Study Of The Highway Collapse Type And Formation Mechanism Under Strong Earthquake

A major earthquake measuring 8.0 Richter scale attacked Wenchuan County of Sichuan province at 14:28:04 on 12 May 2008. The epicenter of the quake was located 31.0 degrees north latitude and 103.4 degrees east longitude, and its maximum seismic intensity wasⅪdegrees with the feathures of high magnitude, shallow seismic focus, strong destruction and wide range.The earthquake induced a large number of landslides, collapses and other secondary geohazards, mainly dominated by collapses which accounted for 93% of the total and was 20 times more than before the earthquake. On the basis of western science and technology issues, 14 highway in the severest and severe disaster areas in Sichuan province for a total mileage of 1,640 km damaged by Wenchuan earthquake were investigated. It was identified that there were 555 points of geohazards along the highway, of which landslides 273, collapses 155, 37 debris flows. With the full study of earthquake engineering geological conditions of collapses and developmental characteristics of collapses along the highway, the study focus on the classification of the highway collapse under strong earthquake, the statistical analysis of the relationship between collapses and height, lithology, slope, aspect, faults, slope structure factors ,the development rules of earthquake collapsed along the highway after a large number of laboratory analysis and statistics, and the formation mechanism under strong earthquake using DDA numerical simulation study. Research has made major achievements as follows:(1) According to buckling failure mode, the collapse can be divided into seven types as crack - sliding-style, crack - dumping-style, crack - staggered breaking- type, crack - shattering -type, crack - fracturing-style, crack - ejection–style and shock - rolling type.,(2) The development rules of earthquake collapses was summarized as follows: statistics showed that the landslide mostly occurred at 0.4 ~ 0.9 slope sections, mainly in the middle and upper position; metamorphic rocks and magmatic rocks had a highest collapse development degree, followed by carbonate rocks, sandy conglomerate and so on; earthquake-induced collapses are distributed mainly within the range of 45°to 70°; earthquake-induced landslides mainly concentrated in the east, southeast, south and southwest of the sunny slope; earthquake-induced collapses mainly developed in intensity ofⅨdegrees in the region and above; landslides mostly occured in the layered structure, mainly in the hard and full rock slopes, followed by the massive structure slopes.(3)The formation mechanism of some typical collapses as sliding-style, dumping-style, staggered breaking- type, shattering–type and ejection–style under strong earthquake was studied by method of DDA numerical simulation and selecting the typical collapse point. Due to the level of earthquake powerful inertia, the trailing edge of slope first of all produced a deep crack that was parallel to the slope and tilted to the slope outside at the back edge of the slope; and then, the deep crack expanded continously because of sustained earthquake and the crack lithodeme damaged to form the collapse depending on the structure of the slope.