Engineering Rock Mechanics

Additional points 1 15

To find the angular error that would exist if the correction were not
made, we compute the angle subtended by the uncorrected vector and
the corrected vector. This is given by the scalar product of the two
vectors, and is computed as

acos(0.490 0.483 + 0.498 .0.571 + 0.715 e0.664) = 5.1".

Depending on the relative orientations of the fractures and the

sampling line, errors appreciably greater than this can be found, and

so we recommend that this correction is always applied to fracture

orientation data.

7.3 Additional points

There is now a considerable body of theory available that can be used for
studying fracture geometry in the engineering rock mechanics context,
and there are computer programs available for analyzing and presenting
the fracture data. The use of the hemispherical projection, demonstrated
through the answers in Section 7.2, enables many geometrical problems
to be solved by hand to an accuracy of 1". Further advantages are that it
provides an enhanced understanding of the geometrical principles and
is a useful spot check of solutions obtained from 'black box' computer
programs.
For further reading about the origin of fractures, we recommend the
book by Price and Cosgrove (1990)9. For further reading about the
engineering characterization of discontinuities, we recommend the book
by Priest (1993)'O. An example of research into the link between the
geometrical fracture properties and the hydrogeological properties of
rock masses is provided in the paper by Panda and Kulatilake (1999) ".
The most well-known software package for reducing and presenting
fracture data is DIPS, available from Rocscience, see http://www.rocscience.com.
A more extensive package, FRACNTWK, has been developed by Kulat-
ilake at the University of Arizona ([email protected]).

'Price N. J. and Cosgrove J. W. (1990) Analysis of Geological Structures. Cambridge

'OPriest S. D. (1993) Discontinuity Analysis for Rock Engineering. Chapman and Hall,

'I Panda B. B. and Kulatilake P. H. S. W. (1999) Effect of joint geometry and trans-

University Press, Cambridge, 502pp.

London, 473pp.

missivity on jointed rock hydraulics. 1. Eng. Mech., 41-50.