Radial consolidation of clay using compressibility indices and varying horizontal permeability

A system of vertical drains, with surcharge load to accelerate consolidation by shortening the drainage path, is one of the most popular methods of soft ground improvement. The conventional radial consolidation theory (including smear and well resistance) has been commonly used to predict the behaviour of vertical drains in soft clay. Its mathematical formulation is based on the small strain theory; and for a given stress range, a constant volume compressibility (m(v)) and a constant coefficient of horizontal permeability (k(h)) are assumed. However, the value of m(v) varies along the consolidation curve over a wide range of applied pressure (Delta p). In the same manner, k(h) also changes with the void ratio (e). In this paper, the writers have replaced m(v) with the compressibility indices (C-c and C-r), which define the slopes of the e - log sigma' relationship. Moreover, the variation of the horizontal permeability coefficient (k(h)) with the void ratio (e) during consolidation is represented by the e - log k(h) relationship that has a slope of C-k. In contrast to the conventional analysis, the current study highlights the influence of the C-c /C-k (or C-r /C-k) ratio and the preloading increment ratio (Delta p/sigma(i)) on the consolidation process. The analytical predictions are compared with the experimental results when a large-scale consolidation chamber was used, and these predictions show good agreement with the measured data. Finally, an embankment case history taken from Muar Plains, Malaysia, is analysed on the basis of the current solution and compared with field measurements.