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The BOR-EX allows for measurements of precise longitudinal dis-placements in rock, soil and concrete structures. Typically it is used for monitoring settlement in foundations, subsidence above tunnels, displacements of retaining structures, and deformations in underground openings.  

The borehole extensometer includes anchors, extension rods and a reference head. The anchor is connected to the head of the instrument by extension rods typically placed within a protective sleeve. This sleeve ensures that the rods can move freely and translate all movement of the anchor to the tip of the rod. Movement of the rock or soil mass relative to the head can then be calculated by measuring the displace-ment of the tip of the extension rod to a reference plate lo-cated in the head of the extensometer.

Three head types are available: one that allows mechanical reading only (BOREX-M), one that allows electrical reading only (BOREX-E), and one that allows simultaneous mechani-cal and electrical readings (BOREX-E/M). The mechanical reading is performed with a depth gauge or with a dial indica-tor, whereas electrical readings are done using vibrating wire or potentiometer sensors.