Strange FISH behavior- digging away at the stones in the tank- is this a typical fish behavior?

I have a single fish in a 10 gallon tank. He is a fresh water community fish- about 4 inches long. Anyway, I have a 1" deep layer of rocks on the bottom of the tank- I keep the tank very clean, filtered, 78 degrees, etc. and I feed him well; 2-3 times a day. I tried only once but he is a hungry fish- will splash you if not fed often! I know it's not ideal for the balance of the tank but it keeps him happy! Anyway, he seems to love moving the little pebble like rocks all over the place. For example, he digs holes straight through the rock so there is a path (like plowing snow off a sidewalk!) that goes under his big rock. He also cleared all the rocks away from the bubble stone so he can swim under the middle of it. Everywhere else in the tank, the excess stones have made mounds that pile up 3+" all around the tank- his digging is significant. Is he just bored or is this a typcial fish behavior? I've had him for year- he was never this bad. Would getting another fish in the tank help settle him down? I'm afraid he might hurt himself. Every-time I look at him, his tail is in the air like he is doing a hands stand and he is digging!!!