Centrifuge modeling of preloading consolidation and dynamic compaction in treating dredged soil

Preloading consolidation with drains (PCD) and dynamic compaction (DC) are often combined to improve the ground condition. A novel method of modeling PCD and DC in centrifuge is developed in this study. 3D printing technique is used to greatly improve the manufacturing precision and simulation ability of sand drains. A loading container, which allows adding sand in it stage by stage, is well designed to achieve uniform surface loading. Based on strong magnet and reliable mechanical principle, a novel device for modeling dynamic compaction is developed, which can realize continuous tamping in centrifuge to a certain extent. An example test using dredged soil sampled from Putian Port, Fujian Province, China, was conducted to validate the performance of the method, including self-weight consolidation, four-stage preloading with drains, and dynamic compaction. The present method performed well to simulate the whole process of pretreating the dredged soil. The surface settlement, changes in excess pore pressure and effective stress, number of drops, crater depth, improvement depth by DC were reasonably predicted. Significant surface settlement and crater depth were observed during the preloading consolidation and dynamic compaction, respectively, indicating that the compressibility of the dredged soil was rather large. Spacing of sand drains behaved to be more effective than the length. The vertical distributions of water content, excess pore pressure, and effective stress revealed that the degree of consolidation decreased with depth, since the drainage condition in the upper part was better. The present method will contribute to a better understanding of PCD and DC, and is promising to be used for the design and evaluation of the current ground improvement methods.

排水预压固结（PCD）和强夯（DC）常结合使用以改善地基条件。本研究开发了一种在离心机中模拟PCD和DC的新方法。采用3D打印技术极大地提高了砂井的制作精度和模拟能力。精心设计了一个可逐步添加砂的加载容器，以实现均匀的表面加载。基于强磁铁和可靠的机械原理，开发了一种用于模拟强夯的新装置，该装置在一定程度上可在离心机中实现连续夯击。以中国福建省莆田港采集的疏浚土为例进行了试验，以验证该方法的性能，包括自重固结、四级排水预压和强夯。本方法在模拟疏浚土预处理的全过程中表现良好。合理地预测了地表沉降、超孔隙水压力和有效应力的变化、夯击次数、夯坑深度以及强夯的加固深度。在预压固结和强夯过程中分别观察到显著的地表沉降和夯坑深度，表明疏浚土的压缩性相当大。砂井间距比长度更有效。含水量、超孔隙水压力和有效应力的竖向分布表明，由于上部排水条件较好，固结度随深度降低。本方法将有助于更好地理解PCD和DC，并有望用于当前地基处理方法的设计和评估。