The effects of existing horseshoe-shaped tunnel sizes on circular crossing tunnel interactions: Three-dimensional numerical analyses

Three-dimensional numerical analyses were conducted to study the effects of the ratio of the breadth of an existing horseshoe-shaped tunnel to the diameter of new circular tunnels (B/D) on the interaction of perpendicularly crossing tunnels in sand. Hypoplasticity constitutive soil model with small strain stiffness was adopted in the study. For different cover depths, the computed results revealed that the induced maximum settlement at the centre of an existing tunnel invert is unaffected by its size. The sagging settlement profile along the existing tunnel crown gradually changes into a hogging shape with increasing B/D ratios for smaller cover depth. The mid-plane deformations of the existing tunnel are vertically elongated and horizontally compressed.