Magnet extensometer is a system - based on British Building Research technique - for measuring either settlement or heave at various depths in soil, embankments, earthfill dams and dikes.
The system consists of access tube with external corrugate pipe, magnet rings, telescopic bottom section with datum ring and suspension head. Magnet rings (targets) are fixed, externally to the access tube, in the ground where movement may occur.
Magnet rings move together with surrounding soil along the axis of the access tube. Readings are obtained with a portable readout, lowering the reed switch probe through the access tube. Comparison of surveys taken over time provide profiles of ground settlement or heave.