Movements Around Transit Tunnels in Mixed Ground

This paper describes the ground movements measured at a Test Section during construction of twin rapid transit tunnels in Cambridge, Massachusetts. The Test Section was located in an area of rock, soft ground and mixed face tunneling, with the alignment of the twin tunnels approximately 100 feet below ground surface. Overburden soils consist primarily of a very dense, saturated glacial till containing cobbles and boulders, with a weakly metamorphosed, fractured shale bedrock below. Instrumentation at the Test Section was installed in three cross-sections: one with the tunnel headings entirely in rock, a second with the tunnel headings in soft ground, and a third in a mixed face area. The field measurements are analyzed to show the effects of ground losses at the tunnel headings vs. distance away from headings, the effects of single vs. twin tunnel construction, and the effects of mixed face vs. rock and soft ground tunneling on ground movements