With the extension of the Nchwaning Mine shaft complex in the Northern Cape
Province, various geological and geotechnical complications needed to be identified in
order to ensure correct use of tunnelling methods and support techniques. An
understanding of the geological history of the area and the resulting geotechnical nature
was important in defining the rock mass quality ahead of shaft development. A total of
12 geotechnical boreholes were drilled, and an additional 18 old boreholes revisited to
accurately detennine the stratigraphy, geological structure and associated weathering
effects. Various soils and rock testing helped quantify the materials encountered.
Sands of the Gordonia Fonnation form the surface cover of this area, and together with
the weathered calcrete, calc-arenite, conglomerate and clay, they form part of the
Cenozoic Kalahari Group. The 30m thick basal unit of red clay is common throughout
this region. This silty clay material is problematic in that it is expansive and
hygroscopic. The clay unit rests unconformably on folded, faulted and highly weathered
shale of the Proterozoic Lucknow and Mapedi Formations of the Olifantshoek
Supergroup. Unconformably below this sequence lies the manganiferous ore deposits of
the Hotazel Member, which is contained within the Voelwater Formation of the
Griqualand West Supergroup.
For the development of the decline shaft through the Gordonia Formation a box cut was
excavated to a depth of 25m. The anticipated poor geotechnical conditions for a further
125m below the Gordonia sands called for high quality permanent tunnel support in the
upper weathered horizons. Barton's Q-analysis was adopted as a recognized tunnelling
quality index to predict and quantify the rock mass characteristics ahead of the shaft.
The highly variable and generally low Q-values from borehole core analysis indicated
that precast tunnel lining be used for 800m (at 11.5°) through the entire weathered
Cenozoic sequence and into the weathered shales immediately below the Red Clay. / Thesis (M.Sc.)-University of Natal, Durban, 2002.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/4108 |
| Date | January 2002 |
| Creators | Puchner, Richard A. |
| Contributors | Watkeys, Michael K., Jermy, Colin A., Maud, Rodney. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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