I'm very fond of SCH40 applications but ground movement can easily shatter glued connections underground. I've always felt that 20' sections of SCH40 with minimal deflection and the use of 4-band mission no-hub couplings underground are the best way to go.

Any pipe you can put in your hand and distort the inside diameter of is going to be a problem with the movement of weight created by good ole mother earth.

Just dig a hole in a ground and fill up a drywall bucket and tell me how heavy that bucket is, when full.