Civil Engineering Reference
In-Depth Information
Figure 13.30
Transformation of
and
if vertical orientations appear (Wittke 1990)
α
β
Discontinuity spacing
A direct spacing measurement of discontinuities during mapping using the scanline
technique (Fig. 13.23), as recommended by the ISRM (1978e), bears the risk that not
every discontinuity can be assigned to a set immediately after measuring its orienta-
tion. It is recommended therefore not to evaluate spacing data of discontinuities before
a detailed mapping and statistical evaluation of pole plots is available, since spacing
measurement on the basis of a mapping is more objective and less time-consuming than
direct spacing measurement during mapping (Wittke 1990).
To evaluate a mapping with respect to discontinuity spacing, at first the traces of dis-
continuities belonging to the individual discontinuity sets should be marked with differ-
ent colors. Then, the apparent spacing values of each discontinuity set should be deter-
mined along scanlines which should be oriented perpendicular to the mean direction of
the discontinuity traces of each set. Subsequently, the apparent spacing values must be
converted into true spacing values from which frequency distributions are established
and statistically evaluated (Wittke 1990).
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