Accurate prediction of foundation settlements is a demanding task. It requires comprehensive field data representing actual subsoil conditions. Also, footing configuration (depth, spacing), loading, construction stages, all have an effect on the actual settlements.
Often times, these analyses are completed with poor soil data (SPT values and soil index properties), while the true 3D nature of the problem cannot be accommodated into the simplified methodologies. And often times the results of such exercises are futile.
In common practices, you may take your prediction and multiply it by two. You have an upper bound value.
Take your prediction and divide it by two, and now you have a lower bound.
Your expected settlements may lie with a bit of luck somewhere within this range.
In our approach, we have in-situ testing methods capable of estimating soil/rock properties/parameters related to elastic, consolidation, and creep deformations. Using 3D FE elements we can now accommodate footing or raft configurations for different loading stages. We do include the soil-structure interaction analysis in our approach. Also, if you provide us with the general stiffness of your structure, we can provide realistic estimates of differential settlements.
Again, our approach may not be the cheapest, but our settlement predictions are accurate and meaningful throughout the entire process of installing the foundation system. This is critical when you need to know how your project will affect your neighbour facilities. You might be able to tolerate an extra 25 mm of settlements in your building. What about your neighbour facility?