THE SQUEEZING POTENTIAL OF ROCKS AROUND TUNNELS - THEORY AND PREDICTION

The deformational behaviour of tunnels, which underwent large deformations, so-called squeezing, have been recently receiving great attention in the field of rock mechanics and tunnelling. Contrary to rockbursting phenomenon in which the deformation of the medium takes place instantaneously, the deformation of the surrounding rock in squeezing phenomenon takes place slowly and gradually when the resulting stress state following the excavation exceeds the strength of the surrounding medium. Although there are some proposals for the definition of squeezing rocks and prediction of their squeezing potential and deformations of tunnels in literature, it is difficult to say that they are concise and appropriate. In the first half of this paper, the squeezing phenomenon of rock about tunnels and its mechanism and associated factors are clarified by studying carefully observed failures in-situ and laboratory model tests. Then, an extensive survey of tunnels in squeezing rocks in Japan is presented and the results of this survey are summarised. In the second half of the paper, a new method is proposed to predict the squeezing potential and deformations of tunnels in squeezing rock. Then, the method is applied to actual tunnelling projects, where squeezing problems have been encountered, to check its validity and applicability. As a concrete example, an application of the method to predict the squeezing potential and deformations of the rock along a 300 m long section of an actual tunnel was made.