Borehole extensometers comprise of rods and anchors installed in a borehole to monitor displacements at various depths. A pre-set length of measuring rod is inserted into a nylon tube to avoid soil friction with the rod tip fixed to a groutable steel anchor.
Preassembled fibreglass rods are coiled at the factory and shipped ready for installation. The complete assembly is inserted into the borehole and then grouted, fixing the anchors to the rock or soil but allowing free movement of each rod within its sleeve.
Relative movements between the anchors and the reference head may be measured manually with a caliper or automatically using linear transducers that are fixed to the reference head and connected to a datalogger for remote monitoring.