Soil Resistance on Buried Pipe 1

[stanier]

I am seeking more knowledge of the behaviour of rubber ring jointed pipes in weak soils. If the soil is weak and thrust blocks are to be avoided thrust restraint fittings can be used at changes of direction. I would like to know of a procedure to calculate how far back from the bend can RRJ fittings rather than restraint type fittings be used.

WHat aprameters of the soil do I need and how do I go about specifying them so that the geotechnical engineers or soils scientist comes up with the right data.

Please no lectures on I should be using PE or other integrated pipe materials.

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[RWF7437]

Try this link:

http://www.acipco.com/international/restrained/index.cfm

It should lead you to data and maybe even some free software.

Good Luck

 

[KRSServices]

Be careful with restraining joints in weak soils. The pipe can and will fatigue due to lack of sufficient ability to resist the thrust loading. Most thrust block designs and detail drawings are premised on fairly weak soils anyway.

I prefer to use a combination of restaining joints and thrust blocks, particularly on hydrants, 90 bends and tees.

KRS Services

http://www.krs-services.com

 

[MikeLittle]

you haven't stated your pipe material; rrjs will not reliably withstand longitudinal forces; options include circumferential insert in circumferential groove in spigot and socket or collar (not sure if these always work); see grp catalogues; and see also paper by des bowland through tyco website which describes tests to establish longitudianl friction on pe coated spigot and socket rubber ring jointed steel pipes.

 

[Ag93]

Stanier, I tried to send you an email but it was returned. What is your email address? Thanks.

 

[CarlB]

This may be the first time for me, but I disagree with KRSServices. I think restrained joints make more sense than thrust blocks in weak soils - or at least are a valid option. Tables I've seen for thrust blocks are for moderate strength soils. In weak soils TB's can settle, rotate, etc so be careful with them as well. And as for using both restrained joints and thrust blocks, be aware that a different amount of deflection is needed to engage the thrust resistance. I read that it takes much less pipe movement to engage restrained joints - so if you have a "shared" system without full joint restraint a joint or joints may fail, then all the load would need to be taken up by the thrust block. I'd say better to use one system and make sure it's adequate.

 

[KRSServices]

CarlB,

Your points are well taken. I however, prefer to look at restraining joints not from the perspective of the soils, but more so from the pipe. The pipes themselves are designed to contain the liquids, and accordingly, have certain safety factors built into them. The restraining joint couplings utilize these safety factors to work within. Consider a tee and the thrusting forces that are acting on the pipe in a pressure surge event. In restraint, the tee itself has to withstand not only the forces of the liquid, but also must react to the resultant forces relative to the surrounding soil. If this soil is weak, the tee and the restrained pipe location must be able to continually resist the forces acting on them (to deflect or shift). A thrust block effectively transfers the forces acting on the tee and pipe to the bearing area on the soil. You are correct, there are many cookie cutter tables for thrust blocks, and in many cases, aare designed for moderate to weaker soils. However, as a component of the design, the soil logs will verify as to the suitability of those designs, and perhaps a larger bearing area is required. I use restrained joints on hydrant assemblies because they are a really good backup to the thrust blocks. You never know who is operating the hydrants, and on longer leads, the restrained joint is good insurance, but in my humble opinion, should not be a replacement to a thrust block. What do others do?

KRS Services

http://www.krs-services.com

 

[stanier]

Hi Ag 93 My email address is blenrayaust@yahoo.co.uk. SOrry for the delay but I have been away snow skiing.

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[BRIS]

You might find the following paper useful "pipe anchorage for large diameter rubber ring jointed steel water pipe" on

http://www.ghd.com.au/papers/DBoland_pipe.pdf

Brian

 

[cr1973]

We design using megalug restraints. On larger diameter pipe, we'll use a combination of thrust blocks and megalugs.

I agree that in weak soils, joint restraint is by far the better choice, however, both methods should be applied if the soil is questionable.

We also use anchor tees for all hydrants.