Crackmeters

Crackmeters are devices used to measure the opening displacement of cracks in rocks, concrete, and other materials. They are common in geotechnical, civil, and mining engineering to monitor crack growth, assess stability, and inform maintenance and hazard assessment. Readings are typically reported as crack opening displacement over time.

There are several technologies. Electrical resistance crackmeters use wires or foil gauges anchored across a crack; as the gap widens, resistance changes to yield the opening amount. They are simple and inexpensive but can be sensitive to temperature and moisture. Vibrating-wire crackmeters use a small spring-loaded element whose tension changes with crack opening; they are durable and well suited to long-term monitoring, with readings obtained from a data logger or remote system. Fiber-optic crackmeters employ optical fibers with Bragg gratings or Fabry-Perot cavities to measure distance or strain across a crack; they are immune to electromagnetic interference and suitable for remote or harsh environments.

Installation typically involves placing anchors or clamps on opposite sides of the crack and to the transducer, with calibration to convert measurements to crack width. Probes are often extended along the crack length, and temperature effects may require compensation.

Applications include monitoring rock slopes and underground excavations, dam and wall cracks, concrete structures, and subsidence or deformation due to loading. Readings are analyzed for trends, sudden changes, or correlations with other data to assess stability and trigger warnings if needed.

Advantages include real-time data and direct measurement of opening; limitations include installation difficulty, potential sensor drift or damage, environmental exposure, and the need for regular calibration.