Large-strain vacuum-assisted consolidation with non-Darcian radial flow incorporating varying permeability and compressibility

A numerical solution has been developed for large-strain consolidation incorporating non-Darcian (nonlinear) radial flow with varying compressibility and permeability coefficients. The solution can accommodate both conventional fill surcharge as well as vacuum preloading. The smear effect caused by mandrel-driven vertical drains is also captured in the analysis. The proposed model is verified by comparing it with FEM simulation, existing laboratory data, other existing theoretical solutions, and its advantage of capturing the multiple factors influencing radial drainage and consolidation is demonstrated. The effects of non-Darcian flow are found to be significant for obtaining an accurate solution, unlike numerous past solutions that are based on linear Darcy flow. The salient finding of this study is that the conventional small-strain theory can overestimate the rate of consolidation with radial drainage, especially for highly compressible soils such as estuarine clays under substantial preloading pressures. It is also found that a considerable difference (larger than 5%) between large-strain and small-strain solutions inevitably occurs once the vertical strain exceeds approximately 15%, which can be regarded as a threshold beyond which the large-strain analysis becomes increasingly important. The proposed model is applied to a case study at Ballina Bypass (NSW, Australia), where prefabricated vertical drains have been installed in soft estuarine clay subjected to a combination of fill surcharge and vacuum preloading.