Performance prediction of prefabricated vertical drains beneath embankment on soft ground by finite element analysis

Abstract

Preloading and prefabricated vertical drain (PVD) is a commonly employed ground improvement technique to expedite consolidation process by means of shortening the drainage path. Advancement in finite element method (FEM) analysis has enabled modeling of PVD in finite element program to acquire settlement magnitudes and time rate of consolidation. Monitoring results in particular settlement data from two adjacent zones were analyzed using Asaoka (1978) method estimating the total settlement and back-calculated coefficient of horizontal consolidation of the soil. Thereon, using the back analyzed coefficient of consolidation, computer program PLAXIS v.8 was used to estimate the total settlement and rate of consolidation by means of finite element method (FEM). Reasonable agreement of settlement curves were obtained between the FEM analysis and actual field settlement of the PVD treated ground. However, in FEM analysis, it was observed that the ultimate settlements predicted were less than those determined by Asaoka method, but the degree of consolidation achieved were higher. The horizontal coefficient of consolidation was determined to be in the range of 1.4 m2/yr to 2.6 m2/yr which generally encompasses the conventional design ch/cv ratio of 2. Sensitivity study of the soil horizontal permeability to smeared zone permeability, kh/ks ratio generally indicates that as the ratio exceeds 4, the predicted settlement is underestimated significantly.