Matric Suction and Volume Characteristics of Compacted Clay Soil under Drying and Wetting Cycles

Abstract

The influence of drying and wetting cycles on matric suction and volume characteristics of a compacted low-plasticity clay soil was studied experimentally. An apparatus was developed in which soil specimens were placed in direct contact with a high-suction tensiometer, then repeated drying and wetting cycles were applied, with drying by means of evaporation and wetting using the application of water droplets. The matric suction, vertical and radial displacement, and mass change of the specimens were all monitored continuously during the cycles. The equipment is the first to provide natural drying, unconstrained shrinkage, or swelling with continuous measurements of volume, suction, and water content in a way that could readily be used in engineering practice. The results indicated that drying-wetting cycles resulted in accumulated irreversible shrinkage. However, the amount of shrinkage decayed very significantly as the number of cycles increased, and the behavior became almost repeatable after the third cycle. It was also observed that the positions of soil water retention curves under drying-wetting cycles shift downwards with the increasing number of cycles; the larger the number of cycles, the smaller the difference between the curves, and after two or three cycles, the difference became steady. The shape of the curves changed very obviously under the first three drying-wetting cycles but less significantly after this.