Experimental Investigations of the Soil-Water Characteristics of a Volcanic Soil

Abstract

Rain-induced landslides are common around the world. To analyse transient seepage and to predict porewater

pressure distribution in unsaturated slopes subjected to rainfall infiltration, it is essential to study soil-water characteristics

and water permeability functions. The soil-water characteristic curve (SWCC) is a relationship between suction

and water content or degree of saturation. Conventionally, only the drying soil-water characteristic curve of soil

specimens is determined in a pressure-plate extractor without the application of any external stress. In this paper, the

influences of initial dry density and initial water content, history of drying and wetting, soil structure, and the stress

state upon the desorption and adsorption soil-water characteristics of a completely decomposed volcanic soil in Hong

Kong are examined and discussed. The experimental results presented are obtained by using a conventional volumetric

pressure-plate extractor and a newly modified one-dimensional stress-controllable pressure-plate extractor with deformation

measurements. The SWCC of a recompacted specimen is very different from that of a natural specimen with the

same initial soil density and initial water content. The SWCC of the recompacted specimen is highly dependent on the

history of drying and wetting. The rates of desorption and adsorption are substantially higher at the first drying and

wetting cycle than at the second drying and wetting cycle. The size of the hysteresis loop of the recompacted specimen

is considerably larger than that of the natural specimens. The SWCC of soil is stress-state dependent. For recompacted

specimens subjected to different stress states, the higher the applied stresses, the lower the rate of desorption and the

smaller the size of the hysteresis loops. However, for natural specimens, the size of the hysteresis loops seems to be

independent of the stress state. Under a higher applied stress, natural specimens exhibit lower rates of desorption and