Real-Time Monitoring of Subsidence Along I-70 in Washington, Pennsylvania

Two longwall coalmine panels were mined at a depth of approximately 156 m (510 ft) beneath I-70 east of Washington, Pennsylvania, such that the highway crossed the width of one panel at two locations. The Pennsylvania Department of Transportation (DOT) assumed responsibility for real-time monitoring of both ground deformation and changes in highway conditions. Innovative monitoring of ground deformation was accomplished with time domain reflectometry to interrogate coaxial cables installed in seven deep holes and an array of 32 tiltmeters along the highway shoulder. Surface monitoring was conducted with Global Positioning System measurements at more than 100 locations. Tiltmeters were connected to a central remote data acquisition system that automatically recorded and stored measurements. When specified tilt values were detected, the system initiated a phone call to key Pennsylvania DOT personnel, who then monitored tiltmeter measurements in real time via a phone-line connection. On the basis of this information, they could alert other agencies, if necessary, and intensify visual reconnaissance to determine if lane closures were necessary.