Extensometers are used to measure movement

Vibrating Wire Displacement Transducer.

The displacement transducers are available in various operating ranges and the square of the frequency signal is directly proportional to the amount of displacement. These units are used in crackmeters and rod extensometers.

Vibrating Wire settlement system

The system uses a vibrating wire transducer buried within fill. The transducer is connected to a pair of fluid filled small bore tues which lead to a datum header tank located outside of the construction area. Settlement or heave of the buried transducer cause a change in applied fluid head on the transducer from the fixed datum allowing settlement to be determined.

Vibrating Wire Soil Extensometer.

Soil extensometers are used to measure large deformations typically in embankments, and generally are installed in a chain so that the strain profile of a longitudinal section in embankment or dams can be determined.

Load Anchor Extensometer.

The extensometer is a similar size to that of a conventional rock anchor used for slope stability and anchoring in tunnels and excavations. The extensometer contains 4 internal rods such that the relative extensions of the unit can be determined. The unit is tensioned in the same way as working rockbolts and is acted on by the same forces as the working rockbolts. The relative movement of the inner rods is normally monitored using a depth gauge, although this can be automated using potentiometric displacement transducers.

Mechanical Rod Extensometer

Rod extensometers are installed generally within boreholes to measure settlement or heave. Extensometer can have multiple anchors fixed within the borehole, each connected via rods to the reference head. Relative movement of the anchors to the reference head is determined by manual measurement at the head using a digital depth gauge.

Vibrating Wire Rod Extensometer.

The vibrating wire rod extensometer is similar to the mechanical rod extensometer, but instead of monitoring movement manually, it is fitted with Vibrating wire displacement transducers allowing readings to be obtained remotely and for data logging.

Magnet Extensometer.

A magnetic extensometer consists of an thick wall tube (or inclinometer tube) onto which annular magnetic targets are installed at various depths within a borehole. Normally, one datum magnet is installed at the distal end of the tube in strata which is considered to be stable and outside of any influence of construction induced settlement. A reed switch probe is used to determine the postion of the magnet targets within the borehole and is referenced to the datum magnet, thus determining the settlement profile within the borehole.

Tape Extensometer.

The tape extensometer is used to measure changes in distance between two fixed points. Typically this is used to measure the profile of tunnels where multiple reference points are installed on a cross section. Successive readings  enable a profile of tunnel deformation with time to be determined.