Impact of thickness and depth on diaphragm wall deflection in a deep excavation project using Top-down method in Phu Nhuan district, Ho Chi Minh city

Abstract

The increasing need for high-rise buildings in big cities has brought about an ascending demand for underground space (basement). The construction of deep excavations is arduous, which can easily lead to accidents due to the displacement of the diaphragm wall, causing serious repercussions for people and property. Therefore, it is necessary to calculate the depth and thickness of the diaphragm wall so that the result is both economical and safe. Although there have been many studies related to the correlation between displacement and thickness and depth of diaphragm wall in deep excavation, only a few studies have clarified the aforementioned correlation for diaphragm wall of deep excavation using Top-down method in the geological area of Phu Nhuan District - Ho Chi Minh City.

The paper focuses on studying the influence of two factors, thickness and depth, on the displacement of diaphragm wall in a deep excavation using the Top-down method in Phu Nhuan District - Ho Chi Minh City by alternating the wall parameters of thickness and depth in the finite element model. The input geological parameters used in the model were selected by the back analysis method. The wall diaphragm deflection results from the back analysis using HS model in Plaxis 2D and the stiffness parameter E =2000N ref 50 for sandy soil (N: the number of blows SPT) and E =500Su ref 50 for clayed soil (Su: undrained soil shear strength) demonstrated a similarity with its field observation. The models analysis show that when changing the diaphragm wall size, the thickness affects the displacement of the diaphragm wall more than the depth. The study also found the correlation formula between the thickness (x) and the maximum displacement (y) of the diaphragm wall y=a.xb (a between 28.141 and 28.508, b between -0.690 and -0.708).

Keywords: correlation, deflection, thickness, depth, diaphragm wall, Top-down.