Civil Engineering Reference
In-Depth Information
As a consequence, drain holes with a spacing of 4 m were sunk from the crest to the
upper inspection gallery in order to drain the upper part of the dam. The draining
of the lower part of the dam was accomplished by drain holes with the same spacing
which were carried out from the upper to the lower inspection gallery (Figs. 24.5 and
24.20).
The new drainage system along with the inspection galleries led to a considerable reduc-
tion of wetted areas at the downstream side. Also the pore pressure acting on the dam's
base could be significantly reduced.
24.6
Monitoring
24.6.1 Program
The monitoring program consisted of temperature, pore pressure and displacement
measurements. For this purpose, 14 measuring cross-sections (MC) were installed (I to
IV, VI to XIII, T1 and T2 - Fig. 24.5).
In the middle of the valley, temperature sensors were arranged in MC T1, T2 and VI (T
in Fig. 24.5). These were installed in boreholes carried out from the crest and the upper
inspection gallery (Fig. 24.20). In MC I, II, IV, VI, IX, X, XII and XIII pore pressure
transducers were arranged (PPT in Fig. 24.5). These allow the distribution of hydraulic
heads in the dam and the rock foundation as well as the water pressure acting on the
dam's base to be determined. Extensometers were installed in MC III, VIII and XI (E
in Fig. 24.5), in order to measure the displacements of the dam at the foundation level
and of the foundation rock at the downstream side. The horizontal displacements at the
crest and in the upper inspection gallery were measured with the aid of a suspended and
inverted plumb line device, respectively, arranged in MC VII (PLD in Fig. 24.5).
In addition, the storage level and the air temperature were regularly recorded. Also,
seepage water measurements were carried out in the upper and lower inspection gal-
leries (1 to 6 in Fig. 24.5) and a crown alignment along the crest of the dam was
conducted.
24.6.2 Temperatures
Figure 24.23 shows the temperature distribution in the dam, measured in winter and
in summer. It is clearly visible that the temperature in the dam's core is nearly the same
in both seasons and takes on constant values in the range of 10 - 12°C. The largest
temperature differences appear at the downstream side and at the upstream side above
the storage level.
The long-term temperature changes at the crest are represented in Fig. 24.24. Between
summer and winter, temperature changes of some 16°C were measured.
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