Soft ground improvement by prefabricated vertical drain (pvd)

Abstract

Soft soil improvement in the project requires the consideration of the preloading programme. This method long track record of success and may be a unexpected time delay. Then one of the solutions is to use surcharge that fill must extend horizontally at certain depth beyond the perimeter of the planned construction. Surcharge must remain in place for months or years, thus delaying construction. Since this project needs to be completed within 2 years and the time given to increase the soil strength is 6 months only. Based on that reason, Prefabricated Vertical Drain (PVD) was added to expedite this process. It decreases the overall time required for completion of primary consolidation and also decreases the amount of surcharge load required to achieve the same desired amount of consolidation over a given period of time.At BH 9 and BH10, without surcharge the untreated ground would required about 2.5 year time to eliminate most of settlement. To achieve 99.3% and 99.2 % degree of consolidation the estimated time required is about 1.5 year. PVD was adopted to expedite the consolidation settlement. The consolidation degree 99.3 % were required to ensure that anticipated consolidation settlement of 895mm and 901mm due to permanent fill alone and compensation settlement permanent fill are completely eliminated and no excess pore water pressure left in the soil for BH9 and 860.56mm and 868.066mm for BH10. With the introduction of PVD and surcharge fill of 1m, the required degree of consolidation, Ureq of 99.3% (borehole 9) and 99.2% (borehole 10) was expected to be expedited within a designed rest perod of 6 months. However the evaluation against settlement monitoring results indicated that the corresponding achieved degree of consolidation over 6 months time was about or more than 90% but less than 99.3%.