Introduction

In recent years, major cities in China have set off a climax of rail transit construction, and the mileage of subway tunnels is also increasing. However, a few cities still lack the awareness of the protection of subway tunnels. After the construction of the subway tunnel or before its operation, due to the excavation of the deep foundation pit around the subway and the heavy load above the subway axis, the tunnel axis shifts and the tunnel structure is affected. damage. In order to ensure the safety of the subway tunnel structure, before the operation of the subway tunnel, some cities adopted the tunnel segment steel ring reinforcement construction technology to eliminate the hidden danger of the tunnel structure. The following introduces the steel plate used for the reinforcement construction technology of a non-operating subway tunnel in a certain city.

Project Overview

A certain section of the tunnel is 747.456 meters long, with 621 loops on the left and right tunnel segments. The outer diameter of the section tunnel segments is ∅6.2m, and the inner diameter is ∅5.5m, which are assembled with common lining rings. Recently, due to the influence of the excavation of the foundation pit on the north side of the section, the left and right tunnels have seen large changes in the arch bottom settlement, horizontal displacement, and lateral convergence. There are many cracks in the segment, the size of the cracks is different, the width is more than 0.2mm, most of the single-ring long longitudinal joints, the longitudinal cracks of the single-ring segment are 3~7, and most of them occur in the range of 45° at the bottom of the tunnel. There are more cracks on the north side than on the south side. At the same time, there are obvious phenomena of loops, longitudinal joints, and serious water leakage in the segment.

Determination of reinforcement construction plan

To ensure the structural safety and operational safety of the tunnel in this section. After research, it is determined that the section with large settlement, horizontal displacement, convergence deformation and joint opening, and cracks and water leakage in the section need to be reinforced with steel ring reinforcement construction plan. Specifically, a Q235B steel arc plate with a thickness of 20mm and a width of 900mm is selected and the outer diameter is 5500. Each ring tube piece is installed in close contact with one bottom block with a curvature of 100°, two blocks with a curvature of 60°, two adjacent blocks with a curvature of 50°, and one block with a curvature of 40°. A total of 6 pieces form a closed steel ring. When the steel ring is installed, it is staggered with the longitudinal seam of the tube, and finally the gap between the steel ring and the tube is filled with epoxy resin.

Main structural reinforcement materials

The construction materials mainly include Q235 steel plate, steel plate epoxy, elastic epoxy grout, elastic epoxy cement and spray-type polyurea elastomer materials.

Construction summary

(1) Rigid epoxy resin slurry is used as a filling grouting material for concrete structures. After curing, it condenses into a high-strength polymer. It is suitable for dry and humid environments. It has low viscosity, strong permeability, and bonding strength (including wet bonding strength), high compressive, tensile and shear strength, and no shrinkage.

(2) The use of steel ring plates to strengthen the segment lining inside the tunnel can reduce the stress and deformation of the tunnel to a certain extent and improve the rigidity of the damaged tunnel structure.

(3) It is recommended to conduct regular monitoring of the tunnel structure in order to grasp the changes in the tunnel structure.

(4) It is recommended to strengthen the protection of subway tunnels under construction. One is the legislative protection of the local government, the second is to set up warning landmarks within the red line of the subway axis under construction, and the third is to strengthen the inspection of the ground construction around the tunnel structure on a regular basis to find out and rectify in time.