Environmental Engineering Reference
In-Depth Information
TYPICAL
EXTENT/OCCURRENCE
DEFECT NAME
DESCRIPTION
FORMED BY
Almost planar surface or crack, across which the
rock usually has little tensile strength. May be open,
air or water-filled, or filled by soil substance, or rock
substance which acts as cement. Joint surfaces
may be rough, smooth or slickensided.
From less than 1 metre, up
to 10 metres.
Shrinkage on cooling (igneous
rocks). Extension or shear (any
rocks) due to tectonic stresses,
or unloading.
JOINT
Joint
Zone with roughly parallel almost planar boundaries,
of rock substance cut by closely spaced (often
<50mm) joints and or cleavage surfaces. The
surfaces are usually smooth or slickensided and
curved, intersecting to divide the mass into lenticular
or wedge-shaped blocks.
More than 10 metres, up to
kilometres.
Faulting, during which small
displacements occurred along
slickensided surfaces distributed
across the width of the zone.
SHEARED
ZONE
(FAULT) (1)
(3)
Seam with roughly parallel almost planar boundaries,
composed of usually angular fragments of the host
rock substance. The fragments may be of gravel,
sand, silt or clay sizes, often mixtures of these. The
finest fragments are often concentrated in thin layers
or 'slivers' next to and parallel to the adjacent rock.
Slickensides are common in the sliver zones and
along the rock boundaries.
More than 10 metres, up to
kilometres.
Faulting, during which relatively
large displacements occurred
within the zone.
CRUSHED
SEAM
(FAULT) (1)
Seam of soil substance, usually with very distinct
roughly parallel boundaries. Thin seams usually CH;
thick near-surface seams sometimes GC or GC-CL
(2).
Less than 10 metres, within
near-surface mechanically
weathered zone, or in rock
disturbed by creep or lands-
liding.
Migration of soil into an open
joint or cavity.
SOIL
INFILL
SEAM
(a)
EXTREMELY
WEATHERED
(OR ALTERED)
SEAMS
Joint
Seam of soil substance, often with gradational
boundaries. The type of soil depends on the
composition of the original rock.
Varies widely, but extremely
weathered seams are usually
within or near the near-
surface weathered zone.
Weathering (or alteration) in
place, of rock substance, usually
next to or within a pre-existing
defect.
(b)
NOTES
(1) In the geological sense,
(2) Group symbols as defined in the United States Bureau of Reclamation Earth Manual, 1963, Figure 3.1,
(3) A 'marker' feature, showing the nature of the displacements. Such features are observed only rarely in
sheared zones.
 
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