A Study On Stability Of Potential Unstable Rock Mass In High Slope Based On FLAC3D

Potential unstable rock mass is generally in the unsteady or limit equilibrium state. When the predisposing factors accumulated to a certain amount, the collapse will happen. High slope is generally on high altitude mountain area for the representative location, especially in southwest of China. Potential unstable rock mass in high slope is the main object of engineering geological and source of geological hazard in mountain area.This paper based on the project of geological hazard prevention in Puer, Yanjin, Yunnan. Through the extensive field research, this paper tried to describe the engineering geological characteristics, analyze the formation mechanism and do a numerical simulation by FLAC3D. Main conclusions are follows:(1) Most of structural planes of potential unstable rock mass are northwestward. These structural planes are the main controlling factor of formation of potential unstable rock mass. As time goes by, potential unstable rock mass will be separated from parent rock by the unloading crack and the rock fall will certainly happen. Therefore, the treatment of potential unstable rock mass is very important.(2) The main stratum of study area is sand and mud interstratifications. From the evolution mechanism of sand and mud, the sandstone has a low weathering level and the mudstone has a high weathering level. Also, the mudstone is sensitive to surface environment and has a high weathering-cracking level.(3) Relative to the fragmental sandstone in main slope, the sandstone which formed to the cliff has a huge thickness and low fragmentation degree. These are the factor of instability and rock fall.(4) From the Flac3D model, we find the stress concentration is obviously. Unstable failure may be happened in the stress concentration area, especially in the contact parts of cliff and main slope. The pulling stress located at the top of cliff may induce the large rock fall. Therefore, the cliff is the most dangerous area for stability.(5) The principal stress of sandstone area has a trend to moving into slope compared with mudstone in same depth. The value of stress is decreased on the surface of main slope. For this counter-dip slope, the tendency of strata has greatly decreased the value of displacement along the slope aspect. This is beneficent to slope stability.(6) There is no unstable damaging area in the non-cavity model, but it still has potential unstable sliding zone. For the cavity model, it was already damaged in the rock which lay upon the suspension area. Though there is nothing damage in the non-cavity model, we should also pay attention to the stability problem.(7) The stress concentration has a great effect to potential unstable rock mass stability in the cavity area. Being to the cavity, stress state has been changed. The cliff is prone to toppling failure along slope aspect. There is a high three-directional pressure in cavity boundary and the mudstone exposure to air. This will aggravate fragmentation of mudstone and expand the cavity area. At last, rock fall will happen.