Impacts of gravels on the moisture evaporation and desiccation cracks in soil

Abstract

Under extreme arid conditions, soil loses moisture and forms cracks, which significantly affect their mechanical and hydraulic properties (e.g., shear strength, soil structure, and hydraulic behavior). Natural soils commonly contain gravels. However, research on the effects of gravels on moisture evaporation and desiccation cracking in soil is limited. To investigate the influence of gravel content on desiccation cracking behavior, soil samples were prepared by mixing clayey soil with quartz sand (particle size predominantly between 2 mm and 5 mm). Desiccation cracking experiments were performed in a custom-built chamber with controlled temperature and humidity, equipped with an automated real-time imaging system. Computer-based image processing techniques were employed to quantitatively describe the cracking characteristics. It was found that under evaporation conditions, gravels in soil hinder the upward migration of internal moisture to the surface. This obstruction leads to the formation of menisci within surface soil pores, generating tensile stress between soil particles due to surface tension. Additionally, the presence of gravels causes uneven settlement in the soil during evaporation, resulting in additional tensile stress between particles. As a result, compared to pure clayey soil, gravels alter the tensile stress field within the soil. This alteration not only accelerates crack initiation but also shifts the initial crack location and modifies the final geometric characteristics of the cracks. Conversely, gravels inhibit the vertical growth of cracks and the lateral shrinkage of soil blocks, thereby reducing overall crack density on the soil surface. This study offers a new perspective for interpreting the mechanisms of desiccation cracking in gravel-containing clay under natural conditions.