Application of stochastic joint network simulation to composite strata of shallow-buried long-span metro tunnels

A large number of shallow-buried tunnels have currently been built in cities, and specific strata, such as thick upper-soft and lower-hard ground layers, are often encountered. For shallow-buried large-span metro tunnels in urban composite strata, it is particularly important to study the effects of rock mass structures on engineering applications; random joint network simulation technology is a suitable method to study this problem. Considering the shallow-buried large-span metro tunnel in Dalian, which is located in a composite stratum, as the engineering background, first, a set of visualizations is developed with a joint network simulation program. The program can also generate several sets of joints and multistratum random joint networks and then combine program-generated data files and UDEC discrete element software-generated random network models. Combined with orthogonal testing, the failure modes of shallow-buried large-span metro tunnels are discussed, and the influences of rock mass structural parameters on tunnel failures are analyzed. The results indicate that the failure modes of all models are shear or tension failure of the overburden strata along weak planes of random joints, which eventually leads to the occurrence of staggered traction slip collapses and clear slip surfaces. This study provides a certain degree of guidance for the deformation and failure of shallow-buried large-span metro tunnels and for the determination of the surrounding rock pressure in urban composite strata.