Performance of Embankment Stabilized with Vertical Drains on Soft Clay

Abstract

The authors have carried out several two-dimensional plane strain analyses of the Muar test embankment in which the rate of settlement was overpredicted unless clogging of the vertical drains was assumed to have occurred. The modeling of drain clogging in the finite-element analysis is an interesting development, and the discussers would welcome clarification of the modeling method and how this differs from the use of a zone of reduced permeability adjacent to the drain. However, while accepting that clogging could have been a significant factor. the discussers suggest two further causes for the authors' overprediction of the rate of consolidation. namely, incorrect modeling of the vertical drains in the plane strain analysis and the use of a constant permeability during consolidation. The discussers have developed a matching procedure by which vertical drains installed in a regular grid can be modeled in a plane strain finite-element analysis (Hird et al. 1992) that has been validated for several case histories (e.g .. Russell 1992a). The method equates Hansbo's (1981) axisymmetric analytical solution for the consolidation of the soil surrounding a single vertical drain, termed a unit cell. with a similar solution for a plane strain unit cell. The method takes into account. if necessary. both well resistance and smear and can be summarized by two equations