GRp Pipe in Reactive Clay

[stanier]

Hi,


This was previously posted in the Civils/Environment Forum but got no responses.

I am researching the behaviour of GRP pipe buried in reactive clays. I am looking for articles or books that cover the analysis of the soil/pipe/embedment structure.
AWWA standards cover the design of GRP in trenches subject to external loading from soil, vehicles, aircraft etc. However reactive clays are going to provide a pressure from below the haunches resisted by the trench and overburden.

I am interested in the stress, strain, combined loading deflection and buckling criteria.

I have found research on PE pipes in such soil but so far none on GRP.

Your experiences in such installations would also be welcomed.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[rconner]

I don't know of a reference to the specific information you seek. However, the terminology "expansive" or swelling clays/soils might be more common at least in the States, and perhaps some helpful for your literature searches here. I noticed also the bolded note caveat and/or recommendations at e.g. 

http://www.subor.com.tr/wp-content/themes/subor/katalog/FLOWTITE_Install_Guide.pdf

 (indicating to me that some problems have likely occurred with such pipes in some such soils). I have noticed many other GRP references also define highly expansive soils/clays further as “unstable” soils (and then  caveat that). I saw that per the reference also at

http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc50813/nrcc50813.pdf

it is stated up-front, “Alternate swelling and shrinkage due to seasonal variations in precipitation and evaporation can cause severe distress and even failure of lightweight structures constructed on or buried in such soils, thereby compromising their service life….” , as well as similar reference on page 4 at

http://web.mst.edu/~rogersda/expansive_soils/DAMAGE TO FOUNDATIONS FROM EXPANSIVE SOILS.pdf

and

http://www.wwdmag.com/water/analyzing-underground-water-pipe-breaks-residual-soils

etc.

I incidentally also noticed per the new AWWA report at

http://www.awwa.org/files/GovtPublicAffairs/GADocuments/BuriedNoLongerCompleteFinal.pdf

that despite availability for many decades his type of pipe is used very little for water piping in the USA (it is not even mentioned in the report data).

 

 

[stanier]

rconner,

Thanks for your efforts but I am seeking more specific information concerning the design and installation and details of actual experiences with this GRP material. I know you champion ductile iron and always have some negative information concerning other materials however in this instance it is not helpful.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[rconner]

Expansive soils exist to considerable extent in some States, and I would not be surprised that this is also true of many other countries. See the report regarding Mississippi e.g. at

http://msucares.com/pubs/bulletins/b0986.pdf,

where it is said such soils comprise 18% of that state’s land area. This particular report also refers to, “depth of a few feet to 500 feet” for some such soil layers.

I am sorry that a link I provided to perhaps a somewhat notable manufacturer’s information (and caution) regarding embedment for the specific pipe material of your inquiry with regard to the subject was not helpful. Fixes I noticed (and mentioned in a response by bimr on the Civil thread you originally posted this inquiry on) apparently include over-excavation to some unspecified extra depth and width, and then hauling off and replacement of whatever that volume of excavation is with better quality, imported embedment, and sometimes with schemes also including geotextiles etc. I think I have even seen piles specified in some cases of some such very weak bearing capacity soils. Large quantities of imported backfill materials, or piles for that matter are quite costly in some areas, as can be also the geotechnical and other consultants to make decisions as to exactly how to construct, if/when you can find such detailed expertise and like the result). Underground pipe on piles by necessity furthermore requires quite strong and sometimes fortified pipes particularly if piles are few/spans are long, to handle the great localized loads imposed in such applications.

Whether it is right or wrong, large aggregate quantities of piping (on all different sizes of projects, with various degrees, sources of funding, and capabilities/knowledge of designers etc.) have thus been/are/will be? installed in some rather “expansive” or reactive soils in more or less more normal fashion (on the other hand, pretty much like in better quality soils).

While I did not advocate ductile iron pipe in my first response, as you have mentioned I will note now I do believe quite strong ductile iron pipe and with flexible joints, and particularly when supplied with polyethylene encasement that is not bonded and thus also allows some movement, does have respectable history in many such demanding applications.

You mentioned you moved your inquiry here as you had gotten “no response” (I guess we shall see if you eventually get any more specific or positive response).

  

 

[stanier]

rconner,

I am particulalry interested in the behaviour of a combined soil/pipe structure where the pipe is GRP. I have information on the geotechnical properties of reactive clay. What I cannot find in my searches is how such systems are analysed to take into accountant the behaviour of the GRP. GRp being anisotropic the stresses and strains are peculiarly difficult to estimate. AWWA M45 does not go into how reactive clays may impact on the GRP.

I agree design with DICL in such conditions is much simpler as it does exhibit substantially isotropic properties.

That said EPCM contractors appear not to take into account the difficulties and risks in design with GRP. They price jobs on a supply $/M basis and forget the other costs/risks.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[BigInch]

"That said EPCM contractors appear not to take into account the difficulties and risks in design with GRP. They price jobs on a supply $/M basis and forget the other costs/risks. "

When do they ever.

From "BigInch's Extremely simple theory of everything."

 

[stanier]

If they ever do they dont win the contract because some fool has priced low and the authority is too inept to understand low price doesnt mean a good job.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[BigInch]

That's the main reason that they don't, but there are others.

From "BigInch's Extremely simple theory of everything."

 

[bimr]

Data are generally lacking concerning the forces that may be imposed on buried piping in clay soils. The reason for this is that design practices generally do not allow such soils to be placed around the pipe. For sanitary sewers for example, design practice generally requires such soils to be removed for certain depths below the pipe if moisture content is variable at such depths.

Here is an example:

If the base soil is unstable (for example, peat, quicksand, muck, landfill, or very soft or highly expansive clay), the site should be overexcavated in width and depth and a firm, compacted base of 1/2-in. to 3/4-in. (13- to 19-mm) crushed rock should be set before the sand or pea gravel bedding is placed. In extreme conditions, a concrete layer may be needed to stabilize the bottom of the excavation. If you have any doubt about the soil's ability to
support the tank, consult a local civil or structural engineer.

http://www.norgam.com/pdf/costa03.pdf

You might consider posting this query in the geotechnical forum or consult with a geotechnical engineer.