Influence of structure in the soil-water characteristic curves of two residual soils of granite

This paper discusses the influence of structure in the soil-water characteristic curves (SWCC) of two residual soils of granite formed in a subtropical environment. One soil has a saprolitic nature (named GrSp) and the other shows lateritic behavior (named GrLt). Both materials occur on a slope which presents a extensive history of landslides in the municipality of Sao Jose, Southern Brazil. SWCC of undisturbed and remolded specimens were determined using the filter-paper technique. Undisturbed specimens were collected and remolded specimens were produced by static compression of disintegrated soil to the same void ratio and moisture content of undisturbed specimens. SWCC of saprolitic soil showed curves which were modelled as unimodal but the lateritic soil required the use of bimodal curves because of the structure developed in micro and macro levels. Suction levels measured in GrLt soil were higher than in saprolitic soil. Remolding process changed the levels of suction achieved, which is due to the structure and more specifically to the size of pores in the remolded soils. Hysteresis were verified in both materials, but were far more pronounced in the lateritic soil. Analysis of mercury intrusion porosimetry were carried out in GrSp soil. They showed that remolding generates a different pore distribution from the existing in the undisturbed soil.