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
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Pipe installation w/ groundwater
- Thread starter cmickey
- Start date
The average soil weighs 2 x more than water, so if your mfgr gives a maximum depth of soil, you could assume that the equivalent hydrostatic load would be found at around two times that with water only.
Just stay within the recommended limits and loads provided by your mfgr to be safe.
Just stay within the recommended limits and loads provided by your mfgr to be safe.
AS 2566.1 Australian Standard for Buried Flexible Pipelines provides for groundwater above the pipe.
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.
"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.
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.
"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.
civilman72
Civil/Environmental
Depending on the height of groundwater above your pipe, infiltration through the joints can become a problem. From what I've been told, joints for a standard gasketed SDR 35 PVC pipe generally can handle about 15-20 pounds of hydrostatic pressure.
There are several issues.
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.
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.
dicksewerrat
Civil/Environmental
Why are you replacing this pipe? broken, leaking? Need more capacity? What size is it? What is it made of?
Richard A. Cornelius, P.E.
Richard A. Cornelius, P.E.
In theory (or on paper) I guess virtually any kind of piping material (or for that matter toilet paper tubes!) can be made to work as sewers at any common depth of cover, providing of course assumed soil support is achieved in the long term. I believe the road to success in deep, wet pipeline construction (in particular, and for many reasons) is however cluttered with some carcasses of crushed, broken, over-deflected and/or leaking pipes, gone broke contractors, and even some initially pretty strong looking, but somehow bent or broken shoring and steel trench boxes etc.! I have incidentally heard there have even been many quite nasty lawsuits over the years on such projects, that sap the time, energy and money of many folks and entities who might be standing around when all this occurs. I will further note the following:
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.
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.
A few comments:
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.
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.
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