Tensile behavior of clayey soils during desiccation cracking process

Abstract Desiccation cracking is a common phenomenon on Earth's surface. It is a typical form of soils' tensile failure caused by drying-induced tensile stress. Understanding soil tensile behavior during the drying process is of great significance for revealing the soil desiccation cracking mechanism. In this investigation, fiber Bragg grating (FBG) technique was employed to develop a new restrained ring, which is able to continuously monitor the evolution characteristics of soil tensile strain as well as tensile stress during the desiccation cracking process. Desiccation tests were carried out on two clayey soils (a lean clay and a fat clay). Saturated slurry samples (inside radius of 25 mm, outside radius of 75 mm and height of 30 mm) were prepared with initial water contents of 58.1% for the tested lean clay and 106.6% the tested fat clay, and were subjected to continuous drying under constant environmental condition (25 ± 1 °C of room temperature, 50 ± 5% of relative humidity). Moreover, a camera was mounted above the soil sample to capture the surface changes as well as the initiation and propagation of desiccation cracks. The results show that the developed FBG-based restrained ring can effectively identify the tensile behavior of the soil during the desiccation cracking process. Both the evolution of tensile stress and graphic variation show three typical periodic features that are well matched with soil vertical deformation, lateral shrinkage and cracking. With decreasing water content, tensile stress gradually increases at first and then increases more rapidly. Once the tensile stress reaches the peak value, desiccation cracks initiate and a sudden reduction in tensile stress is observed. Finally, the tensile stress reaches a residual stage. We consider the maximal tensile stress during the drying process to correspond to the tensile strength of the tested material. It is found that clay content has a significant influence on the cracking tensile strength of soils. The fat clay with a higher clay content shows a larger cracking tensile strength (about 410 kPa) compared with the lean clay (about 90 kPa).