where lR represents the bias factor for resistance. The bias factor includes the net effect of
various sources of error such as the tendency of a particular method (e.g., Hansen’s
bearing capacity) to under-predict foundation resistance, energy losses in the equipment
in obtaining SPT blow counts, soil borings in strata not being representative of the site, etc.
For n number of sources of error with individual factors affecting the strength of resistance
prediction procedure, the mean bias factor can be expressed as follows