Protecting water line...

[mrcaptainbob]

I'm located in south central Michigan and know that the frost line depth is 42". Since it's in the southern part of the state I expect the frost line is not that deep, maybe 38" to 40". The ground I'm digging through is sandstone with the occasional boulder/rocks. Along with the sandstone is much sand. The total pipe run is close to 400' There was a 30' section that was concrete-hard sandstone that I located at a depth of 36". I could not bust through with my dirt-digger, nor could a neighbor with a more serious machine. So...my concerns are the frost, of coarse, but also the tiles of sandstone rubble. The pipe is 1 1/4" PE. I am concerned about the shards of sandstone rubble at the bottom of the trench (regardless the depth), along with covering that PE with my rubble, and also of that one section that is only 36" deep. I have almost a hundred feet of 6" perforated drain tile that I'm considering using to protect the water pipe. It would provide an air pocket to keep the water line 'warm' and also protect from physical damage. Any thoughts or comments?

[Speedbump]

Putting the PE in a sleeve isn't a bad idea, but when the frost gets to the air pocket, it's going to freeze just like the dirt around it. Why don't you add some dirt on top of the hard rock to give you the depth you need.
I lived in SE Michigan drilled and repaired wells for many years and have seen frost go lower than 6'. Part of the reason was an exceptionally cold winter with not much snow cover and the fact that it was at a bar where people drove over the pipes and pushed the frost down. 42" isn't a magic number, it's just an average, so freezing is still possible.

[mrcaptainbob]

I did consider adding to the dirt level. That is in the realm of possibility. What's your opinion about the sandstone rubble? The internal pressure will usually be 40/60, but we all know that's not a forever. There are sure to be those occasions when it gets zeroed out. The wall is pretty thick, and PE is fairly robust. But then so are edges and corners. Layering it with sand first, although preferred, is not an option. That flex drain, I believe, would prevent damage.
Thanks for the quick reply.

[akaothermick]

Creating a thermal barrier on a less than ideal depth water line using a foam closed cell insulation blue board placed above the water line to retard the frost penetration and form a thermal well can sometimes be effective in keeping a line from freezing, using poly pipe insulation to cover the line in the shallow areas and as a protection from damage might be considered

[srity]

Thats great content

[Big James]

Very informative and useful article

[mrcaptainbob]

Glad your reply bumped this thread, Big James. Makes me update what I did. About 80 feet was encased in the plastic drain tile. The remainder was covered with about a foot of loose straw. Well, not real loose, but more those pads that comprise the rectangular bales. Knowing the sandstone will compress the straw, my concern was more to keep pressure off the PE from any edges. I'm not concerned with decomposition, as I did dig up a child's sock near the barn that was buried about three foot deep. Must be pretty dry down there. It's been a couple years now with a couple pretty rough winters. That area does not get used in the winter, so the snow layer is also acting as an insulator. No issues at all.
Sure appreciate all the help and suggestions.