Deep excavation for a new multi-use commercial building and subway station in the downtown Chicago Loop led to concern over possible disruptions of a century-old utility tunnel located only eight feet (2.4 m) from the edge of the site. The tunnel, which was dug by hand and lined with hand-poured unreinforced concrete, currently carries fiber-optic data connections for much of downtown Chicago. An autonomous Internet-enabled monitoring system consisting of displacement sensors, an embedded computer, communication hardware, and an automatically-updated, password-protected project Web site was installed in the tunnel to provide continuous performance data ina readily useful form for decision making. The system automatically recorded displacement measurements hourly for approximately two years, by whichtime the excavation was complete. City of Chicago personnel used the autonomously-generated reports from the Web site in daily construction meetings and had authority to halt construction in case of excessive displacement; ultimately, little movement was observed. This paper will discuss the instrumentation plan, robust communication from the instrumented section of tunnel to a telephone line several blocks away and on to the Web site, andstrategies for reliable autonomous remote sensing in a challenging underground environment.
Samenvatting