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Remote Tilt Monitoring By NSL Monitoring
Tilt monitoring is primarily used for measuring the vertical and horizontal rotation of structures on projects involving deep excavation, heavy demolition or blasting near structures of concern.
Construction operations frequently have sensitive thresholds for movement on and around the site. Tilt meters are a monitoring solution in such circumstances and the Tilt Meters by NSL have the additional advantage of being able to operate continuously as part of our Remote monitoring system.
Incorporating dual-axis motion sensors with the unit allows the evaluation of structure motion, with results delivered via a customized client website. The sensitivity of our equipment enables precise motion detection. By updating results at regular, predetermined intervals, there is no chance of movement occurring without notification.
Our tilt meter system is used to record variance in the inclination of a structure. It is particularly useful in early or historic construction. Variance in inclination is fairly common in such structures and it is important to monitor even slight change. Buildings with non-square or out-of-level walls are not necessarily structurally unsound, but they do warrant monitoring since they may have a greater potential for damage.
Data is typically collected at eight-hour intervals and recorded to a histogram. This frequency of collection will ensure that the non-rechargeable batteries last for around 8-9 months. Web-based presentation and MS Excel graphs are generated for degrees of tilt.
NSL tilt meters are inertially referenced to the most stable baseline of all, the vertical gravity vector. They provide a precise, dependable record of all angular movements with respect to gravity. They can minimize the time and expense spent continuously surveying benchmarks and other data. Simply install the tilt meters and begin your measurements. Rotations induced by settlement or loading can directly be converted to displacements, moduli, movements, and shears using standard engineering formulae.
Tilt meters can also be used for construction safety. Excessive structural or foundation movement during construction or other vibration-inducing events is a precursor to structural failure. Continuously recorded data provides a permanent record of events.
Monitoring criteria for tilt movement at residential premises
There is no standard method for classifying the level of impact caused by tilt. However, Australian Standard AS 2870 - 1996 indicates that local deviations in vertical or horizontal slope of more than 1 in 100 (10 mm/m), will normally be clearly visible and that slopes greater than 1 in 150 (approximately 7 mm/m) are undesirable. However, it is recognised that structures are constructed to varying levels of accuracy.
As reported by Burton (1995), research commissioned by the Mine Subsidence Board in 1991 indicated that a sample of 83 dwellings built at Woodrising in the preceding ten years in areas unaffected by mining, had a mean deviation from level of 2.39 mm/m, with a maximum deviation of 8.7 mm/m. The Mine Subsidence Board, in its Annual Review (1992), published further details of the research project. A review of the distribution of measured tilts arising from this and other pre-mining surveys, indicates that 21% of 156 houses had tilts of more than 4 mm. The maximum tilt measured at a building prior to mining was 15 mm/m, with nine cases being reported between 9 mm/m and 15 mm/m. The acceptable change in tilt, due to mining, will thus vary from case to case and will be dependent upon the tilts existing before mining occurs. The Mine Subsidence Board has adopted the policy that tilts caused by mine subsidence, which affect serviceability, constitute impact that is to be compensated. When the tilts are between 4 mm/m and 7 mm/m, the Board recognises that the tilt, in some instances, could cause problems to roof drainage and wet area floors and, in those circumstances, would expect to carry out remedial works. It is also possible that some adjustment could be required to doors and windows.
There appears to be a consensus that final overall tilts in buildings which are less than 7 mm/m are tolerable and that tilts above 10 mm/m are undesirable. Overall tilts in buildings less than 5 mm/m would generally have negligible impact on building structures though this level of tilt could affect swimming pools and could possibly affect roof, floor or land drainage systems, where existing gradients are less than normal design requirements.