EVALUATION OF THE SEASONAL VARIATION OF THE ULTIMATE CAPACITY OF DEEP FOUNDATIONS IN UNSATURATED SOILS

Abstract

Large part of the Brazilian territory is covered by unsaturated soils, typical of countries with a tropical climate. In this case, the moisture content of the soil varies seasonally along the depth, due to the alternation of dry and rainy periods, with more significant changes in the superficial layers. This variation causes changes in soil suction, which alter the soil shear resistance. In addition to the changes in the soil superficial layer, the alternation of dry and rainy seasons also causes the variation of groundwater table depth. Therefore, deep foundations partially or completely installed in unsaturated soils may be subject to seasonal variations in the shaft resistance relative to the top section and at the bottom section of the pile, caused by the changes of the groundwater table. As consequences of this seasonal effect, the uncertainties in predicting the behavior of deep foundations in unsaturated soils are often the cause of problems of settlement or failure of foundations, or overestimations in the design phase. Therefore, seeing the need to quantify and propose procedures to consider these seasonal effects in the foundations design, and also to advance in the current state of knowledge on the topic at hand, the present research proposal is presented. For this purpose, the researcher intends to investigate the problem by means of experimental methods and probabilistic analyzes. The experiments will be carried out on instrumented piles in the field, with soil suction and groundwater table monitored, and in reduced pile models in laboratory, with controlled soil suction. In order to complement this study, probabilistic sensitivity and risk analyzes of deep foundations in unsaturated soil will be made considering the seasonal effect. (AU)