On August 3

2014

large number of collapse and landslide have been triggered by the Ludian earthquake

it led to damage to the local economy and loss of peoples′lives.The Hongshiyan collapse is the worst one.The collapse volume is approximately1.2×106 m

3

.This collapse formed a barrier dam which was 96 mhigh.The water blocked was approximately2.3×108 m

3

.In this study

we researched the mechanical principle of Hongshiyan landslide by field survey and numerical method

the dynamic finite difference method（FDM）was used to analyse the response of Hongshiyan slope and the main factors inducing the landslide.According to the research

the mai

n factors for Hongshiyan collapse are the earthquake load and local topography

and the damage to rock mass is due to the combined action of shear and tension stress.The collapse of Hongshiyan landslide occurred at 4

6

safter the Ludian earthquake took place

which contained the VGA moment.From analysis of seismic response

the site amplification effect and the stress wave superposition have been found.Under the load of earthquake

the movement direction is normal to the slope surface

this will make more damage effect.