Using the Reference Shrinkage Curve to Estimate the Corrected Crack Volume of a Soil Layer
To estimate the correct soil crack volume based on the shrinkage geometry factor, in addition to measurements with core samples, one also needs to know the shrinkage curve of the soil matrix without cracks. For such a curve one can use the soil reference shrinkage curve that is only stipulated by intraaggregate clay shrinkage without interaggregate cracking. The objective of this work is to illustrate such use of the reference shrinkage curve and, in addition, to argue the necessity to correct the usual estimates of the shrinkage geometry factor in order to correctly estimate the soil crack vol- ume. The illustration is based on available data and reference shrinkage curves for eight soils.
Soil lacunar factor and reference shrinkage
A b s t r a c t. At sufficiently small soil clay content, the clay contributing to the soil aggregates usually contains so-called lacunar pores that are essentially larger than the clay matrix pores. A recently introduced parameter, the soil lacunar factor, determines the volume fraction of the clay matrix pore decrease at shrinkage that is transformed to the lacunar pore volume increase inside aggregates. The lacunar factor essentially influences the soil shrinkage and is a fundamental soil property that can be found independently of a measured shrinkage curve. The aim of this work was to theoretically derive and experimentally validate an expression to estimate the soil lacunar factor through the actual soil clay content and critical soil clay content (when the actual soil clay content is higher than critical one the lacunar pores lack). To validate the approach the available data of sixteen soils were used. K e y w o r d s: soil aggregates, soil physical properties, soil reference shrinkage, lacunar factor, aggregate surface layer
The nature of changes in bulk density with water content in a cracking clay
The effect of changing water content on the bulk density of undisturbed cores of a cracking clay was examined in laboratory experiments. The results were compared with the relationship between bulk density and water content established by core sampling the same soil in the field. Over the water content range measured in the field soil, the laboratory cores shrank three-dimensionally and normally. Small departures from normal shrinkage were attributed to the formation of cracks within the cores, and to the occurrence of some structural shrinkage in cores previously wet to high water contents. Swelling of cores was approximately three-dimensional, except for some unconfined swelling which occurred in the core surface. Unidimensional swelling was induced by confining dry cores to reduce the void ratio before wetting. Subsequent shrinkage was three-dimensional, indicating that the soil particles were reoriented during the unidimensional swelling phase. While the laboratory measurements showed that the soil volume changes were essentially three-dimensional and normal, the field data indicated that unidimensional shrinkage occurred at water contents greater than 0.47 g g-1. These field results were attributed to sampling inaccuracies associated with the use of a small-diameter core sampler, the actual field bulk density relationship being considered three-dimensional.