Back-analysis of PC1 cave propagation and subsidence behaviour at the Cadia East mine

Bre-Anne Sainsbury, David Sainsbury, Diana Carroll
2018 Proceedings of the Fourth International Symposium on Block and Sublevel Caving   unpublished
Based on the successful initiation and breakthrough to surface of the PC1 cave at Cadia East, a back-analysis of the performance was conducted to confirm design parameters to optimise the future draw strategy. A mine-scale numerical model was developed to calibrate the existing caving and subsidence behaviour associated with the initiation of PC1 and development of the crater. The successful calibration of historical conditions has provided significant confidence in the caving and subsidence
more » ... dictions associated with future draw strategies. It has also validated a methodology to simulate the effects of preconditioning in large-scale models. 1 Background Cadia Valley Operations (CVO) is one of Australia's largest gold mining operations and is 100% owned by Newcrest. It is located approximately 25 km from the city of Orange in central west New South Wales and is 250 km west of Sydney. Cadia Valley Operations comprises three mines -the Ridgeway sublevel cave and Ridgeway Deeps (currently on care and maintenance), the Cadia Hill open pit (currently on care and maintenance) and the Cadia East panel cave. Cadia East commenced commercial production on 1 January 2013 from Panel Cave 1 (PC1). Based on the successful initiation of the PC1 cave and its breakthrough to surface, a back-analysis of the propagation performance has been conducted to confirm geomechanical design parameters for the optimisation of the future draw strategy and understanding the impact that preconditioning had on the rock mass strength and subsequent propagation behaviour. Based on observations made during cave propagation, a total of five significant events were established for PC1. The historical conditions were established based on monitoring data that included open holes, visual observations and seismic data. They are summarised below. A hydraulic fracturing program was conducted immediately above the PC1 footprint (4,670 m RL) up to 5,050 m RL. Cave initiation occurred with an initial propagation rate of 3-4.5m/day. This propagation rate continued up to the 5,050 m RL Level (260 m cave height) and continued up to the 5,250 m RL Level with few problems. As the cave passed the 5,250 m RL Level, observations showed that the crown of the cave was beginning to narrow (or neck). During early 2014, the cave back (now 750 m in height) reached a strong and competent rock mass (upper capping porphyry) that is located at 5,470 m RL; approximately 450 m below the ground surface. As the cave back reached this unit, caving slowed, and a stable arch was formed. The mobilised zone from PC1 intersected the 5,050 m RL Level prior to the end of Q1 2014. Back-analysis of PC1 cave propagation and subsidence behaviour B Sainsbury et al. at the Cadia East mine 168 Caving 2018, Vancouver, Canada Due to the cave stalling on the capping porphyry, an intensive hydraulic fracturing program was conducted from the surface to 450 m depth. During October 2014, cave propagation commenced again at a rate of 10 m/day (rapid). Surface breakthrough occurred on 22 October 2014. Each geotechnical observation provides a chronology of the cave performance and provides validation points for geomechanical performance modelling.
doi:10.36487/acg_rep/1815_10_sainsbury fatcat:syflrwnjsnaw3anuxnv4t3j5ey