Abstract:
The objective of this research is to investigate slope instability along the Awakino Gorge road corridor,
North Island, New Zealand, in order to gain an understanding of slope failure mechanisms and the
potential hazards towards motorists. The research focuses on six slope failure sites within the Murihiku
Terrane greywacke of the Awakino Gorge. The six slopes consist of three slightly weathered greywacke
slopes and three highly weathered to residual soil greywacke slopes, which aid in developing an
understanding of the full range of slope failure mechanisms in the Awakino Gorge. In addition, this
research aims to classify the Murihiku Terrane greywacke in order to compare with other key greywacke
terranes of New Zealand, in particular the Torlesse and Waipapa Terrane greywacke.
The research uses a range of methods to develop an understanding of slope instability in the Awakino
Gorge. These methods included (1) fieldwork, (2) laboratory analysis, (3) unmanned aerial vehicle (UAV)
photogrammetry, and (4) slope stability analysis. The fieldwork and laboratory analysis components of
this research provide a detailed classification of the Murihiku Terrane greywacke. A UAV was utilised to
collect high-resolution imagery which was processed using structure-from-motion (SfM) software. This
produced a three-dimensional densified point cloud output that was then used for slope stability analysis.
CloudCompare software was used to extract geologic planes from the three-dimensional densified point
clouds, which were in turn utilised with Rocscience Dips software to undertake a kinematic analysis of
the slopes.
The research undertaken throughout the Awakino Gorge indicates that the predominant failure
mechanism of rock slopes is wedge sliding failure, while in soil slopes planar failure along the soil-rock
interface dominates. It appears that high rainfall in the Awakino Gorge area acts as the primary triggering
mechanism for slope failures by increasing pore water pressure in residual soil slopes and aiding in the
release of fragmented greywacke rock. The comparison of New Zealand greywacke terranes provided
found a dearth of research on mudstone-dominated greywacke facies in the Torlesse and Waipapa
Terranes, making comparisons with the Murihiku Terrane greywacke difficult.