Design of Mechanically Stabilised Earth Walls for Bridge Abutments on the Mackays to Peka Peka Expressway, New Zealand

The new 18 km long, four lane MacKays to Peka Peka Expressway located in the Kāpiti Coast Region of New Zealand is currently under construction. On this project there are 18 bridges which incorporate Mechanically Stabilised Earth Walls (MSE walls) in some form within the bridge abutments. These walls are designed for the high seismicity of the Kāpiti Coast region with a design peak ground acceleration (PGA) of up to 0.98g under ultimate limit state design events. This exceeds typical design practice and presents a significant challenge to wall designers. Furthermore extensive sections of the route are prone to flooding, liquefaction and have complicated geometry (for example highly skewed bridges with piles going through the MSE wall reinforced block). This paper discusses the philosophy and approach adopted for the walls and how these design challenges were overcome.