Effect of fines content on soil moisture responses to wetting & drying cycles

Abstract

Studies of soil moisture responses to climatic conditions are essential for understanding the mechanism of rainfall-induced landslide. This study aims to investigate the effects of fines content on soil moisture responses under repetitive wetting and drying cycles. Remoulded residual soil samples were prepared at 5 different fines contents, i.e. 15%, 30%, 45%, 60% and 75%. The soils were instrumented with soil moisture sensors and they were subjected to 2 cycles of wetting and drying. Results showed that all the soil specimens experienced faster reductions in soil moisture during the second cycle of drying than the first cycle. During wetting, the recovery of soil moisture, however, was less affected by the repetitive wetting and drying cycles. The fines content has a significant influence on the soil moisture reduction during drying. The degree of saturation of the specimen with 15% fines was found to be 3.5–6 times lower than that of 75% fines. The response of soil moisture to wetting was only marginally affected by the fines content. Results from numerical seepage analyses showed that the wetting soil moisture responses can be simulated to a reasonable accuracy. However, the simulated drying soil moisture responses showed relatively large discrepancies with the actual measurements. The results implied that the soil may have experienced changes in soil structure, void ratio or formation of desiccated crack during the repetitive wetting and drying cycles which cannot be captured by a typical finite element seepage analysis.