An Underwater Plate Load Testing for the Sand Compaction Pile Ground at Island-Tunnel Conversion Area

Abstract

The sand compaction pile (SCP) method is a widely used ground improvement technique, especially in offshore engineering. The thick, soft marine clay in Hong Kong–Zhuhai–Macau Bridge was reinforced using this method at its island-tunnel conversion area. A large-scale plate loading test was conducted to evaluate the bearing capacity and deformability of the SCP composite ground. An improved settlement result was obtained by utilizing a high-sensitivity liquid level sensor system underwater. The research results showed that the stress concentration ratio of the SCP composite ground was closely related to the load level, which decreased when the load level increased. When the stress stayed constant, the ratio was found to reduce gradually to a certain value. Three computing theories were discussed in the bearing capacity calculation of the SCP composite ground. The results calculated by the Hughes and Withers method were more consistent with the field experimental results. For the settlement calculation, it was found that the results were closer to the experiment results calculated by Aboshi’s first empirical formula. The experiment results differed greatly when calculated by Aboshi’s second empirical formula and the modified method proposed by Ahn and Kim. The study may provide some useful data for marine SCP composite ground designs and underwater field testing techniques.