Model tests on failure laws of ground with voids induced by shallow tunnelling

The void existing in the ground is an important inducement for safety accidents in shallow tunnelling. Based on model tests, the failure laws of ground with voids at different locations and with different numbers are studied. The results show that: (1) The shallow tunnelling in the ground with voids results in more rapid failure process, more severe failure degree and larger surface collapse of the surrounding rock than that in the ground without voids. (2) When the tunneling is adjacent to the voids, the failures of the surrounding rock are more likely to start from the voids. Therefore, it’s important to take effective measures to deal with the voids before the tunnelling to prevent safety accidents. (3) The location and quantity of voids significantly change the geometrical characters of slip planes in the surrounding rock, such as the angle and the symmetry, which makes the failure laws of the ground with voids more complicated than those of the ground without voids. (4) When the void is located diagonally above the tunnel, the first ground surface crack at the opposite side of the void appears earlier than that at the other side. Moreover, the quantity and size of ground surface cracks at the opposite side of the void are obviously larger than those at the other side. It may provide significant information for deducing the location of a void by observing the distribution of ground surface cracks during shallow tunneling.