ABSTRACT

In simple terms the strength of a material is the maximum shear stress that it can sustain; materials loaded just beyond the maximum stress will fail. Failure may be sudden and catastrophic leading to a complete loss of strength (which is what happens when you break a biscuit, which is brittle) or it may lead to a very large plastic straining (which is what happens if you mould plasticine, which is ductile). For most soils, failure of slopes and foundations involves large straining without complete loss of strength and failing soil structures can usually be stabilized by unloading them.