Effect of the Soil Organic Content on Slurries Involved in Mudflows

The effect of the soil organic content on the stability of a soil involved in a rapid mud flow is here experimentally investigated. The soil is collected form a site where a catastrophic landslide took place (Cervinara – AV) and it is chemically treated to selectively remove different aliquots of its original organic carbon. In particular, The Dissolved Organic Carbon (i.e. the carbon soluble in water)results the 6% of the soil organic carbon and it is removed with a mild chemical treatment to obtain the DOC 6 sample, the 77% and 89% of the Total Organic Carbon (i.e.the pool of oxidizable soil organic carbon)is removed with a strong chemical treatment to obtain the TOC 77 and TOC 89 sample, respectively. The stabilizing effect of the organic carbon is investigated by following the evolution of the particle size distribution of soils induced by a mild mixing of diluted slurries and we showed that the particle size distribution of the original soil sample is unaffected by the slurry mixing, while those of DOC 6,TOC 77 and TOC 89 evolve during time, revealing the breakup of soil aggregates. Our findings highlight the stabilizing effect of SOC in the investigated liquid slurries and, furthermore, they suggest that the organic carbon quality, more than its quantity, plays a crucial role in the soil stability. Indeed, it is enough to remove the Dissolved Organic Carbon to register a soil disaggregation process comparable to that observed for TOC 77 and TOC 89 samples. This suggests that Dissolved Organic Carbon is the fundamental organic fraction stabilizing the slurry microstructure.