Monitoring

The measurement and tracking of the alteration and shape or dimension of a structure/feature whether natural or man made.

Movement (Deformation) Monitoring:

When a client instructs us to monitor for deformation (movement) of a structure, we use specialist, high precision instruments specifically built for this purpose. The total stations we use are either 1" or 0.5", the later of which equates to to 0.24mm at 100m range which is only 2.4mm at 1000m range. That said measurements are usually limited to a maximum range of 50m, therefore giving us an angle accuracy of 0.12mm. The distance accuracy of these instruments remains almost the same as our standard total station, 1mm (+/- 1ppm). We also use Leica precise levels which have a resolution of 0.01mm and are capable of a 1km double run accuracy of 0.3mm when using our Invar levelling staffs. 

The use of these instruments gives us the ability to prove even the most minute movement in any structure. Total stations are used when interested in lean and level movement and precise levels are more accurate but for subsidence movement alone. Our MD (Matthew Harrison ) writes a dedicated spreadsheet for each project.

When preparing to monitor for movement over long periods (sometimes years at a time), great care has to be given to placing of control points. During a topographical survey a simple road-nail in the ground will suffice but these can be subject to slight movements that would be unacceptable in monitoring. Generally we will arrange to dig footings and concrete and place PGM (permanent ground markers) into areas of ground that will remain undisturbed for the duration of the project.

Each monitoring situation is very different from the last, sometimes even requiring a robotic total station be setup to measure continuously to various prism targets mounted on the structure in question. This enables the results to be displayed 'real-time' on a webpage as well as issue automated alerts when movement over a given amount is detected.

Leica TPS1200