Risk-sensitive decision support system for tunnel construction

Comprehensive and realistic tunneling plans must strive for optimal decisions that minimize time and cost while addressing important factors such as geologic uncertainty and variability, uncertainty in tunneling productivity, and the contractor's risk sensitivity. This paper presents a computerized decision support system that incorporates all important tunneling risks. It consists of three interrelated models: the probabilistic geologic prediction model, the probabilistic tunnel cost estimating model, and the risk-sensitive dynamic decision model. The probabilistic geologic prediction model uses all available geologic information to characterize geologic uncertainty and variability along the tunnel profile in the probabilistic form of ground class transitions. The probabilistic tunnel cost estimating model evaluates tunneling time and cost performances for applying different excavation and support methods to different prevailing ground conditions by using Monte Carlo simulation to actual tunneling operations. Both models provide the main input for the risk-sensitive dynamic decision model, the core of the system, to determine the optimal excavation and support sequence and the corresponding risk-adjusted tunneling costs for the project as functions of available project information and the contractor's risk sensitivity. The application of the system to an actual highway tunneling project illustrates both the modeling power of the approach to quantify and incorporate risk, and its effectiveness for making optimal decisions as functions of the contractor's degree of risk sensitivity.