Complete the sentences with words that are punctuated and spelled correctly. the "big dig" (the central artery/tunnel project) has been complex and challenging. located in massachusetts, this tunnel is eight lanes wide and more than three miles long. what is most amazing about this tunnel is that it is constructed under a major highway and skyscrapers located in boston’s financial district. i construction crews used "clamshell excavators" during this dig. these machines carved narrow and then a special substance was pumped into the trench to keep the dirt from caving in. steel beams were lowered into the trench and concrete was pumped in.