Groundwater Level Fluctuation Influence On Slope Stability In Wulan Open-Pit Mine

Groundwater level fluctuation has been studied by so many scholar,where it has been found how it's affected the stability of a slope.In regard of the previous study,the evaluation of groundwater level fluctuation influence on the slope stability of Wulan open pit mine had been studied in this work.A flooding which occur at Wangjiapo coal mine over Shaanxi Province expressed the rise of water level in the whole area,hence the rise of water level in the Wulan open pit mine area.Stability in the area where occur a fluctuation of groundwater level had become a priorities in the whole area subjected to the rise of water level.Landslide and slope failure are the result of a storage water in a slope body without drain condition,and led to a severe lost in material and life.The presence of water in the slope body could led to the increasing of negative pore-pressure in the slope body,thereby affecting the stress state and strength,and leading to change in the stability,thus the rise and fall of water level in a slope could seriously affected the slope factor of safety.A descriptive study on the coal mine area had been done with a detail on the hydrogeology of the vicinity mine.A general knowledge of the groundwater had been established from the existence literature,and based on saturated-unsaturated seepage theory the Thesis has an intensive study of the seepage flow field and the change law of the stability safety factor of the slope stability under the condition of fluctuation of water level.A slope subjected to the pumping of water out from the slope body is consider as drawdown in our study,with our only interesting section is the right side of the slope from the excavated area to the vertical drain boundary,the area where we observed the fluctuation of water level,hence the curiosity of enlighten his influence on the excavated slope factor of safety.Drawdown process is considered in numerical simulation to improve the water level fluctuation of the slope stability.GeoStudio software had been used(Seep/w and slope/w)to compute the pore-water pressure by a steady state and a transient analysis,and the result of the transient analysis were used to compute the factor of safety of the slope.The drawdown transient analysis were separated into to two procedure which are the rapid drawdown and the slow drawdown.In this paper a homogeneous and heterogeneous earth slope case had been used as a sample to enlighten behave of the stability of their slope body thought a drawdown process(groundwater level fluctuation).The slope stability analysis in this work used the limitequilibrium method with Mohr coulomb criterion.A sensitive analysis was done varying the slope angle with the intention of performing an optimization for a better factor of safety of the slope submissive on fluctuation of water level.We present the saturated and unsaturated model review,groundwater fluctuation model analysis of the differences between the two drawdown process and the relationship between the total head and the time on slope stability.It is concluded that the change of slope angle influence on slope stability coefficient is most obvious under fluctuation of groundwater conditions and the change in total head with time also.After all result analysis we preconize for Wulan open-pit mine slope in south,west and north section a slope angle 30 degree maxim to ensure the safety of the flooded mine while draining out the water from the pit in homogeneous or heterogeneous condition of the material of the slope.A rapid drawdown will be better for the drawdown process,by increasing the drain out of the water flow velocity at the fastest speed which can flow the hydraulic conductivity of the material.A permanent monitoring should be done to avoid the water table to reach a total head H=100m i.e.20 m on top from the toe of the excavated slope,to ensure the stability of the slope body and prevent from landslide and failure which can occur in any time when the slope is unstable in surface mining.This study was really benefit to find out a better slope angle to maximize the profit in the exploitation of the coal,and ensure a slope stability of the heterogeneous slope body,a critical height of the water level was determined,consideration an equilibrium condition of the slope i.e.FOS=1,height what the water level should reach in the slope body to avoid landslide,and slope failure.