Initiation mechanism of Jiweishan high-speed rockslide in Chongqing, China

摘要

A rockslide of 5.0-million-m(3) volume occurred on June 5, 2009, in Jiweishan, Chongqing, China. The field investigation indicates that the kinetic process of the Jiweishan rockslide was divided into four stages: the initiation of ejection, flying and scraping, colliding and direction altering, and stopping and accumulating. The rock mass had been considered stable according to the principle of statics. To investigate the possible initiation mechanism, the present research proposes a new initiation model that considers the vibration effects as a shaking force (F), which acts against the rockslide mass in the direction normal to the rupture surface at the same instant when the brittle limestone is ruptured. The amplitude ofFwas best estimated as vertical bar tau center dot A(F)vertical bar, where tau fand A(F)are the shear stress and area of the rupture surface, respectively; under this model, the initial ejection direction agrees very well with the observed direction. The movement characteristics of the slide were later identified by assuming a variety of friction angles (at 0 degrees, 5 degrees, 10 degrees, and 15 degrees) at the weak slip surface. It is observed that when the friction angle ranged from 0 degrees to 5 degrees, the velocity of the rockslide reached 68.3-79.2 m/s and the rockslide mass could fly to the observed scraping area. Furthermore, the velocity and duration at each moving stage were estimated, using the assumptions in the shaking force and friction angle. Results show that the total travel time of Jiweishan rockslide was 66.8-78.6 s, which is close to 60 s as estimated by eyewitnesses and the seismic wave records.