Simple method of modeling PVD-improved subsoil

On a macroscale, the effect of installing prefabricated vertical drains (PV Ds) in a subsoil is to increase the mass hydraulic conductivity of the subs oil in the vertical direction. Based on this concept, a simple method for m odeling PVD improved subsoils is proposed, in which an equivalent vertical hydraulic conductivity k(ve) for the PVD improved subsoil is explicitly der ived. With the proposed simple method, analysis of PVD improved subsoil is the same as that of the unimproved case. The theoretical verification of th e simple method was made under ID condition. The calculated average degree of consolidation and excess pore pressure distribution in the vertical dire ction using the simple method are compared with existing theoretical soluti ons (combination of Terzaghi's consolidation theory and Hansbo's solution f or PVD consolidation). It has been proved theoretically that, in terms of a verage degree of consolidation, in the case of one layer and ignoring the v ertical drainage of natural subsoil, the maximum error of the proposed meth od is 10% compared with Hansbo's solution. For the case of one layer or mul tilayers and considering both vertical and radial drainages with the parame ters adopted here, the maximum error of the proposed method is 5%. The mult ilayer case was analyzed by FEM method, and the proposed simple method is c ompared with that of using 1D drainage elements. Then, 2D finite-element an alyses were conducted for three case histories of embankments on PVD improv ed subsoils. One case is discussed in detail. The analyses using both the s imple method and ID drainage elements, were conducted. It is shown that for all three cases, the simple method yielded results as good as those using ID drainage elements.