Ground Movement and Existing Tunnel Deformation Induced by Overlapped Tunneling.

Tunneling inevitably induces changes in soil stress and, hence, may adversely affect the surrounding ground and nearby existing tunnels. A model test and a series of numerical analyses were carried out to investigate the response of the ground and existing tunnels in sandy soil to nearby tunneling according to the relative spacing. The test results showed that increasing the distance-to-diameter ratio (d/D) changed the settlement trough from W-shaped to U-shaped along the transverse section. In addition, the major settlement area induced by each advancing step along the longitudinal section was within 0.75D in front of the tunnel face. The numerical results showed that the overall downward movement of the existing tunnel was due to the combined action of soil pressure and excavation unloading. In this article, the mechanism of the W-shaped surface settlement is discussed; a modified Peck formula is used to describe the W-shaped settlement trough, and the relation of typical parameters to d/D is analyzed. [ABSTRACT FROM AUTHOR]