Whitehall quarry, Northern Wedge failure: 22 years of investigation
Published:January 01, 2016
D. R. Strang, 2016. "Whitehall quarry, Northern Wedge failure: 22 years of investigation", Developments in Engineering Geology, M. J. Eggers, J. S. Griffiths, S. Parry, M. G. Culshaw
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The Northern Wedge Failure (NWF) is a complex failure mass within Whitehall Quarry, Cambridge, New Zealand. Initiation of failure of the c. 500 000 m3 mass occurred during spring of 1988. Complete failure was expected following displacement recordings of 2.3–5.6 m a−1; however, this did not eventuate. By the mid 1990s, the failure mass was deemed stable. In 2010, an engineering geological investigation was conducted to assess the stability of the NWF at that time. The rock mass that failed comprises moderately dipping interbedded feldspathic sandstone and argillaceous mudstone below a thin alluvial cover. It is bound by two fault planes, both exhibiting up to 100 mm of gravelly clay fault gouge. X-ray diffraction analysis of the gouge indicated the presence of kaolinite and montmorillonite, and Atterberg Limit tests showed the plastic and liquid limits to be 31% and 51%, respectively. Electronic distance monitoring (EDM) was carried out over 12 months. Recorded velocities increased by 17% above the 21 mm/month baseline over the wetter months. Limit equilibrium analysis carried out using historic and recent field and laboratory observations input to the computer software SWedge estimated a Factor of Safety (FOS) of 0.97. Complete failure of the NWF could be initiated at any time by an extended period of heavy rainfall and/or unloading of the toe or the stripping of overburden.
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Developments in Engineering Geology is a showcase of the diversity in the science and practice of engineering geology. All branches of geology are applicable to solving engineering problems and this presents a wide frontier of scientific opportunity to engineering geology. In practice, diversity represents a different set of challenges with the distinctive character of the profession derived from the crossover between the disciplines of geology and engineering. This book emphasizes the importance of understanding the geological science behind the engineering behaviour of a soil or rock. It also highlights a continuing expansion in the practice areas of engineering geology and illustrates how this is opening new frontiers to the profession thereby introducing new knowledge and technology across a range of applications. This is initiating an evolution in the way geology is modelled in engineering, geohazard and environmental studies in modern and traditional areas of engineering geology.