There’s no general definition of Unconsolidated rock in engineering geology field.  Normally, it defines with ISRM geology material strength from R0R2 and it’s also divided with single compressive strength of rock core, which is less than 25MPa., This article discusses the gravel located in LinKo, and poorly consolidated sand layer, and Interbreeded Sandstone and Mudstone, located in Dananwan and KuanYing Mt as the research object of this paper. Also, we takes one of the tunnels (G tunnel as following) in that area as an example to analyze the possibility of Demolition Model while encountering lowstrength, poorly consolidate capability, and easily soften material during the process of excavation in CⅡ(S) tunnel, defined by Public Construction Commission Rock Mass Classification System (PCCRSystem). It further provides the construction filed to have some general idea to design and construct weak rock in tunnels and decrease the risk during construction period.