Optimizing site investigations for gassy soils: A Bi-objective approach using value of information and cost of boreholes

Abstract

Gassy soils, containing flammable gases like methane (CH₄), are commonly found in the shallow layers of Quaternary deposits, posing significant challenges for underground construction. Effective site investigation, particularly the strategic placement of boreholes for gas pressure measurement, is critical for assessing engineering risks. However, the high costs of borehole drilling often limit the amount of available gas pressure data, leading to potential errors in risk assessments at unmeasured locations. Misclassifying hazardous conditions as safe can result in costly penalties. Currently, investigation strategies that balance cost reduction with risk mitigation rely largely on engineering judgment. This study presents a probabilistic optimization approach for planning site investigations in gassy soils, explicitly addressing the trade-off between investigation costs and misclassification penalties. These factors are quantified using Value of Information (VoI) and cost of boreholes (CoB). The optimal investigation strategy is determined through the knee point method, which identifies the best compromise between VoI and CoB. A case study on Hangzhou Metro Line 1 demonstrates the practicality and effectiveness of this approach, showing that the optimal strategy balances VoI maximization with CoB minimization. The knee point method effectively identifies this compromise, ensuring maximum marginal utility by balancing information value and investigation cost.