ABSTRACT
The aim of this research is to present and discuss the results of oedometric tests under controlled matric suction, for lateritic soil samples from an unsaturated soil profile, typical of 14% of the region of Campinas, in the State of São Paulo, Brazil. The soil profile consists of colluvial, lateritic and collapsible silty clay, with approximately 6.5 m thickness. The water level is approximately 17 m. The textural, structural and compositional characteristics of the soil profile demonstrate two distinct sources in the upper layer (from 1.5 m to 5.5 m) as well as in the lower layer (at 6.5 m). The former has a sedimentary source and the later has an igneous and/or metamorphic source. However, in the lower layer, the structural characteristics of the rock source prevail over the upper layers, with the evident presence of igneous origin minerals. The hematon/goetan + argilon aggregates are the most common, followed by ferruginous concretions, magnetite grains and pyroxene pseudomorphs, suggesting a source near the Diabase. All these components are involved in a matrix with clay minerals, oxides and iron hydroxide and an expressive quantity of voids. Although there is the presence of cimentation, from iron oxides, the particles, surrounded or not by hematite and goethite, and microagregates are linked by capilarity forces. This fact indicates that the soil suffers disaggregation when wet. Disturbed and undisturbed samples were collected from this profile, at a 1.5 m depth. Six specimens were made from the undisturbed samples and submitted to oedometric tests. The specimens were wet and submitted to axis-translation technique, with pressure equipment and a pressure control panel. The imposed matric suction values were: zero, 25 kPa, 50 kPa, 100 kPa, 200 kPa and 400 kPa. The levels of net stress applied were 6 kPa, 12.5 kPa, 25 kPa, 50 kPa, 100 kPa, 200 kPa, 400 kPa, 800 kPa and 1600 kPa. Experimental results, obtained by oedometric tests, indicate collapse index varying between 2% and 18.7%; indicating collapsibility. Moreover, the experimental results were inserted into a theoretical model to estimate the LC curve and evaluate its application on this lateritic soil.
