A proposal of structural models for colluvial and lateritic soil profile from southwestern Brazil on the basis of their collapsible behavior

Abstract

This paper aims to propose structural models for understanding the collapsibility of a colluvial and lateritic soil by conducting oedometric tests with controlled suction executed in laboratory. The undisturbed soil samples submitted to experiments were collected by opening a trial pit in Experimental Field for Soil Mechanics and Foundations situated at the State University of Campinas, São Paulo, Brazil. The soil samples were characterized by means of standard geotechnical tests, chemical and mineralogical tests and mercury intrusion porosimetry. Oedometric tests with controlled suction showed the influence of matric suction on the compressibility of the soil samples. It was also observed that the higher the values of matric suction, the higher the Laboratory Collapse Potential — CP. The mineralogical chemical tests indicated the presence of oxides and hydroxides of iron in the samples, compounds usually associated with cementation. The presence of mineral, such as kaolinite, gibbsite, hematite and goethite, was also observed. The impregnated thin-layer plates of the soil samples, as well as the grain-size distribution curves and mercury intrusion porosimetry, indicated the presence of a structure formed by microaggregates. Structural models for soil collapse were proposed basing on the results obtained. There were behavioral differences in each soil sample collected at different depths. The behavior of the sample collected at a 1.5m depth was basically influenced by matric suction. As for the samples collected at 4.5m and 6.5m, besides being both influenced by matric suction they were also influenced by the presence of cementing agents (samples collected at 4.5m) and by the presence of more angular grains of quartz (samples collected at 6.5m).