sand around underground pipeline

[AskTooMuch]

on a pipeline trench detail, why do we use sand around u/g pipe as opposed to other soil type?

 

[LittleInch]

You need to use "intimate fill" material so that hard stones, rocks and other debris ( metal etc.) don't impact or press into the coating and create holes in the coating or when the pipeline moves under thermal expansion or contraction it doesn't rub against these hard points and result in wear or corrosion.

Now what constitutes "intimate fill" is up to you. Some people like to spend a lot of money and import sand, others like to use what they dug out and run it through a crusher or a special sieving bucket.

Sandy soils or clay soils should be able to be used direct so long as there aren't sharp stones or flints.

Too many times people simply use the last drawing they had and repeat it without thinking.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[AskTooMuch]

I'm not referring to mile long pipeline but u/g pipes crossing a road.

So clay soil is also ok to use as long as it does not contain rocks with sharp edges? I thought there is another reason why it needs to be granular material (granular that does not have rocks with shard edges for obvious reason).

 

[LittleInch]

Ah ok you're talking b 31.3 pipes not pipelines ( unlike your post title and the original post. ...)

Sand can allow a little more flexibility in this instance and in many cases is easier than trying to sift out pesky stones for only a few metres of pipe.

But yes clay soil is good.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[AskTooMuch]

I'm reading this article and it does not recommend clay soil in bedding, haunching and initial backfill zones (see page 9).
It did not explain why not to use clay though.

https://plasticpipe.org/pdf/chapter-6_installation_construction.pdf

 

[Dhurjati Sen]

Dear AskTooMuch,

Few disadvantages of clayey soil used as backfill:

a) Water passes much slower through clay than sand.

b) Corrossivity of clay is higher than sand.

Regards.



DHURJATI SEN

https://www.nace.org/people/dhurjatisen

 

[LittleInch]

Sand is much more"flowable" and easier to level than clay which also can be lumpy and difficult to handle. But there are many types of clay so might not be applicable


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[cvg]

I'm reading this article and it does not recommend clay soil in bedding, haunching and initial backfill zones (see page 9). It did not explain why not to use clay though.

https://plasticpipe.org/pdf/chapter-6_installation...

specifically "high plasticity clays" are not recommended because they tend to shrink and swell excessively when the moisture content changes. this can cause stresses on the pipe and settlement or heave of the trench, especially for water or sewer lines that might leak