Monitoring the Effects of a Deep Excavation on Two Adjacent Office Buildings

Described are the instrumentation systems that were developed to monitor the effects of excavations for the Boston Central Artery–Third Harbor Tunnel (CA/T) project on two adjacent modern, high-rise office buildings. These are the Federal Reserve Bank of Boston (FRB) and the One Financial Center (OFC) buildings. The CA/T work adjacent to the FRB and OFC buildings consists of a multilane cut-and-cover highway tunnel extending to a maximum excavation depth of more than 33.55 m (110 ft) below the ground surface and more than 21.35 m (70 ft) below the foundation levels of both buildings. Because even small excavationinduced ground movements may have large effects on modern buildings, the FRB and OFC were extensively instrumented to monitor and help control the effects of the CA/T excavation on these buildings. A comprehensive array of instrumentation was installed to measure excavationinduced movements and stresses in the FRB and OFC buildings. The CA/T instrumentation specification describes threshold and limiting values for all the FRB and OFC instruments, which may trigger responses ranging from more frequent readings to modifications of construction procedures and, in the extreme, to implementation of a specified contingency plan. Presented are typical data and how the data were used to control the adjacent construction process.