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Geotechnical Shaft Reconciliation at Oyu Tolgoi, Mongolia


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Author P Voulgaris, M F Lee and A Purvee and L J Mollison


Oyu Tolgoi is a large Cu-Au porphyry deposit in the south Gobi desert,
Mongolia. The first of several deep, large-diameter, concrete-lined shafts,
Shaft 1, is nearing completion. It will have a finished depth of 1380 m at a
diameter of 6.7 m. These shafts will provide access to and hoisting capacity for
block caving of deep underground ore.

Geotechnical site
investigations, and associated predictions of stability and ground support
requirements, are compared against actual construction performance. Routine
mapping is essential, along with checks against predictions and informing the
contractor of ground conditions and variances.
Advance rates are compared
against predicted rock mass quality. A reasonable correlation exists between
Qwall and advance rate. Overbreak and concrete liner thickness is related to the
blockiness quotient, RQD/Jn.
A ‘tool-bag’ of just a few support elements
(chain-link mesh, fibrecrete and 2.4 m long friction anchors and resin grouted
re-bar bolts) was able to cope with the ground conditions encountered. QA/QC
procedures are essential from the factory, through site storage to