San Martín, JF, Castro, R, Arancibia, L, Endara, D & Vásquez, P 2022, 'Back-analysis of gravitational flow MB N01-S01 at Chuquicamata underground mine', in Y Potvin (ed.), Caving 2022: Proceedings of the Fifth International  Conference on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 1061-1070, https://doi.org/10.36487/ACG_repo/2205_73
(https://papers.acg.uwa.edu.au/p/2205_73_Castro/)
Abstract: Chuquicamata underground mine (MCHS) is currently extracting ore from the first level through macroblocks arranged from North to South. This work analyses the efficiency of the design of drawpoint spacing in terms of gravity flow for macroblocks (MB)N01-S01, with a drawpoint spacing of 16 × 16 m2. The characterisation of gravity flow, in terms of reserve recovery, remaining ore, height of the interaction zone (HIZ) and quantification of fines extracted was performed using numerical simulations in FlowSim BC v6.1 based on the grade of copper extracted and the movement of cave trackers at MB N01-S01 from May 2019 to February 2021.
Isolated and interactive draw flow were compared in FlowSim BC v6.1. Isolated draw considers that the maximum diameter of an isolated ellipsoid is 12 m, which causes isolated flow given the spacing between drawpoints. Interactive draw considers that the diameters of ellipsoids are greater for coarse fragmentation. In the case of the macroblocks N01-S01, extraction ellipsoids diameter were obtained that evolve up to 34 m at 150,000 tons extracted per drawpoint.
Results showed that when isolated draw was used an error of 9.7% was obtained in the copper grade compared with the measured grade, while with interactive draw a 1.3% error was obtained. Both flow models were compared in terms of the movement of markers using 159 cave trackers installed in the western sector of the MB N01-S01. Horizontal movement during flow with interactive draw was found to be more representative of the actual displacement with an error of 2.6% in terms of the horizontal average. In contrast, the displacement obtained by isolated draw showed an error of 66% with respect to the actual records.
In addition, an analysis of the expected loads induced on the apex pillar at the production level was carried out under three extraction conditions: 5 kton, 10 kton and 40 kton extracted. In the first condition, no flow interaction was observed on the main pillar and therefore all the material exerted load with an induced stress of 1.15 MPa. In the 10 kton condition, interaction was observed, and the estimated induced stress was 1.23 MPa. Finally, at the 40 kton level of extraction, a larger broken column on the pillar was noted with the induced stress estimated at 3.92 MPa.
From the flow analysis of MB N01-S01, it is concluded that: