Bore hole extensometer can be of single point or multi point installed in a single hole, quantity as many as five can easily be installed in a NX size hole (Ø76mm).
The basic principle of measurement is; one anchor is grouted/ fixed to a required depth in a bore hole and other end is extended through S.S. rod at the surface of bore hole. The depth
of anchored end is selected just beyond the expected movement
zone. The anchoring is possible by groutable or expandable anchor. Fiber glass rod
Expandable anchors are available in much design like bolt type expandable anchors, snap ring anchors and so on. Most extensively used anchors are of groutable type. Bolt type expandable anchors are useful up to a maximum of two point bore hole extensometer only. Movement measurement can be done either with depth micrometer or dial gage where as vib. wire or potentiometric sensors are available for remote data.
