Engineering Rock Mechanics

Inhomogeneity 167

p=75 *=.

Confining pressure

g3 MPa

?

A

Legend

1.7 A

(^0) A 2.7 3.6 A0 +
' 5.2
6.0

• 7.0
  r 8.0
  0
  Lower bound trends 10
  V / lA
  A'
  /A
  11
  / A'
  I Angle between major principal stress and normal to cleavage - p"
  1 I I I I I I 1 I
  0 10 20 30 40 50 60 70 80 90
  Figure 10.2 Compressive strength anisotropy in dark grey slate (after Brown et al.,
  1977).
  values of a rock property. For example, in choosing the type of cutters for
  a tunnel boring machine, not only the mean compressive strength would
  be required but also the range within which the top, say, 10% of strengths
  occur.
  In Fig. 10.3, we illustrate both the standard statistical procedure for
  characterizing a parameter through the full probability density curve (which
  does not explicitly take the distances between sample locations into account) and
  the semi-variogram of geostatistics (which does take these distances into
  account).
  Where we encounter rock properties varying with location within a rock
  mass, there are three main approaches to the characterization procedure: