Bridges

The Ngauranga Interchange is located at the intersection of two State Highways that provide the only highway access from the surrounding regions to the city of Wellington, New Zealand. Reinforced Earth® walls retain the seaward side of the off-ramp from the Southbound Overbridge of the Interchange and the southern abutment is supported on a 13.4 m high section of wall.A detailed seismic assessment was undertaken to determine the earthquake performance of the walls. This indicated that in a 500-year return period earthquake event some of the panel to strip bolted connections could fail leading to dislodgement of the lower panels. In longer return period events, differential outward movements and settlement of the foundation soils were predicted to increase the pressures on the wall facings, leading to a large number of connection failures. The paper describes the detailed assessment of the walls and the unique features of a soil nail strengthening design that is expected to prevent connection failures in design-level earthquakes.