Performance Assessment of Arch-shaped Primary Lining during Construction in Weak Rock Shallow-buried Tunnel

Tunnels excavated through weak rock masses using the Shallow Tunneling Method (STM) call for rigid lining support to withstand and constrain the mobility of the unstable rock where its performance needs to be assessed with field measured data in case of potential failure. For fear of any further hazards after the occurrence of a rock fall at chainage km 86,685 m in the Longsheng Tunnels, the monitoring plan was specially modified to accurately obtain the relative vertical and horizontal displacements of the steel rib component in the arch-shaped composite rigid primary lining that was simply placed on the heading. In this paper, the weak rock masses’ interaction with the rigid lining is treated as unknown distributed loads divided into radial and tangential directions, where the influence line theory is applied to better understand the response of the lining so as to facilitate a displacement-based back analysis for unknown rock mass loads and the resultant stress outcome. By comparing the back analyzed stress outcome with the measured one, the proposed performance assessing method for the unclosed arch-shaped lining was proven to be time efficient with acceptable accuracy, which is of considerable application potential and can provide a reference for similar engineering.