Raisebore stability and support at deep depth and highly defected rock mass condition: Oyu Tolgoi case study

Authors: Ooi, J; Watt, G; Grobler, H Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2205_61

Cite As:
Ooi, J, Watt, G & Grobler, H 2022, 'Raisebore stability and support at deep depth and highly defected rock mass condition: Oyu Tolgoi case study', in Y Potvin (ed.), Caving 2022: Proceedings of the Fifth International Conference on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 891-906, https://doi.org/10.36487/ACG_repo/2205_61



Abstract:
Oyu Tolgoi (OT) has over 50 raises bored to support the ventilation and material handling for the block cave. Mining of the raisebores occurred at depths of 1,200 m to 1,400 m below the surface, in varied rock mass conditions, on the outer limit of the empirical database updated in 2018 by Penney et al. The stability performance of the raises was considered against the empirical predictions for stability during the early design stage, but site performance was used to improve the design process. Due to faults and defects in the rock mass, the related compressive strength of the rock mass is low relative to the local in situ state of stress and many raise excavations were predicted to be unstable and artificial support was designed. Different pre-support methods were implemented, including spiling using diamond drill steel tubes and resin pressure injection, as well as surface support after excavation, including remote shotcrete and installation of steel cans as lining. Learnings from the support installed were captured to optimise supporting future raises and further enhance knowledge of the response from the different lithologies. An updated design and planning workflow was implemented to assist in the planning and design of support to assist the stability of bored raises. Geotechnical investigation holes are important to ensure the raise stability is properly assessed and mitigation measures are executed. Good collaboration between different teams is imperative to ensure the design and planning objectives are understood and incorporated as design and planning basis, which then reduces the risk of schedule and cost overrun.

Keywords: raise boring, raise support, deep raisebore, high stress, rock defects