Pvc expansion joints

[iwire]

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.

 

[Twoskinsoneman]

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 $]

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.

 

[LarryFine]

I could be wrong. What do you think?

After careful consideration, I concur: you could be wrong. :grin:

 

[Twoskinsoneman]

After careful consideration, I concur: you could be wrong. :grin:

Care to expound?

 

[tonyou812]

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]

True, but you should gauge your installation length based on ambient temperature. If it's cold, extend it; ifr it's hot, shorten it.

what if its warm?

 

[jusme123]

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!

 

[LarryFine]

Care to expound?

Well, your last statement was:

I could be wrong. What do you think?

And I agreed; it's possible. :grin:

 

[Twoskinsoneman]

Well, your last statement was:
And I agreed; it's possible. :grin:

Gotcha. I thought you were going to tell why I was wrong... but you were just stating I could be wrong...

On a side note what do you think about what I said? Do you think I was wrong?

 

[LarryFine]

Gotcha. I thought you were going to tell why I was wrong... but you were just stating I could be wrong...

'Twas a joke.

On a side note what do you think about what I said? Do you think I was wrong?

Not at all. I agree expansion joints should only be necessary on the vertical risers.