Experience using terrestrial remote sensing techniques for rock slope performance assessment

Abstract

This paper reports on projects, which integrate the advantages of terrestrial remote sensing techniques to analyse the performance of rock slopes. The first project is concerned with a bench performance assessment of an inactive open pit mine in British Columbia, Canada; this assessment is part of the design work for the proposed pit expansion. The second project involves characterisation of the rock abutments of an operational concrete hydroelectric dam, in the Washington State, USA. The bench scale stability of mine slopes in blocky to moderately fractured rock mass is primarily determined by structurally-controlled failure mechanisms such as planar, wedge and toppling failure. Conventional design involves the analysis of adversely-oriented discontinuities, which have the potential to generate unstable blocks. These kinematic analyses are used to develop design parameters, including bench face angle, bench width and inter-ramp angle. Bench performance assessment aids in both bench and inter-ramp design, based on detailed quantification of the previously achieved bench geometry. The first case study is from geotechnical investigation work at Bell Pit, near Granisle, BC. The bench performance assessment in this case utilises terrestrial digital photogrammetry to quantify the achieved bench geometry of the pit walls. The advantages of using remote sensing data as opposed to measurements made at the outcrop include: a more detailed and arguably more accurate dataset, reduction of issues related to access, and reduction of safety concerns due to rock falls. Similar advantages are advertised in the literature concerning remote sensing-based discontinuity characterisation, which is now commonly used in the industry. In this case study, a geometric correction is applied to the measured back-break and effective bench face angle in order to enhance measurement accuracy. A discussion concerning the validity of the assessment is provided. The second case study involves discontinuity characterisation of the natural rock slope abutments of the Boundary Dam, a concrete hydro-electric dam located along the Pend Oreille River. These abutments show evidence of past rock block failures where blocks failed along discontinuities. Structural mapping using terrestrial remote sensing techniques allows both the characterisation of these discontinuities and the description of past failure mechanisms, which may highlight potential future failure modes. The procedure is carried out along the Pend Oreille River canyon using a combination of terrestrial and vessel-mounted LiDAR (Light Detection and Ranging) point clouds.