Moisture variations and its effect on shrinkage and swelling characteristics of unsaturated soil

Abstract

Moisture variations during drying process affect the shrinkage and swelling characteristics of unsaturated soil. It is important to study the complex behaviour of unsaturated soil during drying process. Characterisation of suction with moisture distribution during drying process of unsaturated soil is critical in predicting swelling and shrinkage. In this paper, an experimental approach for modelling of moisture variations during drying of unsaturated expansive soil is presented. Non-linear diffusion theory was used to characterise the process of moisture loss during drying. Laboratory tests were undertaken on clayey soil with a swelling index of 42%. Measurement of material characteristics included coefficient of moisture diffusivity, suction and humidity isotherm. The soil–water characteristic curve was determined from the measured suction, air-entry value is obtained from this curve. The results indicated that moisture loss and strains produced during drying process are independent of initial dry density. However, swelling potential is influenced by initial dry density, initial water content and suction. For water contents above 12%, strong influence of water content on shrinkage of soil specimen was observed. In contrast to shrinkage behaviour, swelling characteristics was less affected or unaffected at higher water content.

Keywords:

• Moisture
• diffusion
• suction
• unsaturated soils