Numerical analysis of tunneling in slates with anisotropic time-dependent behavior

Abstract

Slate is a metamorphic rock often contains a dense foliated texture called slaty cleavages or schistosities. The ease of split along the schistosities weakens the slate and its resistance to weathering and erosion. For the tunnel excavation in slate formations, it is common to observe anisotropic deformation; in addition, the deformation caused by stress release also shows time-dependent behavior. Hence, anisotropic and time-dependent behaviors must be taken into account to more properly estimate the deformation of tunnel excavation in slate formation. In this paper, the computer software FLAC with the ubiquitous-joint (UBI) model and the Burger-creep viscoplastic (CVISC) model was adopted for the analysis. To more efficiently obtain relevant parameters of those models, back calculations were performed by the automatic iterative tool Quick Macro. Coupling these two models, the new hybrid UBI/BUR model was developed and implemented as a UDM program, which can be applied for the FLAC analyses. The new model was calibrated by the monitoring data from a slate tunnel excavation project, i.e., the Wanta-Sunglin Project in Taiwan, then applied for detailed analyses. The results indicate that the hybrid model developed in this study is better than the conventional models, and can be used for the simulation of tunnel excavation in anisotropic time-dependent slate formations.