Coupled effect of cyclic wet-dry environment and vibration event on desiccation crack and mechanical characteristics of polypropylene fiber-reinforced clay

This study investigates the role of polypropylene fibers (PFs) in mitigating the combined effects of wet-dry (W-D)
cycles and vibration event (VE), such as earthquake or machine vibrations, on the desiccation cracking and
mechanical behavior of clay through model tests. A comprehensive experimental program was conducted using
compacted clayey soil specimens, treated with various PF percentages (i.e., 0.2 %, 0.4 %, 0.6 %, and 0.8 %) and
untreated (i.e., 0 % PF). These specimens were subjected to multiple W-D cycles, with their behavior documented
through cinematography. Desiccation cracking and mechanical responses were evaluated after each W-D cycle
and subsequent VE. Results indicated that surface cracking, quantified by morphology and crack parameters i.e.,
crack surface ratio (Rsc), total crack length (Ltc), and crack line density (Dcl), increased with progressive W-D
cycles. Higher PF content in soil significantly reduced desiccation cracking across all W-D phases, attributable to
the enhanced tensile strength and stress mitigation provided by the fibers. Following VE, surface crack and
fragmentation visibility decreased due to the shaking effects, as indicated by reductions in Rsc and Dcl. However,
Ltc increased slightly, suggesting either crack persistence or lengthening. Higher PF content resulted in a more
substantial reduction in Rsc and Dcl and a reduced increase in Ltc after VE. W-D cycles led to increased cone index
(CI) values, reflecting enhanced compactness due to shrinkage which enhances with PF content showing
improved soil resistance to loading. Meanwhile, VE reduced CI values following W-D cycles, particularly in near surface layers, PF content mitigates this reduction, demonstrating that PF contributes to a more stable soil
matrix. Also, PF content decreased the soil deformation under W-D cycles and subsequent VE.