Investigation on the strain energy release prior to a major ground collapse of a large section soft rock tunnel

Abstract In this study, the surrounding ground mass energy release was investigated to demonstrate the inefficiency of the support system prior to a major ground collapse in a twin freeway tunnel excavated in a soft surrounding rock mass (with poor mechanical properties) using simulation. Unlike hard rocks, soft rocks tend to soften in the immediate vicinity of the underground excavation, as demonstrated in this case by a nodal output. Through dynamic analysis, it has been proven that the ground energy release has exceeded the energy provided by the support system, and the countermeasure support has a limited safety margin despite supplying sufficient energy. A feedback approach is proposed through a change in the excavation method, which has proven to be an efficient way to reduce ground energy release during the tunnel excavation process.