Stability Analysis On Open-pit Slope For Transition From Open-pit To Underground Mining At Lala Copper Mine

When the open pit mine is about to reach the design boundary,if there are resources in the deep,it needs to be transferred to underground mining,which can effectively solve the problem of sustainable development of the mine.During the open-pit mining process,the stability of the open-pit mine slope is directly related to the safe production and economic benefits of the mine.Some open pit mines have caused some disasters due to slope instability.In this paper,the stability of the slope is systematically studied during the open-pit mining of Lala Copper Mine.The main research contents and achievements are as follows:(1)On the basis of analyzing the existing geological exploration data of the mine,through the on-site geological survey,it is determined that the final slope formed by the open-pit stop of Lala Copper Mine is a typical high rock slope.The slope rock mass belongs to the micro-weathering state,the joint fissure is relatively developed,but the slope rock mass is high.Based on the SURPAC software,the mining area topographic map,geological drilling data and mine design data are used to establish the three-dimensional mining model of the mining area,and the copper is delineated.32 ore bodies with a total volume of 15724657m~3.(2)According to the national test standard,the uniaxial compressive strength of the most representative schist rock in the mining area is 150.75MPa,the elastic modulus is29.50GPa,and the Poisson’s ratio is 0.185.The point load test is used to obtain the uniaxial compression test.The point load strength of the schist irregular test piece is5.0268MPa,and the conversion coefficient of rock saturated uniaxial compressive strength and point load strength is obtained K=30.(3)Three engineering rock mass quality evaluation methods were selected to evaluate the quality of the rock mass in the mining area,and the grade of the rock mass was obtained.The RMR classification method was combined with the Hoek-Brown empirical formula to estimate the mechanical parameters of the rock mass in the mining area.Values provide basic data for quantitative analysis of slope stability.(4)The blasting vibration test was carried out at the site of the mining area.The results show that the vibration generated by the open-pit mining operation has little effect on the slope stability;the peak velocity of the rock mass vibration decreases with the distance from the explosion source;The main vibration frequency is greater than the natural frequency of the slope,and the blasting vibration does not cause resonance of the slope rock mass.From the blasting vibration attenuation function equation obtained from the regression analysis,it can be seen that the characteristics of the rock mass in each area and the geological conditions are different.(5)Using the limit equilibrium method,the minimum safety factors of the four representative slope sections at the end of the open pit are 1.193,1.105,1.684 and 1.755,respectively,through the Geo-studio software.The results show that the eastern slope does not meet the requirements of the specification and needs to be reinforced.The slope stability of the other three regions is good.(6)The FLAC3D finite difference software was used to simulate the open-pit mining process in the mining area.The results show that the underground mining has little effect on the stability of the slope rock mass.The underground mining method uses the filling mining method to the slope and the mining yard.The stability of the rock is very favorable.