Deformation monitoring (also referred to as deformation survey) is the systematic measurement and tracking of the alteration in the shape or dimensions of an object as a result of stresses induced by applied loads. Deformation monitoring is a major component of logging measured values that may be used for further computation, deformation analysis, predictive maintenance and alarming. Deformation monitoring is primarily related to the field of applied

surveying Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is ca ...

, but may also be related to civil engineering, mechanical engineering, construction, and geology. The measuring devices used for deformation monitoring depend on the application, the chosen method, and the preferred measurement interval.

Measuring devices

Measuring devices (or sensors) can be sorted in two main groups—geodetic and geotechnical sensors. Both measuring devices can be seamlessly combined in modern deformation monitoring. *Geodetic measuring devices measure georeferenced (relative to established locations outside the monitoring area) displacements or movements in one, two or three dimensions. It includes the use of instruments such as total stations,

levels Level or levels may refer to: Engineering *Level (instrument), a device used to measure true horizontal or relative heights *Spirit level, an instrument designed to indicate whether a surface is horizontal or vertical *Canal pound or level *Regr ...

, InSAR, and global navigation satellite system receivers. *Geotechnical measuring devices measure displacements or movements and related environmental effects or conditions without external georeferencing. It includes the use of instruments such as extensometers, piezometers,

pressuremeter A pressure sensor is a device for pressure measurement of gases or liquids. Pressure is an expression of the force required to stop a fluid from expanding, and is usually stated in terms of force per unit area. A pressure sensor usually act ...

s, rain gauges, thermometers, barometers, tiltmeters, accelerometers, seismometers, etc.

Application

Deformation monitoring can be required for the following applications: * Dams *Roads *Tunnels *Bridges and Viaducts *High-rise and historical buildings *Foundations *Construction sites *Mining *

Landslide Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated grade (slope), slope failures, mudflows, and debris flows. Landslides occur in a variety of ...

areas * Volcanoes *Settlement areas *Earthquake areas

Methods

Automatic deformation monitoring device - Porto Metro

Deformation monitoring can be manual or automatic. Manual deformation monitoring is the operation of sensors or instruments by hand or manual downloading of collected data from deformation monitoring instruments. Automatic deformation monitoring operation of a group of software and hardware elements for deformation monitoring that, once set up, does not require human input to function. Note that deformation analysis and interpretation of the data collected by the monitoring system is not included in this definition. Automated deformation monitoring requires instruments to communicate with a base station. Communication methods used include: *Transmission cable ( RS-232, RS-485,

fiber optics An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to ...

) *Local area network (

LAN Lan or LAN may also refer to: Science and technology * Local asymptotic normality, a fundamental property of regular models in statistics * Longitude of the ascending node, one of the orbital elements used to specify the orbit of an object in sp ...

) *Wireless LAN ( WLAN) *Mobile communication ( GSM,

GPRS General Packet Radio Service (GPRS) is a packet oriented mobile data standard on the 2G and 3G cellular communication network's global system for mobile communications (GSM). GPRS was established by European Telecommunications Standards Insti ...

, UMTS) * WiMax

Regularity and scheduling

The monitoring regularity and time interval of the measurements must be considered depending on the application and object to be monitored. Objects can undergo both rapid, high frequency movement and slow, gradual movement. For example, a bridge might oscillates with a period of a few seconds due to the influence of traffic and wind and also be shifting gradually due to tectonic changes. *Regularity: ranges from a days, weeks or years for manual monitoring and continuous for automatic monitoring systems. *Measurement interval: ranges from fractions of a second to hours.

Deformation analysis

Deformation analysis is concerned with determining if a measured displacement is significant enough to warrant a response. Deformation data must be checked for

statistical significance In statistical hypothesis testing, a result has statistical significance when it is very unlikely to have occurred given the null hypothesis (simply by chance alone). More precisely, a study's defined significance level, denoted by \alpha, is the p ...

, and then checked against specified limits, and reviewed to see if movements below specified limits imply potential risks. The software acquires data from sensors, computes meaningful values from the measurements, records results, and can notify responsible persons should threshold value be exceeded. However, a human operator must make considered decisions on the appropriate response to the movement, e.g. independent verification though on-site inspections, re-active controls such as structural repairs and emergency responses such as shut down processes, containment processes and site evacuation.

References

:* Literature, B. Glisic and D. Inaudi (2008). ''Fibre Optic Methods for Structural Health Monitoring''. Wiley. :* Literature, John Dunnicliff (1988,1993). ''Geotechnical Instrumentation For Monitoring Field Performance''. Wiley.