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Subgrade stabilisation is a common road construction practice in New Zealand. Stabilisation results in increased subgrade strength and stiffness, and provides a stable platform for the construction of the overlying pavement. It also provides protection of the original subgrade from stresses generated by wheel loads passing over the pavement surface.

This project carried out in 1998 has examined the performance of lime-stabilised subgrade materials using both laboratory and field investigations for three test pavements. The field investigations have shown that the enhanced strength and stiffness characteristics of stabilised subgrade materials can be relied upon for periods of twenty years or more.

Laboratory investigations have been used to examine correlations between the elastic modulus of lime-treated and untreated soils and other basic test methods. Good correlations have been established between the CBR and both unconfined compressive strength and split tensile strength, for the silty clay soil used in the investigation.

The field and laboratory data have been used to develop a design procedure for stabilised subgrade layers using a mechanistic approach. The proposed procedure provides performance predictions that are reasonably consistent with the observed pavement performance.

Keywords: CBR, New Zealand, pavements, pavement design, roads, stabilisation, subgrades, testing, triaxial tests