Project Overview

The project implemented two tunnel structural reinforcement works. Tunnel A is a double-arch tunnel with a length of 200m. The tunnel traverses the Saddle topography, the surrounding rock is tuff, and the Flint Road passes through the fault structure fracture zone and the affected zone in the Saddle area. The surrounding rock joints are well developed, the rock mass is poor in integrity, and the crushed rock structure is formed. The surface water is relatively enriched, the fault zone has a high water content, large deformation occurred during excavation, cracks and subsidence appeared on the surface, and the surface was reinforced by grouting and the lining structure was strengthened. After the tunnel was completed and opened to traffic, there were different degrees of cracks in the 75m area of the second lining, and there was water leakage in the rainy season, which jeopardized the safety of tunnel operation. It was decided to fix the cracks and water leakage and paste carbon fiber sheets to reinforce the tunnel lining structure. . Tunnel B is 1,400 m long, and due to the development of joints in the surrounding rock during excavation, a large collapse occurred. After the completion and opening to traffic, cracks and water leakage occurred within 48 m of the front and rear. After the cracks and water leakage were treated, unidirectional carbon fiber sheets were pasted to reinforce the lining structure.

Tunnel A is a full-section construction of unidirectional carbon fiber sheets. Tunnel B is a 24m full section construction of carbon fiber sheets with many cracks. Two layers were constructed at the original landslide position, and the unidirectional carbon fiber sheet was constructed only within 30cm of the crack area for the other 24m. A total of 3 700 square meters of unidirectional carbon fiber sheets were constructed in the two tunnels

Construction materials and construction technology

1) structural strengthening material index requirements: Unidirectional Carbon Fiber Sheet

unit weight: 300 g/m2; tensile strength: 3 550MPa; elastic modulus: 220 GPa; nominal thickness: 0.167mm.

2) Construction technology

• Concrete surface treatment

• Brush the primer

• Leveling and repairing with leveling glue

• Carbon fiber glue 

• Paste carbon fiber cloth

• Coated with carbon fiber glue

• Maintenance

• Surface protection

Matters needing attention in construction

Lap method of carbon fiber cloth

1) Length direction (fiber direction). When cutting carbon fiber cloth, the length should not be too long. When the design is not required, the length of each carbon fiber cloth should not exceed 3m. During construction, the standard is 2.5m-3m to facilitate the pasting operation. The lap length shall not be less than 10 cm. During the construction, the overlap shall be 20 cm. Pay attention to uniformity.

2) Width direction (direction perpendicular to fiber direction). When the carbon fiber cloth is overlapped in the horizontal direction, it is generally not necessary to overlap. If the surface flatness is poor and there may be gaps between the cloth materials, the overlap is 2 cm-3 cm.

Post-processing of carbon fiber paste

After the carbon fiber cloth is pasted, if defects such as bulging, wrinkles, wrinkles, etc. occur before the adhesive hardens, they should be treated immediately.

1) Bulging: Coating bonding resin on the bulging part, and then rolling it with a rubber knife, rubber slow knife or roller to exhaust the internal air.

2) Wrinkles: Scrape along the fiber direction with a rubber spatula to correct them.

3) Wrinkle: Fiber wrinkle will seriously affect the tensile strength, so it should be corrected with a rubber scraper to make it as flat as possible.

Conclusion

Unidirectional carbon fiber sheet is a relatively common method in structural reinforcement, but there are few examples used in tunnel structural reinforcement. The successful application of this project provides valuable practical experience for similar projects in the future.