Geological Exploration and Risk Reduction in Tunneling


Geologic uncertainty in underground construction promotes design and construction conservatism and has a significant effect on project cost. Site investigation can reduce this uncertainty and decrease costs by reducing the contingency amounts included in bids. This paper presents research findings that provide a better understanding of how subsurface exploration and improved contractual risk sharing can decrease the cost of underground projects. Issues discussed include: the methodology used by tunneling contractors to estimate geologic profiles given a set of available geologic information; the geologic classification methods used to associate the expected profile with acceptable construction alternatives; the spatial prediction of ground classes and the extents over which different excavation and support methods will be necessary; the factors involved in selecting the initial support, the excavation round length and the estimation of the advance rate; the relationship between exploration, risk allocation and bidding behavior; the impact of changed conditions clauses in underground construction contracts; the merits of using well defined geologic conditions as a basis in unit price contracts; and the magnitude of bid contingencies that are actually used in practice


Photios G. Ioannou

Civil & Environmental Engineering Department

University of Michigan

Ann Arbor, Michigan 48109-2125, U.S.A.



Underground construction, tunneling, exploration, geologic information, risk, uncertainty, excavation, contracts.


Ioannou, P.G., "Geological Exploration and Risk Reduction in Tunneling," Journal of Construction Engineering and Management, ASCE, Vol. 114, No. 4, 532-547, Dec. 1988.