Rod extensometers are installed in borehole to monitor displacements at various depths using rods of different material and lengths. A pre-set length of measuring rod is inserted into a nylon tube to avoid soil friction and its tip is fixed to a steel groutable anchor.
Preassembled fibre glass rods are coiled at 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 are measured manually with caliper or linear transducers, assembled on the reference head for remote monitoring.