A Consistent Engineering Approach to Tunnel Design

Currently excavation and support determination in tunnelling 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 Behaviour Types developed from Rock Mass Types and influencing factors. The System Behaviour describes the rock mass-support interaction. An analytic procedure is presented, which allows the
assessment of rock mass behaviour, support requirement, and costs of an entire tunnel deterministically
or probabilistically. This is used for preliminary design of tunnels, comparison of routes and different
construction methods, and risk analyses. During construction geological and geotechnical monitoring, and
observations allow the support and excavation design to be completed. The observed and predicted
behaviours are continuously compared. The procedure is illustrated by a case study from an Austrian
tunnel project