A Hierarchical Rock Mass Characterization for Tunnel Design & A Deterministic and Probabilistic Approach

Currently excavation and support determination in tunneling is mainly based on experience, supplemented by simplified models and calculations. There are no standardized procedures, making it difficult to technically review or audit designs, collect, evaluate and compare data from different sites and designs. In this paper a step-by-step procedure is outlined, which promotes an engineering approach to the design and construction of tunnels. In the pre-construction phase support concepts are based on Rock Mass Behavior Types developed from Rock Mass Types and influencing factors. The System Behavior describes the rock mass-support interaction, which is based on previous experience and numerical simulations. During construction geological face mapping, geotechnical monitoring, and observations allow the support and excavation design to be completed. By evaluating monitoring data, support utilization, and overbreak the observed and predicted behaviors are compared. Deviations lead to a re-evaluation of the process resulting in modifications to the support and excavation methods.