Investigation of Shrinkage and Cracking in Clay Soils under Wetting and Drying Cycles

Abstract

Embankments failure in cohesive soils are often preceded by periods of cyclic wetting and drying due to changing climatic conditions. The resulting desiccation cracks tend to have significant effects on the stability of slopes and other engineered infrastructures founded on such soils susceptible to shrinkage and cracking. This research investigates the shrinkage and cracking behaviour of an engineered clay soil under series of wetting and drying cycles. Experimental cyclic wetting and drying were conducted using an intermediate plasticity Durham boulder clay and synthesis bentonite mix samples. These samples were subjected to four dry-wet cycles, the desiccation rate of the samples was observed and recorded using wind source and oven drying approach at 60 0 C. The surface dimension of the samples cracks were quantified both virtually and using digital image processing. The results of the experiments indicated that the samples with higher plasticity index have a greater crack intensity factor (CIF) irrespective of the drying approach. Also both sample displays a significant increase in the cracks geometries and dimension after the first two cycles and tend to attain an equilibrium state after subsequent cyclic episodes. The mechanism of cracking was observed as initiating from the surficial or textural defects of the sample where the tensile strength is minimum and exceeded by the tensile stress. Further observations of the cracks indicated some obvious mechanism of closure especially the major cracks as the width size reduces with successive cycles. Within the context of this research, some recommendations were provided all directed towards improving the material thereby reducing it susceptibility to shrinkage and cracking.