Environmental Engineering Reference
In-Depth Information
readings are obtained by survey of the top of the coring and lowering a measuring torpedo
down the tube. The torpedo is provided with spring-loaded arms which engage the lower
ends of the cross-arm pipes. It is supported on a measuring tape, and can allow accuracy
of measurement of
1 mm are claimed). Settlements as
much as 15% can be accommodated and the testing can be installed to depths of at least
100 m. The tubing does not have to be vertical (Soil Instruments Ltd., 1985, indi-
cate
3 mm (accuracies as small as
25° from vertical is allowable).
The USBR instrument cannot be installed down a borehole, only in fill as it is con-
structed.
Figure 20.22 shows a magnetic version of the instrument which uses ring magnets
instead of the cross-arms.
Figure 20.22.
Magnet (Soil Instruments Ltd., 1985) settlement gauges: (a) magnets embedded as earth-
fill is placed; (b) magnets placed in a borehole.
