Dear All,

I am currently working on a an underground system with some parts coming above ground.
I recieved a suggestion that to achieve a more precise loads on the supports located at the above ground part, I may have to add the soil weight on the top of the pipes in underground sections as a sort of an uniform load and also to gain an accurate settlement of the buried pipe it is necessary to re-enter the pipe and fluid density in the buried model input.
Personally, i diagree with that since CII calculate the soil stiffness's considering the weight of the soil and all other soil properties and it would be doubeled if any one re-enter the pipe and fluid densities.
i need a more concrete reason to confirm and to convince the clinet.

thanks
pooria

The CAESAR II soil modeler will build stiffness in the vertical direction (both up and down). By simply adding a uniform load to the (CAESAR II-buried) model with no other modification would be inappropriate. You may want to compare the weight of soil above the pipe with the vertical restraint loads in CAESAR II output. If the resulting force up is greater than the soil load down, you may expect greater upwards deflection than what is reported in CAESAR II.
Our modeler focuses on the the pipe-soil interaction associated with thermal pipe strain. I believe it would need some work to be used to predict pipe response due to settlement. Your settlement would have to be an input value, probably as a defined displacement for CNodes on every vertical soil restraint.

.

Mr Diehl

I think I am having a case the way you are saying.
Let me explain please:

I have 14 meter 12" buried piping with 0.45meter depth from soil to top of pipe; then 1 meter goes vertically aboveground and then have a bend to turn pipe horizontal, 1 meter away from the bend there is a support, then the pipe continues horizontally supported.

My concern is that piping is lifting off the first support from the exit point even in sustained and hydrostatic cases.
I have tried just to set W or WW so that I can see load restraint in the support, but it still continues lifting off.

Is this related with the resulting force up of soil, that makes the pipe going up?

I do not have no answer for this.

Thank you

Your description does not provide enough information for me to provide conclusive advice. If the calculated pipe displacement is positive at that first support, I have to think that it is an issue related to deadweight distribution - you only have a 1 meter rise so I don't think it's caused by thermal strain. If it's deadweight, then I figure you must have a very large weight (valve?) just beyond the NEXT vertical support. This weight causes enough bending to lift off that last support. But if it lifts off that last support, then you must also have a positive Y load on the first few soil supports.
I would review the above ground support configuration and also the soil supports to make sure they make sense. Find out what load is causing the +Y deflection.

Dave, I wanted to follow up on this post.

From what I understand above, upon burial, CII will remove the weight of pipe and contents, and provide the stiffness restraints of the soil. As you indicate, this would then be considered a 0 or neutral point where thermal strains can be applied and results determined.

Where you indicate comparing vertical restraint with soil load, it may indicate you get a vertical lift where CII indicates a sag. So does CII have a deficiency in predicting OPErating values for buried piping? It seems this would be the case when you have vertical components to your buried lines.

What if we were concerned about operating values where vertical axis is concerned, which is what I think pooria was getting at. Often we have a buried support u/g, which we will keep 'unburied' to have a hard support with buried piping on either ends. If you look at the restraint summary, there is no load at this support, which would indicate no value for soil weight is being applied to the model. If you wanted to get an accurate value for how the pipe is behaving under an OPErating case (example load on the hard u/g support), would it not be proper to then add the weight of soil as a uniform load to each OPErating case?

The CAESAR II soil modeler addresses thermal strain on horizontal, buried pipe. This approach will not give you the load carried by any added underground support nor will it develop the up/down displacement bias on buried sections with a vertical component (this includes the pipe entering and exiting the soil).

If you include any deadweight on the buried sections, your vertical soil restraints will deflect. I would think that the trench preparation would create a (continuous?) surface that would carry the pipe weight without noticeable deflection. And I wonder if trench preparation is precise enough to be able to predict the load distribution between your hard support and the surrounding soil support.

On a modeling note, you can add restraints to "buried sections" in the buried model.