A 610 m (2000 foot) high portion of the South Wall of the Bingham Canyon open pit has experienced slow-moving slope deformations several times during spring melt until the movement was stabilized approximately 7 years ago. To develop and optimize life of mine (LOM) slope designs, an understanding of the mechanism(s) and associated material strength parameters, was required. A back-analysis and calibration of the strength parameters for the salient rock mass and structural features was undertaken. The back-analysis consisted of understanding the conditions and trigger for the slope movement and adjusting strength parameters to match available monitoring data (TDR cables, inclinometers, IBIS radar data, etc.). The trigger for the movement was attributed to the spring high-perched water levels in the upper part of the wall. The back-analyses was consistent with the conceptual model and indicated that the slide was composed of mixed mechanisms, namely, a structurally controlled mechanism for the upper wall and a rock mass controlled mechanism for the lower wall (toe). Today, the O-Slide instability has been fully managed by rigorous monitoring, implementation of a toe buttress, successful dewatering efforts, and unloading of the movement mass as another slice of mining advanced down the South Wall.
Back- analysis of a large-scale pit slope movement (O-Slide movement) at Bingham Canyon Mine was undertaken to confirm the mechanism of movement and calibrate relevant material properties. The back analyses was undertaken in 3D using FLAC3D (Itasca) The O-Slide is an area that experienced multiple periods of accelerated slope movement between 2002 and 2011. Visual observations and monitoring data showed the progression of the movement. The deformation monitoring prisms indicated an increasing trend during the spring of 2003, 2004, and 2006. The extent and pattern of deformation were also well defined by IBIS radar. In the spring and summer of 2011 deformation rates accelerated, reaching up to 3.6 m (12 ft.) of deformation.
This paper presents a summary of the construction of the South Wall 3D numerical model, back-analysis of the 2011 O-Slide period, the monitoring data utilized for comparison against the back-analysis model predictions, and the learnings from this back-analysis to be applied in future modeling efforts for the mine.