Centrifuge and numerical modeling of cemented stone column-seawall system for land reclamation

Abstract

Reclaiming land from the ocean has been an importance source of land supply for infrastructure development in highly populated coastal cities such as Hong Kong. For environmental protection, non-dredged reclamation has become more increasingly used in practice, where the soft marine clay has to be stabilized in-situ. Stone column is one of the commonly used in-situ soil improvement technology. However, in soft sea mud, stone columns may undergo excessive deformation (bulging) and lose their functionality. To address this issue, this study researches on a cemented stone column-sea wall system for land reclamation. By cementing compactly arranged granular particles, the cemented stone columns have enhanced strength and stiffness, making them well-suited for stabilizing soft sea mud in reclamation projects. The main research work and innovative achievements of this study include: First, the mechanical properties of cemented granular materials (CGM) are studied by laboratory tests. The CGM consists of densely arranged particles bounded by pouring self-compacting cement. This study investigates the influence of cement filling ratio on the mechanical characteristics of cemented granular materials using laboratory tests. It was found that the elastic modulus and splitting tensile strength of the cemented granular material increased linearly with increasing cement filling ratio. The unconfined compressive strength and the peak strain of the cemented granular materials also increased with cement filling ratio, but the growth pattern changed near a filling ratio of 80%. Secondly, this study conducted a centrifuge model test of cemented stone column-seawall system. The strengthening/failure mechanism of cemented stone columns on marine clay and the pile-soil interaction were investigated in the centrifuge testing. The main observed failure mode of the cemented stone columns was bending failure, accompanied by tilting and shear failure. The system would still undergo large deformation if the rigid-body rotation of stone columns is not sufficiently restrained. Thirdly, a parametric study was carried out by using finite element analysis to explore the effects of different factors on the structural stability. The finite element analysis was first calibrated to closely reproduce the centrifuge results. The numerical analysis results showed that reducing the loading rate, increasing the pile diameter, and increasing the depth of embedment of the cemented stone columns into the bearing layer can effectively reduce the deformation of the model and improved its stability. Finally, another centrifuge test was conducted by using an optimized stone-column configuration based on the parametric study. The deformation of cemented stone column-sea wall system can be greatly reduced by using the optimized design configuration with an increase pile diameter and embedment depth. The experimental results demonstrated that the cemented stone columns have increase strength, stiffness than conventional stone columns. They can effectively stabilize the soft sea mud, while maintaining drainage for consolidation. The cemented stone column is promising for non-dredged land reclamation.

Date of Award	2024
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Gang WANG (Supervisor)