Composite vertical drains: an alternative to PVDs under bending conditions

Geosynthetic prefabricated vertical drains PVDs are used to accelerate consolidation of soft soils by shortening drainage paths. However, their discharge capacity often decreases under large settlements due to bending, buckling, and kinking. To address this limitation, a novel Composite Vertical Drain (CVD) was developed by replacing the conventional corrugated polymeric core with a geofoam or Styrofoam core wrapped in multiple layers of polypropylene mesh (PPM). Laboratory tests were conducted to evaluate discharge capacity, tensile strength, and water absorption characteristics, followed by bending-flow tests to assess hydraulic performance under deformation. Equivalent Composite Vertical Drains (ECVDs) with discharge capacities comparable to PVDs were identified, viz. CVD with geofoam embedment (CVDG), incorporating seven PPM layers, and CVD with Styrofoam embedment (CVDs), incorporating six PPM layers. Both configurations satisfied the minimum tensile strength requirement (>1 kN) for field installation. At a 60° single bend, conventional PVDs showed up to 22% reduction in discharge capacity, whereas CVDG and CVDs exhibited only 3% and 9.9% reductions, respectively. The results demonstrate that CVDs provide improved resistance to bending-induced hydraulic impairment, making them a promising alternative to conventional PVDs in highly compressible soft soils.