GRC vs PVC in Rocky Soil

[FaradayFF]

Hello Fellas,
Would galvanized rigid conduit make sense in rocky soil for short run of conduit versus using a PVC?
Thanks,
EE

 

[ActionDave]

I say no. Does anyone use metal for underground sewer or water any more?

 

[Dennis Alwon]

It makes sense if you can't dig down deep enough. I would use it only if I had to.

 

[FaradayFF]

Would GRC make more sense if frost is a concern?

 

[infinity]

I wouldn't worry about frost but as Dennis said if digging down to the required depth for say PVC was difficult I would not heistate to use RMC and only have to go down 6" to the top.

 

[tom baker]

Or you can encase in concrete, and use Sch 80.

 

[Coppersmith]

Since I hate digging, I always use IMC/RMC unless it's such a large job I can sub out the trenching to somebody who will use a machine and be responsible for repairing everything underground it destroys.

 

[ActionDave]

I guess it all depends on what you call rocky soil and how the digging is accomplished.

 

[Cow]

I'd say it depends on how long you want the rigid to last?

May be better off to use sand bedding with pvc if there isn't much to do. Flowable fill(cdf) works well too, but I don't know your budget.

 

[drcampbell]

Is the concern for the digging difficulty, or long-term damage to the conduit?
If it's the latter, you can first backfill with clay or small, non-sharp gravel in immediate proximity to the conduit.

 

[FaradayFF]

I'd say it depends on how long you want the rigid to last?

May be better off to use sand bedding with pvc if there isn't much to do. Flowable fill(cdf) works well too, but I don't know your budget.

Do you have any historical/industry record or documentation that would suggest galvanized rigid conduit will not last long? I understand PVC is better in terms of longevity, but it is not like GRC is expected to last only 5 years in a "typical" soil environment..
Thanks.

 

[drcampbell]

I can't say what's typical, but this spring, I dug up some IMC that had been underground about 30 years.
Central Ohio. Plenty of moisture. Not near a road, so little or no road salt. Mostly clay. I don't have any knowledge of soil chemistry.
It was in decent shape. Most of the galvanizing was gone and there was a thin, smooth layer of rust, no pitting. The threaded couplings unscrewed neatly, didn't break off.

 

[masterinbama]

Do you have any historical/industry record or documentation that would suggest galvanized rigid conduit will not last long? I understand PVC is better in terms of longevity, but it is not like GRC is expected to last only 5 years in a "typical" soil environment..
Thanks.

I recently had to excavate around some GRS feeders I installed in the early 1980s. They are only slightly corroded.

Sent from my LML211BL using Tapatalk

 

[electrofelon]

Do you have any historical/industry record or documentation that would suggest galvanized rigid conduit will not last long? I understand PVC is better in terms of longevity, but it is not like GRC is expected to last only 5 years in a "typical" soil environment..
Thanks.

Here in upstate NY I see GRC that has been in the ground since the 60's and it's totally fine. Most houses have galvy water lines that have been there for 6,7 decades. I hear reports from other parts of the country of galvy returning to nature in no time at all, not sure if that is BS or there is something dramatically different about the soils.