Graaf, JH & Parrott, T 2013, 'Guidelines for the design and construction of underground portals in open pits – a case study of the Gateway Mine', in Y Potvin & B Brady (eds), Proceedings of the Seventh International Symposium on Ground Support in Mining and Underground Construction
, Australian Centre for Geomechanics, Perth, pp. 421-436.
Numerous papers have been written on empirical and deterministic methods of ground support design, yet there is limited published information detailing the application of these methods for underground portals. Newmont Jundee Operation recently started a new underground development called Gateway in the base of an existing pit last mined in the 1990s. Due to the requirements of ventilation and a secondary means of egress, the mine design comprised twin declines from within the existing open pit. To maintain adequate separation between the two portals to avoid ventilation recirculation, the underground design required that one portal be cut in rock of ‘good’ rock mass quality and the second was to be developed through weak, highly weathered materials.
This paper describes the process for determining a suitable portal location in an old open pit with the use of mapping, modelling and diamond drilling. In addition to the data collection process, the ground support design, ground support installation and portal excavation methodology for two different types of ground conditions are discussed.
In addition to the design process, the lessons learnt from the ground support installation and initial excavation processes are documented so that others planning a new mine can utilise these learnings associated with portal design and construction. It is intended that this paper provides a guideline for engineers for ground support design and selection requirements for a portal. Consideration is also given to the installation process and the practical execution of these requirements.
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