Virgin state of stresses and discontinuities of rock masses

The current representation of in situ stress measurements of the earth’s crust suggests a functional relationship between stresses. In the light of this observation the static equilibrium of rock masses is explored. The nature of the equilibrium is determined by the ratios of the variations in horizontal stress to that of vertical and shear stresses. Ratios compiled for different parts of the earth’s crust show that equilibrium is such as to favour discontinuities. Practical formulae for calculating rock mass stresses occurring in a consistent rocks are presented. The vertical stress is not necessarily proportional to the thickness of the rock cover measured vertically though this could be the case in deep strata. The differences in altitude of the terrain affect shear stress which is negligible when compared to the vertical stress in deep strata. Two families of line of discontinuity are likely to exist. Each family comprises one or more parallel curves which cannot end within the rock mass.