Effect of wetting–drying cycles on profile mechanical behavior of soils with different initial conditions

• Soil mechanical behavior changes is related to the critical water content.
• W–D cycles lead to degradation of soil mechanical behavior.
• W–D cycles create structure defects and cracks in soil.
• The effect of W–D cycles depends on soil initial state.

Wetting–drying (W–D) cycles can cause significant modifications on soil hydro-mechanical behavior. In this investigation, both initially saturated slurry specimens and unsaturated compacted specimens were prepared and subjected to three W–D cycles. The temporal–spatial evolution of soil profile mechanical behavior during each drying path was characterized by penetration test using a micro-penetrometer. The results show that the employed micro-penetrometer provides a simple, quick and reliable tool to evaluate soil profile mechanical behavior. As initially saturated soil is subjected to drying, the overall profile penetration resistance changes slightly before a critical water content is reached. After that, it increases quickly with decreasing water content. The drying induced improvement of soil mechanical behavior exhibits evident delayed effect in profile. The effect of W–D cycles on soil profile mechanical behavior depends on soil initial state. For initially saturated slurry specimens, the overall profile penetration resistance generally decreases with increasing W–D cycles, and the reduction between the 1st and 2nd drying paths is much higher than that between the 2nd and 3rd drying paths. While for initial unsaturated compacted specimens, the overall profile penetration resistance during the 1st drying path is lowest, and reaches the maximum value during the 2nd drying path. It is also found that, whatever the initial state, profile structure defects are created after the specimens are subjected to the 3rd W–D cycle. During the 3rd drying path, the penetration resistance shows evident fluctuation in profile, and this phenomenon is more pronounced at relatively low water content condition.