Environmental Engineering Reference
In-Depth Information
Hanna (1985), ANCOLD (1983), US Department of Interior (1981) and Bureau of
Reclamation (1987) give details of the instruments used. Up to date information can be
obtained from instrument manufacturers. A brief overview of the types of instruments
used follows.
20.4.5.1
Vertical displacements and deformation
Vertical displacements and deformations are measured using mechanical or magnetic
devices which are either embedded in the fill as the dam is constructed, or installed in
boreholes. Figure 20.21 shows the principle of the USBR type mechanical device.
The base tube is installed in the dam foundation and a cross-arm anchor placed in the
dam foundations. Telescoping tubing is placed in the fill as the dam is constructed, with
cross-arm anchors being installed at intervals to allow differential settlement within the
fill to be measured. Typically cross-arms will be spaced at 2 m or 3 m intervals. Settlement
Figure 20.21.
USBR type cross-arm settlement gauge.
