Environmental Engineering Reference
In-Depth Information
50
J
J
J
J
J
J
J
A
B
proposed
thrust face
J
J
J
45
C
joints with up to 50 mm of high
plasticity infill clay; dip 0º to 20º
downslope
J
J
cleavage,
strike and dip
J
SILTSTONE, slightly weathered to fresh,
very strong substance, but infilled joints
show that the mass has dilated
SILTSTONE, mainly fresh, very strong
0
123
4
5m
dam outline
Scale
bore hole
near-vertical joints with up to 10 mm of
infill clay and roots up to 5 mm
J
Figure 17.18.
Sturt River Dam, upper right bank and thrust block, part of log of foundation at initial design
level.
of altered or weathered rock. When steeply dipping, they may extend well below the oth-
erwise acceptable foundation surface. If it can be shown that they do not combine with
other defects to form kinematically feasible blocks or wedges, such features may simply
represent:
- Local zones of possible underseepage through potentially erodible materials, and
- If wide enough, local zones of unacceptably high compressibility.
In such cases they can be treated locally by excavation and backfilling with mortar or
concrete.
Figure 17.19
,
based on Nicol (1964), shows this form of treatment applied to a
fault (2 m to 6 m thick sheared, partly crushed zone) which passed beneath the valley floor
and left abutment at the 137 m high Warragamba Dam, near Sydney. In the valley floor
the dam excavation was taken down to below the zone. Beneath the left abutment the
zone was mined back for about 17 m from the main excavation and backfilled with con-
crete. In the right abutment the fault did not appear as a major defect; it may have been
represented by polished surfaces in a shale unit.
17.8.3.2
Rock found to contain weak defects which provide kinematically feasible
failure surfaces
As discussed in Section 17.8.1 rock containing weak defects which provide feasible failure
surfaces should not normally occur at or below the design foundation surface. When such
defects are found during foundation excavation, the design must be re-examined and, if
necessary, modified. The following are examples of this and illustrate some types of treat-
ment which have been applied.
