Limit state in soil mechanics and the use of partial factors : Fleming, W G K Ground EngngV22, N7, Oct 1989, P34–36

Abstract

This note is intended to promote discussion on the difficulties encountered when attempts are made to apply to soils to widely varying characteristics the limit state partial safety factor concept developed for manufactured structural materials which are relatively uniform. It discusses partial factors in soil mechanics and methods of measuring parameters; behaviour models in soil mechanics; the 'lump' factor method; structural deformation tolerance and deformation in soil mechanics problems. It is concluded that there is a theoretical problem in all partial factor systems presently used, because they confuse ultimate and deformation considerations; as the range of deformability characteristics in soils is very much greater than in structural design, such partial factor systems are inappropriate for use in soil mechanics. Pure elastic methods do not adequately represent soil behaviour as they do approximately in structural mechanics; soil sampling and testing are not uniform and soil behaviour models are wide ranging. In the author's view geotechnical engineers have to rely far more on experience when making design decisions than do their structural colleagues.