Creep leakage process of remaining soils in near-surface fissures in a karst area with bedrock outcrops

As a global ecological environmental problem, rocky desertification is derived from the exposure of large areas of bare rock on slopes, and soil remains only between rock exposures and in fissures. These remaining soils are crucial to vegetation growth and the amelioration of rocky desertification, but they are prone to leakage loss. This study aimed to reveal soil creep displacement (SCD) and the characteristics, process and mechanism of soil particle leakage in fissures on sloping land in karst areas. Six fissures on the karst plateau of Guizhou were studied by paint marking and soil particle analysis techniques, and SCD was monitored during three rainfall periods (cumulative rainfall of 104.5, 151.2 and 332.7 mm). The results showed that for 104.5 mm of rainfall, the SCD of the fissures was 1.0 similar to 2.5 cm and accounted for more than 62.5% of the displacement observed after a total of 332.7 mm of precipitation. Additionally, the SCD was 0.2 similar to 0.3 cm at 181.5 mm of rainfall. Therefore, rainstorms or downpours are a key factor driving soil fissure leakage, and the leakage form is mainly soil creep. Under three rainfall observation periods, the particle content with different particle sizes at soil-rock interfaces and soils in six fissures showed that fissure soils do not show uniform downward leakage; instead, some particles in the soil layers or at soil-rock interfaces randomly leak to lower layers during the process of creep leakage loss. Hence, the occurrence of soil layers and particles is random, and the soil particles at the soil-rock interfaces and in soil layers in fissures may leak downward. The results indicate that soil creep leakage in fissures is a complex process that depends on both internal factors and external factors (such as rainfall).