Research on the dynamic failure behavior of fissured tunnel subjected to combined dynamic and static loads

With the development of mining shifting to deep underground, the effect of in-situ stress on the stability of deep tunnels cannot be ignored acted upon by dynamic disturbance loads. Numerical simulations of the failure behavior of fissured tunnel model acted upon by the effect of coupled dynamic disturbance loads and in-situ stresses are conducted by using finite difference software AUTODYN. The tunnel model containing a mode I crack was made with green sandstone, a large-scale drop-hammer impact test equipment was used as dynamic disturbance loading device. The crack initiation time (CIT), crack growth rate and crack arrest time were obtained by using the crack propagation gauge (CPG). Subsequently, a series of simulations were conducted under 0.5 ∼ 3 MPa in-situ stress and dynamic loads combined conditions. The obtained results indicate that with an increasing in the level of in-situ stress in the practical tunnel, the CIT, crack propagation length, and average crack growth rate are less than that of the tunnel in the absence of in-situ stress. The dynamic circumferential tensile stress concentration at tunnel spandrel and foot increases with the level of in-situ stress. In addition, the maximum value of the dynamic initiation toughness (DIT) reaches at in-situ stress of 1.5 MPa, and then the DIT decreases with the level of in-situ stress.