Surface subsidence characteristics of fully overlapping tunnels constructed using tunnel boring machine in a clay stratum

摘要

This study investigates the characteristics of vertical soil deformation induced by fully overlapping tunnels constructed using a tunnel boring machine (TBM). The Peck formula is improved to consider the variation in the tunnel axis depth and stratum loss ratio. Comparing the settlements both monitored and simulated on the fully overlapping tunnels of the Tianjin Metro, it is shown that our improved Peck formula is suitable to predict the surface settlement of fully overlapping tunnels. The present comprehensive research shows that during the construction of fully overlapping tunnels, the ultimate maximum settlement value is more affected by the construction of an upper-line tunnel than by the construction of a lower-line tunnel. The width of the ground settlement trough in fully overlapping tunnels construction is only affected by the lower-line tunnel, but the final settlement value is not simply the sum of the settlements of the two tunnels. The overlapping effect between the upper and lower lines reduces the stratum loss and the maximum settlement caused by excavation of the upper-line tunnel.