An investigation of the geotechnical properties of loess from Canterbury and Marlborough
T.W.D. Jowett · UC Research Repository (University of Canterbury) · 1995
Tunnel gully erosion is common in the loess deposits of the South Island of New Zealand. The loess deposits found on the Wither Hills (Marlborough) and Port Hills (Banks Peninsula) are prone to extensive tunnel gully erosion which has caused significant damage in both rural and urban areas. However, the loess deposits found on the Timaru Downs (South Canterbury) and the hills surrounding Akaroa (Banks Peninsula) are significantly less affected. Geotechnical tests including pinhole erosion, uniaxial expansion, crumb test and dispersion % were carried out to determine the erosive and dispersive characteristics of loess samples from locations in the aforementioned areas. From this data, the extent to which geotechnical properties influence the incidence of tunnel gully erosion was determined. Other geotechnical characteristics such as grain size, clay mineralogy, exchangeable sodium content and insitu dry density were also evaluated in order to determine the controlling factors on the erosive and dispersive characteristics of the different loess samples. In general, it was found that laboratory test results did not correlate fully with field erodibility. For instance, the two non tunnel gullied soils exhibited characteristics which suggested that they should be prone to tunnel gully erosion. The lack of correlation between laboratory test data and field erodibility suggests that other factors such as climate, land use and soil profile characteristics are important in determining the occurrence of sub-surface erosion. A comparison was made of the loess stabilising properties of an enzyme based product known as Endurazyme and quicklime (CaO), a commonly used loess stabiliser. Tests were carried out on samples from the Timaru Downs and the Ahuriri quarry on Banks Peninsula. It was found that Endurazyme has a negligible effect on important geotechnical properties such as erodibility, dispersivity, durability, strength and maximum dry density/optimum moisture content.