It looks like an older version of the distribution boxes in my neighborhood for underground electrical services. I have a transformer in my yard, but down the street there are boxes that the drops to my neighbor's houses plug into the mains. My drop plugs in at the transformer. I wouldn't go poking around with a shovel. Call 811/Miss Utilities and have them mark your utilities, it's free. If I'm right, you'll have a bunch of red lines radiating out from that box. If they're orange, it is a telco or cable TV box.