Research on Spatial Distribution Pattern of Stability Inter-Controlled Factors of Fine-Grained Sediments in Debris Flow Gullies—A Case Study

Abstract

Studies on the stability inter-controlled factors of fine-grained sediments in debris flow gullies play an important role in predicting the scale and danger of debris flows. However, up to the present, few studies have been carried out on the spatial distribution pattern and causes of stability inter-controlled factors of fine-grained sediments in debris flow gullies, leading to difficulty in finding the dangerous section of debris flow gullies to be monitored and controlled to reduce disaster losses. Therefore, the objective of this paper is to analyze the spatial distribution pattern and causes of stability inter-controlled factors (grain size, permeability coefficient, shear strength, and porosity), taking the Beichuan Debris Flow Gully, China, as a case. After collecting soil samples in the field, we carried out experiments to measure the stability inter-controlled factors and, from these, the results show that (1) fine-grained sediments in this case are mainly silty loams, which are stable under non-heavy rains; (2) the grain size of silty loams is mainly concentrated between 10 and 20 μm, with a spatial distribution pattern of fine in the middle and coarse at both ends; (3) the permeability coefficient of silty loams is concentrated between 1.15 and 2.17 m/d, with a spatial distribution pattern of high in the middle and low at both ends; (4) the average cohesion of silty loams is mainly concentrated between 20 and 30 kPa, with a spatial distribution pattern of low in the middle and high at both ends; and (5) the internal friction angle of silty loams is concentrated between 18.98 and 21.8°, with a spatial distribution pattern of high in the middle and low at both ends. The main reasons for these spatial distribution patterns are analyzed from three aspects of shear strength, water flow velocity, and terrain, which can provide a scientific basis for the prediction of debris flow disasters in such areas.