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Precast Sewer Structures...

SeaMac

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Jun 2, 2012
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549
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27.2730° N, 80.3582° W
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Hello fellow HEF members,

I've heard of although never seen a Sewer Structure where the bench and channel/s are precast into a monolithic base. Here we do it the old-fashioned way with bricks and mortar, same for the chimney, frame and cover atop the corbel/cone. I can certainly see the benefits of it being precast where the concern for invert alignment and elevation is aleviated by the invert boot. Another benefit of cast-in benches and channels is the prevalence of lined/coated structures where if Mason's have to build the B/C's it's an added step to apply the lining/coating on top of the masonry work. My question is, anyone here use these precast structures? Also, I know they precast grade rings to sit atop the corbel/cone but again we still do it the old-fashioned way we're required to have at minimum two (2) courses of brick to a maximum of five (5) to set the frame at final grade. Anyone use these too?
 

heavylift

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Sep 5, 2009
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1,046
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KS
We first used them in the 70's. Some with inverts cast, where you used about a sack of Quickrete to finish the edge around the pipe.
At first they were opened bottomed, they were set on cinder blocks, then the base and invert were poured.
A few years later they started coming bases poured but no invert.

The invert poured ones used a hole with a gasket w/wedge...A PAIN in the drain LOL
The others had a u shaped hole, so an exact grade wasn't required for setting. Just put a rubber on the pipe, place the mud, some around the outside on the pipe, then finish the invert.
 

SeaMac

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Hi heavy,

In your opinion, are they economical and labor saving in the long run? I know first hand how miserable it can be in the August/September heat of summer with 90+ percent humidity to climb down inside a structure to build the B&C. I have seen those online while researching where the base, walls, B&C are all monolithic and in some cases lined. I'm not sure if it's common industry wide but all our structures are provided with rubber boots cast-in-place that only require two stainless-steel hose clamp type bands. We do however use brick and mud to lock in place the DIP or SDR then seal both inside and out. Since you said the 70's that only further confirms my long-time suspicion that in certain aspects Florida is woefully behind the technological curve.

I'm thinking that locating or convincing a local precast yard to form and pour such structures just might be worth it. The time and money saved should - I hope- offset the cost of brick and portland. Considering how many bricks -at 43cents each- get left behind, broken or needlessly discarded not to mention all the 94lb bags of #2 Portland that get wasted or left uncovered -a whole other peeve of mine- you begin to see the cost savings in materials alone.
We first used them in the 70's. Some with inverts cast, where you used about a sack of Quickrete to finish the edge around the pipe.
At first they were opened bottomed, they were set on cinder blocks, then the base and invert were poured.
A few years later they started coming bases poured but no invert.

The invert poured ones used a hole with a gasket w/wedge...A PAIN in the drain LOL
The others had a u shaped hole, so an exact grade wasn't required for setting. Just put a rubber on the pipe, place the mud, some around the outside on the pipe, then finish the invert.
 
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Acivil

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Jan 30, 2010
Messages
154
Location
Tennessee
Precast are all I've ever used for new sanitary. I've done some brick work and rebuilds on older manholes, but everything around here from the 70's on has been all precast. We still use brick on the occasional storm manhole or CB, but only when it's more practical than precast which is rare. The bench and invert aren't actually mono poured though... They pour the floor monolithically with the walls, then core it, most plants put the chunks from the cores in the benches then pour over them forming the invert and benches. IMO it just depends which plant they come from how well the inverts end up working out, but you generally have enough play in the boot to make it work then grout it in. I have used brick, concrete doughnuts, 30" RCP on end, and HDPE Rings to set castings. We also developed a form system which you place inside the chimney section, it expands then your pour concrete around it and set the casting in the wet concrete for a perfect seal and grade/cross slope. For me the main reason to use precast is an exponentially smaller amount of seams which imo is an exponentially smaller chance for infiltration that my kids or grand kids will have to pay to fix.
 
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SeaMac

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Huh,

Seems we really ARE behing the curve here in South Florida. Of course I never thought of cutting rings out of RCP, better than smashing the bones to bits and having it hauled away. Then again getting the cut good enough for grade purposes relies on he who holds the cut-off saw. We don't use HDPE enough so having scrap around doesn't apply for us. I like the idea of having things all sealed up -the Inspector's like it too- so we religiously use Ram-Nek then mud the seam inside and out. As for the castings, all it takes is an errant blade and off it slides, what I've seen online is the use of precast grade rings where they apply a thin layer of grout then Redhead the frame down permanently, an idea I am fond of for sure. Getting some really valuable input here, keep it coming and thanks...

Precast are all I've ever used for new sanitary. I've done some brick work and rebuilds on older manholes, but everything around here from the 70's on has been all precast. We still use brick on the occasional storm manhole or CB, but only when it's more practical than precast which is rare. The bench and invert aren't actually mono poured though... They pour the floor monolithically with the walls, then core it, most plants put the chunks from the cores in the benches then pour over them forming the invert and benches. IMO it just depends which plant they come from how well the inverts end up working out, but you generally have enough play in the boot to make it work then grout it in. I have used brick, concrete doughnuts, 30" RCP on end, and HDPE Rings to set castings. We also developed a form system which you place inside the chimney section, it expands then your pour concrete around it and set the casting in the wet concrete for a perfect seal and grade/cross slope. For me the main reason to use precast is an exponentially smaller amount of seams which imo is an exponentially smaller chance for infiltration that my kids or grand kids will have to pay to fix.
 

stretch

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Southington, CT
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It's all we use up north too. We only use bricks and mud to seal up around the pipes in and out of the structure where we'd cut or smash a hole in.
 

SeaMac

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Hi stretch,

Yeah, like I said, it would appear we're woefully behind the curve with respect to our precast yards. However we don't have to core or smash the invert hole, at least that's done for us with a boot installed to boot. We've got a busy week ahead but I plan on making some calls about having the B&C's cast-in to the base and why our yards don't offer that option. It will be interesting to hear their responses.

It's all we use up north too. We only use bricks and mud to seal up around the pipes in and out of the structure where we'd cut or smash a hole in.
 

buckfever

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Aug 12, 2010
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813
Location
southwest pa
all we use is pre-cast manholes. I didn't even think they still build manholes (storm or sanitary) out of brick. As for the cost around here a good roll of thumb is about $150 per foot. The time you guys spend lating brick would be insane. You can build a manhole in less then an hour. Thats base, riesers, cone, and frame.
 

SeaMac

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Hey buckfever,

We don't build the entire structure out of brick although I have seen some old one's built that way. No Sir, I'm referring to the Bench & Channel or Invert at the base. Here we build up the bench with bricks then scuplt out the channels or inverts if you will. We also build the chimney out of bricks 2-course min., 5-course max then set the casting on top. I have seen online the "base" structure being monolithic precast including the B&C. WHAT a flippin' labor and dollar saver! I've also seen precast "grade rings" to use in lieu of bricks for the chimney.

Having said that, we did get quite a few drainage structures and a boat load of RCP delivered today and I asked one of the drivers about such structures. He informed me that yes, the yard "can do" but has only been asked once prior, by who other than an out of state contractor. Our PM is going to look into the cost and labor savings since we have yet to order the sanitary structures, hey, maybe I'll actually get to see and set one in the near future...


all we use is pre-cast manholes. I didn't even think they still build manholes (storm or sanitary) out of brick. As for the cost around here a good roll of thumb is about $150 per foot. The time you guys spend lating brick would be insane. You can build a manhole in less then an hour. Thats base, riesers, cone, and frame.
 
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Deeretime

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High River Alberta
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when you use precast manholes generaly do they have pipes comeing out of them like we do or do you always grout your pipes in ?
All i have to do is e-mail drawings to the precast place and they bench all of the inverts and install either a bell or a pre beveld piece of pipe for me in all different sises and droop structures
 

SeaMac

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Deeretime,

Our precast structures come with rubber boots set at the proper invert elevation. We do however lock the DIP or SDR in place with bricks then mud the opening both inside and out.

when you use precast manholes generaly do they have pipes comeing out of them like we do or do you always grout your pipes in ?
All i have to do is e-mail drawings to the precast place and they bench all of the inverts and install either a bell or a pre beveld piece of pipe for me in all different sises and droop structures
 

buckfever

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Messages
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southwest pa
Ok I understand what your saying Seamac. I have never seen a sanitary base without a pre-pored invert. Most of the storm bases come without a invert and we either order concrete from a local concrete company. If we do only a couple we get out our mixer and 80 pound bags of gravel mix.

On a sanitary base the only thing that needs grouted is around the pipe where it enters the flow line.
 

SeaMac

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Hey buckfever,

As a rule we don't do anything to the base of drainage only sanitary and that's where we seem to do it the "hard" way. If the PM get's good numbers then maybe we too will join the 21st Century 'til then nothin' but brick-n-mortar.

On a sanitary base the only thing that needs grouted is around the pipe where it enters the flow line.
 

buckfever

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southwest pa
Then how do you keep garbage from building up in the bottom? We have installed catch basens with the intent of going back after 4 or 5 are set. after sitting through one or two rains you could already see gravel and road dirt building up in the bottom.

Around here no engineer will sign off on your work unless the bottom is poured and the pipe comming in and going out are both grouted.
 

SeaMac

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Don't get me wrong, we absolutely grout the inlet/outlet of drainage structures. When still under construction we regularly change and religiously keep Mirafi paper under the grate. If "crap" starts to build up in the basin we have a Vac Truck to remedy that. All the cities and counties 'round here have Vac Trucks too, it's how they keep 'em clean as well. I've never seen any bench or channel poured into or built in a drainage structure. Again, it would appear that down here we may be a little behind the curve.

Around here no engineer will sign off on your work unless the bottom is poured and the pipe comming in and going out are both grouted.
 

390eric

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Feb 24, 2009
Messages
274
Location
pittsburgh PA
Hey Buckfever ever install and mainline for McCandles township Sewar Authority? See you are in the same area I am. They make you pour them by hand, not pre-pours. They have to be smooth as glass, they test it with toliet paper if they run it across the invert and it snags anything, gotta chip it out. The trick I have learned is first thing next morning gotta polish them with around 400 sandpaper.

The pre-pours are really nice compared to doing them the other way. A lot less work.
 

SeaMac

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Hey 390eric,

Here's a trick we use if the Inspector/s and Spec's approve, we add white plaster mix to our portland #2 cement and do so in a 2:1 ratio. It not only sets and cures faster but you can make a VERY smooth finish easily. Of course it all depends on the Inspector and Spec's, some allow some strictly forbid. Just a thought but then having it precast and ploymer lined affords a finish which is basically slicker than Owl snot, which I've heard is pretty darn slick. Again, just a thought...


Hey Buckfever ever install and mainline for McCandles township Sewar Authority? See you are in the same area I am. They make you pour them by hand, not pre-pours. They have to be smooth as glass, they test it with toliet paper if they run it across the invert and it snags anything, gotta chip it out. The trick I have learned is first thing next morning gotta polish them with around 400 sandpaper.

The pre-pours are really nice compared to doing them the other way. A lot less work.
 
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Dominion 410

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Aug 7, 2008
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240
Location
Ontario,Canada
Hi,

We've used pre-benched manholes with pipe entry gaskets on sanitary sewer applications almost exclusively for over 10 years now. Quicker and easier than pouring a bench especially when dealing with an existing sewer flow.

Dominion
 

buckfever

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southwest pa
Hey Buckfever ever install and mainline for McCandles township Sewar Authority? See you are in the same area I am. They make you pour them by hand, not pre-pours. They have to be smooth as glass, they test it with toliet paper if they run it across the invert and it snags anything, gotta chip it out. The trick I have learned is first thing next morning gotta polish them with around 400 sandpaper.

The pre-pours are really nice compared to doing them the other way. A lot less work.


Cann't say I have but I do reconise the name.

It's funny how some places have crazy specs for some things but look right past some others.

Case and point. had a guy from Cecil twp. that made us go in after a structure was built and vac. tested and cut any con-seal that was sticking inside. But they didn't care that the manhole that was installed 2 years ago that we were coring into had a Meannnnnnnnnnnn lean to it. I'm talking a lean that when you looked down to the bottom you had vertigo. Had to make sure you didn't get dizzy and fall into the hole.
 

390eric

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Feb 24, 2009
Messages
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Location
pittsburgh PA
O yeah trimming con-seal, always the last part of the mainline inspection, really sucks when you are in a 20 foot manhole hanging on with one hand and trimming with the other.
 
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