MONITORING OF TBM-INDUCED GROUND VIBRATIONS, METROWEST WATER SUPPLY TUNNEL PROJECT

From 1998 through 2000, Hager GeoScience, Inc. (HGI) has been periodically monitoring tunnel boring machine (TBM) vibrations associated with mining of the MetroWest Water Supply Tunnel (MWWST), a 17.6-mile long, deep-rock, pressurized tunnel outside Boston, Massachusetts. The purpose of the monitoring program is to detect TBM-induced vibrations in residential areas above and adjacent to the tunnel alignment, to assess the possibility of structural damage and the degree of human disturbance. The challenges have been twofold: 1) design a cost-effective program using “off-the-shelf” equipment while incurring minimal additional capital expenditures; and 2) establish suitable monitoring locations in a residential areas.

Monitoring has been conducted at the ground surface as the TBM passes underneath the sensors at depths between 200 and 400 feet, with data collected as the TBM approaches, passes beneath, and recedes from the monitoring location. Data were analyzed using EVT© signal analysis software developed by HGI. At times, TBM mining occurred simultaneously along three tunnel headings with variable geologic settings. HGI has monitored at locations along each heading and determined that 1) TBM-induced ground vibrations are measurable and can be analyzed to determine the potential for structural damage to nearby residences; 2) TBM vibration data can be collected using commercially available equipment and signal analysis software; and 3) a combination of mechanical and geologic parameters affect vibration characteristics at the ground surface.