ABSTRACT
Tunnelling in soft soils is difficult and constructing large vehicular tunnels in such soils is even more challenging. Ground improvement is often used to strengthen the soil surrounding the tunnel opening, however, failure mechanisms and stability of large vehicular tunnels in improved soils are still unknown. This paper presents centrifuge modelling of a rectangular tunnel of vehicular dimensions in cement-treated soils. The strength and thickness of improved soil zone surrounding the tunnel were varied to study the possible failure modes. From post-test examination, bending or flexural leading to roof collapse was found to be a dominant failure mode. The stability increased with strength or thickness of improved soil zone surrounding the tunnel, however the failure mechanism did not vary much for different tests. Based on the failure mechanism, an analytical method was proposed for finding the critical tunnel support pressure at the springline of a tunnel.
