Resistivity of Irish glacial deposits

Abstract

Irish glacial soils or boulder clays are often difficult to characterise using conventional sampling and laboratory testing due to the high quantity of coarse particles. Therefore, electrical resistivity tomography (ERT) is often used in geotechnical investigations in Ireland. A feature of ERT measurements in Irish boulder clays is that the resistivity values are much higher than those published for similar materials elsewhere. In order to study the factors that control the resistivity values of these boulder clays, a detailed in situ and laboratory study was carried out at five sites. The sites were chosen to correspond with soils derived from the most prominent rock types found in Ireland. Measured resistivity values were found to reduce with increased density, increased water content, reduced porosity and increased degree of saturation. The influence of coarse particles was found to be the primary reason why Irish boulder clays have relatively high resistivity values. It was also found that pore water content plays a dominant role in the measured resistivity values, which overrides the influence of other factors. Simple correlations between soil type and resistivity values can be misleading and the context of the in situ state of the material and the nature of the soil particles needs to be considered.