Centrifuge Modeling and DIC of Dynamic Compaction on Sandy Soils with Shallow Water Table

Abstract

The objective of this study was to investigate the effectiveness of dynamic compaction (DC) on sandy soils with shallow groundwater table in a geotechnical centrifuge. A total of five model tests were conducted on two different soils with fines contents of 0% and 10%, with water and hydroxypropyl methylcellulose (HPMC) as pore fluids. All models were tested at 30 gravities using the 4.5-m radius large beam centrifuge facility available at the Indian Institute of Technology (IIT) Bombay, India. A custom designed and developed in-flight actuator was used in the study, and a tamping energy level of 208 t-m was simulated to replicate the field DC process. The results were interpreted in terms of pore pressure developments and ground vibrations induced during tamper blows by analyzing instrumentation data recorded by pore pressure transducers and accelerometers. Furthermore, digital image cross-correlation (DIC) analysis was applied on photographs of the front elevation of the models captured during the centrifuge tests, and corresponding crater formations, displacement vectors, contours of displacement, and volumetric strains were plotted for quantitative assessment of ground improvement induced by DC. The effectiveness of pore fluid substitution in dynamic centrifuge modeling was investigated in the context of DC using water and HPMC pore fluids. It was observed that the performance of DC on sandy soil without fines was independent of pore fluid type. However, in the case of silty sand with 10% fines, pore pressure developments were found to be significantly different with and without HPMC, indicating the importance of viscous pore fluid substitution for modeling DC on low-permeability soils in centrifuges. For effective application of DC on soils with permeability on the order of 5×10−5 m/s or less, tamping should be executed in passes in order to dissipate excess pore water pressure induced by DC.