Research On Isolation Layer Thickness And Slope Stability During Turning Open Pit To Underground Mining Of Huogezhuang Mine

Determination of isolation layer thickness and the open pit slope stability are two key security issues of Huogezhuang Mine from open pit to underground mining.In view of the above problems,isolation layer thickness and slope stability in open pit to underground mining of Huogezhuang Mine are researched by means of theoretical analysis and numerical simulation.The mathematic model of isolation layer thickness is established based on the index function analysis method.And the safety factors of open pit slope are calculated by VAM under different mining stages and conditions.(1)The stability of the slopes are well at the end of open pit mining.Huogezhuang Mine could transfer to underground mining on the basis of existing open pit slopes.During underground mining at the first stage,the potential slip paths of the top slope and foot slope are from mined-out area to slope top and slope foot to top respectively.The safety factors of the top slope increased with the increasing of isolation layer thickness,and the safety factors of the foot slope are basically remain the same.(2)On the basis of other system comprehensive evaluation method,the index function analysis method is proposed.This method is a multi-factor comprehensive analysis method which could determine the optimal solution of elements by establishing the functions between an element and its evaluation indexes.Based on the index function analysis method,the mathematic model which considers the indexes including the safety factors of slope and isolation layer,the ore recovery rate,the isolation layer capacity is established to calculate the isolation layer thickness,and determined the optimal isolation layer thickness of Huogezhuang mine is 36.2m with the model.(3)Under the optimal isolation layer thickness(36.2m),the top and foot slope of Huogezhuang Mine are in steady state in undergroud mining.And the minimum static load safety factor and dynamic load safety factor of the open pit slope appear in the top slope under the first stage mining,which are 1.248 and 1.176 respectively.To compared with the static loading condition,the reduction rate of slope safety factors is less than 7% when considering the blasting vibration in existing blasting conditions.