Factor of safety of cuttings and embankments

A global ‘factor of safety’ has traditionally been applied as a minimum acceptable value against ultimate limit state failure of cuttings and embankments and is in line with other soil mechanics practice for the design of foundations and retaining walls. The selection of a factor of safety depends predominantly on the consideration of two sets of circumstances:

The circumstances are interlinked and both need to be considered with regard to the stability of new earthworks and existing assets. The assessment of existing assets is discussed more fully in Chapter 14.

An extreme example of the consequence of failure is new dam construction as described by Johnston et al. (1999). The required factors of safety reflect the impact of failure that could result in a catastrophic flood event.