Geomechanical characterisation of greywacke rock masses for dynamic slope-stability analysis, Wellington New Zealand.

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Geomechanical characterisation of greywacke rock masses for dynamic slope-stability analysis, Wellington New Zealand.

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Presented by Chris Massey, GNS Science, Wellington

Torlesse greywacke comprises about 19% of New Zealand’s rock mass at/near the surface. Wellington is New Zealand’s capital city and is underlain predominantly by closely jointed greywacke. The region is also seismically active, and the central city is dissected by the Wellington Fault, which could generate a magnitude M7+ earthquake, with an estimated return period of about 800 years. This research has been carried out as part of the multiyear, multidisciplinary Stability of Land In Dynamic Environments (SLIDE) research project, whose goal is to improve the resilience of New Zealand’s buildings and infrastructure through better knowledge of the behaviour of slopes and develop strategies for more robust remediation approaches. To investigate the seismic response of the greywacke slopes we drilled eight boreholes and used full waveform sonic, and optical and acoustic televiewer downhole survey tools to characterise the insitu rock masses. These results – coupled with field mapping and laboratory unconfined and tensile strength testing of cores containing small-scale, short persistence and closely spaced discontinuities – have been used to derive rock-mass strength properties for dynamic slope stability analyses. This paper will discuss the relationships, or not, between the different scales of observation and measurement and their impact on deriving rock mass geomechanical properties at the slope scale.

This is an updated version of Chris’ presentation at the 2021 NZGS Symposium in Dunedin.

Chris Massey is an engineering geologist with more than 23 years of consultancy and research experience in the investigation and analysis of complex geological and geotechnical data for landslide and slope stability including landslide monitoring, foundation design, underground/surface rock support and groundwater problems. He has applied these skills to geohazard and risk assessments, oil and gas pipelines, highway, railway, mining engineering and town planning projects in Africa, the Himalayas, Europe, South East and Central Asia and Australasia. Chris has a degree in geology from Leeds University, UK; a masters in Engineering Geology from Imperial College, London, UK; and a PhD in engineering geology from the University of Durham, UK. Dr Massey has published many peer-reviewed journal papers and has given lectures and workshops around the world.

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