[TowerTalk] Expansion joint in conduit

[Patrick Greenlee]

Thermally induced expansion and contraction is not the only effect to 
consider.  Expansive soil will expand and contract with variations in 
soil moisture independent of temperature. I am currently in the process 
of repairing a 1 1/2 inch  PVC water line that began leaking at a Tee 
fitting originally installed sometime before the 90's. Along came a 
significant (worst since records were kept before statehood) drought and 
soil movement in turn moved/pulled on the pipe.  The Tee, of course, 
presented significant resistance to movement along the direction of the 
"main line." The line was about 3 ft or a little more below the 
surface.  Code depth here to avoid freezing is 18 inches.  At a depth of 
3 ft temperature changes are moderated.

The quoted statement below is true, sometimes.  Some areas have 
expansive soils that introduce significant motion to anything "planted" 
in the ground, i.e. foundations.  There is an entire industry in this 
part of the country for foundation repair due to expansive soil not 
being properly taken into account when the foundation was designed.

To avoid a repeat of my current waterline repair I am building in a 
rectangular "loop" that will allow significant soil motion without 
stressing a fitting. Unfortunately that remedy is not particularly 
amenable to conduit where cables may need to be added or removed.

Patrick

On 11/4/2017 2:38 PM, dwkanepe--- via TowerTalk wrote:
> Unless you expect the ground temperature at that depth to be subject to large changes, it is unlikely that expansion/contraction will be an issue.
>   
> 73
> Don
> WB2BEZ
>   
> In a message dated 11/4/2017 12:37:52 PM Eastern Standard Time, 00tlzivney at bsu.edu writes:
>
>   
>   My conduit run between towers will be 3 to 4 feet deep and 200 feet long.
> 2 inch nominal PVC conduit.
>
> Should I use an expansion joint underground?
>
>
> Are they truly waterproof?
>
> Terry N4TZ
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