Suction stress characteristics in granite red soils and their relationship with the collapsing gully in south China

The main goal of this research is to study the relationship between the soil suction stress and soil properties within four different soil profiles of collapsing gullies in the hilly granitic region of southern China. Large differences were found in the four soil layers between granite red soils, which are manifested in terms of soil bulk density, porosity, particle composition, clay minerals, micromorphology, organic matter, cation exchange capacity, permeability, oxide and hydraulics properties. The suction stress of the upper soils increases rapidly and almost linearly monotonously with the increase of matric suction, whereas C layers increases rapidly first, followed by a slow increase. The suction stress of the lower soils is significantly smaller than the upper soils under the same matric suction. These findings illustrate that the collapsing gully starts from the lower part of the granite red soil, and finally caused the gravity collapse in the upper soils, which is the main aspect that is different from the other types of soil erosion. Furthermore, suction stress has a very significant correlation with soil properties, with a positive correlation to the fine particle content, iron and aluminum oxide, and a negative correlation to coarse particles. In addition, suction stress can also be explained as being directly proportional to weathering degree. Our research provides a theoretical basis for the mass failures of the granite-derived red soil in southern China.