The NZGS guidelines on ground improvement are the starting point for any vibrocompaction design on the North Island’s east coast, and Napier’s gravelly alluvium demands a precise analytical approach. Much of the city rests on fluvial deposits from the Tutaekuri River, where loose sands and silty gravels extend to depths exceeding 12 metres. The 1931 earthquake raised sections of the seabed by nearly two metres, creating the coastal plain now occupied by Ahuriri and Pandora — ground that was never naturally consolidated under its current overburden. A vibrocompaction scheme here must reconcile the seismic demands of NZS 1170.5 with the variable grain-size distribution encountered across the Heretaunga Plains. Rather than applying generic spacing grids, our design process models the required relative density target against the site-specific fines content, because even a small increase in silt fraction can shift the compaction mechanism from liquefaction-based densification to displacement-dominated behaviour.
Vibrocompaction in Napier is not a standard grid exercise — it is a depth-specific response to post-1931 fluvial deposits where relative density governs seismic performance.
