Geological report on the Tekapo B stilling basin - S100

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Mansergh, G.D. 1974 Geological report on the Tekapo B stilling basin - S100. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 172 37 p.

Abstract: The Tekapo B Stilling Basin is sited on the contact between the Tekapo Formation and the Mt John Formation. Till, ice contact and fluvioglacial deposits are recognized in the area, but till is the dominant material present. Mapping of the formations, and units within these formations, is based on field observations, the result obtained from six Benoto shafts and eight percussion holes, (logs of which, except for shaft S36 which was not logged by geological survey, are attached to this report,) and open pits and aerial stereo-photo pairs. Map Fig. 1 shows the distribution of these units and Fig. 2 gives three cross-sections through the proposed structure. Further information comes from disturbed samples taken at five foot intervals from all six shafts; the results of soils tests on shafts S36 and S52 only were available to the author at the time of writing. Gradings for each geological formation are presented from these data on Fig. 3. Peremability tests were carried out in six boreholes and one shaft and the results of these are entered on the borelogs. Three plate bearing tests were conducted at the penstock intake site by M.O.W. and have been reported on by D. Langdon (1972). The engineering geological problems are those of leakage and possible instability resulting from saturation of the glacial deposits. (auth)