HDPE Under Full Vacuum - Constrained Pipe Resistance to Collapse 2

[ubique345]

Hello,

I hope someone with experience can clear something up for me.

I'm trying to size required DR for a water pipeline under full vacuum. The pipeline will be buried 3m, and I intend to achieve a soil reaction - E' = 2000-3000 psi through material type and high compaction.

Now, when calculating the DR, if the pipe is considered constrained for the entire length a DR 21 pipe will be suitable and achieve a factor of safety of ~2.5-3 for vacuum / soil prism / live loads relative to critical collapse pressure.

However, if the pipe is considered unconstrained, the external pressure of the vacuum exceeds the critical collapse pressure. In the case of unconstrained pipe, DR 13 would be the suitable choice.

My question is, is it safe to assume through diligent supervision of the construction, and tight specifications for the embedment,and primary / secondary fill, that the DR 21 will be sufficient?

Is it common practice to only consider the pipe under constrained conditions for buried pipelines?

Thank you for any help you can provide.

 

[ubique345]

I'm not too sure what you mean here, but what I meant was: DR13 Pipe Cost = DR21 Pipe Cost * 2.5

 

[BigInch]

Sorry, I wanted to say that as an engineer you should do as I believe you are doing and always strive to make an optimum design, balancing functionality and serviceability with cost, but there are few other factors that can enter the equation, such as when we don't have infinite knowledge, all the relevant information, privy to all the same knowledge of the owner, or Mother Nature's guarantee that 3000 psf soil will always hold 3000 psf. We often have to add some fudge to account for some unknowns or another, which usually adds expense, but the advantage is that we get to sleep a bit better at night hoping we added just enough so that the result was still an optimum design (even better than before), and the extra functionality was worth the cost trade off. Keep up your good intentions, without making false economies, especially at only your own expense. They will pat you on the back when you save them a buck, but take that same buck again ... with interest, out of your hide, should something happen later.

Engineering they say can be more difficult than doctoring. A patient dies and the doctor is rewarded by a quick burial. A bridge falls down and is often still on public display years afterward.

Reaction to change doesn't stop it