Ground response due to sheet pile braced excavation in Bangkok subsoils

Abstract

The sheet pile bracing system is the most common used for excavation in Bangkok soft marine clay in case of the excavation depth is less than 9-10 m. The lateral sheet pile wall movement caused by lateral earth pressure is often used to evaluate the performance and behavior of sheet pile braced excavation. This research aims to verify the behavior and performance of sheet pile braced excavation of the project in Bangkok city for 6.90-m depth of excavation with three bracing layers at -1.00 m, -3.25 m, and -5.30 m. Three inclinometers were installed fixed to the sheet piles of 16-m depth. The mode of the first excavation shows the sheet pile cantilevered mode, while the later stages of excavation, the mode is shifted to a bulging mode. The maximum lateral sheet pile movements occur around the depth at which excavations are undertaken due to the strict control of installation of struts after excavation. The back analysis by means of Finite Element Method (FEM) based on Mohr-Coulomb failure envelope shows that the appropriate ratio of Young's modulus (Eu) and undrained shear strength of soil at the final excavation stage are in the order of 150-250 and 2000 for soft clay and stiff to very stiff silty clay. The behavior of Bangkok clay shows the nonlinear stress-strain-strength behavior depending on the order of shear strain of sheet pile wall. Based on case histories of sheet pile excavation work in Bangkok subsoil, the modified boundary of relationship between maximum deflection ratio and factor of safety against basal heave is proposed.