Effect of braced excavation in anisotropic soft clay

• Main Author: Goh, Bryan Zhen Yi
• Other Authors: Goh Teck Chee, Anthony
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Civil engineering::Geotechnical
• Online Access: https://hdl.handle.net/10356/139582
• Institution: Nanyang Technological University

The core of braced excavation is the retaining walls and its support system which prevents soil from caving in, ensuring that construction can be completed 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. The objectives of this project were to investigate the effect of braced excavation in anisotropic soil. The numerical analysis for this project is done using PLAXIS 2D. 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 22 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 bending moment, maximum strut forces experienced in each strut and the basal heave Factor of Safety of the entire braced excavation process. The results on the behaviour of maximum wall deflection and maximum wall bending moment illustrated that as the ratio of anisotropy increased, the flexible sheet pile wall experienced a decrease in maximum wall deflection. As for the behaviour of strut forces, a correlation is established between the ratio of anisotropy between the soil and strut force whereby the strut force increases with a decrease in ratio of anisotropy. In addition, the third strut of the braced excavation will experience the largest compressive force in the system. Comparisons would be made in with regards to Peck’s Apparent Pressure Diagram. With regards to the overall basal heave Factor of Safety (FS) of the whole excavation system, it showed an increase in the factor of safety as the ratio increases. However, the Factor of Safety showed minimal changes when the wall stiffness increased. Future research can focus on other parameters that affect braced excavation behaviour besides those studied here.