my country has a vast territory and complex geological conditions. A large amount of corrosive minerals such as sulfates are distributed in the mountains that the highway tunnels pass through. With the increase of operation time, the concrete is eroded by groundwater, resulting in diseases such as crystal loosening, strength reduction, peeling, etc., resulting in a gradual decline in the bearing capacity of the lining structure, which seriously affects the use function and operation safety of the tunnel, and must be reinforced.

In the reinforcement of tunnel structure engineering, the commonly used methods include grouting method, embedded arch (rail) and steel belt reinforcement method, sleeve arch reinforcement method, lining replacement arch method and so on.

one、grouting method

For small cracks that do not affect the safety of the structure, they need to be closed and filled in consideration of crack propagation and aesthetic effects. According to past experience, when the crack width is 0.2-1 mm, high-strength sealing mortar should be used to seal the crack surface to prevent the oxidation of steel bars in the crack, and at the same time, it can sew and prevent the crack from developing further. When the crack width is greater than 1mm, in addition to sealing the crack surface, epoxy resin and high-strength glue should be filled in the crack by injection and other methods.

High-strength mortar sealing has high stiffness and strength, and has the function of connecting the crack surface and preventing crack expansion, so it can effectively seal various types of cracks. Crack fillers are mainly used to prevent dislocation friction between the upper and lower surfaces of cracks, thereby preventing crack shear and compression shear damage.

Fillers in cracks are only effective for compressive shear fractures and shear fractures, and are invalid for tension cracks or tensile shears. The filler in the crack can be filled fully, and the pressure should not be too large, because the excessive pressure is not conducive to the stability of the crack structure.

two、Embedded arch (rail) and steel belt reinforcement method

When the cracks in the tunnel lining are serious and the structure has a strong bearing capacity, the structure can be reinforced by the method of embedded arch (rail), steel belt, mesh and sprayed (steel fiber) concrete.

The embedded arch (rail) method and the steel strip reinforcement method enable the lining structure to be effectively supported by circumferentially supporting (or grooving and burying) steel strips, steel arches or steel rails in the lining structure. The reinforcement of the embedded arch (rail) can be directly performed outside the lining according to actual needs, or it can be installed in the original lining. The specific construction method can be comprehensively selected according to the emergency degree, reinforcement purpose and building boundary factors.

Three、set arch reinforcement method

When the tunnel clearance allows and the lining structure has a certain bearing capacity, the casing arch structure is re-applied outside the existing lining. The new construction structure and the original structure form an integral body to jointly bear the surrounding rock pressure, and ensure the safety of the tunnel on the basis of making full use of the bearing capacity of the original structure.

According to the different operating scope of the sleeve arch structure, it can be divided into integral sleeve arch and partial sleeve arch. It should be noted that part or part of the concrete structure needs to be removed before the construction of the sleeve arch, and the effective connection between the original structure and the new construction structure should be ensured. The set arch can be constructed by moulding concrete or by shotcrete (steel fiber, carbon fiber) concrete. Adding steel fiber and carbon fiber to the shotcrete can effectively enhance the bearing capacity of the structure and reduce the thickness of the set arch structure.

Four、 lining replacement arch method

When the original structure of the tunnel has lost the bearing capacity or the structural clearance is not allowed, and the bearing capacity cannot be guaranteed by the use of steel strips and embedded arches, the original lining structure needs to be removed and replaced. Similar to lining sleeve arch, lining replacement can be divided into overall replacement and partial structural replacement.

In addition to the above-mentioned disease treatment technologies, new materials, new technologies and new processes have also been tried and applied in my country's highway tunnel lining reinforcement projects. The methods of spraying carbon (steel) fiber concrete and adding mesh, pasting carbon fiber composite materials, and sticking steel plates have also been applied in different highway tunnels and subway disease treatment projects.