Optimal rock slope support and geological survey from value of information analysis

Abstract

Slope stability is a crucial concern in rock engineering which often requires balancing the costs of slope support with uncertainties in geological conditions, particularly the orientation of discontinuities. Traditional approaches generally encompass a risk-averse behaviour where, to face the uncertainty on the estimation of the orientation of discontinuities, the rock engineer assumes the worst-case scenario, generally resulting in overdesigned structures. However, geological surveys can help in reducing uncertainty and lessen the range of plausible values of the orientation of discontinuities that one may be expected. To address this issue, this study employs a Value of Information (VoI) analysis to determine the optimal number of joint orientation measurements, offering a framework to balance survey costs against stabilization expenses. The research focuses on a theoretical case study of a plane failure mechanism where rock properties are considered deterministic except for an uncertain joint dip angle. The semi-probabilistic verification criteria adopted in the Eurocodes are used for stability calculations. The analysis accounts for a reduction in uncertainty as additional measurements of the joint dip angle are conducted. Finally, VoI analysis compares two scenarios: one relying on worst-case assumptions without surveys and another incorporating measurement-based designs. The results demonstrate the practicality of VoI in identifying an optimal number of measurements, which varies based on the cost ratio between geological surveys and the slope support solution.