Use of the excavation compliance indicator at the Oyu Tolgoi copper–gold mine, Mongolia

Systematic assessment of ‘as-built’ open pit mine slopes is required to verify that slope design criteria are appropriate for the ground conditions and that slope designs are being correctly implemented by mine operations. It is imperative that design bench geometry and inter-ramp slope angles are delivered (in order to meet scheduled production targets), slope design acceptance criteria are achieved, and that geotechnical design risks are appropriately managed, so that the design intent is met. The excavation compliance indicator (ECI) as developed by Seery and Lapwood (2007) and presents a methodology for quantifying compliance to design via measurement of the ‘as-built’ individual geometrical elements that comprise the bench geometry; i.e. bench face angle (BFA), crest position, toe position and catch bench width (CBW). Measurements of these elements are combined and weighted in order to deliver an overall slope design conformance metric (i.e. the ECI score). The technique enables valuable insights into the contributing factors that adversely affect design implementation conformance, thereby enabling operational practices to be modified in order to deliver improved design achievement. This paper outlines how the Oyu Tolgoi (OT) open pit geotechnical team implements ECI and how it is integrated into their design reconciliation workflow. This paper also provides some recommendations for improving the ECI process.