3D Numerical Simulation Of The Airblast Generated By Erlongji Rockslide

Erlongji rockslide occurred at approximately 14:29 P.M. on April 25,2010 (local time) at the 3 km location of No.3 highway on the Sai Gong Gek Mountain, approximately 20 km northeast of Taipei, the capital of Taiwan. In this rockslide, near half of the hill gave way, in which more than 200,000 m3 of dirt and rocks crashed onto the highway and destroyed an overpass, resulting in a road closure and blockage of this 6-lane highway between Keelung and Taipei. According to the statistics, there were three cars and 4 people buried during this geological disaster.When Erlongji rockslide moved in a high speed, it generated airblast. The airblast and rockslide impacted on the No.3 highway respectively. In this thesis, author not only used the FLUENT numerical modeling software for calculating hydromechanics to reproduce the whole process of the Erlongji rockslide, but also analysed particularly the relevant characteristics and regular pattern of the airblast. In addition, author conducted the study on the surface pressure of the highway through setting the monitoring points in the numerical modeling. The main results of these numerical simulations are as follows:(1) The movement distance of the rockslide is 130 m. The whole process takes about 8 seconds. At the 2nd second, the front part of the rockslide has already rushed out of the toe of slope. Then the sliding mass breaks through the slope protection and crashes down the southbound lane of No.3 highway. At the 3rd second, the sliding mass has hit the southbound line and crashes down the north line with three lanes. At the 4th second, the sliding mass has been rolling the northbound line. At the 5th second, the debris maintains a high-speed reaching opposite side of the slope, and begins to climb the lower part of the slope, acceleration decreases accordingly. The maximum velocity of the debris-flow appears at 6s with its value reached 30 m/s. At the 8th second, the velocity of the rockslide has been around 4 m/s. The terrain has significantly impact on the movement of the rockslide. The debris-flow crashes down from the slope with the first peak value of velocity at the first time. After hitting the ground and sliding horizontally, the velocity rockslide begins to decrease. And then the sliding mass crosses down from the southbound line to the north line, resulting in the occurrence of the second peak value of velocity. As striking the slope in front part, the velocity of sliding mass begins to decrease again. Then debris-flow climbs over the slope with a small increasing velocity.(2) The maximum affected distance for the airblast is about 80 m away the toe of rockslide. Sliding mass is affected by the topography, drives the air above move as a disturbance zone. That is, the speed of the air imitates the speed of rockslide. Debris-flow can fall over and jump in the path of topographic transition, coming up with the negative pressure within the sliding mass; and make air above debris-flow have a "negative pressure envelope". Additionally, at about 6th second, there is a maximum value of airblast pressure, equivalent to the 10th level of wind, which is capable of uprooting trees and damaging buildings.(3) On the surface of highway, the airblast pressure shows steadily increasing trend, with an undulating of eddy current and wind effect, where the maximum blast pressure is more than 560 Pa. While, the pressure caused by the sliding mass is mainly affected by the thickness distribution of sliding mass and the motion path. Generally, the pressure increases at first and then decrease. The maximum pressure has exceeded 700kPa.