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Infrastructure Technology Institute

Automated Deformation Monitoring Improves Safety of Urban Excavations

The automated motorized survey instrument (green instrument at top) and Internet-controlled camera (white instrument at bottom) deployed at the Museum of Fine Arts excavation.

In the summer of 2007, the ITI team drew on experienced gained during the construction of the Olive8 development in downtown Seattle in 2006 to design and deploy an even more sophisticated system for monitoring the effects of excavation on nearby structures. The Museum of Fine Arts (MFA) in Boston is undergoing a complex construction project in which a new section of the building will be built upon what had previously been a courtyard.

Because of the proximity of the excavation to the existing structure and the fragility of the collections contained therein, ITI has teamed with the Schnabel Foundation Company to install an automated motorized total station (a type of surveying instrument) and an Internet-accessible camera to monitor the effect of the excavation on the adjacent building. The restrictions on the movement of this structure, imposed by the structure owner, its neighbors, and operators of nearby utility infrastructure, are similar to those for excavations that border transportation infrastructure such as tunnels and rail lines. To track building movement, the total station measures the precise bearing and distance from itself to twelve targets installed on the construction site as well as to four additional targets located sufficiently far from the construction site that they could be assumed to be fixed. These data are collected every two hours and immediately transferred to the ITI data center on Northwestern’s Evanston campus where they are integrated with historic data and immediately made available over the Internet to authorized parties. Schnabel, the MFA, and ITI are also able to view real-time, full-motion video from the construction site.

This construction site presented a unique challenge to the ITI engineering staff because the sensitive electronic equipment had to be placed high above the construction site with no convenient access for a technician to perform system maintenance after installation. To address this issue, ITI engineers designed, built, and installed a rigid, lightweight mounting apparatus that would hold the equipment perfectly level while protecting it from the elements and the construction activity below. ITI engineers also deployed a new commercially-available wireless communication system with a custom Internet-enabled software package to control the total station using a wireless PDA on-site or from the ITI laboratory at Northwestern. This secure Internet-accessibility combined with the system’s on-site intelligence represent a significant innovation in the field of autonomous surveying.

The system operated continuously for the entire 10 months of the project’s excavation, providing the engineers with real-time feedback on the effectiveness of their soil stabilization and construction techniques as well as the ability to analyze the construction process after the project is complete. The technique developed and tested at the MFA has immediate practical applications for the monitoring of sensitive urban transportation infrastructure located near excavations or other construction projects.