Prefabricated Vertical Drain Installation Research Articles

Improvement of ultra-soft soil using prefabricated vertical drains

A case study of using prefabricated vertical drains (PVDs) to accelerate the consolidation of an ultra-soft fine-grained soil with high moisture content for a land reclamation project is described in this paper. Large-scale laboratory model tests were carried out to assess the suitability of the selected PVD and the effectiveness of the PVD in the consolidation of the ultra-soft soil. The model tests indicate that the discharge capacity of the drain can decrease substantially after the drain has experienced large deformations. To overcome this problem, PVDs were installed in two rounds. The first round was before the application of surcharge, and the second round was after substantial settlements have taken place. Field instrumentations were utilized to monitor the performance of PVDs during consolidation. The monitored settlement and pore water pressure results are presented and discussed. The study shows that it is effective to use PVD for the consolidation of the ultra-soft soil if special care has been taken in selection and installation of PVD and in fill placement to overcome the difficulties involved in the consolidation of ultra-soft soil.

Innovations and performances of PVD and dual function geosynthetic applications

Full-scale test embankments, which were constructed on separate locations but within the site of the Second Bangkok International Airport and at the Campus of the Asian Institute of Technology, confirmed that prefabricated vertical drain (PVD) installation not only accelerated and facilitated uniform consolidation settlements but also aided in recharging the subsoil. Thus, PVD can mitigate the negative piezometric drawdown of the subsoil caused by the excessive pumping of groundwater down to the depth of PVD installation. The compressibility and flow parameters were back-calculated from the performance of the full-scale tests. Further back-analysis proved that every stage of preloading corresponded with certain rate of consolidation, and hence the variation of compressibility parameters of PVD-improved soft clay. Another full-scale test embankment employing vacuum-assisted preloading revealed that the rate of settlement has increased by 60% and the period of preloading was reduced by 4 months. Moreover, the use of electro-conductive PVDs could further shorten the required time of consolidation. In addition, dual function geosynthetic had been proposed to prevent excavation slope failures caused by the drawdown of water level along irrigation/drainage canals.