Introduction of new technology into the foundation engineering, necessity to transfer the high loads on deep layers of soil, rapid development of underground construction, raised up serious problems for soil mechanics as a theoretical base of practical geotechnics. Extensive development of empirical methods shows that basic principles of classical soil mechanics often fails to explain physical background while creation of calculation methods and technology development. For non-cohesive and frictional soils it can be explained by ignoring of dilatancy – the fundamental property of granular media.
There are several properties of granular soil called fundamental. That properties define the behavior of the granular media under stress and finally the strength appearing in specific conditions. These properties are internal friction, cohesion and dilatancy. In classical strength theories of soil mechanics we find such parameters as internal friction and cohesion but no dilatancy. Nevertheless this phenomena can be the definitive factor of stress condition and strength. The absence of dilatancy evaluation and absence of laboratory an field methods of its estimation are one of the main reasons of many problems of classical soil mechanics which could be expressed with no exaggeration as a crisis. This crisis display itself for instance in impossibility to develop the calculation methods for the design of deep foundations load-holding capacity, stability of anchored walls and reinforced slopes and many other cases. Introduction to basic ideas of dilatant soil mechanics is given in publ.
On fig. 1 and 2 we have very simplified examples of free and constrained dilatancy. On fig 1a narrow strip (let it be for instance the reinforcement element) is placed on the surface of a dense granular soil. It means that out of the failure zone there are no grains mutual movements and, naturally, plastic deformation.