Aspects of vertical drain design: Darcian or non-Darcian flow

The classical consolidation equations developed by Barren in 1944 and 1948 are well known among engineers working on soil improvement by preloading in combination with installation of vertical drains. These equations have been gradually refined and are generally utilized in conventional design, The design may seem simple in theory but is connected with a great number of uncertainties from a practical point of view. The problems connected with the choice of consolidation parameters will be commented on and practical advice for the design will be given. In this paper, a number of case records will be presented and compared with, on one hand, the conventional method of design and, on the other hand, the so-called lambda method developed by the author in 1960 to take into account the effect of smear. The lambda method is based on an exponential correlation between hydraulic gradient and flow velocity, We find that the correlation between the conventional theory and practice, based on back-analysis of field data, is less satisfactory than for the lambda method.