Research reveals what lies beneath Wellington's reclaimed land

Wellington waterfront damage after the 2016 Kaikōura earthquake. Photo / University of Canterbury

New research following the 2016 Kaikōura earthquake reveals what lies beneath the surface of reclaimed land on Wellington's waterfront.

The Toka Tū Ake EQC funded research has given engineers a better understanding of where liquefaction might be a problem in the future, so they can improve building design accordingly.

University of Canterbury researcher Ribu Dhakal has spent four years on the project.

More than 100 cone penetration tests in a small 0.5 km2 area were carried out at the port, as well as drilling dozens of soil samples for testing.

The research team discovered liquefaction in the southern part of the harbour had been severe, including gravelly soils where experts historically may not have expected it to occur.

Dhakal said some of the land area settled by half a metre.

"All this data has provided us with invaluable information to truly quantify the seismic hazard of different types of reclaimed land.

"Engineers working in this area will now have a much better understanding about where they can expect liquefaction and how much ground movement may occur."

Ground motion from the Kaikōura earthquake was relatively minor in Wellington, compared to what would occur in an earthquake on the Wellington fault, Dhakal said.

"But the damage to the ground and consequent effect on buried structures and building foundations was still quite significant and more severe than we would have historically expected."

Ribu Dhakal working in the geolab at the University of Canterbury. Photo / University of Canterbury

Relatively new buildings like Statistics House partially collapsed on Wellington's waterfront as a result. It was one of several buildings which had to be demolished.

CentrePort was hit particularly hard by the earthquake and was forced to immediately suspend operations while it dealt with damage to its buildings and liquefaction.

Dhakal said the port had a well-documented case history including ground motion recordings for several earthquakes with detailed liquefaction observations.

This made the area a good candidate for an in-depth study of liquefaction problems, he said.

"Our project is unique in that it is possibly one of the most well-documented liquefaction case histories of reclaimed soils anywhere in the world."