A finite element continuum model for consolidation due to pumpage

• Main Author: Kang, Jae-Sun
• Published: Swansea University 2005
• Subjects: 628
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637758

Modelling the mechanical behaviour of engineering phenomena has occupied the attention of researchers since Karl Terzaghi's pioneering work on settlement due to consolidation in 1925. Soil improvement methods using vertical drains in combination with pre-loading were used for soil stabilization at the San Francisco- Oakland Bay Bridge in 1926. Over the next decades, other drain methods, including prefabricated and pack drains, were developed and used for practical purposes. In the mid-1990s, vacuum-induced consolidation became a reliable technology, thanks to a rethinking of theoretical principles that led to the Menard vacuum system. The Menard system was used successfully, for the first time in South Korea, for construction of the Kimhae sewage treatment plant. The drain method is based on Terzaghi's one-dimensional consolidation theory and Barron's vertical drain. Even when using finite element simulation, numerical solution for consolidation problems involves averaging material properties such as elastic modulus, Poisson's ratio, and coefficients of permeability. But the results are too unreliable to use for practical purposes. Classical mechanics alone do not provide sufficient information on the global motion equation of fluid in a porous media. A new approach is presented in this paper to the problem of continuum modelling of vacuum-induced consolidation due to pumpage. This finite element continuum model uses the interior boundary condition instead of installed vacuum tube as a line, with changing pore pressures at the installed material being treated as boundary conditions of the interior part. An innovative linear equation solution method for separate fixed boundary conditions is presented. The efficacy of this model for field construction is shown by comparing results with the results obtained from field measurements at the Jangyoo sewage plant. Because the properties of material are not exact in their natural states, the results of the calculated finite modelling are similar but not a mirror image of field measurements. Whereas conventional one-dimensional calculation uses only one point, the finite element continuum model shows displacements and pore pressures for a whole section. Once the exact material properties have been determined, the model can be applied effectively to field analyses, predicting settlements due to pumpage and facilitating decision making about when pumpage should start and stop. The finite continuum model for consolidation due to pumpage can be applied to other soil improvement methods, such as prefabricated and pack vertical drain, with some modification.