Site Investigation - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 383

Discontinuity aperture
Many attempts have been made to measure discontinuity apertures in the field and the
laboratory. According to the conventional mapping method, apertures can be measured
by a feeler gauge or a rule (ISRM 1978e). Another approach is to scan the two surfaces
of an open discontinuity using a surface profiler (Brown & Scholz 1985, Keller &
Bonner 1985, Brown et al. 1986). Alternatively, a material such as Wood's metal, poly-
urethane grout, cement grout, silicone polymer resin, fluorescent epoxy or a silicone
rubber mixture is injected into the open discontinuity and aperture is determined from
the resultant cast (Gale 1987, Pyrak-Nolte et al. 1987, Gentier et al. 1989, Hakami &
Stephansson 1995, Hakami & Larsson 1996, Kostakis et al. 2003). More refined tech-
niques are analyzing digitized images of transparent casts of natural discontinuities to
obtain aperture distributions (Hakami 1995, Persoff & Pruess 1995, Isakov et al. 2001)
or the use of X-ray scanners for aperture measurements in the laboratory (Keller 1998).
Extent and persistence of discontinuities
Exploration adits and shafts as well as test excavations allow an exposure of the rock
mass in three dimensions. The mapping of the roof, of the sidewalls and, where possi-
ble, also of the invert can provide valuable information on the extent and persistence of
discontinuities (Fig. 13.25).
Figure 13.25 Exploration adit as a three-dimensional exposure of a rock mass (Wittke 1990)