Effective Porosity Measurement of a Marine Clay

Effective porosity commonly represents only the voids in soils or rock that contribute to the advective transport of groundwater. In the extreme case, all the pores or fractures are interconnected and contribute to the transport of groundwater. However, in most cases, some pores or fractures are dead-ended or isolated and, therefore, do not contribute to the advective movement of water through the soil or rock mass. The effective porosity is often estimated to be some fraction of the total porosity. The purpose of this study was to compare a glacial marine clay deposit’s effective and total porosities. The inner connection of the soil pores and the importance of the clay minerals on the pore spaces are at the root of the effective porosity testing described herein. Based on the results of three tracer tests on a low-plasticity, glacial marine clay, the effective porosity was found to be approximately equal to the total porosity within an error of less than 10%. Based on visual appearance of this uniform clay, the longitudinal dispersivity was assumed to be small compared to the tracer specimen length. However, it was found that larger test specimens would have made the tracer breakthrough curves less complicated.