3D Numerical Simulation Of The Airblast Generated By Yigong Rock Avalanche

During the rapid motion of rock avalanche, it compresses air and generates destructive airblast in the front and on both sides of its motion path. The airblast formed by the air compressed by rock avalanche also can cause huge geological disasters and should be attached serious attention, compared with the hazards caused by the rock avalanche itself. Based on the characteristics of Yigong rock avalanche occurred on April 9th,2000 in Yigong Township of Bomi County, Tibet, a three-dimensional proportional model for numerical simulation had been established in this thesis. And with the application of computational fluid dynamics software Ansys Fluent 14.5, the law of Voellmy, which is summarized previously and appropriate for the description of rock avalanche motion, had been introduced into computational procedure through the User-Defined Functions (UDF) of the software FLUENT and the method of C language programming. This method successfully achieved the three-dimensional numerical simulation of the whole moving process of Yigong rock avalanche and the airblast occurrence.The main conclusions are as follows:(1) Yigong rock avalanche continued for 150 seconds. The total long run-out is approximately 10 km. The maximum velocity of 75 m/s appears at the 30th second. During the movement of the debris-flow, the maximum velocity at every moment appears at the part near the front zone of the sliding mass. The difference in speed between the front and rear parts is significant.(2) The maximum velocity of the airblast appears between the 15th-30th second with the approximately value of 50 m/s. There are two peaks in the value of the airblast pressure. One peak value is the start pressure 660Pa. The other is formed while the debris mass enters into the main gully of Zhamunonggou, and the value is 1500Pa. The destructive power caused by the former corresponds to the wind power of a hurricane, while the latter is equivalent to the wind power of a severe typhoon.(3) Along the sliding direction from the front to forward part, the sphere of the airblast influence on both horizontal and vertical direction is within approximately 1 km. The airblast pressure decreased with the increase of elevation from the front of debris mass. It generated a negative pressure above the front part in the depositional phase of the rock avalanche.(4) The terrain of the valley has a significant impact on the pressure of the airblast generated by the debris-flow. It is suggested that it affects the airblast pressure mainly through the thickness of the debris-flow in this study. The debris-flow in deeper terrain of the valley can push the air more violently, due to the limited terrain of both sides of the motion path increases the thickness of the debris-flow.