Geoscience Reference
In-Depth Information
3.10 Discontinuity scale effects
The scale effects are an order of magnitude only, with significant overlap.
Table 3.10 Discontinuity scale effects.
Discontinuity group
Typical range
Typical scale
Defect thickness
2 mm to 60 cm
20 mm
Bedding, foliation, jointing
0.2 m to 60 m
2 m
Major shear zones, seams
20 m to 6 km
200 m
Regional fault zones
2 km to 600 km
20 km
3.11 Rock defects spacing
The rock defects are generally described using the following sequence of terms.
[Defect Spacing]; [Depth (metres from surface), Defect Type, Defect Angle (degrees
from horizontal), Surface roughness, Infill, Defect thickness (mm)].
Table 3.11 Defect spacing.
Description
Spacing
Extremely closely spaced (crushed)
20 mm
<
Very closely spaced
20 mm to 60 mm
Closely spaced (fractured)
60 mm to 200 mm
Medium spaced
0.2 m to 0.6 m
Widely spaced (blocky)
0.6 m to 2.0 m
Very widely spaced
2.0 m to 6.0 m
Extremely widely spaced (solid)
6.0 m
>
3.12 Rock defects description
The defects are also called discontinuities.
The continuity of discontinuities is difficult to judge in rock cores. An open
exposure is required to evaluate (trench, existing cutting).
Even in an existing cutting, the defects in the vertical and on lateral direction can
be measured, but the continuity into the face is not readily evident.
Table 3.12 Rock defect descriptors.
Rock defects
Descriptors
Typical details
Joints
Type
Bedding, cleavage, foliation, schistiosity
Joint wall separation
Open (size of open) or closed (zero size) filled or clean
Roughness
Macro surface (stepped, curved, undulating.
irregular, planar) micro surface (rough, smooth, slickensided)
Infilling
Clays (low friction); Crushed rock (medium to high friction);
Calcite/Gypsum (May Dissolve)
Faults and
Extent
Thickness
Shear zones
Character
Coating, infill, crushed rock, clay infilling
 
 
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