elbows in underground water pipe


Today I saw the town maintenance man repair the elbow in a 2" plastic water pipe, two feet deep in sandy soil.
He said water pressure had separated the joint. His solution was a steel stake on either side of the joint. That's what he had before, and it failed.
It seems to me that enough pressure to separate a joint could also, in time, move a stake in wet, sandy soil. Is that the best way to brace an elbow undeground?
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I can think of a lot of things, tie the posts together with strap, just strap the 2 legs of pipe making a triangle, use something threaded for the joints, glue it properly to begin with......
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With the proper primer and glue, joints aren't supposed to come apart. I don't think, anyway.
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The guys in my area use bags of premixed concrete for 8" underground irrigation pipe. Pressure won't exceed 80 psi probably. Most often it stays under 50. They just put the bags in around the elbow. The pipe is 5' deep or maybe a little more. It might work to put a partial bag around the pipe you described. Tamping it in around the elbow would help.
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A properly glued joint will easily withstand the force assoicated with "normal / reasonable" flow levels in "small diameter" piping.
Unless the flows in this system in the 100's of gpm the elbow forces will be small.
High flow rates and / or large diameter pipes can require a "thrust block" but I seriously doubt a 2" line would need one or if it needed one, that a "stake in sandy soil" would do the job.
Do oyu have any idea what the flow is?
cheers Bob
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DD_BobK wrote:

I don't know the flow, but it feeds an office with one dentist 200 yards up the road. Halfway, there's a tee that feeds an office across the road. I don't recall seeing more than two cars there. Static pressure is about 40 psi.
I wonder if suddenly shutting the water off might have broken the connection.
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E Z Peaces wrote: ...

Back on more likely than off but given general US weather patterns I'd wonder if a cold snap didn't have an effect.
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E Z Peaces wrote:

I'm curious what kind of plastic pipe it is and is it glued, clamped, or crimped to the elbow?
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Tony wrote:

I saw only that the plastic is white. The original was apparently glued. What if the pipe was wet when they glued it years ago? They clamped a copper elbow in place of the plastic one.
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Clear about 6 inches in all directions around the elbow and fill it with cement.
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Concreting completely around an elbow in 2" line with 40 psi static pressure is totally unnecessary, the wrong solution here. Even if a thrust block was required, completely encasing the fitting is frowned upon.
If water hammer is a potential problem, better to mitigate with a properly sized and installed water hammer arrestor than "brute forcing it" with concrete.
Thrust blocks are generally not needed for piping below 4"...plus 40 psi static pressure is a pretty wimpy system.
My bet is on a bad glue joint.
cheers Bob
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DD_BobK wrote:

That sounds right. Maybe he didn't reglue it because he couldn't get it dry with water continually trickling out. (I wonder how a pro would have reglued it.) Maybe he has seen a lot of glued joints break in this town because a lot of underground joints were glued badly.
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I was going for fast and simple. Beats digging it up every 6 months.
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