The squeezing potential of rock around tunnels: Theory and prediction with examples taken from Japan

Large deformations of surrounding media around tunnels are often encountered during excavations in rocks with squeezing characteristics. These deformations may sometimes continue for a long period of time. Predictions of deformations of tunnels in such grounds are urgently needed, not because of stability concerns, but also of their sevicability. In the present study, the squeezing phenomenon of rock around tunnels and its mechanism and associated factors are first clarified by carefully studying failures of tunnels, and a survey of tunnels in squeezing rocks in Japan is presented, and its results are summarised. Then, a practical method is proposed to predict the squeezing potential and deformation of tunnels in squeezing rock and this method has been applied to actual tunnelling projects, where squeezing problems were encountered, to check its applicability and validity. Finally, an extension of this method to the time-dependent behaviour of squeezing rocks is given and an application of this method to an actual tunnel is presented.