Alternately referred to us Optical Survey Monitoring; this employs techniques using Survey Total Stations to read prisms or observation targets placed strategically on the surfaces or walls of buildings adjacent to a construction or excavation sites. The readings (coordinates) are then referenced to prisms installed in places beyond the activity’s area of influence. The measurements are then computed for movements with yield accuracies of up to 10,000ths of a foot. The first or initial readings taken shortly after installation becomes the baseline, where succeeding measurements are compared.
This set-up may be manual, which could be taken periodically, once or twice a week or automated with readings taken as often as in one hour intervals by an Automated Motorized Total Station or AMTS.
This set-up could take three dimensional movements, X & Y on the horizontal and vertical or settlement.
In a tunneling operation a series or battery of AMTS could be installed in advance of the area being tunneled and as tunneling progresses, the AMTS in the area behind the current tunneling operation may be decommissioned (taken over by other modes of monitoring) and re-installed further of the operation in a sort of leap frog arrangement, as what is usually done in New York on track & subway works.