Evaluation on displacement risks of dismantling temporary lining in tunnel and optimization on temporary lining configuration

In tunnel engineering, the temporary lining is adopted as an effective countermeasure in mitigating tunnel failure potential, often featured by extra-large cross-sections and/or driven through weak ground conditions. However, dismantling temporary linings negatively impacts primary linings. In this paper, the comprehensive research is conducted on the displacement risk caused by dismantling temporary lining based on two alternative tunneling methods (TM-1 and TM-2). Besides, the following three influence factors are taken into consideration: the axial forces in temporary linings, the thickness of preliminary linings, and the deformation modulus of ground. After that, the tunneling method optimization plan is proposed from the view of these three influence factors. The results show that TM-1 always induces invert uplift, whereas TM-2 mainly brings about invert uplift or sidewall bulging depending on which transverse or vertical linings are dominant in terms of axial force values. For TM-2, the axial force in transverse linings can suppress the development of maximum deformation increment (MDI) value at invert when the axial forces in transverse linings are smaller than those in vertical linings. It is also found that with the further increase of the axial force in transverse linings in TM-2, MDI relocates to the sidewall. Moreover, on the basis of the displacement risk evaluations, an optimization on the temporary lining configurations has been developed by replacing temporary linings with pre-tension anchor cables to reduce the risk of dismantling temporary linings. All the research results can provide some important reference for the similar tunnel engineering in the future.