Study On Influence Of Underground Mining Disturance On Open Pit Slope Stability

In the process of surface coal mining, large amounts of coal resources are pressed beneath the high slope caused by open pit mining. Many mine enterprises recover coal resources using underground mining method in order to improve the coal recovery and mine’s economic benefits. However, underground mining beneath the slope has great influence on slope stability and it has complicated mechanism which is different from normal slope sliding and surface subsidence caused by single underground mining. Research on slope stability under underground mining should consider influence of many factors, such as slope sliding, slope rock movement and surface subsidence. Therefore, this paper analyze the slope rock movement mechanism combined slope engineering with mining subsidence. Meanwhile, the northwest slope of Jingdong industrial square is chosen as project examples, slope stability conditions before and after underground mining are analyzed, and the law of slope unstable failure is generalized.[1] Take the northwest slope of Jingdong industrial square as research object, the landslide situation of slope engineering is analyzed considering slope’s geological data and engineering background. Effect of different factors on the open pit slope stability are analyzed from three aspects, including slope factors, natural factors and human factor, in which natural factors and human factor are external cause and slope factor is internal cause. At the same time, internal and external factors play roles not alone but combined.[2] Influencing mechanism of slope stability under underground mining conditions is studied combining slope engineering with mining subsidence. The mechanism is as follows: the effect of underground mining on slope stability manifest as the influence of goaf and blasting vibration on slope stability. The function of blasting vibration is expressed that it contribute to the develop of fracture and make fracture more wide and fissure, and it acts all over the underground mining process. Stress of overlying rock releases and rock stress redistributes, which make overlying rock cave and rock mass deform and move. With underground mining advancing, goaf becomes bigger and the influencing range of underground mining becomes bigger, also. It manifest as surface subsidence when acting on ground surface, and manifest as the movement towards goaf and free face when acting on slope surface. In addition, deformation and failure of slope rock layer induces cracks inside the slope, which make rock mass strength reduced. It induces slope sliding under the function of external factors, such as rainfall and earthquake.[3] With the help of the finite element software ABAQUS which is powerful and easy to operate, slope stability before and after underground mining is studied. After comparing some different classical constitutive model, mohr-coulomb constitutive model is chosen considering complicated stress-strain relationship of rock mass. Meanwhile, the principle of strength reduction is elaborated in detail, and three kinds of criterion are analyzed. They have their own adaptability, choosing the entirely run-through of plastic zone as characteristics and the displacement of characteristic points as criterion after taking slope’s actual situation into account.[4] The physical and mechanical parameters of rock and soil mass are determined using site sampling and laboratory testing. And then, slope stability before underground mining is studied using numerical simulation method, and the safety factor is 2.71, which indicate that the slope is safe. Then, slope stability after underground mining is studied, and slope mass’ s deformation and stress field is gotten, and the reason of the change is explained using the mechanism of influence of underground mining to slope stability. The safety factor becomes small after underground mining.[5] Influence of goaf in different place on slope stability is studied using software ABAQUS, through comparison between different conditions, conclusions are as follows: firstly,the relative position of slope surface and goaf has great influence on slope stability. Secondly,there are shear stress concentration areas nearby the ends of goaf inside the slope and there are movement towards goaf and slope free face, when the goaf is close to slope surface. The influence of goaf on slope surface reduces and slope’s vertical displacement is subsidence towards goaf mainly. Lastly,more close the goaf to slope surface, the safety factor is smaller.