Connecting passage for tunnel Steel pipe piece It is also called special lining ring for tunnel. It is installed between two tunnels to connect the two tunnels, which is convenient for maintenance, fire fighting and escape. It is widely used in subway tunnel, highway tunnel and railway tunnel. Because it is designed according to the structure and use requirements of the tunnel, the steel is processed, welded and treated with anti-corrosion. Therefore, it has high strength, easy to install, and the middle connecting passage is easy to dismantle and construct. According to the design requirements, it is divided into half ring and integral ring.