Soil Corrosivity to ductile iron pipe 2

[Arizona3106]

We normally just use the AWWA 10 point scale for soil samples collected from test borings to help provide some guidance on polywrap requirements. However, pipes are always bedded and shaded with select material. Therefore, is it appropriate to test the native soils in the trench to determine corrosivity potential, or could we just be testing the bedding and shade material?

 

[rconner]

You ask if you should test "select" material used for backfill in addition to the tests you normally do on native soil. While you don't mention exactly what your select materials are, nor e.g. how long you have been employing same etc., it would probably make sense to test them as well alongside the others. If the same select material has however been used in the area for a long time with no problems with iron pipe, that experience would be valuable probably mean you're not likely to have problems with this one. If either soil is potentially corrosive, polywrap should normally be employed.

 

[Arizona3106]

I guess that's what I was wondering - If the pipe is surrounded by shade material, does the native soil even need to be tested. The shade is tested yearly by the manufacturer. From your answer, it sounds like the surrounding native soil can also cause pipe corrosion and needs to be tested, not just the shade immediately surrounding the pipe. It makes sense that the surrounding native soil can easily migrate to the pipe through the granular shade.

 

[EdStainless]

Good backfill/bedding will slow the negative effects of the soil, but not stop it.
Perhaps you can get buy with slightly worse soils with select fill than you could if you went direct burial.
But when it comes to very wet and highly organic sites wrapping will still be needed.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube