Civil Engineering Reference
In-Depth Information
17.8
Monitoring of Water Level and Water Pressure
Monitoring of water level and water pressure in boreholes is the most important means
for the observation of groundwater conditions. A detailed description of the installa-
tion and instrumentation of groundwater observation stations and wells is given in EN
ISO 22475 (2007).
Groundwater monitoring can be carried out by means of water gauges, also referred to as
“piezometers”, or pore pressure transducers, which are inserted into boreholes in which
backfilled standpipes are installed. At the bottom of the standpipe, a filter with perforated
casing consisting of sand or fine gravel must be installed to avoid penetration of particles
into the measuring system. The filter must be located entirely in the rock mass layer in which
the groundwater level or the water pressure needs to be monitored. Above the filter the
standpipe must be backfilled by a sealing consisting of clay or bentonite to avoid pressure
compensation in the borehole outside the pipe. The particle size distribution of the filter
must be adapted to the sealing and the surrounding rock mass to be stable against clogging.
In multi-aquifer formations, for each groundwater story a separate borehole should be car-
ried out. If several standpipes are installed in one borehole, it must be ensured that the
different groundwater stories are sealed off from one another to avoid hydraulic connection.
Figure 17.25, for example, shows a groundwater measuring system consisting of a hand
reel with a tape of up to 200 m length onto which a water gauge is attached. The gauge
is lowered into the standpipe consisting of a measuring tube with screwed telescoping
sleeves. As soon as the electrode installed in the gauge touches the water table a circuit is
closed and a light signal is released. The depth of water table in relation to a fixed point
at the ground surface then can be read from the tape.
Figure 17.25
Measuring of groundwater table using a water gauge (Glötzl GmbH)
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