SETTLEMENT OF SOFT CLAYS WITH PREFABRICATED VERTICAL DRAIN

Prefabricated Vertical Drains (PVDs) are being used to accelerate the consolidation of sub-soil for construction of high embankments on soft ground. The construction is carried out in stages. For each stage construction, estimation of the total primary settlement is critical for deciding the subsequent stage of construction. Conventionally, the primary settlement is predicted using laboratory compressibility data, hyperbolic method or inflection point method. The inflection point method for determination of primary settlement has previously been established for vertical drainage. In this paper, authors have extended this procedure for three dimensional drainage when PVDs are adopted for subsoil improvement. The inflection point is the point where slope of settlement/log time versus time plot changes on semi logarithmic scale. The primary settlement and degree of consolidation at inflection point are evaluated using laboratory and field data from a case history, where in an embankment of height 3-6 m and length 4.5 km has been constructed over PVD improved soft marine clay at Vishakhapatanam, India. This method of settlement analysis may complement the existing methods for estimation of primary settlement. It is concluded that this method has the potential for field application to provide a practical means of monitoring the progress of consolidation.