Concrete Retards 1

[juany]

I'm designing/profiling a 12" WL. There is a segment that will be very steep (25%) and requires concrete retards.. Has anyone detailed these? or where can I find stadard details/specs

Thanks

 

[PELS]

When I first read the title of this thread I thought you were talking about a concrete contractor or city/county plan checkers.

I think you are referring to cut-off walls, which are basically a concrete collar placed around the pipe to minimize groundwater flows in the backfill and bedding of steep trenches. In our area this expertise lies with the geotechnical consultant (soils engineer), who can size them and determine the frequency of their placement.

 

[cvg]

if they are simply to retard water flowing in the trench, clay dikes or lean concrete backfill can also do the trick. However, if they are to anchor the pipe to prevent it from sliding downward, then they are a structural element and there are standard designs out there. Or get your geotech to recommend it as previously recommended by PELS

 

[juany]

Thank U PELS & CVG for the info..

 

[rconner]

While I did quite a bit of work in a prior life with concrete in many different applications basically as an engineering student struggling to survice and I still consider it in areas a quite useful material now, I will not take offense to the subject! Pipes are of course installed and supported in various fashions and in all manners of directions from vertical to horizontal, but in my opinion very steep slopes that call into the question the stability of the hillside as well as the pipeline are indeed special cases that require the attention of competent engineers skilled in all aspects of such work. There is however some minimal guidance for the installation of ductile iron water pipes e.g. on most commonly rather gentle earthen slopes contained in AWWA standard C600, AWWA Manual M41 (including a section in this manual on generic buried and exposed ductile iron “pipe-on-supports” design), and there is at least minimally conceptual anchorage on steeper slopes depicted from some manufacturers such as ACIPCO at

http://www.acipco.com/international/engineeringlibrary/engineering-data/poss.cfm.

As talked about in these references, belled pipes are most often installed with the bells facing uphill.
Basic guidance for steel water pipelines and designs etc. including piping on slopes is contained in AWWA manual M11, and the section “Anchors and Thrust Blocks” also contains the following statement, “An all-welded pipeline laid aboveground on piers may be stable when filled and under pressure but may require heavy anchorage at angle points and particularly on steep slopes to resist stresses resulting from temperature changes when the pipe is empty.”
I am aware of multiple projects where e.g. even very large diameter ductile iron piping has been installed on very steep slopes. The one I’ve seen the most detailed information on (with regard to supports/anchors and contacts etc.) was the installation of a 48” restrained joint ductile iron pipeline (used to pump a lot of Kentucky River water) up a steep “400-foot cliff” near Lexington, KY in the very early 1990’s. I believe a cut into solid rock was first made for the pier supports/anchors for that pipeline, by workers (with hand-held rockdrills and jackhammers) tied off to a life line with safety belts etc. After making the cut and drilling rock anchors several feet into same, concrete saddle supports were placed to support/anchor the pipes. Special pipe bands and rigging were fabricated that allowed the pipe to be lifted and suspended at the appropriate angle defined by the support saddles, and the system also allowed the pipes to be unhooked for assembly while the lifting device (a helicopter!) went to get another pipe. With this planning, I understand the actual placement of the ductile iron pipe up this cliff onto the supports subsequently took a total of less than six hours flying time, which made the cost of the helicopter services easier to bear. More information, pictures, and contacts etc. would be available through the pipe manufacturer, as the project was subsequently featured in the Winter 1993-1994 “Pipe Progress” magazine.
Beyond this, I would only mention that (like all other work and regardless of means of installation) I believe safety should be a paramount consideration and it should be remembered that particularly with work on a very steep slope virtually anything (even any tool etc.) of any size and mass can easily become a potent missile or bowling ball powered by gravity toward anything/anyone below! As far as basic slope stability or movement of water etc. along conduits or sloping conduits, this may be an arguably some different matter though I am aware that the USACE and probably also other folks have talked at length about this subject e.g. at least as it relates to issues of dams and dikes etc. (“anti-seepcollars”, “cut-off walls” or “water-stops” etc. might be good key words to find out more about such functions/applications). While not purporting to be an expert in the geotechnical etc. matters involved, I suspect however keying multiple substantial supports into a firm underlying structure (e.g. the solid rock of a cliff) of at least a non-leaking pipeline probably won’t hurt the future stability of the pipeline nor at least any soils between.