Early warning limits for uneven settlement of metro tunnels based on vehicle–track interaction simulations

Abstract

Metro shield tunnels in soft soils often exhibit uneven settlement, which causes leakage, cracking, dislocation, and bolt failures. Excessively uneven settlement affects the safety and durability of a tunnel structure and aggravates the track irregularity, thereby impeding operational safety, ride comfort, and steady function. As ride safety and comfort are more sensitive than tunnel structure safety to uneven settlement, they can potentially be used as indexes for the early warning of uneven settlement. Accordingly, a 20 m long metro rail car model with 10 degrees of freedom was established, and its behaviors were analyzed under different settlement amplitudes and running speeds. The results indicated that the rail car operational comfort index was more sensitive than the safety index to uneven settlement. An early warning value was then determined on the basis of the comfort index ranges for settlement length and vehicle speed, enabling the development of an early warning strategy for uneven settlement. The proposed strategy was subsequently applied to a case study, which monitored the uneven settlement of an interval of a metro shield tunnel using inclinometers.