Engineering Rock Mechanics

162 Anisotropy and inhomogeneity

A10.1 In the picture, the limestone beds have been deformed to a
vertical position. The bedding planes form fractures and there is a
variety of other fractures visible, making the rock mass Discontinuous.
Note that one weak stratum where the engineer is standing has been
eroded by the action of rainwater. Thus, the bedding planes, shear
planes, joints and erosion features form the fractures. The rock mass
is Inhomogeneous because the strata have different property values at
different locations (the eroded material was the weakest).

The rock mass is Anisotropic because the fracture frequency and other

properties in different directions are significantly different. Such clearly

defined fractures will also have a strongly 'Not Elastic' character.

410.2 With reference to the photograph in Q10.1, explain why

inhomogeneity and anisotropy can be related.

A10.2 The diagram to the right shows four strata with different prop-

erties: there is ikhomogeneity-within

and between the strata.

Assume strata 1 and 4 are internally

homogeneous, but strata 2 and 3 are

internally inhomogeneous. A scanline

perpendicular to all the strata will

therefore give different rock prop- J'