The Transport And Disaster-causing Mechanism Of Large-scale High-speed Remote Viscous Debris Flow In Donyuege Valley Of Nu River

Dongyuege valley is located on the left bank of the Nujiang River and Nujiang River Basin belongs to the low latitude landform characterized by alpine canyon.The new tectonic movement in the region is strong and the relative height difference is large,and displaying the three-dimensional climate characteristic.The valley is characterized by narrow "v" character,and vegetation coverage is close to 100%,and bedrock is exposed and gravel is accumulated,and there is perennial water flow.On August 18,2010,large-scale high-speed and long-distance viscous debris flow occurred in the Dongyuege valley,and the migration distance of the slurry was nearly 10km.Debris flow accumulation area houses have been destroyed,factories destroyed,and road transport infrastructure gone,which brought serious losses to the social economy and people's property.The mountainous area is a debris flow-prone area,but it is rare to be able to remotely migrate and cause such a great disaster.It is very important to study the mechanism and the disaster characteristics of the debris flow in the Dongyuege Valley and it is of great significance to scientific research and debris flow disaster prevention and control.Through the investigation of the debris flow in the Dongyuege Valley,and taking the indoor and outdoor model tests as a means to analyze the debris flow migration and disaster characteristics.The main conclusions are as follows:1.The biofilm of the surface bedrock and the pebble surface can significantly reduce the surface friction coefficient,reduce the flow and the energy loss of the debris flow slurry on its surface,and thus increase its velocity.In the Dongyuege Valley,the debris flow can migrate nearly 10km in the trenches with a groove bed ratio of 131 ‰,which is related to the biofilm grown in the trenches.2.Debris flow slurry is easy to accumulate on both sides of the trench,but not easy to produce residual in the wet valley or shallow water environment.The main reason is that in the wet,shallow water environment,biofilm can reduce the frictional resistance of the surface of the bedrock pebble and make debris flow slurry in this environment easier to move.3.Debris flow circulation area in the lower part of the is flat and open,and the slope is small,especially in the range of 500 meters from the accumulation area with average the slope of about 5 °,which is the stage of debris flow reduction and decay,and the debris flow in the Dongyuege Valley still caused great disaster.The results of field investigation and model test show that in the 500 meters away from the accumulation area of the debris flow the leading dam broke out,forming the secondary debris flow,and instantaneous massive slurry high-speed jet accumulation area occurred,which is the key factors of this debris flow disaster.4.Through the five groups of different height debris flow leading dam breakout model test,considering the Dongyuege Valley morphology,debris flow slurry mixed with lots of boulders and large trees and other phenomena,it is concluded that during the process of slurry migration,there should be a phenomenon that the debris flow which was clogged and dampened in a short time and broke out,causing the secondary debris flow.During the process of debris flow migration,the surge of debris flow occurred 13 times which should be associated with debris flow caused by repeated clogging phenomenon.