ANALYTICAL SOLUTION TO CONSOLIDATION OF UNSATURATED SOIL WITH VERTICAL DRAIN CONSIDERING DRAIN RESISTANCE AND SMEAR EFFECT

Former researches of unsaturated vertical drain foundations mostly treated the foundations with ideal radial boundaries. The drain resistance and smear effect are important factors affecting the consolidation of unsaturated soil with vertical drain. This paper is based on Fredlund's one-dimensional consolidation theory for unsaturated soil mechanics and the equal strain hypothesis. The coupled governing equations of excess pore pressures are transformed into equivalent linear partial differential equations by introducing variables. This paper further takes into account the drain resistance and smear effect conditions in the analytical derivation. Separation of variables and the method of undetermined coefficients are mainly adopted to obtain the analytical solution to consolidation of unsaturated soils with vertical drain under instantaneous load. Moreover, the validity of the solution is verified by degenerating and comparing with the existing solution in saturated soils. A typical example is used to illustrate the influence of drain resistance and smear effect on consolidation of vertical drain foundation. The results show that the decrease of the smear effect-and drain resistance-related coefficients(i.e., drain resistance factor G, ratio of influence radius to vertical drain radius N, smear coefficient α, ratio of smear radius to vertical drain radius S)can lead to an obvious increase in the consolidation speed. When the drain resistance factor G is less than 0.1, the influence of the drain resistance can be neglected in practical engineering; When the ratio of smear radius to vertical drain radius S is bigger than 5, the influence of smear effect cannot cause much more remarkable difference than when S=5. It is expected that the permeability of vertical drain foundation in unsaturated soils should be improved and construction disturbance should be reduced to decrease the influence of drain resistance and smear effect in practical engineering.