My niece wants to increase the size of a hole in the sidewalk where a tree is growing. It looks to me like the job would require cuts of about 8 feet of concrete -- five feet along one edge, and three along another edge. I haven't dug into the thing to see how thick the sidewalk is, and I don't know if there's steel inside. I do want to make clean cuts, so a big sledgehammer isn't the right approach.
What are my options for cutting the concrete? I've seen guys with a tool that has an abrasive blade -- or maybe it is diamond -- and a chainsaw engine. Is that the right thing for this job? I've also seen guys with big water-cooled saws which they walk behind. If that's the right tool, it isn't a DIY task. What advice does anybody have?