Revealing drying-induced crack networks and hydrological pathways in loess using image recognition and continuous X-ray CT

In semi-arid loess landscapes, desiccation cracks significantly affect evaporation, rainfall infiltration, preferential flow, and shallow slope instability. However, existing research largely focuses on crack morphology, lacking insight into continuous three-dimensional crack evolution and its feedback on evaporation-seepage pathways. To address this, we conducted evaporation-cracking experiments on remolded loess with five initial water contents (45%, 50%, 55%, 60%, 65%) under constant 50 °C drying. By integrating continuous image capture, Continuous X-ray computed tomography (X-CT) scanning, and pore-scale seepage simulations based on real 3D crack structures, we revealed the coupling mechanism between moisture migration and crack network evolution. The results show that cracking exhibited significant staging across all specimens, summarized as three phases: crack incubation, rapid propagation, and late-stage stabilization. Cracks initiated earlier in the 45% and 50% groups. Although initiation was delayed in the 55%, 60%, and 65% groups, once started, crack area, total length, and 3D crack volume increased more rapidly, ultimately forming more complex and better-connected crack networks. Continuous X-CT results indicate that higher initial water content led to larger crack volumes, 3D surface areas, and numbers of connected throats. The evaporation process also displayed distinct stages: a secondary rise in evaporation rate was highly synchronized with the surge in crack volume, indicating positive feedback by increasing effective evaporation area and shortening migration paths. Seepage simulations based on X-CT derived structures further revealed that absolute permeability after drying increased with initial water content, from 233.17 D (45%) to 453.83 D (65%). Flow paths concentrated along cracks and connected throats. These findings provide an experimental basis for evaluating hydrological responses, erosion initiation, and shallow stability in loess regions under alternating rainfall-evaporation conditions.