Civil Engineering Reference
In-Depth Information
Figure 17.9
Sliding micrometer (Solexperts AG)
Settlement gauges
While extensometers can be used in vertical, inclined and horizontal boreholes, settle-
ment measurement devices, such as magnetic settlement gauges, metal plate settlement
gauges and mechanical settlement gauges, can only be used to measure vertical dis-
placements in vertical boreholes.
Figure 17.10, for example, shows a magnetic settlement gauge system consisting of a
hand reel with a tape of up to 100 m in length on which the gauge is attached. In a bore-
hole with a diameter of up to 200 mm a plastic leading tube equipped with magnetic
rings is grouted. Displacements in the rock mass are transmitted directly to the mag-
netic rings. The change of position of a magnetic ring is recorded with the settlement
gauge. As soon the gauge passes the magnetic fi eld of the ring a light signal is released.
Then the location of the ring can be detected and its depth in relation to a fi xed point
at the ground surface can be read at the tape. Under favorable conditions an accuracy
of
2 mm is attainable.
With metal plate settlement gauges and mechanical settlement gauges the same order
of accuracy can be achieved.
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