Pipe installation w/ groundwater
Pipe installation w/ groundwater
(OP)
Hi, I'm reviewing options for replacing a sewer line that is 25-30ft deep. I've read some about different pipe materials (PVC and RCP are approved), but I'm wondering if groundwater impacts design? It would seem that the external hydrostatic pressure would influence the pipe but I can't find any sources that address this to say it does or does not affect the pipe's performance. I've found maximum cover heights from manufacturers but no mention of groundwater. Any guidance? Thanks





RE: Pipe installation w/ groundwater
Just stay within the recommended limits and loads provided by your mfgr to be safe.
RE: Pipe installation w/ groundwater
At this depth directional drilling and installing a PE line would appear to be the obvious solution. PE is thick wall to withstand the rigours of this installation method. It is thus of a relatively high stiffness and can withstand external pressure.
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RE: Pipe installation w/ groundwater
RE: Pipe installation w/ groundwater
You must account for groundwater during construction. This may require dewatering which is not normally included in the base price.
During design, you must check the deformation due to the groundwater. Buried Pipe Design by AP Moser has a procedure to evaluate the deformation. PE Pie and Design, AWWA Manual M55 also has a procedure.
RE: Pipe installation w/ groundwater
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Pipe installation w/ groundwater
1. Deep, wet pipeline projects are in general more difficult and costly to have constructed than shallow work.
2. For these sorts of projects the cost of the pipe may be a small, or very small percentage of the overall cost of the project.
Along with doing a little more homework and getting a contractor etc. experienced in such conditions with the piping involved, I think a quick web search of some experienced utility specifications for particularly deep work will reveal that having a very strong piping material, and with a robust joining system for same, probably goes a good way towards avoiding some of these problems. Various trenchless methods are indeed also now an option for some sewer work with multiple piping materials, but keeping particularly slick and lightweight pipes on grade (without sags etc., in the face of Archimedes) is per some authorities not much of a gimme with these as well.
RE: Pipe installation w/ groundwater
An empty plastic pipe will tend to float if it is light enough therefore being a problem to install.
Have you considered inertion into the existing? This will only require a deep pit at either end which will be much easier to dewater.
Regarding the pressure from the water, water creates boyancy which thus reduces the soil overburden pressure. I have not done the numbers but I would expect that the pressure would not be that much greater with a small depth of groundwater.