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The Application of Rock Stress Inputs to Stability Assessments at Ok Tedi Mine, Papua New Guinea

I A de Bruyn, N R P Baczynski, M F Lee, K W Mills, J Mylvaganam and D A Prado
Wednesday, July 16, 2014
First presented: 
Proceedings, AusRock 2014: Third Australasian Ground Control in Mining Conference, (The AusIMM: Melbourne), pp. 43-54
Published paper
Rock Mechanics

This paper presents the second part of a study of the assessment of rock stress inputs on the performance of various new mining designs at the Ok Tedi large open pit mine in Papua New Guinea. Over the years, four programs of rock stress measurement have been completed at the Ok Tedi, each providing different interpretation of the in situ field stresses. Details of three of these programs and interpretations are provided in the precursor to this paper, entitled ‘Rock stre sses at Ok Tedi, Papua New Guinea’ (Lee et al, 2014).

This paper explains how the various stress interpretations were utilised in the modelling of the proposed new open pit and underground mining excavations, comparing where possible their expected effects on stability. The modelled performance of three specific mine components have been discussed here as case studies, including:

1. the below-pit drainage tunnel, as the floor of the open pit workings is mined down from 350 m above, to within just 75 m above the crown of the tunnel

2. the stability of the 1000 m high slo pe of the proposed West Wall cutback

3. the proposed sublevel open stopi ng extraction sequence in the Gold Coast orebody beneath the East Wall, for which only the likely ‘worst-case’ stress regime was used to asse ss sequencing and stability issues.

The benefits of scheduling the collection of detailed rock stress measurements and other input data from a range of different sources at various stages of the projects are discussed.

Alternative in situ stress models have less stability impact on open pit slopes than on underground mine excavations.

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