Abstract:

 Deep foundation pits in thick waterrich sandy strata are characterized by a high groundwater table, thick sandy layer, and high permeability; hence, water connections between the interior and exterior of the foundation pits cannot be cutoff completely. Therefore, a case study is conducted on a metro station in Nantong, China, to investigate the deformation patterns induced by dewatering in deep foundation pits within such strata. A threedimensional fluidsolid coupling finiteelement numerical model is constructed to systematically analyze the deformation indices such as lateral deflections of the diaphragm wall, ground settlements outside the foundation pits, and uplift of the foundation pit floor. The results reveal the following key findings: (1) The excavation of the foundation pits and subsequent dewatering activities result in severe lateral deflections of the diaphragm wall and surface settlements outside the foundation pits. The maximum increments in the lateral deflections of the diaphragm wall and surface settlements outside the foundation pit, caused by dewatering during the excavation, account for 20%~40% and 20%~60% in total, respectively. (2) The influence zone of dewatering in the first confined aquifer ranges from 0 to 90 m, whereas in the second confined aquifer, it extends beyond 180 m. (3) With increasing excavation depth, the antiuplift piles demonstrates an enhanced restraining effect on the heaving of the foundation pit floor.