Finite element modeling of soft soil treated with prefabricated vertical drains

Abstract

The Changi East Reclamation Project in Singapore consists of land reclamation and ground improvement works of the foreshore for the future expansion of the Changi International airport. Modeling of the deformation behavior of marine clay under reclamation fills and surcharge was carried out by the finite element method with the Plaxis 2 dimensional numerical modeling software. The analyses included the modeling of the consolidation behavior of marine clay under reclamation fills with and without prefabricated vertical drains. Modeling of the marine clay with vertical drains was carried out by both the axi-symmetric unit cell and full-scale analysis methods. Modeling of marine clay which was not treated with prefabricated vertical drains was carried out by means of full-scale analysis. The numerical analysis of marine clay deformation with and without vertical drain was carried out at two case study locations namely the Pilot Test Site and <i>In situ</i> Test Site. The test sites comprise of vertical drain treated sub-areas and untreated sub-areas which were reclaimed and preloaded under the same conditions. The results of the finite element modeling analysis was compared with that obtained by means of observational methods. Reasonable agreements were obtained from the finite element modeling analysis as compared to the actual field settlements for both the vertical drain treated embankments as well as the untreated control embankments at both the <i>In situ</i> Test Site and Pilot Test Site. The axi-symmetric unit cell and the full scale analysis of vertical drains were found to be in excellent agreement with each other and with the actual field settlement results. Ultimate settlement and degree of consolidation assessed by using Asaoka, Hyperbolic, piezometer and finite element modeling methods have also been compared for each of the sites and are also found to be in good agreement.