ABSTRACT
This paper is to present a theoretical approach for predicting deformation, development and progress of plastic zones around tunnels in soft rocks and for determining the loosening pressure which has to be taken by rock bolts or lining of tunnels. Influence effects of the mechanical properties of soft rocks on the loosening pressure are examined and discussed. The judgement charts used to assess the extent of rock failure are calculated according to the ground characteristic curve. It is clarified that the ground characteristic curve shows a lowest point that refers to the minimum support pressure and the controlled tunnel wall strain when the competency factor (i.e. ratio of compressive strength to the initial in-situ pressure), Srp, is smaller than the critical value, [Srp], which can be illustrated based the proposed theoretical equations.
