I installed some drainage pipes in my backyard using six inch plastic pipe. The surface drains use the grates that just slip into the end of the pipe to allow the water to enter. To protect the pipe/drains from damage, I'd like to pour a small concrete pad around the pipe however I'm not sure if this is a bad idea. I thought about pouring an 18 inch square perhaps 3 inches thick but was curious if you think heaving will be a problem and any other tips that may make this work better. I'm not a concrete expert so I'm all ears......