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.