Laboratory determination of volumetric shrinkage behavior of bentonites: A critical appraisal

Montmorillonite-rich clays such as bentonites are extensively used in many engineering applications. Determination of volumetric shrinkage behavior is important for the analysis of flow, compressibility, and shear strength behavior of unsaturated bentonite clays. Volumetric shrinkage curve (VSC) provides volume of the soil specimen with changes in the water content. VSC data of bentonites are estimated using several laboratory test methodologies designed for non-plastic soils. The influence of wax coating method, clod test, balloon method, and direct measurement techniques on the measured shrinkage data of four different Indian bentonites was analyzed. The limitations associated with the shrinkage tests were discussed in this work. Laboratory shrinkage tests were found to be incapable of establishing the shrinkage behavior of plastic clays over the entire range of water contents. Two theoretical models were fitted to the measured data for analyzing different shrinkage characteristics. The models demonstrated an excellent fitting to the measured data with coefficient of determination varied between 0.987 and 0.999. The measured soil water retention data, in terms of gravimetric water content versus matric suction, were combined with the measured VSC data from different tests to establish the SWCC data in terms of degree of saturation versus matric suction. The influence of measurement errors in VSC tests on the estimated SWCC data was discussed on two of the studied bentonites.