Water Main Split Buttress Design

[bsmarks]

The design company that I work for is working on a 20" DIP water main that is being partially replaced. The main is being replaced because it is from 1850. The pipe will be cut and capped temporarily while the replacement pipes are being installed. My manager has asked me to design a split buttress to hold down the pipe during construction. I'm looking for guide on how to design such a thing. My understanding is that it has two concrete blocks on either side of the pipe and beams run between the two blocks. See the link provided for an example. I was giving a detail that is similar to what we need. The attached is for tapping at the end of a main. Both the existing and replacement pipe are 20" so the two beams that hold the pipe would be on a 20" pipe. So, this would not be a tapping job.
The intention is to use this for temporary restrain of the pressurized main. Once the replacement pipe is installed it will be connected to the existing pipe and this system would be removed and used in another location. My understanding is that this kind of thing is used often for temporary restrain of pipes.
DIPRA has a guide on how to calculate the thrust for a thrust block but it does not go into the design of a system like this one. I've search high and low for a design guide and found nothing. Is it called something else? If anyone knows of a guide that would be great. Any info would be very much appreciated.

 

[bsmarks]

Sorry, looks like the link isn't working. Hope this one works.

 

[dicksewerrat]

The thrust blocks will have to take any static pressure and any water hammer from the existing main. I am not sure the small blocks will hold it. You have to figure at least 120 psi working pressure in the main and then calculate your water hammer spike.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[bsmarks]

I already calculated the thrust force. It's about 68,000 lbs. It's the structure system that I'm having issues with.

 

[CarlB]

This thread was about jacking pit design, but has some similar concepts.
thread255-184604

 

[bsmarks]

I am not sure how to apply the thread to my application.

 

[structSU10]

I am not specifically familiar with such a design, but could possibly help. You are trying to resist a vertical load or horizontal load? From the diagram it looks vertical with the two thrust blocks having soil all around.

You need to understand the bearing pressure on the blocks - with an open face on one side I would think you would have a reduced allowable bearing capacity. You should get info from a geotech engineer for this.

The beam spanning between blocks is a simple design - standard simply supported beam - maybe fixed depending on if the concrete is sufficient to carry the negative moment at the interface. I believe PCI manual has a design for an embeded steel member that may be useful.