Pilot Tunnels: Contractor's Position

Abstract

Geologic uncertainty in underground construction promotes design and construction conservatism and has a significant impact on project cost. Site investigation can reduce this uncertainty and decrease the contingency amounts included in bids. Pilot tunnels are one of the best geologic exploration methods, but they are also one of the most expensive. This paper presents the contractor's view concerning the usefulness of constructing a pilot tunnel as part of the site investigation program and offers guidelines for evaluating its benefits. These benefits can be realized both prior to and during construction. They include furnishing information about the geology and its behavior, and facilitating design development and construction operations. Pilot tunnels are generally most useful in large projects with limited surface access, and where the geologic conditions are unfavorable. Depending on project conditions, the construction of a pilot tunnel can reduce bid contingencies up to 20% of the project cost.