The water content is a crucial factor in evaluating the causes of
Benggang collapse. The soil–water characteristic curve (SWCC) is an
important parameter for the quantitative study of soil water content.
However, limited research has been carried out on the SWCCs of the
Benggang soil profile. We studied two typical collapsing gullies in
southeast China and conducted desorption experiments using a pressure
plate extractor to analyze the SWCCs of the undisturbed soils of
collapsing walls. The results show large variations in the SWCCs for
different soil horizons of a collapsing wall that can be accurately
fitted by the van Genuchten (VG) model (NSE≥0.90). With increasing soil
depth, the a and θs parameters of the VG model first decrease and then
increase, red soil layer had the highest a and θs (the average value of
0.046 and 0.369, respectively), whereas the n parameter of the VG model
exhibits the opposite trend, sand soil layer had the highest n (the
average value of 1.563). The θr parameter of the VG model decreases with
increasing soil depth, red soil layer had the highest θr (the average
value of 0.194). The red soil layer has the highest water-holding
capacity, whereas the sandy soil and detritus layers have lower
water-holding capacities. The SWCCs are related to the soil material
composition, particle composition and porosity. The gravel content and
the particle morphology (the aspect ratio, sphericity, and specific
surface area) are also the significant influence factors for the SWCC
that cannot be neglected. The difference among the SWCCs for the soil
profiles of collapsing walls can be used to explain the mechanism for
the collapse of collapsing wall. The results of this study provide a
theoretical basis for understanding the process of the collapse of
collapsing wall in Benggang in southeast China.
Analysis of the soil water balance for large-scale reforestation with Eucommia ulmoides in the hilly red soil region of southern China