Environmental Engineering Reference
In-Depth Information
- seepage water chemistry and pH;
- seepage water turbidity measurement;
- seismic ground motion.
20.3.2
Some examples of well instrumented embankment dams
Figures 20.5 to
20.8
show examples of quite intensive monitoring for Prospect Dam (a
100 year old 35 m high puddle core dam, constructed of erodible soil with no filters in the
original construction); Cethana Dam, a 110 m high CFRD; Trinity Dam (150 m high earth
and rockfill) and Svartevann Dam (129 m high earth and rockfill) (all from ICOLD 1989).
Table 20.11
is based on ANCOLD (2003) guide for the frequency of monitoring for
embankment dams based on the consequences of failure category. These would be appro-
priate for a dam without known deficiencies, and after first filling.
During construction and first filling, more frequent readings of monitoring instruments
would be appropriate.
Table 20.12
gives an example for a large embankment dam, showing how the frequency
of readings changes as the satisfactory performance of the dam is confirmed.
20.3.3
Dam safety inspections
Dam safety inspections are the most important part of any dam surveillance program. As
pointed out by ANCOLD (2003), inspections should be carried out by experienced people,
Figure 20.5.
Monitoring for Prospect earthfill dam (ICOLD, 1989). (a) Cross section showing old dam
and fill buttressing. (b) Cross section showing monitoring systems. (c) Rubble filled
drainage tunnel. (d) Puddle clay core. (e) Clay shoulders. (f) Alluvial clay foundation. (g)
Filter drainage cutoff trench along downstream foundation extending to rock. (h) Vertical
sand drains. (i) Lateral drains. (j) Filter zone. (k) Stabilizing fill material (shale) constructed
in two stages. (l) Inclinometers. (m) Surface settlement points. (n) Seepage collection and
measurement. (o) Pneumatic and electric piezometers. (p) Foundation settlement installa-
tions. (q) Open standpipe piezometers.
