Site Investigation - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 364

Figure 13.9 Determination of discontinuity orientation on an oriented, vertically drilled core
(Wittke 1990)

In principle, discontinuity spacing values may also be measured on drill cores. From the
apparent spacing d ij between two discontinuities Di i and D j measured along a scanline,
the true spacing s ij can be calculated as follows (Wittke 1990):

(13.1)

in which is the average angle between the discontinuities and the core axis (Fig. 13.10).

With respect to roughness, drill cores allow only statements which apply to a very small
scale. Also, the aperture of discontinuities intersected by drill cores cannot be reliably
estimated.
Soft, cohesive fi llings of discontinuities are often washed away during the drilling pro-
cess. However, traces of the fi llings may remain which, whenever possible, should be
described with regard to mineralogy, particle size and strength (ISRM 1978e).