Finite element analysis of braced excavation in sand

• Main Author: Lee, Si Min
• Other Authors: Goh Teck Chee, Anthony
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Civil engineering::Geotechnical
• Online Access: https://hdl.handle.net/10356/158399
• Institution: Nanyang Technological University

Through human ingenuity, land-scarce Singapore has found innovative ways to overcome her natural constraints by going underground. Currently, Singapore’s underground houses pedestrian underpasses, expressways, an underground transport system, electrical substations and storage facilities. The development of underground facilities has necessitated braced excavations to provide access for manpower and equipments into the ground underneath to carry out these construction projects. Deep excavations involve the removal of large quantities of soil, and this will inevitably alter the soil stress state, which may cause large and dangerous ground movements around the excavation. Therefore, the robustness of the braced excavation system is imperative for the safety and stability of the construction project. Unfortunately, there are limited parametric studies on braced excavation in sand, and most existing studies were based on the limited Mohr-Coulomb constitutive soil model. This project aims to address the research gap through studying the effects of several design parameters on the stability of the braced excavation system in sandy soils using the Hardening-Soil model. The Plaxis 2D finite element software was used to examine the effects of excavation depth, soil friction angle, wall stiffness properties, wall embedment depth and seepage on the lateral wall deflections and compressive strut forces in sand. The results show that the wall deflections and strut forces were relatively independent of the wall stiffness properties and wall embedment depth. On the other hand, higher strut forces and larger wall deflections occurred when there is an increase in excavation depth, decrease in soil friction angle or seepage. It was also shown that sand deposits are susceptible to toe kick-out failure and quick condition. These failures can be prevented by ensuring adequate wall embedment depth.