HDPE for use under a parking lot

[damonweiss]

As a munipal engineer, it is my job to review land development plans in my area for compliance with local, state and federal regulations. Sometimes, however, I notice questionable design practices that are not covered by the regulations at hand. Today, for example, I am reviewing a plans for a proposed office park, consisting of four buildings and a considerably-sized parking lot. The parking lot runoff is conveyed to a retention pond via a system of HDPE pipes, ranging in size from 18" to 27" in diameter. Should I be concerned that the HDPE pipes will not be sufficiently strong enough to handle the anticipated vehicular traffic? Has anyone witness strength problems with HDPE pipes along these lines. In my review letter, I've already commented on the fact that no utility trench restoration detail has been provided. What should I look for in a trench restoration detail and does anyone know of any outside resource I can consult for more information. The project is located in the state of Pennsylvania, by the way.

Thank you very much for any insight that you may be able to provide.

Damon

 

[bltseattle]

I think a call to a manufacturer would be the best way to clear up your questions about loading and performance. In general, it should not be a problem so long as the proper pipe is selected for the loading and cover, and installed correctly.

The owner's engineer has the responsibility to design the pipe for anticipated loads and soils. In my opinion, If the installation is on private property, and is constructed from plans/specs sealed (stamped) by the owner's engineer, and HDPE is not excluded by your municipal standards, and there is only minuscule risk to public safety, it shouldn't be of concern to the municipality.

Based on my experience with corrugated plastic pipe (CPEP), you have to be careful to backfill the trench properly, particularly for diameters 24" and greater, to ensure proper strength development between the pipe and soil. The pipe zone compaction levels are different than for more rigid pipe. For larger diameters, it can be difficult to obtain good compaction due to pipe deflection during construction. Therefore a pipe installation/trench & backfill compaction detail is desirable. The Washington DOT has a standard detail for this.

It is not clear from your question if you are referring to the electrofused continuous HDPE variety or standard CPEP that is coupled with mechanical connections. With electrofused HDPE you also have to be careful about thermal expansion/contraction, which can be extreme for black HDPE, and handle the pipe to prevent it from heating up before the connections are made, because when it cools and contracts it could mess up the connections at structures.

Hope this helped,

BT

 

[KRSServices]

There are three issues that need to be addressed prior to your approval.

1) The Engineer should be able to demonstrate that the live loading, the soil loading and the pipe class are compatible.

2) The pipe bedding and backfilling detail are very important. It is very likely that hand compaction or the use of fillcrete (or similar product/methodology) is going to be required to ensure the pipe is properly supported.

3) Hydraulics, specifically scour. HDPE does not lend itself too well to scour resistance.

KRS Services

http://www.krs-services.com

 

[sapaeng]

I would agree with bltseatle. In North Carolina we use HDPE storm drainage pipe fairly regularly. NCDOT has approved HDPE for use within their right-of-ways. The structural strength for HDPE comes from the pipe bedding conditions and backfill material and methods, therefore the engineer should have very specific requirements/details for installation to ensure the contractor knows how to install it. If the contractor installs HDPE in the same manor as RCP, the HDPE will deform. NCDOT is a conservative agency and they require stone bedding up to the haunch and 95% standard proctor density to grade. FYI

I am sure the manufacture’s sales representative would be more than happy to drop by for a visit.

 

[SiPaul]

When I was a consultant I specified HDPE regularly and had never observed a problem. I agree that the compaction is critical to the installation. Usually much handwork is needed but it can go quickly.

As a municapl engineer I am reluctant to allow HDPE because of the inspection required to insure proper installation. I believe that the track record is pretty good (so far) with HDPE when installed properly - even with highway loads.

As mentioned above, scour can be a problem.

 

[ndpw]

I realize that this the odds of this happening are low, but I thought I'd post it anyway. There is a small town in Connecticut that has prohibited plastic drainage pipe because apparently some juveniles lit a fire in this type of pipe, subsequently causing some partial road collapses. I know this isn't really applicable to private property, but I thought people would be interested to hear this.

 

[cvg]

This can be a problem for hdpe, pvc and even possibly cmp. What happens if someone dumps some used turpentine down the storm drain and somehow it gets set on fire. The fire may destroy the pipe. Noxious fumes from the burning plastic are also a potential hazard.

 

[TerryScan]

I have been designing with HDPE storm pipe for a while. I have had reports of failures. They have always been related to improper installation. In one instance, the pipe was placed in the trench, backfilled in one lift and driven over with heavy equipment before it was compacted. This site had many failures. This example gave the product a bad image with the client, yet I do not really fault the product. I believe this kind of treatment of any pipe is likely to lead to failures, only of different types.