Soft soil consolidation using Prefabricated Vertical Drains: Case study of “Radès la Goulette” bridge project

This study examined the consolidation settlement of Tunisian soft soil at the Radès la Goulette bridge project using prefabricated vertical drains (PVD) installed to a depth of 10 meters, combined with incremental preloading. Extensive field instrumentation monitored settlement throughout construction. Laboratory model tests replicated field conditions, using two setups: a single vertical drain model and a multiple vertical drains model with three drains in a triangular arrangement. Barron’s radial consolidation theory and Asaoka’s observational method were adopted for consolidation settlement predictions and the estimation of the radial coefficient of consolidation. The multiple vertical drains model showed faster consolidation compared to the single vertical drain model, with reduced time to achieve 50% settlement. Field data closely matched laboratory results, with discrepancies attributed to soil heterogeneity and smear zone effects. The study found that optimized drain spacing and accurate selection of consolidation coefficients significantly improved prediction reliability. Results demonstrated the effectiveness of combining prefabricated vertical drains with preloading to accelerate settlement, reduce post-construction deformation, and enhance ground stability, offering valuable insights for future soft soil improvement projects.