Multi-scale soil moisture dynamics in arid mined Loess Plateau arise from crack evolution and microstructure collapse

Coal mining-induced subsidence and mining-induced cracks significantly disturb soil moisture dynamics in the arid Loess Plateau, yet the multi-scale mechanisms remain poorly understood. This study integrates field monitoring, soil experiments, physical simulations, and numerical modeling to systematically investigate how mining-induced cracks affect soil moisture redistribution. Dynamic monitoring of cracks at different scales (micro, small, medium, large) throughout their formation-development-stabilization process revealed distinct evolution characteristics: micro/small cracks stabilized slowly (~ 20 days), while medium/large cracks developed rapidly (8-10 days), with crack width and proximity jointly determining soil moisture loss rates. Scanning electron microscopy (SEM) and soil water characteristic curve analyses demonstrated that surface mining-induced cracks alter loess microstructure, leading to (1) looser particle arrangement with reduced particle size and shifted contact patterns (from line-line to point-point/line), (2) increased porosity (large pores: + 10.49%-25.89%; large-diameter pores: + 7.08-9.66%) and connectivity, accelerating evaporation/infiltration, and (3) weakened aggregate interactions and reduced water retention capacity (micro-cracks > small > medium > large). Hydrus-2D simulations incorporating a dual-domain model effectively captured preferential flow patterns near cracks, with results aligning well with field measurements (high R², low RMSE). The findings highlight the synergistic effects of crack evolution and microstructure collapse on soil hydraulic properties, providing critical insights for ecological restoration in mining-disturbed loess regions.