Multi-Scale Approach to Cracking Criteria for Drying Silty Soils

Cracking is a most unwanted development in soil structures undergoing periodic drying. Desiccation cracking arises in the apparent absence of external forces. Hence, either an internal, self equilibrated stress pattern resulting from kinematic incompatibilities, or stress resulting from reaction forces at the constraints should be contemplated to arrive at cracking criteria. Three circumstances are considered for drying cracks: drying shrinkage, kinematic constraints impeding the shrinkage inducing reaction forces, and consequent tensile effective stress reaching tensile strength. An earlier tubular micro-scale model of porous drying medium is considered with constrained at restrictive inter - pore solid contacts. At the meso-scale tubular drying pores are considered in the vicinity of an imperfection, inducing a stress concentration near its tip, in the presence of significant pore suction. This approach allows one to use the effective stress analysis, which otherwise, away from the stress concentration usually yields compressive effective stress and hence a physically incompatible criterion. Recent experimental results from an idealized configuration of a cluster of grains provide geometrical data suggesting that an imperfection as a result of air entry deep into the granular medium penetrates over 8 internal radii of the typical pore