Although the 'Geo-Install' workshops have shown significant advances towards modelling installation, many of these methods are currently not available in commercial packages.
Cavity Expansion
A common method used to model both stone column and pile installation is cavity expansion. This is the process of expanding a cylindrical cavity of zero thickness in a radial direction until the radius of the cavity equals the radius of the pile or SC. This is an effective method for modelling the excess pore pressures, in particular, generated during pile/SC installation.
Interface Strength Reduction Factor
PLAXIS allows for an input of an 'interface strength reduction factor' in order to take into account a reduction in soil strength arising from installation. Typical values range between a value of 0.6 to 1.0 depending on the particular soil type. This strength reduction factor can only be applied when using interface elements, however, and thus may not be applicable to SCs. During the installation of SCs, the stone and soil being treated become interlocked. Thus modelling SCs using interface elements may over-predict punching of the stone columns in the soil.
In PLAXIS 3D, the user can select between volume piles and embedded piles to model a pile foundation. Embedded piles comprise of beam elements and have special interfaces. Thus strength reduction at the pile-soil interface can not be modelled using embedded piles.The differences between these two types of pile will be covered in another post in more detail.
