Gully erosion are very common in areas with gneiss basement rocks. Their development is strongly influenced by subsuperficial processes, although the surface ones are also important. This study aimed to investigate the subsuperficial erosion mechanisms of these gullies and to understand how mineralogy and texture could influence the saprolite erodibility. Some basic trials and erodibility tests were carried out in representative samples, with imphasis to especially the pin-hole test. The results showed that seepage erosion does not occur and that saprolite present variable susceptibility to piping erosion, even if they are in the same geologic unit. The data confirm that soils with Bw horizon (Oxisols) are less erodible than any of the tested saprolites. Preliminary data suggest that saprolites with a silty texture (determined without dispersant and agitation) and poor in aggregant materials, such as clay minerals, are more prone to piping erosion.
soil; erosion; gully; texture; B horizon
