5. CONCLUSIONS

In this study, field GPR physical imaging techniques and infiltration experiments were applied to investigate the effects of crack properties on preferential flow paths. Many soil cracks filled with fine fragments were present in karst. By evaluating the influence of crack inclusion (sand grains and rock fragments), crack width (1, 1.5, and 2 cm), and configuration (I-shape, V-shape, and Λ-shape) on infiltration, we found that isolated soil cracks could enhance preferential flow with some properties.
The isolated soil cracks accelerated the infiltration process supported by infiltration rate, maximum dye-penetration depth, cumulative infiltration, and wetting advancing rate. These indicators reached a relatively stable increase or decrease in infiltration over time until the 40th min. The transport depth of Brilliant Blue FCF was 1.2–3.8 times slower and the infiltration rate was over 1.5 times slower than that of water during the entire infiltration process. The retardation of the Brilliant Blue FCF necessitates calibration when applied to field infiltration tests.
The inclusions, crack width, and configuration significantly affected the preferential flow indices (p < 0.05), of which the configuration has a greater effect on preferential flow. Only I-shape and Λ-shape of the soil cracks filled with rock fragments generated preferential flow. The effect of linear cracks on preferential flow in the field cannot be ignored.
The configuration of isolated soil cracks can be identified by GPR envelopes. The GPR envelope can be used to directly reflect the possible occurrence of preferential flow during rainfall conditions in crack soils.
Our research proved that isolated cracks control preferential flow and relationships between envelopes and preferential flow indices in crack soils. These findings offer new insights for underground hydrological processes and vegetation restoration in karst areas. Further research should be directed towards the future development of a combination of complex crack structures at large scales.