The picture below shows a veritcal construction joint of an approximately 50 years old reinforced concrete industrial structure. The expansion joint was likely originally sealed with a flexcell which due to age and water ingress has deterioriated and come away from the joint exposing a peforated metal pipe.

My question is does any one know why the pefortated pipe was installed there originally approximately 50 years ago? Does it have a drainage purpose? The joint should have been waterstopped. Is this a second line of defence? If so where do you expect it to drain to? Has anyone seen a similar detail to this before?

perforated pipe within construction joint


1 Answer 1


Yes, it is a hydrostatic pressure relief pipe (part of the drainage).

Behind all the retaining walls, swales, subdivision's low land lots, you need to have a trench or channel filled with aggregate and a perforated pipe leading to surface runoff drainage as a minimum.

The Aggregate mus be stratified from 1.5" near the pipe to sand 18" out.

I suspect in your photo corrosion has washed the aggregate out.

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    $\begingroup$ Corrosion washed the aggregate out? More likely water. $\endgroup$
    – Solar Mike
    Commented Apr 7, 2020 at 5:11
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    $\begingroup$ My theory is that behind the flexcell and surrounding the perforated pipe there was originally aggregate. The perforated pipe allows ground water to flow down the pipe into a drainage channel and finally into a sump pit where it can be pumped out. This system prevents excess ground water pressure from building up against the flexcell sealant which could cause it to fail. However, in the case that the sump pump failed this would have allowed excess ground water pressure to build up against the flexcell failing it and allowing the aggregate to wash into the basement exposing the perforated pipe. $\endgroup$
    – egg
    Commented Apr 7, 2020 at 7:49

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