Recent developments in site investigation and testing for hard rock TBM tunnels

Engineering geological site investigation and testing are crucial to obtain the basis for: · Overall planning of the project, including siting and design optimisation. · Analysing stability and planning rock support. · Evaluating alternative excavation methods, selecting equipment and predicting performance. · Evaluating environmental effects and the use of excavated material. · Estimating cost and preparing tender documents. For several recent TBM tunnel projects, unexpected ground conditions have been encountered, causing extra cost, considerable delays and in some cases major claims. Undoubtedly, in most cases such incidents have been due to insufficient or irrelevant investigation of engineering geological and rock mechanical conditions. On this background, this paper is discussing what types of investigation and testing should be carried out for a planned TBM project, and, depending upon the complexity of the planned project and the ground conditions, what extent of investigation should be carried out.