Extensometers

Are used to locate and measure movement along a single axis.

Magnetic Extensometers

  • Are used to measure and locate settlement and heave in soil and rock.
  • Typically used in excavations, embankments and foundations, behind retaining structures, and above tunnels and underground openings.
  • Comprise of a central access tube along the length of which magnetic targets are placed.
  • Are read manually using a Reed Switch Probe which is drawn through the central access tube, emitting an audible beep when it passes through a magnet. 
  • Readings are referenced to the base magnet and data obtained identifies the depth and position of settlement/heave as well as the total amount of movement.
  • Designed to be simple and accurate, and provide long term reliability at a low cost.
  • Can easily be extended upward with embankment construction or shortened with excavation.

Rod Extensometers

  • Are used to measure and locate settlement and heave in soil and rock.
  • Typically used in excavations, embankments and foundations, behind retaining structures, and above tunnels and underground openings.
  • Consist of a reference head and one or more in-hole anchors, each of which is placed at a known depth and connected to the reference head by either a rigid or flexible rod running inside a flexible sleeve. 
  • Can be read either manually using a depth indicator or dial micrometer, or automatically using an electrical displacement sensor.
  • Readings are referenced to the reference head and data obtained identifies the depth and position of settlement/heave as well as the rate and total amount of movement.

Soil Extensometers

  • Are used to measure lateral and longitudinal deformation of soil and rock.
  • Typically used in embankments, retaining walls and abutments, foundations, natural and cut slopes, quarry and mine excavations, and rock formations.
  • Consist of a displacement transducer connected to an extension rod and fixed between a pair of anchor beams. As movement occurs, the rod is moved within the housing. This movement is recorded by the displacement transducer. 
  • Are read automatically using the displacement transducer.
  • Sensors can be installed in a chain, with anchor bars connected together.
  • Data obtained identifies amount and location of displacement as well as the rate and total amount of movement.

Tape Extensometers

  • Are a portable device used for measuring displacement between reference eye-bolts fixed to a structure.
  • Typically used in tunnels and shafts, retaining walls and abutments, natural and cut slopes, quarry and mine excavations, and embankment dams.
  • The instrument consists of a precision punched steel tape incorporating a repeatable tensioning system and digital readout. Both the body and end of the tape have hooks which connect to eye-bolts between which the readings are to be taken.
  • The instrument is read manually. The user will connect each end of the tape to an eye-bolt, tension the instrument to the correct tension, and record the reading on both the tape and the digital display.
  • Data obtained accurately identifies displacement between points over time.