3Qs: For Big Dig, light at the end of the tunnel?
Boston’s Big Dig — the most costly highway project in United States history — has been plagued with problems since ground was broken in 1991. Last week, inspectors discovered a sinkhole beneath the surface of the I-90 connector tunnel, possibly caused by a ground-freezing process used during construction. We asked Thomas Sheahan, a professor of civil and environmental engineering at Northeastern University, to explain why the ground-freezing process was used and whether it caused the sinkhole to form.