Engineering Rock Mechanics

Ramifications for analysis 171

Figure 10.5 Use of the classical Kirsch solution for plane strain stresses around a

circular opening for studying the effect of anisotropy of rock strength (from

Daemen, 1983).

was given in Chapter 3), it is included as a point property. The key point
about these two types of property is that, within the numerical analysis
techniques which have been developed, variations in point properties can
be accommodated relatively easily (although not necessarily compre-
hensively). For example, using the finite element technique we could
incorporate variations in density, i.e. a form of inhomogeneity.
Of the four attributes, all the numerical techniques can, to a greater or
lesser extent, accommodate wide variations in problem geometry and the
presence of discontinuites. This is not the case for the inhomogeneity,
anisotropy and constitutive behaviour relating to volume properties,
because the individual elements in these numerical formulations should
not be assigned a single value relating to a volume property which may
be varying on a scale commensurate with the elements themselves.

Table 10.1 Examples of rock properties classified according to whether they are

point properties or volume properties

fi

I

Point Property

(Mt dependent on discontinuites)

Density

F’rimary porosity

Permeability of intact rock

Point load strength

I

Cuaability

state of stress

Volume Property

(dependem on discontinuities}

Modulus of deformation

Secondary pomsity

Permeability of the rock mass

D-tinuity frequency

RQD

Rock mass classification indices