Behavior of Granular Materials Under High Stresses

Triaxial tests at mean normal stresses up to 1,200 kg per sq cm on a medium-grained, uniform quartz sand show that the nature of sand deformation varies with pressure. As mean normal stress increases, crushing becomes more pronounced and dilatancy effects gradually disappear. Beyond breakdown pressure, at which all effects of initial void ratio disappear, sand behaves essentially as a linearly deformable solid with modulus of deformation E proportional to mean normal stress q. In the same range, sand strength is characterized by a constant angle of internal friction, φ, equal to the angle of interparticle friction from the low pressure tests. Below breakdown pressure, E increases as a power function of q; however the exponent of this function varies with pressure and, to a certain degree, with the initial void ratio of sand. The strength envelopes in this range are all curved and depend on the initial void ratio of sand. Relative compressibility of granular materials generally increases with pressure and may be responsible for scale effects in a number of passive pressure phenomena.