Simple Method of Modeling PVD-Improved Subsoil

Abstract

On a macroscale, the effect of installing prefabricated vertical drains (PVDs) in a subsoil is to increase the mass hydraulic conductivity of the subsoil in the vertical direction. Based on this concept, a simple method for modeling PVD improved subsoils is proposed, in which an equivalent vertical hydraulic conductivity k v e for the PVD improved subsoil is explicitly derived. With the proposed simple method, analysis of PVD improved subsoil is the same as that of the unimproved case. The theoretical verification of the simple method was made under 1D condition. The calculated average degree of consolidation and excess pore pressure distribution in the vertical direction using the simple method are compared with existing theoretical solutions (combination of Terzaghi's consolidation theory and Hansbo's solution for PVD consolidation). It has been proved theoretically that, in terms of average degree of consolidation, in the case of one layer and ignoring the vertical drainage of natural subsoil, the maximum error of the proposed method is 10% compared with Hansbo's solution. For the case of one layer or multilayers and considering both vertical and radial drainages with the parameters adopted here, the maximum error of the proposed method is 5%. The multilayer case was analyzed by FEM method, and the proposed simple method is compared with that of using 1D drainage elements. Then, 2D finiteelement analyses were conducted for three case histories of embankments on PVD improved subsoils. One case is discussed in detail. The analyses using both the simple method and 1D drainage elements, were conducted. It is shown that for all three cases, the simple method yielded results as good as those using 1D drainage elements.

Theoretical and Numerical Perspectives and Field Observations for the Design and Performance Evaluation of Embankments Constructed on Soft Marine Clay

“…A simple approximate method for modelling the effect of PVD is proposed by Chai et al (2001). Because PVD increases the mass permeability of subsoil in the vertical direction, it is logical to establish a value for vertical permeability which approximately represents the effect of vertical drainage of natural subsoil and radial permeability toward the PVD.…”

2D and 3D Numerical Modeling of Combined Surcharge and Vacuum Preloading with Vertical Drains

“…Various conversion procedures have been proposed earlier (e.g. Shinsha et al 1982;Hird et al 1992;Bergado and Long 1994;Chai et al 2001;Indraratna et al 2005). Cheung et al (1991) employed the conversion procedure which assumes that the settlement response at 50% degree of consolidation is the same for both 2D and axisymmetric (3D) conditions (Shinsha 1991).…”

Effect of Anisotropy and Destructuration on Behavior of Haarajoki Test Embankment

“…The problem of water flow into a vertical drain under an infinitely wide fill is axisymmetric, and therefore the vertical drain system must be converted into an equivalent plane strain model for numerical simulations. Several authors ͑Hird et al 1992Chai et al 1995Chai et al , 2001Indraratna and Redana 1997͒ have shown that vertical drains can be effectively modeled by using appropriate mapping methods to represent the typical arrangement of vertical drains in plane strain finite-element analyses. However, certain simplifying assumptions are made, as discussed later on.…”

“…However, certain simplifying assumptions are made, as discussed later on. The two most useful mapping approaches from a computational point of view are those by Chai et al ͑2001͒ andHird et al ͑1992͒, as accounting for the effects of the smear zones around the drains does not require separate discretization. In this paper the combined mapping purposed by Hird et al ͑1992͒ is used in the analysis of the behavior of PVD improved subsoil in combination with complex elastoplastic models, namely MCC, S-CLAY1, and S-CLAY1S.…”