Estimating the in situ porosity of sandy soils sampled in boreholes

This paper deals with sandy aquifers. It explains how to use parameters of borehole samples, and data of mechanical tests performed in boreholes, to assess the in situ values of porosity. The concepts of maximum and minimum void ratios, emax and emin, are presented with the results of studies trying to predict their values. Predictive equations are proposed to link the values of emax and emin to that of the coefficient of uniformity CU of the grain size distribution curve, and the roundness factor RF of solid particles. Once the values of emax and emin have been estimated, those of the in situ void ratio e and porosity n can be assessed from the data of in situ mechanical tests, for example split spoon tests. An example evaluation is presented for an unconfined sand aquifer, which was investigated using boreholes, field tests, laboratory tests, slug tests in monitoring wells, and a long-term pumping test.

► Sand is characterized by its grain size distribution and roundness factor.
► Equations are proposed to predict the maximum and minimum values of porosity.
► The in situ porosity is assessed by mechanical tests, such as split spoon tests.
► An example is given with the assessment of the in situ hydraulic conductivity.