THE USE OF TARANAKI ASH FOR CONSTRUCTION FILL. NEW ZEALAND ROADING SYMPOSIUM 1987. VOLUME 1

The engineering properties of Taranaki brown ash are unusual relative to other soils with high clay contents and the material is often rejected as unsuitable for construction fill. However, the material often exhibits high strength and stiffness in natural conditions and this is shown to be due to the influence of the chemical structure provided by iron oxides. When the structure is destroyed, the high water contents retained by the allophane clay minerals is released leading to the construction difficulties often experienced in the field. A model for the behaviour of the ash is developed which demonstrates the material can be successfully used using careful handling and placing methods which minimize disturbance to the iron oxide structure. The potential for improvement and stabilisation together with requirements for maintenance of good drainage conditions to avoid reduction (loss of chemical structure) are also discussed. In natural conditions, changes in oxidising conditions due to variations in the water table or exposure during excavation may have a significant influence on performance. Sampling and testing methods must also be designed to minimize changes to ensure results are representative of field conditions. For the covering abstract of the symposium see IRRD 810782. (Author/TRRL)