Instrumented Plate to Study Soil Cracking Dynamics during Wetting–Drying Cycles

Abstract

This work presents a new apparatus to study the cracking behavior and tensile-compressive forces developed in soils subjected to drying-wetting cycles. The device is fully instrumented and based on active principles that enable measuring the forces generated in soils during both drying-triggered shrinkage and wetting-induced expansion. The test setup includes a balance to track the water content changes during drying and wetting and a digital camera used to take pictures at predefined time intervals. An image analysis software was used to learn about the evolution of key characteristics of the crack network (i.e., crack intensity factor and crack aperture). The digital image correlation (DIC) technique was adopted to track the displacement field during soil cracking and healing. The study was based on slurry and compacted specimens made up of a bentonite/kaolin mixture. The developed device produced novel results by continuously tracking the time evolution of the forces induced in soils during drying and wetting cycles. The results show that the tensile force was much higher in the 1st drying (more than three times) than those in subsequent dryings. The maximum compressive force developed during wetting was substantially smaller than the higher tensile force measured during drying. The crack intensity factor (CIF) and crack aperture study indicate that the crack networks tended to be denser as wetting-drying cycles progressed. Note that after each drying and wetting stage, new cracks grew in the soil. Both cracks spacing and aperture decreased after each cycle. The results reveal that the methodology developed in this work can study the soil behavior under drying-wetting cycles, and it can assist in a better understanding of this complex problem.