Tunnel Overhead Inspection

The other week I was out in East Boston to inspect the Callahan Tunnel exhaust plenum as part of the Overhead inspection.

The Callahan Tunnel was constructed in 1960, 60 feet below Boston Harbor. The tunnel has an inside diameter of 28 ' and carries two travel lanes with an ADT of 20,000. We inspected the exhaust plenum from station 8+77.8 to 57+72.1 which comes out to be almost a mile each way hunched over.

The exhaust plenum carries exhaust from the tunnel out at the vent buildings located at each end of the tunnel. The ceiling panels are held up by hangers and supplementary hangers labeled L2, L1, M, R1, R2. The hangers which have gaps require a supplementary hanger that cannot be loose. Many of the hangers have  supplementary and very few had gaps without a  supplementary . The concrete liner had numerous hollow areas and a few areas of cracking with efflorescence.  

Moving around in the plenum is difficult and depending where in the tunnel the air can be come very still and hot. By the end of each day your clothes, mask and exposed skin are covered in soot. This is pretty common when inspecting an exhaust plenum though.