Abstract:
A field, laboratory and numerical modelling methodology was developed to investigate the main mechanism controlling the development of deep-seated gravitational slope deformation (DSGSD) in the Tararua Range, New Zealand. The key components of the methodology included: building an inventory of DSGSD features within the Tararua Range and selecting field sites, systematic description and characterisation of the rock mass and observed geomorphology, along with kinematic analyses and numerical modelling (limit equilibrium and finite element) to assess the stability and deformability of slopes within the study area. It was found that a number of factors control the formation of well expressed DSGSD in the Tararua Range, including high local relief along with favourable rock mass strength and discontinuity orientations. Slope stability analyses showed that the modelled slopes appear stable – even when using lower rock mass strength values, suggesting that catastrophic failure is unlikely without external triggering forces. The effects of elevated pore water pressure and coseismic ground acceleration on slope stability and deformability were considered, and results suggest that regional earthquakes may control the timing of episodic deformation in the study area. This research is the first study of its kind to be carried out in New Zealand and sets out a working methodology for identifying, characterising and modelling the stability of DSGSD features. In addition, many avenues for further research have been presented to build on our knowledge of the behaviour and long term development of DSGSD locally and globally.