Proceedings, Slope Stability 2011: International Symposium on Rock Slope Stability in Open Pit Mining and Civil Engineering, Vancouver, Canada (September 18-21, 2011) Integrated Numerical Modelling and Insar Monitoring of a Slow Moving Slope Instability at Bingham Canyon Mine T.D. Styles AMC Consultants (UK) Ltd., Maidenhead, Berkshire, UK D. Stead Resource Geotechnics, Simon Fraser University, Burnaby, Canada E. Eberhardt Geological Engineering, University of British Columbia, Vancouver, Canada B. Rabus MDA Systems Ltd., Richmond, BC, Canada M. Gaida Bingham Canyon Mine, Rio Tinto, Salt Lake City, UT, USA J. Bloom Bingham Canyon Mine, Rio Tinto, Salt Lake City, UT, USA Abstract Remote sensing using satellite-based Interferometric Synthetic Aperture Radar (InSAR) provides a unique opportunity for monitoring slope deformation during the assessment of large open pit slope kinematics. This case study presents the results of an integrated numerical modelling - monitoring investigation of a large open pit slope at Bingham Canyon Mine, Utah, USA. Development of the pit slope geomechanical model involved the use of a two-dimensional finite-discrete element code incorporating a discrete fracture network. The analysis of mapping data from mine reports provided a solid foundation to understand the joint fabric and develop a discrete fracture network, which was imported into the numerical model and explicitly simulated. This approach proved successful in analysing slope deformation through combined brittle fracture and sliding along non- daylighting shear zones, previously identified through subsurface monitoring. Development of kinematic release along the shear zones was simulated by a combination of internal deformation, intact rock bridge fracture and shearing within the assumed joint network. To simulate on-going slope deformation, the key driving factors had to be considered with several simulations incorporating the potential seasonal effect of a perched aquifer. A major outcome from the study was the development of techniques to interpret InSAR data and comparison of the results with mine-based geodetic monitoring. This provides a valuable future constraint for geomechanical modelling of large pit slopes directly incorporating the key aspects of the slope deformation mechanisms. 1 Introduction Current practices in the mining of large open pits often involve push backs to increase achievable depths whilst minimising the footprint. Slope behaviour within large open pits can be complex, with deformation mechanisms involving a combination of both material (rock mass) and discontinuity control, with subsequent time dependent motion as damage and creep processes occur within the slope. Advanced numerical codes can be used to simulate slope instabilities, increasing our understanding of both rock mass strength and potential slope deformation mechanisms. Such methods require integration with monitoring methods to correctly calibrate models and provide an appropriate representation. Targeted monitoring and improvement of in-ground techniques were important discussion points during the slope monitoring forum the 2007 Slope Stability Conference held in Perth (Slope Monitoring Forum, 2007). Targeted monitoring using conventional prism-based techniques is difficult in early stages of slope deformation when the extent and the time dependent nature are undefined. Interferometric synthetic aperture radar (InSAR) is a relatively new tool within the mining industry that is suitable for large-scale reconnaissance as well as detailed monitoring; examples can be taken from the few industrial case studies where InSAR has been used for mine slopes (Rabus et al., 2010; Herrera et al., 2010; Akcin et al., 2010), and the numerous applications to the monitoring of landslides, subsidence due to coal mining, and subsidence resulting from aquifer abstraction