Environmental and material controls on desiccation cracking in engineered clay embankments

Abstract

Desiccation cracking is a natural phenomenon commonly associated with drying of expansive soils. The role of cracks in surface permeability increase and overall deterioration of infrastructure slopes makes it a key factor in climate-related slope instability processes. Despite this significance, the controls on soil cracking in engineered slopes still represent a poorly understood area. In this study, soil cracking behaviour in clay embankments exposed to cyclic wetting and drying was investigated to improve understanding of this phenomenon for application in geotechnical practice. A complimentary field and laboratory study was undertaken, approaches commonly conducted in isolation in the literature. The field program involved direct investigation of natural crack development in a heavily instrumented, clay embankment (BIONICS, Newcastle University). Crack morphology parameters were quantified under engineering, meteorological and near surface soil hydrological conditions to understand how temporal change influences these. Laboratory experimentation was carried out on materials representative of typical embankment fills and construction methods in the UK in a bespoke climate control system. Time series photographs of the crack networks were analysed using image processing technique to compare their intensities across the experimental conditions. Syntheses of field and laboratory results show the influence of factors related to the embankment geometry (i.e. slope aspect, layer thickness), material properties (i.e. soil density and plasticity) and environmental condition (i.e. wetting and drying cycles) on the cracking behaviour in engineered clay slopes. The sensitivity of cracking intensity under given climate conditions critically relates to the rate of moisture loss and the material strength. Overall, this research presents how newly gained understanding of cracking can potentially impact upon improved construction techniques of engineered clay embankments and the susceptibility of historic embankments constructed to lower densities to climatic changes, including how drying/wetting cycles can exacerbate crack development.