A bikeway underpass culvert had to be constructed at the edge of Nerang-Broadbeach Road, Gold Coast, Queensland, Australia. This was achieved by modifying the side slope of the existing road embankment, which was founded on a soft compressible soil deposit, incorporating reinforced soil system (RSS) steep walls. Site investigation involved field tests (piezocone tests including pore pressure dissipation and vane shear tests) and laboratory investigation included consolidation tests. An observational approach involving field instrumentation (with settlement plate and piezometers) was adopted for this construction. Preloading was conducted to accelerate the settlement and from the field monitoring of the settlement, it was observed that the settlement was continuing even after 300 days at a rate of 25 mm/month. Surcharge load was applied to enhance the post construction settlement after 300 days of preloading. To predict the performance of preloaded soft soil, nonlinear, fully coupled, elasto-plastic, Finite Element Analysis (FEA) was conducted using the UNSW@ADFA modified version of the nonlinear stress analysis program AFENA. The input material parameters for the model were determined from laboratory experiments and correlations with piezocone and piezocone dissipation test data. It was found that Modified Cam Clay model under predict the ultimate field settlement. The long term and short term stability analyses were also conducted using the Limit Equilibrium Approach and observed that preload could be applied safely.
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