Slope Stability Geotechnical Guidance Series, Unit 7B.1 – Auckland provides targeted guidance for geotechnical practitioners addressing slope stability challenges unique to the Auckland region. The document highlights Auckland’s complex geological setting, shaped by volcanic activity, sedimentation, and tectonic processes, resulting in a diverse range of rock and soil types. It outlines the regulatory framework, including the Auckland Unitary Plan and recent Plan Change 120, which set requirements for managing land instability risks in development. The guidance emphasises the importance of understanding local geology, groundwater conditions, and the specific characteristics of geological units such as the Waipapa Group, Northland Allochthon, Waitematā Group, and volcanic fields, each presenting distinct slope failure mechanisms.
The document details common types of slope instability in Auckland—translational and rotational slides, rockfalls, debris flows, and soil creep—and provides recommendations for investigation, analysis, and mitigation. It stresses the need for thorough site-specific investigations using appropriate techniques (e.g., boreholes, test pits, CPT), careful selection of geotechnical parameters, and robust analysis methods, including both qualitative and quantitative approaches. Mitigation strategies range from earthworks and drainage to retaining structures and vegetation, with case studies illustrating practical responses to recent landslide events.
Comments on Unit 7B.1 should be addressed to the NZGS secretary (secretary@nzgs.org) and should be forwarded no later than Friday 23 January 2026. PDF Markups are preferred where this is possible.
Thank you to the authorship team of Heather Lyons, Stephen Parkes and Aaron George!