Extensometers are used to measure movements of soil and rock along a single axis. Applications for extensometers include:
The Rod Extensometer consists of anchors set at specified depths, rods inside protective tubing, and a reference head. Measurements are taken at the reference head by micrometer or by an electric sensor.
The Magnet Extensometer consists of a series of magnets that are installed with an access pipe. The magnets are anchored at specified depths. Measurements are taken by lowering a probe through the access pipe to detect the depth of the magnets.
The Sondex system consists of a series of rings attached to a flexible corrugated pipe. Measurements are lowering a probe through an inner access pipe to detect the position of the rings.
The Borros Anchor Settlement Point settlement point is used to monitor settlement of soil under an embankment. It consists of an anchor and and two concentric riser pipes that are extended up through the embankment. Measurements are made with a graduated tape and optical survey.
The Settlement Hook is used to monitor settlement in telescoping inclinometer casing. Measurements are taken by lowering the hook device through the casing. The hook is catches on the telescoping joints and a depth reading is obtained from a steel tape.
The soil strainmeter is used to monitor spreading of embankment material. It is typically installed in trenches.
The tape extensometer is used to monitor convergence in underground openings, such as tunnels.