Case study: rockfall assessment and mitigation at the Newmont Boddington Gold mine

Abstract

The risk of rockfall due to previously mined deteriorating pit wall conditions above operational areas of open pit mines is ever present. This paper presents a case study documenting rockfall assessment and subsequent mitigation measures after a rockfall event onto an operational ramp at the Newmont Boddington Gold (NBG) open pit mine. NBG is located two hours south of Perth, in Western Australia, and extracts over 90 Mt per year from operational pits. The South Pit has a current planned depth of over 650 m with a 36 m high and 15.2 m wide batter/berm configuration for an inter-ramp angle of 60.8°. Information collected during unmanned aerial vehicle/rope access inspections and scaling works provided relevant data including block size and size distribution, enabling further assessment. Detailed rockfall assessment is undertaken using the 3D software Trajec3D™ to help gain a better understanding of how in situ pit conditions can influence the trajectory of falling rocks compared to 2D assessments. The work includes an assessment of object shape, assessment based on block size and size distribution, interpretation of rockfall source area, a step by step run through of modelling, and probabilistic interpretation of results including a sensitivity analysis based approach considering different potential particle size distributions. A Coefficient of Restitution is adopted from previous research. The paper also presents data assessment methodology used to interpret various aspects of model output data including gaining knowledge of linear and rotational energy and the interoperability and functionality of the Trajec3D and GEM4D™ software. The information is used to help assess the design criteria of a rock catch fence solution for this area of the pit. Rockfall assessment results are presented for both ‘fence’ and ‘no fence’ scenarios.