A monitoring survey is an effective tool to use for monitoring building movement, a process involving monitoring specific locations at regular intervals. used to see if or how far a building or structure has moved over time. These intervals are either daily, weekly, fortnightly, monthly or yearly, depending on the nature of the project. There are different techniques, amounts of detail, and types of equipment involved in carrying out a monitoring survey, with four most common types:
- Laser Scanning: the structure is scanned using a laser, capturing millions of points which can be compared over time to ascertain any movement.
- Fixed Position Monitoring: this involves identifying fixed points on the structure and observing their movement over time.
- Tilt Sensor Monitoring: this involves checks to see whether a wall tilts to a particular direction, and to what degree.
- Crack Monitoring: this is done to observe if a crack on the building undergoing a Monitoring Survey is opening or closing over time
Why are Monitoring Surveys Useful?
Typically, monitoring surveys are carried out on a structure if a structural engineer determines that it is at risk of moving. They help with detection of the early signs of a building’s movement to avoid disaster. If heavy construction work is ongoing – like basement excavation, piling, or demolition – carrying out a monitoring survey would be beneficial. Monitoring surveys offer the chance to prevent further movement because if the structure collapses, the repair costs would be higher than to have it checked. There could be a potential loss of life or properties if a building or structure moves or tilts too far from its original position.
How are Monitoring Surveys Carried Out?
- Laser Scanning
The structure is scanned using a laser, and by comparing scans over a time period, a “heat map” can be produced showing any areas of movement. Compared to fixed point positioning, laser scanning will scan the whole structure rather than just a few specific points.
- Fixed Position Monitoring
The local survey control network and monitoring targets should be set up and attached to the structure at predetermined spots with drilled screws or glue.
The local survey control network is made up of reflective target stickers or survey prisms (survey targets), but these will be placed away from the structure. A total station – a highly accurate optical tool used for measuring angles and distances – would be used to carry out the survey. Usually mounted on tripods, a total station operator uses the tool to observe the survey points through a lens.
- Tilt Sensor Monitoring
Tilt sensors accurately measure angles and send the data to a central hub at regular intervals. They are usually attached to the wall of the building involved in the monitoring survey. Tilt limits can be set, where an alarm will be triggered if a certain limit is reached.
- Crack Monitoring
There are two methods to monitor a crack to detect motion:
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- Crack Gauges
Crack Gauges should be glued or fixed on both sides of a crack so that as it opens or closes, its movement can be observed on the gauge.
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- Monitoring Studs
Two Monitoring Studs should be glued to both sides of a crack and a calliper should be used to record the distance between them. This distance should be periodically checked and any changes that indicate that the crack has either widened or closed should be recorded.
At Lucion, we offer reliable, accurate and precise monitoring surveys. Contact us for help with your project.
