Pvc expansion joints

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iwire

Moderator
Staff member
Location
Massachusetts
The pics posted are not necessarily expansion/contraction related.
Says the guy from the Sunbelt. :grin:

I agree that poor backfilling can be the cause of the pull apart but in areas that get real winters what is pictured commonly happens from freezing thawing cycles as well.

Here is a road experiencing 'frost heaves'



Here is a sidewalk



When your yard pushes up around the house in the winter and then settles back down in the spring you can get risers pulling out of meter sockets.
 
Agreed the the ground moves around but is someone making the argument that expansion joints should be installed in underground PVC conduits? Like actually buried in the dirt or just were the PVC emerges?

I doubt they are needed underground... I wouldn't think there would be a large difference in the coefficient of thermal expansion between the pipe and the dirt... not like pipe on the outside of a concrete building. I could be wrong. What do you think?
 

Smart $

Esteemed Member
Location
Ohio
Agreed the the ground moves around but is someone making the argument that expansion joints should be installed in underground PVC conduits? Like actually buried in the dirt or just were the PVC emerges?
I'm not making an argument for using expansion joints in undeground runs... but I don't see any current stipulation in the code exempting underground PVC installations from the requirement of 352.44.

I doubt they are needed underground... I wouldn't think there would be a large difference in the coefficient of thermal expansion between the pipe and the dirt... not like pipe on the outside of a concrete building. I could be wrong. What do you think?
Well after decades of underground installations, I not aware of any widespread problems as a result of not using expansion joints in horizontal runs... but I'm far from an expert on the matter ;)

One thing needs pointed out about the difference between above ground and underground expansion and contraction of adjacent materials. Above ground, the adjacent materials have "room" to expand and contract three-dimensionally... whereas underground I believe the expansion and contraction of the soil is mostly limited to vertical only (i.e. where there is a consistant soil base). I'm uncertain if expansion and contraction of PVC conduits are somehow bound to this same vertical-only direction because of the pressures exerted on it by the soil or not... but the code does not have any considerations for compression.
 

tonyou812

Senior Member
Location
North New Jersey
I put them in. When I worked for other EC's I dont think I ever did. But now that its my name on the work I use them, especially here in the Northeast. A 2" expansion fitting is only like 15 bucks
 

jusme123

Senior Member
Location
NY
Occupation
Electron Traffic Controller- Journeyman
Says the guy from the Sunbelt. :grin:

I agree that poor backfilling can be the cause of the pull apart but in areas that get real winters what is pictured commonly happens from freezing thawing cycles as well.

Here is a road experiencing 'frost heaves'



Here is a sidewalk



When your yard pushes up around the house in the winter and then settles back down in the spring you can get risers pulling out of meter sockets.
great examples bob!
 
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