Study on Failure Mechanism of Gongjiafang Bank Slope in Wu Gorge of the Three Gorges, the Yangtze River, China

During running period of the Three Gorges reservoir ,failure mechanism of bank slope is one of the important scientific problems of geological disaster mitigation for reservoir bank. GongJiafang bank slope is located in left of Wu Gorge in Three Gorges of the Yangtze River, where damage events appeared in 175 m experimental water storage in 2008 and 175 m normal water storage in 2011.Study shows that, GongJiafang bank slope located in the core of the Heng Shi stream anticline developes two group of tectonic fractures .The first one is unloading fracture of bank slope, whose upper part is in transfixion or intermittent transfixion status,and the second one belongs to shear shear fracture. Bank slope presents cataclastic rock mass structure ,whose water physical properties are poor. The shear strength parameters of bank slope soil reduce after being immersed, a decreas of about 52 % on cohesion, and 30 % on friction. Regional new tectonic stress field control the macroscopic law for failure of GongJiafang bank slope .Especially max2 shear zone in new tectonic stress field is consistent with the first group fracture, which strengthen progress of the unloading fracture developement .Bank slope basically appear unstable failure along with the first group fracture. About 50% unbroken lower part of unloading fracture in GongJiafang bank slope locate in reservoir water level change belt between 145m and 175m.During the reservoir water level rising, stability coefficient of bank slope decreases from 1.31 to 0.88 after being immersed, and it is inevitable for bank slope to fail suddenly. Research results for further exploration on the formation mechanism of bank landslide in the Three Gorges reservoir and its mitigation has positive significance.