Thrust Block design using H-piles

[keevin33]

I have a situation where municipality is requesting I design thrust block using H-piles behind a 24x24 water tee because there is an electric line less than 3 feet behind this.

Trying to figure out exactly how this should work. Thoughts?

 

[bimr]

It does not seem you have the space to put in a thrust block. However, joint restraints are the modern method.

If you use thrust blocks, the thrust block must be designed for the soil conditions, which are commonly not known. The thrust block must also be installed correctly which is rarely done. Should you have to dig in the vicinity of a poorly designed and installed thrust block, you risk a catastrophe.

 

[fel3]

I agree with bimr. Restrained joints are the better approach here. You don't have much room and future maintenance or construction crews will appreciate not having a concrete block and H-pile in the way.

The Ductile Iron Pipe Research Association (DIPRA) has a nice publication that covers joint restraint:

http://www.dipra.org/app/uploads/Design-Thrust-Restraint.pdf.

These calculations can be applied to PVC, steel, etc.

Also, if you use Mathcad (or even if you don't), I posted a .zip file on the PTC Mathcad forums with model thrust block and restrained joint calculations in both Mathcad Prime 3.0 and Adobe Acrobat formats:

http://communities.ptc.com/docs/DOC-4895

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[keevin33]

thanks guys. besides the h-pile blocking the other option the reviewer has suggested I use an in-line thrust collar with weld-on ring placed at the opposite end of the replacement pipe section with all restrained joints between the thrust collar block and tee

 

[keevin33]

i attached a sketch of what I am thinking. i dont have much large diameter experience. thanks for input

 

[keevin33]

manufacturer info for thrust collar

 

[bimr]

Perhaps you can explain your scope of work. Are all the pipes new? Are you going into a building?

 

[rconner]

It looks like you may be cutting in a new DI tee and branch into an existing 24" cast iron line. If this is a solid tee you will also likely need one or more long pattern mechanical sleeve(s)on the run to get same in place/joined, and perhaps also drop-in spacer pipes within same to fill assembly space gaps before you button up. Do you know the pattern/actual diameter of the existing line (would need to make good connections)?.
It is also best to have the thrust wall keyed in to soil that has not been disturbed recently (some designers over the years have only assumed available bearing area of the wall being that bearing on undisturbed soil). For this reason, it is probably not good to have the thrust wall too close to the run pipe (lest it be tempted to try to bear primarily on the disturbed soil). Finally, if this is a new mechanical joint end valve that could have differential pressure on the thrust wall side, it will also likely be necessary to restrain the valve-pipe mechanical joint as well.
Finally what is your thrust restraint design pressure and soil conditions (and I think as bimr may also be wondering, is there also existing cast iron or other existing piping to the left on the branch as well? Might also need to consider any thrust foci on the existing run line out of your sketch.