Degree of consolidation of clayey deposit with partially penetrating vertical drains

A simple approximate method for calculating the average degrees of consolidation of subsoil with partially penetrated prefabricated vertical drains (PVDs) under instantaneous load has been developed. The basic ideas adopted are: for the layer with PVDs, the average degree of consolidation (U1) can be calculated by the combination of the unit cell consolidation theory for radial drainage due to PVD and the Terzaghi’s one-dimensional (1D) consolidation theory for vertical drainage of natural soil, and for the unimproved layer, the average degree of consolidation (U2) can be calculated by Terzaghi’s 1D consolidation theory and multiplied by an empirical factor (α2). α2 is a function of U1, spacing of PVDs and the ratio of the horizontal hydraulic conductivities of natural soil (kh) and smear zone (ks). The empirical equations for calculating α2 are proposed based on the results of finite element analyses with an axisymmetric unit cell model. The validity of the proposed method has been confirmed by comparing the calculated results with the results of finite element analyses as well as other existing solutions.