Site Investigation - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 376

Geomagnetic and geoelectric methods are affected by perturbations due to metallic ob-
jects. When applying geoelectric tomography, for instance, electroconductive bodies are
not allowed to be present. The range of exploration of this method is only about 2 m to
10 m (Girmscheid 2000).
More detailed information on seismic and other geophysical methods can be gathered
from the corresponding recommendations of the ISRM (ISRM 1981, ISRM 1988,
ISRM 2004, ISRM 2006).
From advancing drillings more reliable results can be obtained than by means of geo-
physical logging. Their conduction, however, is usually connected with interruptions of
the advance. However, if the drill carriage is moveable, the drillings can be carried out
simultaneously with advance (Maidl et al. 2008).

13.9 Mapping of Rock Surfaces

13.9.1 Mapping Techniques

General
A detailed mapping of rock surfaces exposed in test pits, exploration adits and shafts,
test excavations and the temporary face of a tunnel should include the following fea-
tures as far as possible (Wittke 1990, Wittke et al. 2002):

- rock types and rock boundaries (boundaries of layers),
- degree of weathering of the intact rock,
- orientation of discontinuities,
- location, spacing and trace lengths of discontinuities, that is, intersection lengths of
discontinuities with the exposed rock surface,
- roughness profiles of visible discontinuities,
- apertures of open or filled discontinuities,
- fillings and coatings of discontinuities,
- location and dimensions of large discontinuities and faults,
- location of seepage water access and quantity of discharge.
Apart from this, information on closely spaced discontinuities, which cannot be re-
corded individually for reasons of time, should be noted. Half-quantitative descrip-
tions such as “strongly jointed” or “strongly fractured” are sufficient in this context.
Furthermore, statements on roughness and the degree of weathering of discontinuity
surfaces should be made. Discontinuity fillings as well as types of discontinuities such
as joints, bedding- and schistosity-parallel discontinuities, if they can be unequivocally
recognized, should be characterized and labeled by color or signature. During mapping
samples for complementing laboratory tests should also be taken.