Abstract
When excavating shallow tunnels in ground consisting of granular materials like sands, both surface subsidence, due to loosening of the ground, and earth pressure acting on a tunnel lining, become serious problems. In order to solve these problems, model tests have been conducted in the laboratory by using a group of alminum bars, in which a circular hole is made as a model of a tunnel. In the tests, a new piece of equipment has been developed, which can apply air pressure on the internal surface of the hole. The air pressure is then gradually reduced from a certain level to represent an excavation operation of tunnels. Thus, it enables to us to determine the minimum pressure necessary to stabilize the hole. The experimental results discussed in comparison with those obtained by a conventional method, applying constant displacement all over the internal surface of a tunnel.
