B-bar analysis modeling tips

The following tips are good to keep in mind when carrying out excess pore water pressure analyses in Slide:

  1. Excess pore pressure models are really two stage models.  If a materials weight creates excess pore pressure (checkbox in the material properties dialogue) then it’s assumed that this material is added to the system in the second stage (like an embankment in Tutorial 12) and its weight creates pore pressure in an underlying material.  If the materials weight does not create excess pore pressure, it’s assumed to exist in the first stage.  Second stage materials lying above it will generate excess pore pressure if their weight is defined as creating excess pore pressure.
  2. If a material in Slide has zero initial pore pressure, it is assumed to be unsaturated and any load will not create an excess pore pressure.  So if Ru is 0, no excess pore pressure will be created.  To get around this, define a very small value of Ru (say 0.00001).  This will trick the program into having almost zero initial pore pressure for a material yet adding excess pore pressure. 
  3. If you are doing a B-Bar analysis then you should be using effective parameters.  See Tutorial 13, all the materials use effective values with a water table defined.  Whether it’s rapid drawdown or a loading condition that creates the excess pore pressure, you use effective stress parameters.  See Tutorial 12 for an example of an embankment load creating excess pore pressure.
  4. Excess pore pressure is only created in the saturated zone.  The saturated zone is any area in which the initial pore pressure is greater than zero.