# Some new manhole questions



## rino1494 (Jan 31, 2006)

I am bidding a new development. There is no sewer adjacent to the property. I have to run the 8" line out through a 18' wide easement (200' long and 9' deep) and run across a state road to tie into an existing sewer line. I will be 9' deep in the road and the state requires backfill with flowable fill. I have to throw road plates over the trench overnite to let the flowable fill dry and pave the next day. 

The existing line, runs perpendicular to the new line and is in the berm on the other side of the road. I need to cut that existing line and set a new manhole. I am not sure of the gallons of flow per day or the size of the existing line. I am going to contact the sewer authority for those answers. I know that I will need to do by-pass pumping. I have never done that before, so any thoughts or tips ?? 

Here is my real question. The new manhole that I need to set in the berm will be 14' deep. My shoring options are manhole boxes or slide-rail. Can you double stack manhole boxes ?? I am hoping to complete this manhole install in one long day, but I am afraid that if I don't, i'll have to pull the slide-rail system and re-install the next day. Reason being, part of my overdig will be in the road. I will have flagmen and 1 lane shut down. How long does it take to install the slide rail system ?? I have a feeling this is gonna be a very expensive project for just 12 lots.


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## S.R.E. (Apr 8, 2010)

rino1494 said:


> Here is my real question. The new manhole that I need to set in the berm will be 14' deep. My shoring options are manhole boxes or slide-rail. Can you double stack manhole boxes ?? I am hoping to complete this manhole install in one long day, but I am afraid that if I don't, i'll have to pull the slide-rail system and re-install the next day. Reason being, part of my overdig will be in the road. I will have flagmen and 1 lane shut down. How long does it take to install the slide rail system ?? I have a feeling this is gonna be a very expensive project for just 12 lots.


Yes you can double stack manhole boxes if they are rated for that depth. Why can't you leave the shoring in the hole? Just make sure the top of the box is low enough to lay the plates overtop. Pull off plates the next day and install a short box on top if you need to meet your 2' of free board.


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## guyute65045 (Nov 23, 2006)

I dont know if it is OSHA compliant or not, but the manhole box I use has metal "ears" welded onto 4 corners with holes in them to pin another box on top of it. I have never had to stack another one on top of it but it looks like it can be done.
As far as leaving the hole open overnight if you place your road plate over it and barricade it off with jersey barriers and such I would think it would be ok. Of course I am in east podunk and see the state and towns do things that make me cringe every day.


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## rino1494 (Jan 31, 2006)

guyute65045 said:


> As far as leaving the hole open overnight if you place your road plate over it and barricade it off with jersey barriers and such I would think it would be ok. Of course I am in east podunk and see the state and towns do things that make me cringe every day.


If this was some backwoods road, I wouldn't care, but this is a heavily traveled road. My overdig would be partway in the road and I would definitely have to backfill it. I don't think leaving plates overnite over a 14' deep hole is a good idea. If I had to, I would just backfill with modified and dig it up in the morning. Penndot is very strick when it comes to their roads. If I can double stack manhole boxes, then I don't see a problem. I have never used one before. Can a 200 size hoe handle them ??


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## PipeGuy (Oct 8, 2004)

rino1494 said:


> ... I need to cut that existing line and set a new manhole. I am not sure of the gallons of flow per day or the size of the existing line....I know that I will need to do by-pass pumping. ..any thoughts or tips ??
> Here is my real question...Can you double stack manhole boxes ?? I am hoping to complete this manhole install in one long day......part of my overdig will be in the road.


If you want to talk in detail about the ins and outs of sewer by-passing then PM me after you have the sizing/flow information and I'll give you my cell#. Another good resource is your local Godwin pump rep. They'll look at what your dealing with and quote a by-pass "package" based on the job specific requirements. 

Also - the type of existing pipe you're dealing with might make a difference in wether you "cut-in" to the existing pipe or "build-over" the existing pipe. In the case of a build-over it doesn't sound to me, given what you've described, that you'd need to do any by-pass pumping.

Yes you can stack manhole boxes - if they're set up properly with accessories that allow them to lock together. I like to use 12 x 12 boxes on deeper manholes rather than the more typical 10 x 10. At 14' deep you might want to go with an 8' tall box and a 4' tall extension.

At the depth you describe you'll really need to hump to get the new manhole dug, cut-in and backfilled in one long day. To have any chance of doing so you'd need to have the by-pass equipment set up the day before and everything else will need to go off without a hitch. Whatever the case, you oughta' figure on having a way to secure an unbackfilled hole overnight if the need arises.


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## S.R.E. (Apr 8, 2010)

rino1494 said:


> If this was some backwoods road, I wouldn't care, but this is a heavily traveled road. My overdig would be partway in the road and I would definitely have to backfill it. I don't think leaving plates overnite over a 14' deep hole is a good idea. If I had to, I would just backfill with modified and dig it up in the morning. Penndot is very strick when it comes to their roads. If I can double stack manhole boxes, then I don't see a problem. I have never used one before. Can a 200 size hoe handle them ??


I have plated over a hole with boxes in it before. If your local authority approves that they should require you to place cold or hot mix asphalt at the edges of the plates to provide a smother ride and more importantly to prevent the plates from sliding on the road. A 200 size hoe can handle some manhole boxes, it depends on their weight(obviously), which varies a lot depending on how they are built. i.e.... wall thickness, size, thickness of spreaders, and various other factors. You will have to talk to your shoring supplier to figure out which boxes you can use for you application. And by the way you can stack trench boxes over 30' deep if you use the right ones. Although if your going to be digging over 20' deep I would recommend at least a 450 size hoe.


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## S.R.E. (Apr 8, 2010)

You also might want to set it up for a two shift job if possible and plan on working day and night till you get it installed. Nothing sucks more then getting your hole dug, shoring installed, and base prepped and then having to pull out the shoring and fill it in only to repeat it again the next day.


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## PipeGuy (Oct 8, 2004)

rino1494 said:


> ...I don't think leaving plates overnite over a 14' deep hole is a good idea. If I can double stack manhole boxes, then I don't see a problem. I have never used one before. Can a 200 size hoe handle them ??


If it's properly shored the depth of the excavation should have nothing to do with whether its safe to leave roadway plates over it overnite. Keep in mind you'll need roadway plates heavy enough to span the manhole box.
A 200 will pick and set a 10 x 10 x 8 box just fine. It's the removal part that can get dicey.


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## WC&T (Feb 22, 2010)

you should be able to use a bottomless precast MH to set over the existing pipe. Cut U's from the bottom of the sides up at the pipe penetrations to get the structure over the pipe. Then cut the top half of the pipe out leaving the flow line of the pipe. pour the bottom in the MH and either use the existing pipe as the channel or plug the line for 10mins with a test ball while you cut the last of the pipe out and Jet Set your new channel. You shouldn't need to bypass your sewer if the local PW is okay with that method.


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## rino1494 (Jan 31, 2006)

WC&T said:


> you should be able to use a bottomless precast MH to set over the existing pipe. Cut U's from the bottom of the sides up at the pipe penetrations to get the structure over the pipe. Then cut the top half of the pipe out leaving the flow line of the pipe. pour the bottom in the MH and either use the existing pipe as the channel or plug the line for 10mins with a test ball while you cut the last of the pipe out and Jet Set your new channel. You shouldn't need to bypass your sewer if the local PW is okay with that method.


I like this idea. They can make doghouse manholes, I forgot about that. The one thing I was worried about is if the precast company didn't pour the holes exactly right for the existing line.


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## WC&T (Feb 22, 2010)

rino1494 said:


> I like this idea. They can make doghouse manholes, I forgot about that. The one thing I was worried about is if the precast company didn't pour the holes exactly right for the existing line.


They don't have to be tits on. If they are off a little than cut it out with a hot saw w/ a diamond blade.


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## jmacd (Jul 14, 2009)

I did something like WC&T is describing and completed. The road was closed and the depth wasn't near as deep as you though. We poured a floor in and cut basin on site. Took 2 days here are some photo's:


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## earthmover (Feb 17, 2009)

rino1494 said:


> I like this idea. They can make doghouse manholes, I forgot about that. The one thing I was worried about is if the precast company didn't pour the holes exactly right for the existing line.


Thats what I was thinking when I read the first post. Sounds like the perfect situation for a dog house manhole.


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## Upchuck (Apr 7, 2009)

If allowable doghouse manhole is definitely the way to go. I prefer they leave oversize openings on either side. I rather use more brick & mortar then having to cut manhole. Some places around here don't allow doghouse manholes. They want manholes to have rubber boots.

BTW, did you mean 18" or 18' easement. Easements for utilities are usually 10' min. around here. Mostly for maintenance.


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## rino1494 (Jan 31, 2006)

Met the with sewer authority today. I know those boys real well. They do not want a doghouse because they tend to leak and hard to fix. There are few houses on the road that are gravity fed into the sewer system. There is 2 developments up the road that feed the system via a 4" pressure main. The sewer authority will pump down the station and shut off the pump until we are done with our hook up. We are gonna get a manhole with a solid bottom, but no poured channel. We will shove a pipe all the way through the pipe and fernco it on each end then run our drop in and cut the top of the pipe where the drop lays. 

I think we are gonna sub this part out. We are really not geared up for it. We have to rent the 2 manhole boxes, and rent more road plates. We have a guy that does nothing but pipe work that does this all the time. I'll just have him get us across the road and we'll take it from there.


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## Little (Jul 22, 2006)

Yup we never use the doghouse manholes anymore due to their leaking.


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## PipeGuy (Oct 8, 2004)

Little said:


> Yup we never use the doghouse manholes anymore due to their leaking.


A leak-free doghouse is easily installed over rigid pipe. While I've never tried to build one over plastic pipe I'd imagine it'd be awfully hard (if not impossible) to do. We build doghouse manholes all-the-time over concrete, terracotta, cast/ductile-iron and transite that remain free of infiltration despite high groundwater tables.


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