Will CIPP work if piping is evident?

[debgallery]

Here's the scenario:
36" CMP (maybe 20 years old or more) conveys a creek under a parking lot (FEMA 100-year flow =358-cfs). The CMP runs through a drop manhole so as to avoid water and sewer mains that run through the parking lot(about 4' drop - currently getting the survey done). The total length of pipe is about 150' and the elevation difference between the inlet and the outlet is about 14.5'. There is a tall embankment on the downstream side of the parking lot that failed this spring, crushing the outlet. At the time it was not possible to actually inspect the culvert because the water was too high but the manhole had actually moved and you could see that there are void spaces around the manhole. We also can't even find the outlet to the pipe but there is water flowing out of the debris. I'm working on getting it video'd.

We've been hired to come up with alternatives to fix this thing temporarily because the whole site is being redeveloped. Obviously, alternative 1 is to replace the whole thing with an appropriately sized system.

Here's my question: If we proposed rehabilitating the pipe with a CIPP or other liner is there anyway to stabilize the bed material or the obvious voids around the MH so that piping does not continue? Also, is it even possible to use CIPP or other liner with a drop manhole?
Thanks, any thoughts are appreciated

 

[beej67]

That sounds like a total disaster. There's no way in hell I'd spec CIPP for what you're describing. Rip it out and replace it with RCP or something that will last. I highly question the use of CMP on a live stream to begin with.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[dicksewerrat]

Is the drop manhole accessable? CIPP can be designed for the depth and other loads. The CIPP will seal the water intrusion. It will not fill voids. If you can locate the voids. you can fill the voids with grout. Then Line. you will need to expose the outlet. The lined pipe will give you better flow rates than the CMP. 'N' value for CMP is about .023, after lining around .015-.018.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[cvg]

358 cfs through a 36" cmp? are you sure about that? I think you would be lucky to get 80 cfs through it. Number 1 - the velocity and pressure is way too high for cmp number 2 - I believe you need to replace the manhole now. the cmp has failed at the manhole so you will need to replace part of the pipe I would expect also. Once you do that you could line the rest, but don't expect any great increase in capacity, you are already way undersized. I think you also need to re-evaluate the effectiveness of the drop manhole. I would guess that water coming into the manhole at 20 fps and then turning 90 degrees could have caused it to jump around a bit...

 

[debgallery]

Hey everyone, thanks for your responses
358-cfs is FEMA's 100-year peak flow estimate, 36" CMP is what was installed many many years ago.

Since traffic interruption isn't an issue and redevelopment of the site is far off, we're going to recommend a complete replacement of everything with appropriately sized culvert(s). I'm going to try to eliminate the manhole as well, just not sure if its possible with the existing water and sewer mains.

Thanks again!

 

[beej67]

Dick -

I've read that lining reduces manning's n values, but it also reduces your flow section, doesn't it? You seen any data on exactly how much it reduces your flow section?

cvg -

You can get any amount of flow through a pipe with enough head. But if that pipe happens to be CMP, then you'll get water squirting out the joints during big storms, because they can't handle the pressure. Then you get undermining of your pipe, and piping, and a general scenario like debgallery is talking about. It could be the flows are right and the original design was just vastly inappropriate.

deb -

Sounds like you made the right choice to me. Do your own analysis on the flow and size an RCP for it.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[cvg]

beej67 - do the calcs - I did - you really can't possibly get 350 cfs through a 150 foot long cmp without extremely high pressure. Ignoring entrance losses and the manhole losses (which should not be ignored), nearly 70 psi at the upstream end. cmp is not rated for pressure flow. 10 feet of head is approximate limit I would recommend which give about 80 cfs

 

[beej67]

Yeah, I didn't bother with the calcs, so I'm sure you're right, but then again the pipe might have been sized for the 10 year or less if it was old, depending on the regs.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[cvg]

Deb
you can keep the manhole if you want, but design it for pressure flow as well as surge. This wont be your ordinary manhole but a heavily reinforced concrete structure. Potentially bolt down the cover to prevent it from flying. Or plan on surges coming out and use a grated cover. Any pipe bends should also have thrust blocks. Recommend using some sort of pressure pipe, 72 inch might be better.

 

[beej67]

I wouldn't design anything carrying stormwater in a live stream for pressure flow, as a rule of thumb. Parking lots maybe, but no way on offsite water, at least down here. You have to think about what you're doing. To get your stormwater pipe into pressure flow, what do you have to do? Raise the HGL. Which increases the tailwater on the upstream creek, which changes the 100 year flood extents up the creek, which can get legal even if you're not in a FEMA regulatory floodway. If you're my downstream neighbor, you can't pond your stormwater into my property during storms, at least under the sorts of stormwater regs that we have in the SE US. Been that way since the Code of Justinian.

And fyi, if this were a new development instead of redevelopment, the Corps wouldn't let you do it at all on a live stream, without jumping through a bunch of new "habitat connectivity" hoops, which seem to change from job to job in my experience. At least in our region.

If it were me, I'd size a nice, fat RCP culvert for the 100 year storm, being sure not to change the ponding extents on my neighbor. I'd check with the municipality to make sure they didn't want me to use a future land use map when doing the watershed delineation. I'd stay under 300 feet of new creek disturbance to dodge the Corps. I'd also check for local and state buffer rules.

And if you're in a scenario where you're in complete redevelopment, and you're not yet out of the land planning stage, and your unit yield or impervious footprint isn't very tight, I'd lay in a swale or refurbish the creek. Cheaper and greener.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[dicksewerrat]

The liners are designed acording to the existing pipe depth, shape and other live loads. Unless the pipe is about to collapse and is 10% oval, the liner is not very thick. A 36 inch pipe, 5% ovality and 12 feet deep would be in the range of 17-18 mm thick.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com