Response of deep foundation due to fluctuation in ground water table

Abstract

Phreatic line or Ground water table (GWT) changes with natural/artificial recharge, flow and extraction of ground water. GWT follows the ground profile and moves under effect of gravity. It also moves from recharge areas to discharge areas. In well-graded and high permeable soil, the movement of GWT is higher. In the Indo-Gangetic-Brahmaputra plane, there is significant fluctuation in the GWT, due to extended summer and heavy monsoon. Flash or seasonal floods enhance it however, huge extraction due to dense population deplete it. Drawdown of the GWT can cause the soil to consolidate, which induces settlement. With softer, more compressible soils, settlements can become large. Building and infrastructure damage occurs where differential movements exceed the thresholds that the buildings or infrastructure can sustain. Effect of lowering of groundwater on shallow foundations buildings had been studied in literature. In the present study, the effect of GWT variation on behavior of pile foundation has been studied. Numerical analysis has been performed using geotechnical package GEO5. A group of six piles having length 10 m and pile cap thickness 1 m has been considered in the study. A concrete of grade M20 having longitudinal and transverse reinforcement of Fe240 has adopted for pile. Pile foundation has been considered in Clayey Sand and Silty Sand, explicitly in two different cases. GWT has been varied to simulate the foundation in complete dry to fully saturated soil condition. Behavior of pile under axial and lateral loads has been observed. Evident change in settlement behavior of the pile group has been reported.