The value of hydrogeological information in tunnel design in rock Evaluating VOIA to support pre-investigation decisions

Abstract

This thesis investigates the value of hydrogeological information in the design of in frastructure tunnels in fractured rock, with a focus on the Kolmårdentunneln project in Sweden. Uncertainty in hydraulic conductivity within fracture networks presents a major challenge in predicting groundwater inflow. To support design decisions under such uncertainty, this study applies a Value of Information Analysis (VOIA) framework integrated with hydrogeological modeling. Two grouting alternatives, Alternative A1 (standard cement-based grouting) and Alter native A2 (cement with supplemental silica sol), were evaluated and compared against a no-grouting baseline (Alternative A0). Hydraulic conductivity for both general and Getå fractures was modeled using triangular probability distributions, and inflow sim ulations were performed using MODFLOW with multiple realizations. The analysis specifically examined tunnel sections prone to failure. The VOIA was applied through a pre-posterior Bayesian framework, incorporating the reliability of hydraulic testing methods to estimate the benefit of future investigations. Cost-benefit analysis was used to determine whether additional data collection is eco nomically justified. Although a positive expected value of information (127,861 SEK) was found, the optimal decision did not change from prior analysis, indicating that fur ther investigation was not warranted under current conditions. The results highlight the importance of incorporating uncertainty in tunnel inflow mod eling and the potential of VOIA to support risk-informed and cost-effective design. Rec ommendations for future work include integrating spatial variability, improving com putational efficiency, expert judgment for conditional probability, and combining VOIA with multi-option decision making.