Dilatant geornaterials, i.e. fissured rocks, dense sands, stiff clays, increase the porosity when subjected

to sufficiently high deviatoric stresses. If these materials are saturated with a pore fluid and the pore

volume increases more rapidly than the fluid can flow into it, the pore pressure decreases, This means

an increase in effective compressive stress which inhibits further inelastic deformation up to a certain

limit. The phenomenon is called dilatant hardening or strengthening and was first discussed by

Reynolds in 1885 in his studies on granular material