Determinant criterion for safety of large section subsea tunnels and its application during construction

Because of the complexity of construction methods and support system of subsea tunnels, it is difficult to judge the surrounding rock and support safety only by using one stability index. Five determinant indexes about the surrounding rock and support safety are put forward based on their mechanical characteristics, including three quantitative indexes of surrounding deformation, deformation rate and deformation acceleration and two qualitative indexes of groundwater state and support state of tunnels. The hazard zones are classified based on the displacement control criteria as follows: unstable state, dangerous state, abnormal state and normal state. The allowable deformation rate of surrounding rock and support is determined for different hazard grades based on the total deformation U, displacement control criteria U0 and deformation time of surrounding rock and support t. Finally, the determinant criterion for safety of large cross-section subsea tunnel during construction is put forward by analyzing qualitative and quantitative indexes. It is instructive for judging the safety of surrounding rock and support and for forecasting the collapse of tunnels. This criterion has been implemented in Xiamen East Passage subsea tunnel.