Interrelationship among weathering degree, pore distribution and water retention in an unsaturated gneissic residual soil

Abstract

It is widely recognised that the engineering behaviour of soils is a function of its structure. In residual soils, which are those derived from the in situ weathering of the mother rock and have not been transported from its formation site, the structure varies with the weathering degree of the material. It is also known that residual soils are usually unsaturated in nature. This study presents and discusses results of mercury intrusion porosimetry tests and soil-water retention tests performed in three sets of samples of a phacoidal gneiss residual soil, each one weathered to a different degree as preliminary defined through field observations and confirmed through extensive laboratory characterization tests and microtomography images. Based on a simplified definition of porosity ranges and through the introduction of a new porosity index, it is shown that the weathering degree affects, in differing ways, pores distribution and soil-water retention characteristics of the double-structure type of tested soils.