Engineering Rock Mechanics

Geometrical properties of discontinuities

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Figure 7.11 Variation in discontinuity frequency for a sampling line passing

through one, two and three sets of mutually perpendicular discontinuities-three-

dimensional case (from Antonio, 1985).

The dip angle is defined as the steepest line in the plane, i.e. the line down
which a ball would roll; the dip direction is the compass bearing of this line,
measured clockwise from North. Here, we will use the notation a/p for dip
directioddip angle: the reader should be aware that there are a number of
alternative nomenclatures in current usage. In the field, the use of a
geological compass will provide direct readings of the dip direction and the
dip angle.
In general, a large number of alp data pairs will be obtained during the
course of a field survey. Consequently, it is useful to present these data in
a graphical form to aid rapid assimilation and understanding. Thus, we
wish to present information about planes in three-dimensional space on a