface in the tunnel, forming the buffer layer positioning steel bar structure (3); Step 2, installation of the tunnel waterproofing board (2): before installing the tunnel waterproofing board (2), first inspect and process the initial support surface of the tunnel to ensure that it meets the flatness requirements and then lay the geotextile; The number of hot-melt pads on the back of the tunnel waterproofing board (2) should be appropriately increased, with a control of 2 to 3 points / ㎡ for the arch and 3 to 4 points / ㎡ for the side wall; Step 3, laying out and typesetting: laying out and typesetting the buffer layer unit (101) on the tunnel waterproofing board (2); The installation dimensions of the buffer layer unit (101) are controlled to be 1803 mm in length and 602 mm in width, and the buffer layer unit (101) is parallel to the tunnel axis in its length direction; the vertical joints of adjacent buffer layer units (101) along the tunnel circumference are staggered by 1 / 2 of the unit length; Step 4, making the buffer layer unit (101): installing two fixing strips (1012) on each buffer layer unit (101), and bonding the fixing strips (1012) to the XPS board (1011) with adhesive; Step 5, installing the buffer layer unit (101); Step 6, treating the plate seams: the plate seams between adjacent buffer layer units (101) are taped with a double layer of self-adhesive tape (102) to prevent cement slurry from seeping in during concrete pouring; Step 7, installing the positioning steel bar structure (3): the concrete protective layer pad (303), the circumferential steel bar (301), and the longitudinal steel bar (302) are all connected by tying to form the positioning steel bar structure (3); Step 8, acceptance: After the buffer layer (1) is installed, it is promptly accepted and any defects found are rectified. Only after it passes the inspection can the secondary lining construction be carried out; Step 9, construct the secondary lining: tie the secondary lining steel bars, install the lining trolley, and pour the secondary lining concrete.

2. A tunnel XPS buffer layer construction method according to claim 1, characterized in that: In step 1, the buffer layer positioning steel bar structure is designed as follows: the support thickness of the concrete protective layer pad (303) is 25 mm, and the concrete protective layer pad (303) is set at one position every 300 mm along the circumferential steel bar; the longitudinal steel bar (302) and the circumferential steel bar (301) are both made of φ20 mm steel bars, wherein the longitudinal steel bar (302) is spaced 1.0 m apart, and the circumferential steel bar (301) is spaced 0.6 m apart.

3. The method for constructing a tunnel XPS buffer layer according to claim 1, characterized in that: In step 5, the buffer layer units (101) are installed layer by layer from both sides to the dome, as follows; A. Before installing the buffer layer unit (101), clean up the dust, dirt and other debris remaining on the tunnel waterproofing board; B. Apply adhesive to the contact surface between the XPS board (1011) and the tunnel waterproof board (2); C. Weld the fixing strip (1012) at the lower end of the XPS board (1011) onto the already laid tunnel waterproof board (2) using a heat welding machine according to the layout position, and then immediately stick it together with the tunnel waterproof board (2); D. After the XPS board (1011) is pasted, the fixing strip (1012) at the upper end is thermally welded to the tunnel waterproof board.

4. The method for constructing a tunnel XPS buffer layer according to claim 1, characterized in that: In step 5, the offset height between adjacent units should be less than 1.5mm; The bonding area between XPS board (1011) and tunnel waterproofing board should be no less than 80%.

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