Optimising Precast Cantilever Walls Founded In Sydney Sandstone

Linear Infrastructure projects requiring grade separations have historically used a multitude of retaining wall systems, such as gravity, piled and reinforced soil structures (RSS), depending on ground conditions. L-shaped cantilever cast in- situ walls have been used extensively in road projects in the Sydney region. These walls are costly as they use a significant amount of concrete and steel, while achieving an aesthetically pleasing finish is difficult. Such walls may not take full advantage of rock foundations prevalent in the Sydney Basin. This paper presents an updated concept for optimising retaining walls under appropriate conditions, combining precast and cast in-situ elements while increasing the effectiveness of the load transfer mechanism to the ground.

In essence, this system is a retaining solution comprising full-height precast wall facing units secured to a cast-in-situ footing forming a monolithic cantilever concrete wall. The facing units are each precast with a set of counterforts on the rear side to transfer load to the footing. This paper discusses and investigates both the design of this precast solution, focussing on counterforts and footing, and the adequacy of the solution from a geotechnical point of view, as it relates to the prevalence of rock foundations in the Sydney Basin.