Deformation monitoring

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 the application of stress to it. Deformation monitoring is a major component of logging measured values that may be used to for further computation, deformation analysis, predictive maintenance and alarming.

Deformation monitoring is primarily related to the field of applied surveying, but may be also related to the civil engineering, mechanical engineering, plant construction, soil and rock sta-bility mechanics.

The causes for deformation monitoring are changes in the bedrock, increase or decrease of weight, changes of the material properties or outside influences.

The used measuring devices (1) for a deformation monitoring depend on the application (2), the chosen method (3) and the required regularity (4).

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 displacements or movements in one, two or three dimensions. It includes the use of instruments such as total stations, levels and global navigation satellite system receivers.


 * Geotechnical measuring devices measure non-georeferenced displacements or movements and related environmental effects or conditions. It includes the use of instruments such as extensometers, piezometers, rain gauges, thermometers, barometers, tilt meters, accelerometers, seismometers etc. Or refer to geotechnical sensors for more detail.


 * Other techniques e.g. radar measuring devices.

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 and Volcanoes Slopes
 * Settlement areas
 * Earthquake areas

Methods
Deformation monitoring can be made manually or automatically.


 * Manual deformation monitoring is the operation of sensors or instruments by hand for the purpose of deformation monitoring.


 * An automatic deformation monitoring system is a group of interacting, interrelated, or interdependent software and hardware elements forming a complex whole 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. An automatic monitoring system may be used for periodic or continuous monitoring.

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.

Risk management
Deformation monitoring systems provide a proactive control of a hazard related to possible change or failure of a structure. Policyholders can reduce risk exposure before and during construction and throughout the lifecycle of the structure and hence decrease the insurance premium. Refer to Risk Management for more detail.