Numerical modelling of natural prefabricated vertical drains in soft clays : Progress & challenges
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Installation of vertical drains to provide an alternate drainage path is one of the most popular methods for accelerating consolidation in soft clays. Typically, these drains are band-shaped where a core made of plastic or coir is surrounded by a filter made of a synthetic fiber. The first numerical model for the consolidation process in these drains was given by Hansbo (1981) where the classical theory of consolidation was applied to an equivalent circular drain. Over the years a considerable amount of improvement has been carried out by various researchers over and above the initial model proposed by Hansbo. However, most of these numerical models tend to neglect a number of factors that might occur in a typical drain installation on the field. In this paper, we conduct a critical review of these numerical models and take a look at their assumptions and propositions. Since most of the numerical models were developed with synthetic drains as the subject, their applicability in natural drains needs to be examined. Numerical modeling in natural drains tends to become more complicated owing to effects of mandrel withdrawal and the high absorption capacity of natural fibers which introduces unsaturated zones during the initial consolidation process. All these challenges have been discussed in detail and a number of suggestions for adapting these numerical models to natural drains have been provided. Finally, we list down all the requirements of an all-encompassing numerical model that can accurately model the consolidation process in a natural/synthetic vertical drain in field conditions.