Study of installation of prefabricated vertical drain through a geotextile tube bund

Traditional coastal protection and containment structures, such as sand dykes and concrete seawalls and barriers, are increasingly being replaced by geotextile tube bund as a sustainable alternative. In this application, it is common to encounter a layer of seabed soft clay beneath the bund. Ground improvement treatment of this soft clay layer using a cost-effective method, such as Prefabricated Vertical Drains (PVD), will be necessary. However, there are concerns regarding the difficulty of PVD’s mandrel penetrating the high-strength geotextile material of the tube. To address this, a laboratory testing apparatus was developed at the National University of Singapore (NUS) to simulate PVD penetration through geotextile sheets anchored in a round frame. A full-scale anchor plate and a full cross-section size of mandrel were used in this test. The study tested two different anchor plate designs on one or two layers of geotextile. Results indicated that while anchor plate design affects the penetrating force and zone of disturbance to the geotextile, the force required to penetrate through geotextile using any of the tested anchor plate designs remains small compared to typical PVD installation forces through sand layers above soft soil. Field data of the PVD installation process was also collected to validate these lab test findings. Field data show minimal differences in the force-depth relationship when PVDs were installed through areas with and without geotextile tubes. Contractors also reported no change in the production rate of PVD installation due to the presence of geotextile tubes, demonstrating that geotextile tubes can be effectively integrated into containment bund structures without impacting PVD installation performance.