The importance of desiccation cracks in water migration inside expansive ground

Abstract

Highly plastic clays are generally regarded as very impermeable materials. However, it is well known that desiccation cracks, as well as inherent fissuring, increase the in-situ apparent permeability inside the active zone. The paper presents long-term measurements of matric suction and moisture sensors installed under a mat foundation, on the shaft of bored piles, and at the free field in expansive marls in area of Nicosia, Cyprus. The data reveal the ease with which rainwater percolates in the ground due to the presence of shrinkage cracks, especially adjacent to foundation elements. Several episodes of full saturation conditions are recorded under the mat close to its perimeter during the course of a hydrological year after significant rainfall events, even during the dry season. Moreover, rapid migration of rainwater along the gap forming between the soil and pile shaft during the dry season can lead to brief full saturation incidents down to at least 1.5m depth. Back-analysis of field wetting experiments using the finite element method indicates that the equivalent in-situ saturated hydraulic conductivity of highly expansive marl near the ground surface is 3 to 4 orders of magnitude larger than the one measured on intact marl samples in the laboratory.