Environmental Engineering Reference
In-Depth Information
Figure 20.26.
Borehole inclinometer (Soil Instruments Ltd., 1985).
The authors' experience is that a high degree of reproduceability is possible, although
considerable care must be taken with instruments significantly off the vertical. The
authors also feel that inclinators are best utilised to show distinctive trends in shear dis-
placement rather than small displacements of 1-2 mm.
Hanna (1985) indicates that the grooves in the casing may spiral, and individual lengths
need to be checked for this.
ANCOLD (1983) describe an inclinometer which can be used in smooth pipe. It con-
tains two servo-accelerometers. The device was developed for monitoring displacements
of the face of concrete face rockfill dams and has an accuracy of
3 mm.
Borehole inclinometers are a valuable tool for investigating dams with potential insta-
bility, or large internal deformations. However, as for piezometers, great care must be
taken in drilling the holes using dry drilling methods and grouting around the tubing in
stages using a tremie system, so the core is not damaged by hydraulic fracture.
20.4.6
Thermal monitoring of seepage
There have been relatively recent developments in detection of localized seepage using
thermal measurement techniques. These rely on the difference of temperature of the reser-
voir water and that in the dam generally. Hence if the reservoir water is colder localized
