Single & Multi Point Borehole Extensometer

Bore Hole Extensometer is used for measuring and monitoring of rock and soil movements in dams underground activities, slope stability etc. The single rod extensometer employs a rod, anchored at one end of a drill hole, passing into a reference tube fixed in the hole collar. Relative movement between the end anchor and the reference tube is measured witheither a dial depth gauge or an electrical transducer, inserted through the reference tube, registering on to the free end of the rod. A range adjustment screw fitted to the end of the rod extends the reading range beyond that of the dial gauge. Multiple rod installations monitor displacements at various depths using rods of varying lengths. Several single rod units may be installed in close proximity in drillholes of smaller diameter. Alternatively, severalrods may be installed side by side in a single larger hole. Each rod is individually isolated by a close fitting plastic sleeve. The complete assembly is grouted in place, fixing the anchors to the rock or soil but allowing free movement of each rod within its sleeve. A multipoint reference housing receives all rods from one drill holeinstallation. Facilities are available for manual or remote readout. A visual alarm system to give warnings of excessive movements is also available, which can also be used for indicating when a reading is to be taken. Rod extensometer units can be surface mounted to measure displacements across tension cracks or joints or can beburied in fill or cast in concrete.