Analysis stages

Analysis stages

1. How are the initial stresses set up?

   • The first stage of any geotechnical FE analysis involves setting up the initial stress
   • There are two methods of stablishing initial stress in an FE analysis
     • Direct specification
     • Gravity switch - on
       • In cases of non-homogeneous stress profiles, such as with sloping strata, the initial stress is generated by activating the self-weight of the ground and by specifying the initial pore pressures in the model.
       • the model must be in equilibrium with an error of less than 1% and no significant plastic yielding. Where there is a small equilibrium error or a few Gauss points yielding, performing a plastic nil-step should restore equilibrium and return all stresses within failure limits

2. How are the construction stages set up?

   • Any geotechnical FE analysis of new or existing structures must consider explicitly how the structures were constructed because this affects stress paths and ground behaviour. The time periods for construction are also important for temporal effects such as groundwater flow and excess pore pressure dissipation in low-permeability soils or creep effects.