Rock mass characterization and numerical modelling of coastal cliff stability in the Auckland region

Abstract

While numerous publications exist concerning the strength of the Waitemata Group sediments, upon which New Zealand’s largest city (Auckland) is constructed, little emphasis has been placed on the stability analyses of coastal cliffs using numerical modelling techniques. This thesis reviews previously published strength parameters of the Waitemata Group to construct slope stability analysis numerical models, which have been used to investigate the sensitivity of the coastal cliffs around the Auckland region. Knowing the factor of safety for such cliffs is important due to the continued expansion of the city. Photogrammetry was employed for the first time in the Auckland area to further characterize the discontinuities present in the rock mass. It was found that the material properties and strength parameters of the Waitemata Group did not in itself cause the failure of cliffs in the Auckland region but rather that addition of groundwater, and the presence of discontinuities (such as joints, faults and bedding planes) enabled the failure of cliff slopes to occur. Using the information gained from this thesis the distance at which a house or building can be constructed from the cliff edge can be reviewed and altered in areas of high activity, while providing the geology, geotechnical and engineering geology communities with more information regarding the structural behaviour of the Waitemata sediments.