Influence of biodegradable natural fibre drains on the radial consolidation of soft soil

Natural prefabricated vertical drains (NPVDs) produced from biodegradable materials such as jute and coir have some distinct advantages over conventional polymeric prefabricated vertical drains (CPVDs). For instance, NPVDs are not only able to discharge excess pore pressure effectively but are also beneficial to the environment thanks to their biodegradability. However, due to the biodegradability of the natural fibres, NPVDs can sometimes deteriorate too quickly in an adverse environment such as in highly acidic clay, which hampers the dissipation of excess pore pressure. In this paper, an analytical solution for radial consolidation that considers the time-dependent decay of drain discharge capacity is therefore proposed. The solution is applied to an exponential form of reduction of the drain discharge capacity, and then verified with the experimental results obtained in previous studies. The effect of drain degradation on soil consolidation is simulated using a finite element method (ABAQUS) and these numerical results are then compared to those obtained from the analytical approach. In addition, a new and flexible method using a matching factor to convert the parameters from axisymmetric to plane strain models is introduced and applied to radial consolidation. The modelling outcomes indicate a significant retardation of excess pore pressure dissipation due to drain degradation and this suggests the need to exercise caution when using biodegradable NPVDs.