Impact of Drilling Fluids on Borehole Hydraulic Conductivity in Geotechnical Investigations

The objective of this study is to assess the influence of drilling fluids on boreholes carried out for geological and geotechnical investigation, with a specific focus on tests intended for determining the hydraulic properties of soils through infiltration tests. Hydraulic conductivity was measured in situ from boreholes drilled with water, and subsequently compared with those measured in tests using the following additives: xanthan gum (XG), carboxymethyl cellulose (CMC), and a combination of XG and CMC. Additionally, undisturbed samples were retrieved for measuring the laboratory hydraulic conductivity at constant and variable loads. Tests were performed in a residual silty-clay soil site characterized through an extensive site investigation campaign that included geophysical survey and borehole drilling. The measured values of field hydraulic conductivity coefficients indicate a natural average variation of ± 10, with no significant reduction in permeability observed when using polymers compared to water. Phenomenological and micromechanical permeability–porosity relationships proved to provide realistic assessment of the field hydraulic conductivity. Overall, the scatter was considered typical of the natural heterogeneity of residual soils and support the application of polymer fluids in borehole drilling field infiltration tests.