Environmental Engineering Reference
In-Depth Information
seepage flow. “Blind Spots” are sometimes present e.g.:
- Filters only taken to full supply level, leaving the dam susceptible to internal erosion
under flood conditions or if the dam crest is cracked and settles under earthquake load-
ing. The authors have seen engineers modelling the rate of wetting of the soil related to
the permeability of the core, arguing the flood loading is too short to cause saturation.
It must be recognised that the crest of the dam is susceptible to cracking due to differ-
ential settlements, desiccation, and earthquake and piping can develop very quickly
through the cracks. The permeability of the compacted soil is irrelevant in this
situation.
- Filters not being taken around conduits which pass through the dam. Figure 10.46
shows Zoeknog dam which failed by piping. The filter stops half way up the conduit
and fails to protect the areas adjacent to the lower part of the conduit where com-
paction in the narrow (1 m wide) zone would have been difficult and arching could
have led to low vertical stresses, making hydraulic fracture likely.
Figure 10.46.
Zoeknog Dam - Details of filter near the conduit (Keller, 1994).
