Design Of Slope Stabilizing Piles For Reinforced Soil Walls On Hunter Expressway

The Hunter Expressway will provide a 40 km long four-lane divided carriageway motorway between the F3 Interchange at Newcastle and the New England Highway at Branxton, New South Wales Australia. The project is due to be opened by the end of 2013. The Hunter Expressway Alliance (HEA), comprising Roads and Maritime Services (RMS), Thiess Pty Ltd, Parsons Brinckerhoff and Hyder Consulting, is responsible for the design and construction of the 13 km eastern section of new freeway and local road adjustments. There are 28 bridges and major culvert structures and 29 Reinforced Soil Walls (RSWs). This paper discusses the design challenges faced by the RSW designers and the innovative engineering solution developed for RW17, a 120 m long RSW up to 10m in height on sloping ground with foundations containing bands of low strength tuffaceous claystone. To achieve the minimum design factor of safety (FOS) of 1.35 for the overall slope stability of the RSW as stipulated in RMS Specification R57, three rows of 450 mm/750 mm diameter and one row of 1500 mm diameter bored piles were designed and adopted at various selected sections along the 120 m long slope. Both the limit equilibrium program Slope/W and the finite element program PLAXIS were used to assess the FOS for the global stability of the RSW, ground movements during and after RSW construction and forces in the piles. Two inclinometers were installed to monitor the field lateral ground movements during and after construction to verify the design assumptions. This paper describes the challenging ground conditions, the development of the stabilising pile design, the analytical models used and the results of the construction phase monitoring of the completed RSW.