SMALL DAMS PETITS BARRAGES

downstream and bank to bank) can be taken. In the following figure are presented two
different types of benchmark used in earthfill dams.
Fig. 6.7 – Two types of benchmarks installed at the downstream slope.
For small dams, the most common (and very often unique) measurement is settlement,
which in general changes very little after a few years. It is important to start the settlement
measurements as soon as the last layers of fill are compacted. The survey targets sealed into
the dam body are positioned on the crest of the fill or near it and also along the downstream
berm.
Measurement of the relative internal displacement of the foundation and earthfill using a
vertical device with several places that measure the settlement each 5 m, for instance, it is
usually more recommended for medium and large dams, and it is not usual to small dams.
6.4.2 Guidelines on Dam Monitoring
Recommended Types and Amount of Instruments
The monitoring of small dams usually have to reduce to a minimum the cost with the
instruments to be installed, but installing them where it is really important and essential to the
dam supervision safety. In order to have a good quality system and with a minimum of
instruments, in the following paragraphs are presented some recommendations about the type
and number of devices to be installed, for dams with PIC (Potential Impact Classification) class
3 and with 100 to 300 m in length. For “Normal Geology” it means when it is enough to monitor
only one foundation layer with piezometers, for instance the contact soil-rock, and “Special
Geology” when it is convenient to instrument two different levels at the foundation, as a
consequence of the existence of different horizontal layers and pervious materials at the
foundation.
Table 6.3 – Recommended types and amount of instruments for small earthfill or rockfill
dams (PHC = 3)
Instrument
Location Normal Geology Special Geology
(Parameter)
Piezometer
(uplift water
Right abutment 2 5
Central section 3 to 5 6 to 8
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