As deep as 85 ft under midtown Manhattan and the East River, a joint venture of Skanska USA Civil and E-J Electric Installation Co. is wrapping up the first phase of the $1.6-billion East River Tunnel (ERT) Rehabilitation program, which is restoring and upgrading all four of the 116-year-old, nearly 4,000-ft train tubes that were damaged by Superstorm Sandy in 2012. The rehab is one of Amtrak’s “New Era” projects, fueled largely by the Infrastructure Investment and Jobs Act .  The tunnels connect New York City to destinations east, and is used by some 450 Amtrak, Long Island Rail Road, and NJ TRANSIT trains a day.…