Geophysical evaluation of geological model uncertainty for infrastructure design and groundwater assessments

Abstract

Uncertainty in geological models, mainly caused by natural heterogeneity and inadequate data, often leads to substantial societal risk including failures of engineered structures, geohazards, and groundwater and environmental problems. These models mainly depend on geological knowledge about evaluation of rock mass quality, fractures/faults and clay. Traditionally, geotechnical parameters of rock mass quality classification, such as rock mass integrity index (Kv) are obtained by drilling tests. However, the boreholes approaches are time-consuming and expensive, provide limited data and have topographic constraints. Alternatively, the inexpensive integrated approaches of geophysical methods can reduce geological ambiguity by bridging the gaps between accurate subsurface models and inadequate borehole data. In this work, we incorporate electrical resistivity tomography (ERT) with inadequate drilling data, and determine Kv over large area even where no borehole exists. Our results reduce a large number of wells and evaluate the subsurface thoroughly using 2D/3D imaging of Kv. The ambiguity in water-clay differentiation caused by low resistivity was resolved by integrating ERT with induced polarization (IP). The integration of ERT, Kv and IP identified several localized fractures/faults. Our novel approach, compared with the past studies, reduces uncertainty in the geological model and provides a thorough insight into the subsurface for infrastructure design and groundwater assessments. Our approach is applicable in most cases.