ASSESSMENT OF THE FAILURE-MECHANISM OF A HIGHWALL SLOPE UNDER SPOIL PILE LOADINGS AT A COAL-MINE

The design of a highwall in coal mining involves the consideration of many factors. The evaluation of a lignite strip coal mine at Yatagan i n Southwest Turkey has provided an opportunity to combine both qualita tive and quantitative factors in highwall design. In this paper an att empt has been made to illustrate an instability problem that occurred in a highwall externally loaded by a spoil pile in the southern part o f the pit. Geotechnical data with slope monitoring information were ev aluated, and shear strength of the highwall material was determined us ing nonlinear failure criterion for jointed rock masses in conjunction with rock mass classification. Using a model for the loaded highwall, these studies were complemented by limit-equilibrium back analysis an d finite element stress analysis incorporating the effect of the spoil pile loadings. The results of the back analysis and numerical modelli ng, which confirmed each other, and detailed examination of geotechnic al data with movement monitoring records indicate that the instability occurred by shallow seated circular failures mainly caused by the str esses exerted by the pile. The progressive failure developed through a combination of sliding along structural discontinuities and failure t hrough the moderate quality, low strength rock mass. In addition, the calculated slip surfaces match the actual slip surfaces, and the non-l inear shear strength failure criterion confirmed that the mobilized sh ear strength appears realistic for design purposes.