I work in a public works dept doing a lot of this type of work.In this situation it would be faster, easier,to use 2" copper in large rolls,or even 2" black plastic rolls.This way you can dig a long trench,unroll it quickly,throw some sand on it,and under for a nice bed.Then once all pipe is layed finish back filling.This goes quick.Try to keep your pipe run in an area that doesn't run under a road,driveway etc as traveling on top of pipe will drive the frost a lot deeper than normal.Also when making connections at either end put a bit of a goose neck in the pipe. If the ground does move it will allow the pipe to move by straightening out some instead of pulling joints apart.Just my 2 cents from 25 years of pipe laying.