Boston’s Big Dig tunnel has one more problem. Thawing from ground-freezing technology used to excavate the I-90 connector system 11 years ago has apparently caused a large swath of soil to settle. Engineers fear that a deep water-filled void may be lurking beneath.
The area of concern beneath the I-90 tunnel base slab measures 190 ft long by 60 ft wide, says Frank DePaola, appointed Massachusetts Dept. of Transportation’s new highway administrator on August 11. It is one of the largest and perhaps deepest applications of ground freezing in the U.S., reaching 130 ft. at its deepest level, he says.