Response of a double-decked metro tunnel to shield driving of twin closely under-crossing tunnels

Abstract Twin tunnels on Shenzhen metro Shekou Line were driven by EPB shields through weathered granite gneiss closely under-crossing a double-decked tunnel embedded in strongly weathered granite gneiss on Luobao Line. The performance of the existing tunnel as affected by under-crossing tunnels was continuously monitored by means of an automatic high-performance total station measuring system. Displacements of the existing tunnel caused by under-crossing tunnels in different under-crossing stages were measured. The measured data were timely processed and fed-back to related operators to realize an information-oriented project. Based on the measured data discussions and analyses were carried out in terms of the impact of the under-crossing shield tunnelling on the existing tunnel, effect of rainfall infiltration on the performance of the existing tunnel, allowable deformations of the existing tunnel, possibility of reducing the number of measuring points in a monitoring cross section and the influence on the existing tunnel caused by twin tunnels. Thanks to the staggered single tunnel under-crossing and other favorable factors, the measured deformations of the existing tunnel were well below the predefined allowable values. Under the guidance of monitoring, the under-crossing project was smoothly completed without interruption of metro traffic. This is a valuable example for evaluating the shield tunnelling induced effects on adjacent existing tunnels and establishing criteria to guide shield tunnelling under similar conditions.