Buried, Steep Slope Pipe Anchor Design?

[JMM540]

How do you calculate the size and spacing of concrete anchors along a buried pipe with a steep slope? I've looked at other sites and have not been able to find a good example of an anchor design for this type of application.

 

[ishvaaag]

What I would do.

First check the slope itself is stable longterm. For loads on the anchor points the first thing is to ascertain the safety factor without any supplementary support to friction, and counting the vertical loadings imparted from the surface (consider also cases with the wedge of earth above and its weight laying on the pipe). If it stisfactory enough this way, you need not any supplemental block.

In other case you may decide impart the difference in inclined force to get your wanted safety factor from the concrete blocks. Counting the overall inclined resulting force from the whole weight should be overconservative and I think it unnecessary.

A 1.5 safety factor minimum should be provided in total for this a sliding situation; maybe even more given that the flowing water will impart some dynamical movement to pipes and fixity points, under pressure pipes try like long balloons for the children to straighten corners.

Then, you may try to extract resistance either from footings or piles. Respect the first case you have the resistance of footings with inclined piles; you may find them stated in Bowles. Only the part of vertical weight not accounted in getting the safety factor along the pipe could theoretically be counted at the footings; better not; hence if you have spent all in deriving a safety factor without the blocks to add against sliding, you will have only a horizontal force on a footing, for the differential as to get say an 1.5 safety factor, that you need deal with either with friction or passive push.

You may deal with this with piles and passive push reaction on them. Essentially if as in the previous case you have determined your horizontal force that way, you have a pile with a horizontal force atop embedded in a slope. You may dismiss part of the superficial depth in this, and for the passive push coefficients, use the proper formulations accounting for the unfavourable disposition of the slope (Caquot-Kérisel, graphically within limits, or some stated for the situation).

Examine as well how the nature of the soil and the presence of the water affect your design. You may need to count on diminished standing friction or just count on the adhesion-friction available for the wedge if a cut in clay.

Put extra blocks atop and at bottom.

What above for a straight section along the slope and pipe. If the pipe goes skewed along the slope, modify the reasoning above accordingly.

 

[bimr]

Try this excellent book:

Structural Mechanics of Buried Pipes
By Reynold King Watkins, Loren Runar Anderson
Contributor Reynold King Watkins, Loren Runar Anderson
Published by CRC Press, 1999
ISBN 0849323959, 9780849323959
444 pages

http://books.google.com/books?id=K0...i=book_result&resnum=4&ct=result#PPP15,M1

You can probably find it on worldcat at a library near you:

http://www.worldcat.org/oclc/42476619&referer=brief_results

 

[bimr]

The Reynold King Watkins, Loren Runar Anderson book gives a design outline starting on page 179 of the book.

The design will vary depending on the size of pipe, the slope, and the soil conditions.

 

[eea]

Oregon DOT also has a standard concrete pipe anchor. I don't know if it provides the design level of detail you want, but it can be found at:

http://www.oregon.gov/ODOT/HWY/ENGSERVICES/roadway_drawings.shtml

ftp://ftp.odot.state.or.us/techserv/roadway/web_drawings/roadway/2008_Original/rd332.pdf

 

[ishvaaag]

By the way, I find astounding that the book on buried pipes when addressing block anchor design for pipes at an angle states a force equal to the vectorial composition of the resultants of the pressure from both sides. Frankly, this for pipes rigid and mechanically strong sounds like a fantastic hyperestatement of what required. You can throw a boomerang shaped inflated to some pressure at a trench, bury it, and not exert any of such block anchor forces. Methinks those supporting such practices as of general application need urgently comments of those what not.

 

[bimr]

Forgive me for not understanding your point, but perhaps you can copy the page in question and post it.

 

[ishvaaag]

Yes, will try to find again. I found it when checking this question 10 or 15 days ago.

 

[cntw1953]

Friction between the pipe and the anchorages should be something to look into.

 

[ishvaaag]

The attachment takes 4 pages of the book quoted above

Structural Mechanics of Buried Pipes

from which I quote from the 4th

"Thrust blocks are the most common restraints in use
for pressurized gasketed pipes."

In such context I think it quite proper to inmovilize any corner since otherwise the gasket could fail.

By whatever the reason I was thinking of continuously welded and/or mechanically jointed pressurized pipes. These show rigidity in their form and even if restraints and supports need be considered, the likelihood of not needing a thrust block augments. As in the example above, you lay a steel tube on some supports in free air, have of course to sustain anything the use imparts to them, and may well need not any thrust block at the corner.

 

[ishvaaag]

Sorry, the attachment...

 

[ferminbertha]

jmm540, did you ever get a response on this problem. I have similar situation.