Comparison of soil physicochemical properties and mineralogical compositions between noncollapsible soils and collapsed gullies

This study aimed to compare soil physicochemical properties and mineralogical compositions, including the cohesive force and internal friction angle, using direct shear tests with designed water contents and temperatures, between noncollapsible soil and collapsed gullies. Two pedons were collected from Longmen Town (Anxi County, Fujian Province) with severely collapsed gullies that developed from granitic rocks, and another two pedons were collected from metamorphic regions (Gande Town) without soil erosion. The samples were subjected to X-ray diffraction (XRD) analysis, and their soil physicochemical properties were compared. Noncollapsible soils had superior physicochemical characteristics, e.g., these soils contained higher amounts of cations, especially total iron oxides (Fet). Furthermore noncollapsible soils were able to resist shearing due to their greater cohesive force, and the internal friction angle did not differ considerably from that of the collapsed soils. Kaolinite, illite, hydroxy-interlayered vermiculite (HIV) and gibbsite were the dominant clay minerals in the noncollapsible soils. However, in the collapsed soils, kaolinite accounted for > 85% of the total clay mineral composition. The cohesive force and internal friction angle were significantly correlated with sesquioxides of all non-collapsible and collapsed pedons, such as Fed (free Fe-oxides, 0.762**, 0.637**) and total iron (Fet, 0.783**, 0.708**), as well as magnetic susceptibility (0.650**, 0.740**) (P < 0.01). In stepwise regression analysis, some of these factors did not exhibit dominance, which merits further in-depth research.