Vertical Drain Depth Optimization in Vacuum and Surcharge Preloading Using Finite Element Method

One of the most challenging parts of every project including prefabricated vertical drains (PVDs) combined with vacuum and surcharge preloading for ground improvement is the determination of the PVDs depth of installation and its configuration. In this paper Finite element was used for modeling and verification of a full-scale test embankment (TV2) which was constructed to study the effectiveness of PVDs combined with vacuum preloading for accelerating the consolidation along with surcharge at Bangkok airport. Different depths and scenarios were modeled and the results were compared and analyzed. Since the ultimate goal of soft clay soils treatment is attaining pre-determined settlement, the settlement curve under soil embankment was used for investigation of the results. A new Finite Element Modeling (FEM) based procedure as "One and Between Configuration" has been introduced. Based on the results, it was shown that; 1) the inward forces of vacuum preloading in proposed configuration is greater than the conventional method and lateral displacement reduced by 15 percent; 2) As a result of the lesser penetration of the mid PVD, the disturbance of the soil and accordingly, the smear zone becomes lesser; 3) Because of the "one and between" installation, in a case that a percentage of the every PVDs become clogged in any possible length, which may vary from PVD to PVD, the overall performance of the PVD itself, and in relation to adjacent PVDs don’t diminish as much as common constant penetration method.