What Gives?

For the past month or so guys have been cutting and digging trenches down each side of our street. During the really hot weather, they worked at night. I could appreciate the need to wait til it was cooler, but the huge grinding blade they used to cut the pavement was really off-putting. It also caught people who normally park on the street by surprise.

Being a curious type, I have checked on their progress from time to time and am still puzzled as to what their mission was/is.

After cutting through the pavement, the debris was removed, leaving a neatly cut foot-wide trench. What looked like reinforcing bars were installed then dirt was packed in to street level. [I've never saw any pipes, cables or anything else installed.] Not long after, the crew returned, dug-up the compacted dirt and poured in paving material. The same is being repeated on the opposite side of the street right now.

Our street isn't what I'd call heavily-travelled and there are usually few potholes at the end of winter, so why all the digging and filling? Surely D.C. isn't into "make-work" projects for contractors . . . Anybody know what's going on?