The Role Of Tunnel Engineers In Implementing The Observational Method On Site

The observational method is widely used in tunnelling works. For successful implementation of the observational method in tunnelling, proper understanding of support system behaviour, an efficient monitoring regime, data evaluation and proper interpretation by an experienced site engineer is of prime importance. Site engineers play a key role in successful implementation of the observational method. Hence, it is very important for site engineers to understand the key behaviours to be observed, issues that could be resolved at the site and the systematic approach to be implemented to understand the tell-tale signs.

This paper describes the concept of observational method as described by Peck in 1969 and the development of its definition into CIRIA R185 and Eurocode 7. These serve as a basis for considering observational approach in the design and highlight the conditions under which the observational methods must not be used. To explain this, this paper discusses a case study on observational method implemented for a shotcrete-lined tunnel and observational “approach” implemented to adjust TBM compressed air pressures during TBM cutter head intervention to maximize the working man-hours in the cutter head chamber while ensuring face stability. For a shotcrete-lined tunnel, a practical procedure for predicting and comparing displacement behind the face in relation to face advance and time is presented along with spatial visualization tool for tunnel lining displacements. For TBM compressed pressure adjustment, an iterative procedure based on groundwater pressure monitoring and water ingress is presented in the paper.