Trapezoidal Reinforced Soil Walls – Design Development And Challenges

The widening of the existing rail bridges and approach embankments for the Gosford Passing Loops Project necessitated the construction of retaining walls adjacent to existing embankment slopes. Trapezoidally-shaped reinforced soil walls (RSW) were proposed to cater for the various constraints and challenges faced, including allowance for the uninterrupted operation of the existing rail lines during construction. Due to the unconventional wall geometry and load transfer mechanisms, design of trapezoidal RSW is not covered by typical standards and codes, such as RMS R57. The assessment process necessitated consideration of wall design based on first principles, and variations on the conventional assessment of failure mechanisms to ensure the wall achieved the design intent. Numerical modelling was undertaken to verify achievement of wall stability and serviceability requirements. The successful implementation of these walls is demonstrated by the observed stability of the existing rail track and RSW during and after construction, which is further supported by conforming instrumentation records.