Gravity flow of grout in new PVC vs existing steel pipe

[jeffvdp]

Hi all,

I've been banging my head against the wall with this one and can't seem to get it.

Background: I am a mechanical engineer working for a federal agency reviewing a test report regarding grout formulation provided to us by a contractor. The grout will be for waste stabilization of underground tanks and pipes.

Set-up: See attachment for test set-up rig. Pipes are made of Sch 40 PVC. Three of the six pipes are capped and three are not. Using a particular formulation of grout (composition and material properties shown in attachment), the result of the test is that the grout completely filled the vented 4" and 6" lines and the capped 6" line, the grout traveled 18' in the vented 2" line, 5' in the capped 4" line and 1' in the capped 2" line.

Problem: Existing conditions are not brand new, smooth PVC pipe, but 50 year old steel pipe that has had highly radioactive and highly toxic water and goo flow through them on an occasional basis. I would like to focus particularly on the vented 2" pipe and estimate how far the grout would flow if the pipe was more like real world conditions.

Any thoughts or ideas about how to do this would be much appreciated by Uncle Sam (and me). I hope I did leave out any relevant information. Thanks!

 

[BigInch]

I feel that the results will be much more heavily influenced by how the air in the pipe is displaced, as I believe you have already seen, rather than by any differences between the test and actual materials or conditions of the pipes into which you are placing the grout. That said, I certainly wouldn't expect to see any better results from 50 year old pipe with gunk residues still inside and predicting the results with any small degree of certainty when trying to consider those effects would certainly require some roughness data at the very least. I also think that there would be different effects due to the material, but perhaps more attributable to surface roughness or perhaps even electro-chemical bonding between the grout and pipe, PVC being much more difficult to actually obtain any kind of a bond onto it than it would be for concrete and most anything else to bond to steel. You can see that just from splatter hitting both materials. Most will easily drop off PVC, but stick to the steel. I don't think its entirely a roughness effect, but rather how water runs against steel, but "stands up" when running along PVC.

In general, since this isn't a real pipe flow problem anyway, I would recommend that, if you need better than what you're seeing now, that you concentrate on a more effective method of grout placement, such as actually pumping it in under pressure, inserting a vent tube in the unvented pipes and withdrawing it as the pipe fills, or perhaps introducing a smaller amount of grout and vibrating it until it reaches the bottom of the pipe, then introducing another small batch on top and vibrating that down, rather than depending on gravity flow on a 3% sloped pipe. Those are much more standard reliable methods for placing cement grout and concrete that minimize the possibility of the development of honeycombs and voids.

 

[BigInch]

Regards to your uncle.

 

[1gibson]

Go to a scrap yard and grab some used steel pipe to run your tests with again?

 

[jeffvdp]

BigInch, thanks for your input. You've kind of got to the reason I want to analyze these test results. I would like to have some engineering analysis to support why a gravity fill of in-place piping may not work. The air displacement certainly seems to be a big part of it. For runs greater than 20', maybe the 4" and 6" pipes wouldn't completely fill either. I am trying to figure out what the best path of analysis would be: Comparing the force of the weight of the grout vs the internal fluid fricition forces and friction forces of the piping or using a friction factor based on a Reynolds number (this doesn't seem to apply since there is no flow at the point the fluid stops and I don't think it is Newtonian anyways) or something else?

1gibson, it would be nice to re-run the test with scrap pipe, but this money has already been spent and contractual obligation has been met. So, unfortunately its not a possibility.

 

[BigInch]

It would seem that there isn't much going on to do with friction, either weight and sliding friction or fluid flow friction either. I really think it's a grout placement issue and the air's ability to get past the inflow that controls the filling, for sure in the cases where its not vented. The vented cases might relate to friction somehow, but its pretty limited data to make any definite statement on that.