Simplified calculation of settlement due to dewatering of phreatic aquifer in loess area

Abstract

Focusing on the uneven settlement of surrounding buildings caused by deep foundation pit dewatering in loess area, this study analyzed the mechanism of ground settlement induced by foundation pit dewatering, deduced the simplified calculation formula of ground settlement caused by dewatering based on the layer-wise summation method and shear displacement method. First, the equation of the cone of depression was derived from Dupuit formula by ignoring group well effect and lateral displacement. The soil around the pit was divided into a drained zone and a saturated zone by the precipitation curve. Then introduce modification factor, and the effective stress increment caused by the reduction of pore water pressure in different loess layers was corrected. Finally, the constraint function of lateral friction located in soil-pile interface towards soil settlement was considered. The settlement at different distances from the dewatering well was calculated respectively, the actual settlement was the sum of the both. Instance calculates was performed based on an engineering example of foundation pit dewatering by finite element software Abaqus, and comparative analysis was carried out between numerical results and measured field data. The research results show that the position where the constraint effect of lateral friction became most significant was at the interface of soil and pile; the accuracy of settlement calculation in this paper was much higher than that of the normative method in the range of 1.5 times of precipitation depth, which can better predicted the ground settlement at different distances around the foundation pit in loess region during dewatering. The study could provide reference for calculating ground subsidence in similar phreatic aquifers.

Keywords

• loess area
• dewatering of foundation pit
• settlement of the ground
• lateral friction
• numerical simulation