Magnetic Mastery: Introducing Our Magnetic Extensometer

​Magnetic extensometer GXM system monitors settlement and heave typically in deep excavations, dams, foundations, and embankments.

An access casing with multiple positioned magnetic targets on the exterior coupled to the surrounding soil is installed into a location to monitor movements down or up as settlement or heave occurs. A reed switch probe is lowered down the access casing to monitor the relative position of the magnetic targets via an activated buzzer and responding depth indicated on the tape.

Data obtained identifies the total amount, position and depth of the settlement that occurred. In stable ground the reference for depth of each magnetic target is the datum magnet fixed to the bottom of the access casing, in unstable ground the depths of the targets is referenced from the top of the casing, which is surveyed prior to readings being obtained.

Product Features

  • 70mm ABS inclinometer casing or 33mm access casing
  • Reed switch probe for readings (up to 200m depending on reel)
  • Plate magnet targets for settlement in fill
  • Spider magnet targets (3 leg or 6 leg) for in boreholes
  • Telescopic access casing for when lager movement is predicted

Product Benefits

  • Multiple variations and combinations of casing and targets to suit individual applications
  • Identifies depth, position and amount of settlement or heave
  • Can be used with and without a stable anchor point at base of casing
  • ±1mm accuracy


Magnetic extensometer systems can successfully be installed in a range of applications including boreholes, fill, and where inclination data is also necessary.

The GXM settlement monitoring range contains variants of the magnetic extensometer and associated magnetic targets to suit individual applications including variants with inclinometer casing as access to additionally monitor inclination, spider magnetic targets for borehole application, settlement plates for placement in fill, and telescopic casing where lager settlement or heave is expected.


Typical applications include:

  • Tunnelling
  • Mining
  • Deep excavations
  • Dam construction and monitoring
  • Displacement monitoring
  • Settlement monitoring
  • Rock displacement
  • Embankment monitoring
  • Retaining structures.

Geomotion offer installation and monitoring services to support this system. For more information please email or contact any of our locations.