A review of the performance of slopes in historical earthquakes, a review of relevant literature describing recent research, consideration of New Zealand’s distinctive topography and seismicity, and limited numerical analyses have been carried out. Steep slopes have failed in past earthquakes, with the initiation of failures in the upper part of slopes indicating the contribution of topographical amplification of earthquake motions. Landslides have been concentrated in hanging wall areas relative to fault rupture, particularly in thrust fault rupture earthquakes.
Past research and numerical analyses show that topographical amplification at the crest of a ridge and terrace slopes is likely, with the magnitude of the amplification being dependent on the frequency of the earthquake motions relative to the shape of the topography. The presence of weathered rock (or soil) overlying unweathered rock was shown to rise to larger amplifications of ground shaking. Amplification was also found to be likely at the top of cut slopes, even when the cut slopes do not extend to the ridge/terrace crest.
Guidelines have been developed for the seismic design of high cut slopes along transportation routes. A resilience-based design approach is proposed, to achieve an economical design, consistent with the resilience expectations for the transportation route.
Keywords: cuttings, design, earthquake, guidelines, landslides, seismic, slopes, topographic amplification