Underground transportation systems development often involves multiple tunnels with a closer distance especially at downtown of the metropolis. During the construction of new tunnels, it is important to assess the settlement and deformation that are induced in the existing structures due to tunneling. Previous studies mainly focus on the interaction of circular tunnels, deformation and stress transfer mechanism of a non-circular tunnel subjected to circular tunneling are not well investigated. The main objectives of this study are to gain a better understanding of the role of the existing tunnel shape on crossing tunnels interaction. Furthermore, this research aims at providing high-quality physical data for numerical modelers and engineers for verifying their designs.

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Underground transportation systems development often involves multiple tunnels with a closer distance especially at downtown of the metropolis. During the construction of new tunnels, it is important to assess the settlement and deformation that are induced in the existing structures due to tunneling. Previous studies mainly focus on the interaction of circular tunnels, deformation and stress transfer mechanism of a non-circular tunnel subjected to circular tunneling are not well investigated. The main objectives of this study are to gain a better understanding of the role of the existing tunnel shape on crossing tunnels interaction. Furthermore, this research aims at providing high-quality physical data for numerical modelers and engineers for verifying their designs.

A total of five centrifuge tests were conducted out in dry Toyoura sand. Factors affecting the interaction of crossing tunnels, such as the shape of the existing tunnel, pillar depth and cover depth, were investigated. During tests, bender elements were first time used to measure soil stiffness change along the new tunnel construction. Three-dimensional numerical back analyses were carried out to improve the understanding of the stress transfer mechanism, strain and stiffness change in crossing-tunnel interaction. Hypoplasticity constitutive model which can capture small strain stiffness was adopted in this study.

The measured and computed bending strains at the invert of the horseshoe-shaped tunnel were three times larger than those at the invert of the existing circular tunnel in the transverse direction. This is due to hoop stress along the tunnel lining in the existing horseshoe-shaped tunnel was discontinued and smaller than that in the circular tunnel. therefore, the hoop effect on the horseshoe-shaped tunnel is smaller than that in the circular case.

The response of the existing tunnel with different cross-section geometry is strongly influenced by the pillar depth-to-diameter ratio (P/D). Results reveal that the existing horseshoe-shaped tunnel experiences hogging under a smaller pillar depth while sagging with a larger pillar depth at invert. The existing circular tunnel under a smaller pillar depth shows compressed vertically but elongated horizontally. However, opposite deformation trend was observed for the circular tunnel with a larger pillar depth. These results demonstrate that both pillar depth and shape profoundly affect tunnel deformation mechanisms.