Abstract: In order to study the effect of the particle size grading on the stability of super-high bench dump,and taking Dumu Waste Dump in Gongchangling Open Pit Mine as an example,two kinds of slope models of considering size grading are set up.On this basis,the finite difference software -FLAC is used to analyze the dump stability,and study the impact of the particle size on the stability.The results indicate that:the size classification or the content increase of large particle size bulk material would increase apparently the safety factor of dump.Based on this conclusion,the dumping processes are improved by two approaches of increasing the content of large particle size bulk material and discharging the rock mass along the dump height according to the particle size from large to small.But the weak layers within slopes caused by the size classification need to be paid attention and be eliminated.This study provides two kinds of effective approaches for the stability analysis of super-high bench dumping and has important reference significance for other similar projects.

Key words: Size grading, Particle size, Dumping stability, Matlab curve fitting toolbox