Effects of internal erosion on the cyclic and post-cyclic mechanical behaviours of reconstituted volcanic ash

Abstract

Internal erosion is the transportation of soil particles from within or beneath the main structure inside the ground due to seepage flow. Internal erosion impacts the mechanical and hydraulic behaviour of soil. The present study investigates the impact of internal erosion on the cyclic and post-cyclic mechanical behaviours of volcanic ash sampled from Satozuka, Japan. A series of experiments using volcanic ash with loose, medium, and dense conditions have been performed using an erosion triaxial apparatus. Further, reconsolidation after application of cyclic loading was considered to study the impact of reconsolidation on the post-cyclic mechanical behaviour. The results show that the cyclic resistance of eroded specimens is improved regardless of the percentage of eroded fines and the initial relative density. The higher cyclic resistance for the eroded specimens is found to be due to a decrease in the intergranular void ratio after the erosion, change in fabric, and pre-strain history during erosion. Reduction in the critical state friction angle (φcri) and peak stress ratio (Rpeak) for the monotonic loading due to cyclic loading is greater for the eroded specimens. However, reconsolidated eroded specimens show increases in φcri and Rpeak, which are lower than those of the non-eroded and eroded specimens without cyclic loading. This could be due to the change in the soil fabric during cyclic loading where the positive impact of erosion is lost after cyclic loading. Such limited recovery of deviatoric stress with deformation is density-dependent.