Collapse mechanism of deep tunnels with three-centered arch cross section

The possible collapse of different circumstances is derived with the help of the limit analysis theory. Analytical equations related to collapsing mechanisms in deep tunnel with smooth three-centered arc cross sections are derived on the basis of Hoek-Brown failure criterion and upper bound limit analysis. The pore water pressure is considered in the analysis, as a work rate of external force. Numerical results about the shape of detaching curve and the weight of collapsing block per unit length corresponding to different parameters are obtained with the help of mathematical software. The shapes of collapsing block are drawn with respected to different parameters. Furthermore, the effects of different parameters on the shape of detaching curve and the weight of the collapsing block are discussed.