Desiccation cracking of soil subjected to different environmental relative humidity conditions

Relative humidity (RH) is among key environmental and climatic factors that affect the evolution of soil desiccation cracking. This study aims to investigate how RH variations influence soil desiccation cracking, addressing an overlooked aspect in prior studies. A set of laboratory tests were performed to examine a fat clay undergoing desiccation cracking at various controlled RH levels of 15.0%, 44.0%, 66.0%, 76.0%, 83.5% and 93.7%. During testing, all samples were weighed and photographed simultaneously to monitor evaporation and surface cracking. The evolution of the surface crack network was quantitatively analyzed by an image processing technique. Results highlight the strong dependence of soil desiccation cracking on RH conditions. Increasing RH is found to decrease the overall evaporation rate and increase the water content at which cracking starts. Under high RH levels, the formation of surface cracks exhibits an evident hierarchical process with wide primary cracks developing first followed by fine sub-cracks propagating from the primary ones. Different cracking developing rates between a primary crack and sub-crack give rise to the remarkable multi-stage growth of crack length. Besides, owing to an increase in RH, desiccation cracks at a given water content tend to be wider and the width distribution of the final crack network changes from a unimodal to a bimodal feature. Lowering RH causes a faster cracking rate and makes the hierarchical process invisible, resulting in the formation of a longer total crack length at the end of evaporation. This study is expected to help analyze the underlying formation mechanisms of desiccation cracking-inducing geohazards and assess the long-term performance of earth structures under future climate changes.