Assessment of structurally-controlled slope failure mechanisms and remedial design considerations at a feldspar open pit mine, Western Turkey

A variety of structural discontinuities crossing the slopes of Alipasa feldspar open pit mine, in western Turkey, caused different types of slope failures which led to interruptions in ore production. Thereupon, extensive geotechnical investigations, including geological characterization, in-situ and laboratory geotechnical testing, long-term movement monitoring, back-analyses and possible remedial measures, were conducted. Field observations and subsequent analyses suggested that the failures were limited to benches and the movement developed down-slope along discontinuities due to the following reasons: (i) unfavorable orientations of the foliation planes and joints, (ii) low shear strength along discontinuities and (iii) exceptionally heavy rains filling the tension cracks prior to failure. Comparisons between movement vectors and orientation of discontinuities showed a good agreement that indicates two types of instability, namely, planar and wedge failures. A back analysis procedure for the assessment of failures along the rough discontinuities, with non-linear failure envelopes, was successfully applied to the unstable slopes in the pit. The results of the 2-D limit equilibrium back-analyses and movement monitoring data suggested that the wedges and/or planar blocks formed at the uppermost benches tended to move down to fill the gap which resulted from the previous movement of the blocks in the benches. Remedial measures such as dewatering and reduction of height of the benches were suggested. Results of stability analyses conducted for possible remedial measures were presented and discussed.