Measurement of tensile strength of clayey soil during drying and cracking

Upon drying, desiccation cracks would occur in clayey soils due to evaporation and volume shrinkage. The presence of cracks can significantly alter soil hydro-mechanical properties and results in various engineering problems. It is commonly considered that desiccation cracking of soil is one form of tensile failure controlled by tensile strength. Better understanding the characteristics of tensile strength during drying is therefore essential to study the mechanisms involved in desiccation crack initiation and propagation. However, it is still difficult to directly measure soil tensile strength especially at very high water content. In this investigation, several groups of initially saturated slurry specimens were prepared and then dried in room condition to different water contents. Direct tensile tests were performed on these specimens to measure the tensile strength by employing the specially developed apparatus. The tensile strength characteristic curve (tensile strength versus water content) was established over a large range of water content (10-70%). It is found that the tensile strength generally increases exponentially with decreasing water content. For the tested clayey soil, the critical tensile strength at onset of cracking is determined and is about 90 kPa.