Influence of wall stiffness on braced excavation behaviour
Wong, Zachary Jun Jie
Date of Issue2017-05-15
School of Civil and Environmental Engineering
As Singapore continues to develop and advance with globalisation, more people from around the world have come to live here and call Singapore their home (Singapore, 2016). This population influx, coupled with the paucity of land in Singapore, has brought about a surge in infrastructural demands with regard to the construction of housing and transportation systems. With an ever-diminishing land space to build above the ground, the need for underground excavation as an alternative arises. The core of braced excavation is the retaining walls and its support system which prevents soil from caving in, ensuring that construction can be accomplished safely. However, such deep excavations are accompanied by high risks due to potential catastrophic events resulting from failure of the structure. Human lives and other infrastructures in the vicinity are at stake if mistakes were to occur in the construction and excavations. This study utilizes Finite Element Method (FEM) analyses, carried out by using PLAXIS 2D, to evaluate the influence that specific parameters such as wall stiffness, excavation width and undrained shear strength of clay have on braced excavation behaviour. A total of 72 cases were simulated with the PLAXIS software and the parameters were interchangeably varied and fixed to assess how independent parameters would influence the performance of the braced excavation. The factors determining its performance consist of maximum wall deflection, maximum strut forces experienced in each strut and the basal heave Factor of Safety of the entire braced excavation. The results on the behaviour of maximum wall deflection illustrated that as wall stiffness increased, the diaphragm wall experienced a decrease in maximum wall deflection. In addition, for any particular wall thickness, e.g. 1.0m, the maximum wall deflection decreased when the width of excavation decreases or when the undrained shear strength of the clay increases. As for the behaviour of strut forces, a correlation is established between the wall stiffness and strut force whereby the strut force increases with wall stiffness. The strut force experienced in each strut would decline when excavation is carried out on clay with higher undrained shear strength. However, when the excavation width increased, strut forces in each strut remained similar except for the bottom-most strut. With regard to the overall basal heave Factor of Safety (FOS) of the whole excavation system, it decreased when the excavation width was wider or when the undrained shear strength of the clay was lower. However, the FOS tended to increase marginally as the wall stiffness increased. Future research can focus on other parameters that affect braced excavation behaviour besides those studied here.
Final Year Project (FYP)
Nanyang Technological University