Vol14 No.4: 611-620
【Title】Mechanisms involved in triggering debris flows within a cohesive gravel soil mass on a slope: a case in SW China
【Author】CHEN Ning-sheng; ZHU Yun-hua; HUANG Qi; IQBAL Javed; DENG Ming-feng; HE Na
【Addresses】1 Key Laboratory of Mountain Hazards and Surface Process, Institute of Mountain Hazards and Environment, Chinese Academy of Sciences and Ministry of Water Resources, Chengdu 610041, China, 2 University of Chinese Academy of Sciences, Beijing 100049, China, 3 Southwest Petroleum University, Chengdu 610500, China, 4 Southwest Electric Power Design Institute CO, LTD, Chengdu 610021, China, 5 Department of Earth Sciences, COMSATS Institute of Information Technology, 22060 Abbottabad, Pakistan
【Citation】Chen NS, Zhu YH, Huang Q, et al. (2017) Mechanisms involved in triggering debris flows within a cohesive gravel soil mass on a slope: a case in SW China. Journal of Mountain Science 14(4). DOI: 10.1007/s11629-016-3882-x
【Abstract】The triggering mechanisms of debris flows were explored in the field using artificial rainfall experiments in two gullies, Dawazi Gully and Aizi Gully, in Yunnan and Sichuan Provinces, China, respectively. The soils at both sites are bare, loose and cohesive gravel-dominated. The results of a direct shear test, rheological test and back-analysis using soil mass stability calculations indicate that the mechanisms responsible for triggering debris flows involved the decreases in static and dynamic resistance of the soil. The triggering processes can be divided into 7 stages: rainfall infiltration, generation of excess runoff, high pore water pressure, surface erosion, soil creep, soil slipping, debris flow triggering and debris flow increment. In addition, two critical steps are evident: (i) During the process of the soil mass changing from a static to a mobile state, its cohesion decreased sharply (e.g., the cohesion of the soil mass in Dawazi Gully decreased from 0.520 to 0.090 kPa, a decrease of 83%). This would have reduced the soil strength and the kinetic energy during slipping, eventually triggeredthe debris flow. (ii) When the soil mass began to slip, the velocity and the volume increment of the debris flow fluctuated as a result of the interaction of soil resistance and the sliding force. The displaced soil mass from the source area of the slope resulted in the deposition of a volume of soil more than 7 - 8 times greater than that in the source area.
【Keywords】Debris flow; Cohesive gravel soil; Triggering mechanism; Slip; Soil erosion