Monitoring

Movement (Deformation) Monitoring:

When a client instructs us to monitor for deformation (movement) of a structure, we use another instrument specifically built for this purpose. It's slightly more accurate, capable of 0.5 second angle accuracy, this equates 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).

The use of these instruments gives us the ability to prove even the most minute movement in any structure. Not only this but a dedicated spreadsheet written specifically for each project by our chief surveyor and company owner (Matthew Harrison) coupled with multiple measures taken to the same reference points, gives us the ability to obtain sub millimetre accuracy and repeatability.

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 nail in the ground will suffice but these can be subject to slight movements that would be unacceptable in monitoring. Generally we'll dig footings and concrete 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 next, sometimes even requiring a robotic total station to be setup permanently to measure continuously to various prisms mounted on the structure in question. This enables the results to be displayed 'real-time' on a webpage for anyone to see, as well as an automated alert system put in place to ring alarm bells when movement over a given amount is detected. These systems are generally used on larger, high risk projects as they are expensive to set-up and require security personal to guard the equipment full time.