A method to derive hydrogeological information from geotechnical data

Groundwater flux estimates require reliable hydraulic conductivity values. These are normally acquired by pumping or packer tests. However, these are not obtained upon commencement of engineering projects and often lead to additional project costs. This study illustrates that results obtained from these methods vary by orders of magnitude. In contrast, geotechnical data is normally collected on project commencement as part of project feasibility studies in core logs and/or geophysical data. This data is readily available and normally more abundant than pumping or packer test data. Analytical formulas were developed to convert this data into hydrogeological parameters, which are commonly site specific and disregard heterogeneity. This study describes methodologies to calculate hydraulic conductivity from core logs and calibration of results with piezometric levels. Calibration is performed by groundwater modelling, ensuring data which represents measured groundwater levels. The procedure is illustrated by computing inflow into a tunnel in Karoo Supergroup lithologies.