Burying Sch 40 PVC on rock?

[Paulcmaine]

Running a 4" waste line to the septic from the house. This is in Maine so we need as much depth as we can get for frost. We've hit one or two sections where a large flat piece of granite is in the way and extends laterally too far to just trench around it. It's only a few inches higher than our pipe grade so we have been breaking it up with the hammer drill which works but is slow going! My question is, what is the best way to protect our pipe with minimal depth? I don't want to chip out 4" of rock just to fill back with sand if there's any way to avoid it. Can I take a piece of 5" pipe and split it in half and use that to protect the 4" pipe from the rock? What about 1" blueboard? Is there an off-the-shelf product to do this? We're only talking about 4' total linear distance so cost is not really a concern.

One other question. On this island what they had on hand was sched 40 potable water well casing pipe. There is no reason not to use this for a DWV line, correct? I know you shouldn't use DWV for potable/pressure applications but my understanding is that if anything the well casing pipe is stronger than the DWV and will work just fine.

 

[Reach4]

Can I take a piece of 5" pipe and split it in half and use that to protect the 4" pipe from the rock? What about 1" blueboard? Is there an off-the-shelf product to do this? We're only talking about 4' total linear distance so cost is not really a concern.

Only 4 ft of linear distance? So that space must be near the house.

I think burying a 4x8 sheet of maybe 3 inch thick XPS or EPS might be good. So you are trying to make the heat path around the insulation long. So put the insulation right above the pipe and extending out from the pipe. I am not a pro.

https://terrylove.com/forums/index....eed-to-house-from-freezing.76513/#post-561235

 

[Sponsor]

 

[Paulcmaine]

Only 4 ft of linear distance? So that space must be near the house.

I think burying a 4x8 sheet of maybe 3 inch thick XPS or EPS might be good. So you are trying to make the heat path around the insulation long. So put the insulation right above the pipe and extending out from the pipe. I am not a pro.

https://terrylove.com/forums/index....eed-to-house-from-freezing.76513/#post-561235

Different situation actually. The concern is that the pipe will be laying directly on top of rock for about 4' (the run is more like 40') and I want a solution to protect the pipe from pressure damage against the rock. Typically we would bed it in sand or good compacted soil but that would require chipping away quite a bit more rock, I'm looking for a way to bed that pipe that only requires (ideally) 1" or less of vertical space. We will also be using some blueboard to make up for where we can't get enough depth of bury.

Thanks.

 

[Reach4]

We will also be using some blueboard to make up for where we can't get enough depth of bury.

Blueboard and greenboard are not something you would want to bury with your pipe. They are not water-resistant enough.

Different situation actually. The concern is that the pipe will be laying directly on top of rock for about 4' (the run is more like 40') and I want a solution to protect the pipe from pressure damage against the rock. Typically we would bed it in sand or good compacted soil but that would require chipping away quite a bit more rock, I'm looking for a way to bed that pipe that only requires (ideally) 1" or less of vertical space.

How about laying the pipe on a strip of mortar? Push the pipe into the mortar, and you have a form-fitting cradle. Or similarly, push the mortar in from the sides. Mortar does not have the big aggregate that concrete has.

 

[WorthFlorida]

You didn't state how deep this rock is and will this home be used all winter long, weekend use or not used at all? If it is pitched correctly the pipe should remain fairly dry. Any small amount of water and a freeze won't hurt anything. Heated wastewater and compose of waste from the septic tank will also generate heat. You mention about pressure from above. The only problem would be any vehicle traffic over the pipe would be an issue, anything else is minimal. SCH 40 is pretty tough. The ground below it (rock) will not heave at all. It's the fore and aft of this 4' rock could move with a deep freeze, therefore, try to have the couplings as far as possible from the rock. A 10 ft pipe could leave about 3 feet on each side. Having a coupling near the rock and the pipe moves due to a freeze, the pipe will pivot at the coupling. The coupling itself is strong, it's the glue to hold it can fail if its moved too much but very doubtful. 3" joint is a lot of surface for a good bond.

For any protection I would just use foam board under it.

 

[Reach4]

Having a coupling near the rock and the pipe moves due to a freeze, the pipe will pivot at the coupling. The coupling itself is strong, it's the glue to hold it can fail if its moved too much but very doubtful.

I wonder if a flexible coupling, such as Fernco 1056-44, would be preferable to a glued coupling.

 

[WorthFlorida]

I wonder if a flexible coupling, such as Fernco 1056-44, would be preferable to a glued coupling.

Good suggestion.

 

[Sylvan]

Good suggestion.

Some codes do not allow a non shielded coupling (fernco)

 

[Fitter30]

Just run the 40' pressure test then slide 5" -6" over. Two fernco couplings each side with 2' piece between.

 

[Breplum]

Avoid unshielded couplings, use shielded only. Unshielded can offset under differential ground pressures and cause a source for blockage.

 

[Sylvan]

Avoid unshielded couplings, use shielded only. Unshielded can offset under differential ground pressures and cause a source for blockage.

EXACTLY