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The application of the Austroads Pavement design guide to Taranaki 'brown ash' has been investigated. The study was designed to determine if the subgrade strain and deflection criteria given in the guide was appropriate for use on volcanic soils.

The research involved:

• Task 1 – site selection and collection of data on the pavement history, present condition and traffic loadings.
• Task 2 – site testing to characterise the materials and pavement dimensions.
• Task 3 – comparison of the modulus values derived from the various site tests and analysis of the expected performance of the pavement using the measured parameters. This theoretical performance was then compared with the actual performance of the pavement.

It has been concluded that the deflection criteria given in the guide is not appropriate for use on the Taranaki 'brown ash' subgrades, but that pavement design based on the sub grade CBR compares favourably with the Austroads guide.

Keywords: Taranaki brown ash, pavement design, subgrade strain, pavement deflection design