What is the best way to knock down some huge snow piles?

We have had a lot of snow here in the past couple of weeks. Between the accumulation and the city plows piling the snow on my sidewalks, I have some gigantic snow piles I need to get rid of. The snow is hard and the piles are at least three feet tall and several feet long. I don’t own a snow blower and can’t afford to pay someone, but the sidewalks have to be cleared. What is the best method for tackling these huge piles of snow?