Council invests in Omokoroa landslide research

9 November 2017

Doctoral students at the University of Waikato think they might have found a way to stabilise Omokoroa’s sensitive soils and reduce the number of landslides.

Western Bay of Plenty District Council will contribute $10,000 annually over the next three years towards a University of Waikato Doctoral Research Project on Omokoroa’s geology centred on soil stabilisation. The project, led by Earth Sciences senior lecturer Dr Vicki Moon and undertaken by doctoral student Tom Robertson, is focused on discovering how to improve the stability of the material in the sensitive soils that make Omokoroa’s peninsula cliffs prone to slippage.

Dr Moon and her colleague Dr Willem de Lange, presented an update of their research to Council’s Operations Committee this week. The team has been studying Omokoroa’s landslides since 2009, focusing on the Bramley Drive landslide that occurred in 1979. Dr Moon said their attention is on the failure of the sensitive soils at the base of landslides.

Omokoroa has two types of landslides – translational and flow slides – the most damaging are the flow slides due to the fragility of the sensitive soils. These soils are mainly made up of halloysite – a mineral that forms in old volcanic ashes typical to Omokoroa. The latest findings of the research project indicate that a form of salt can act as a stabiliser in halloysite-rich soils by `locking up’ the soils over a period of time.

Dr Moon said initial laboratory testing shows huge promise with a big uptake of the salt and a near-doubling of the peak strength of the soil. However, more testing is required over a wide range of stresses to confirm the early results.

A small field trial in Omokoroa will be carried out when possible to install soil mixed columns and monitor how quickly concentrations of the salt can be achieved.

On-site research has been stalled since Cyclone Debbie caused further slippages in April this year, making the cliff sites too unsafe for researchers.

Credit: Western Bay of Plenty District Council