Lime stabilisation of expansive Auckland soils

Significant areas of Auckland, New Zealand are situated on soils termed at risk of shrink or swell, also known as reactive or expansive soils (Brown, et al., 2008). The movement of buildings as soils shrink or swell can cause structural damage (Elsaidy, et al., 2019). Under NZS 3604:2011, residential building platforms must meet the requirements of ‘good ground’ conditions; otherwise, a specific engineering design is usually required. This paper considers whether expansive soils in the north and south of Auckland can be stabilised within the top metre using burnt lime (CaO) to meet ‘good ground’ standards for building construction. This study found that treatment of these specific expansive soils with burnt lime (5%, 7%, and 9% by weight) improved the sample strengths and reduced shrinkage. After 28 days curing, all lime dosage rates effectively brought linear shrinkage to within the NZS 3604 ‘good ground’ threshold. Longer curing times (28 days versus 7 days) resulted in an increased unconfined compressive strength (UCS). The curing time had a greater effect than the lime dosage. There is potential for this methodology to be upscaled and implemented in construction, to improve reactive soils to meet NZS 3604 requirements. This would mean that specific foundation design can be replaced by simple slab- on-grade foundations, as the building is no longer at risk of differential settlement. However, more research is needed to determine the feasibility and costs associated with this approach. Prolonged testing will be needed to determine the longevity of the effects. In addition, environmental impacts should be investigated.