Throwing rocks at research

In a small, unassuming container on  Ilam
campus, rocks are being fired at building materials to
simulate a volcanic eruption. Associate Professors Ben Kennedy and Thomas Wilson and PhD student Mr George Williams are putting exterior building claddings to the test with the help of a full-scale ballistics cannon.

The cannon can accurately fire rocks at the same velocity as
they would be flung from a volcano – about 160 kilometres per hour.

(Below: PhD student Mr George Williams and Associate Professor Thomas Wilson.)

Chronicle George Williams Thomas Wilson

“It can fire rocks at the actual speed they come out of a volcano, andin turn we can work out the exact velocity and masses required to puncture holes in roofs, and also work out what the danger might be to people beneath those roofs,” says Associate Professor Kennedy.

The team has tested a number of building materials, including roofing iron, timber weatherboards and concrete slabs, with
quite destructive results. However, as George points out, that doesn’t necessarily mean rocks will breach buildings during a
volcanic eruption.

“I was testing just a single layer of sheet metal, for instance, and if you lower the speed just a little bit that drastically reduces its energy and its potential to keep carrying on through the house,” he says.

The programme of study, which has been building over the last five to eight years, is collecting empirical data in a controlled environment. Its focus is on three specific elements:

  • the hazard (rocks falling out of the sky)
  • what assets are exposed
  • what relates the first two elements, the vulnerability of built infrastructure and how much it can sustain.“Generally the New Zealand components performed better and were stronger than more fragile overseas infrastructure, which is probably due to our building systems to meet earthquake standards,” says Associate Professor Wilson.

    “Although volcanic eruptions rarely occur in a built environment the value of the research is immeasurable, particularly for advice if people are trapped in buildings, where is the safest place to take cover?

    “It will help us better design for disasters.Fundamentally it should help us save lives.”