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Sumps, Bleeders and Drainage

Feb 14 '14 24 Last Comment
wurdan freo
Feb 14, 14 4:54 pm

do bleeders always slope down from inside the foundation to outside the foundation? If there is a sump in a basement, is it usual/allowed for it to catch under slab moisture for removal? 

 

gruen
Feb 15, 14 10:03 am

What's a bleeder?

A sump can catch whatever you want it to. If you expect to have trouble w a high water table (water under the slab) then you can direct it to a sump. But beware that you cannot stop groundwater and you may get so much that its hard to pump is all away. Yes, you can put a network of pipes and take them to a sump.

Miles JaffeMiles Jaffe
Feb 15, 14 10:57 am

I'll assume that in this instance a bleeder is an open drain. French drains are a common way to drain basements if the intrusion is from ground level. If the intrusion is from high ground water it's counterproductive.

Sump pumps are typically installed in pits, the idea being to start pumping water away before it reaches the top of the slab. If the basement is occasionally *in* ground water there really isn't any way to keep water out unless you build it like  a swimming pool and eliminate all penetrations.

gruen
Feb 15, 14 12:36 pm

Maybe a bleeder is a pipe that moves water from under the slab to the footing drain?

You can pipe a footing drain to a sump if you can't drain it directly to the storm sewer.

citizen
Feb 15, 14 3:32 pm

"We've got a bleeder!"

wurdan freo
Feb 17, 14 10:50 am

franks and beans...

bleeder is a drain that is in the footing. it moves water from under slab area to drain area outside of footing... at least that's the way I understand them. 

Miles JaffeMiles Jaffe
Feb 17, 14 1:27 pm

You could probably hook up a sub-slab drainage system to a footing drain but you'd need check valves to keep the water from coming in. Now you're relying on a hidden mechanical system that is at best difficult to service. It seems nonsensical to me: if the bottom of the slab is wet it's presumably in groundwater and would have to be pumped out as there is nowhere "down" to drain it to. And that's absurd because if you're in groundwater there is no pumping it out without large mechanical systems running continuously. Is a pump house part of the program?

wurdan freo
Feb 17, 14 4:09 pm

Every project I've worked on in Wisconsin since 2006 has had the plumbing sub installing "bleeders" in the footing. Maybe it's a regional thing. Maybe I've understood it wrong this whole time?  If the ground water level is high then we would build the swimming pool type installation. Bleeders have been installed in "typical" conditions where ground water level wasn't an issue. 

Miles JaffeMiles Jaffe
Feb 17, 14 4:38 pm

If it's wet below the slab it stands to reason that it's wet outside the footing as well. Unless there are some major league leaks inside ... like surface level intrusion. Could this have something to do with deep frost conditions where the ground pretty much liquifies from the top down as it thaws?

gruen
Feb 17, 14 4:59 pm

I think you are right miles. If you are building a basement w no expected groundwater issues, the crushed stone capillary break keeps "moisture" away from the slab & the vapor barrier takes care of the rest.

If you expect a groundwater issue, it needs to be built like a bathtub, bentonite waterproofing. it can be drained to a footing drain to a pump if necessary. Generally a footing drain should solve the problem w/o under slab drainage though, since the footing drain should lower the groundwater in the entire area, unless the slab is very large.

gruen
Feb 17, 14 5:01 pm

Can't imagine that the bleeders hurt anything. Maybe the soil is clay so the water does not perc well, bleeders take water from gravel under the slab to the footing drains?

mightyaa
Feb 17, 14 7:40 pm

It depends on the soils and what you are doing.  So, here we deal with expansive soils regularly.  I'm seeing more 'moisture conditioned soils' in which case you absolutely do not want them to dry out.  Nor do you want gravel under the slab since moisture tends to wick to it. 

So, is it a watertable thing or a soils mitigation thing?

I'm also confused about the "bleeder".  If it's what I think it is, we call it a drainage mat which is a series of perforated pipes below the slab to intercept moisture and get it out before it saturates the slab.  I slope them to a collector and make sure the gravel and such is protected from silts.  I also avoid sumps like the plague if you can daylight somewhere.  Sumps have a notorious life span of about 5 years.  When they fail, you tend to backwash and those pipes are wonderful for making sure the issue isn't just localized. 

wurdan freo
Feb 17, 14 10:25 pm

see second bullet point or ctrl-f "bleeder"

http://blog.armchairbuilder.com/2332/tips-for-a-dry-basement/

wurdan freo
Feb 19, 14 9:59 am

from my plumber friend.

The bleeders that you are talking about are installed by the masons that put in the footings.  They are actually there to allow ground water into the building so that it can be pumped out the sump pump. If they weren't installed hydrolic pressure on the basement walls would put unneeded pressure on them.  On any new construction it is a code requirement to put them in as long as it is not slab on grade.

This is SE wisconsin so maybe because we do have a lot of "clayey" soils the water has no where to go?

mightyaa
Feb 19, 14 10:14 am

Sounds rather like drain mats we use here vertically along the outside face of the foundation wall.  At the bottom is a perimeter drain system sloped to daylight or sump.  The intent is water flowing through the gravely/bedrock type soils we cut into is intercepted and given a way to drain out.  Otherwise hydrostatic pressure, and potential water leaks through the foundation wall can occur.

Funny regional differences.  We'd seldom ever do a masonry foundation.  Concrete.  So I'm also wondering if it's a weep for the masonry foundation.  I know I've done some investigations here (Colorado) in the mountains where the cmu voids filled with water and due to the freeze, the resultant ice shattered the blocks.  Could have been avoided by providing a drain.

Miles JaffeMiles Jaffe
Feb 19, 14 10:20 am

So drains are being used for structural purposes? Hard to imagine hydraulic pressure on foundation walls being greater than frost pressure. 

This seems nonsensical to me unless there are some bizarre soil conditions. Maybe the building dept. can shed some light. 

mightyaa
Feb 19, 14 5:53 pm

Just think of it this way Miles... Ever witness a slump test?  Wetter tends to spread out more laterally than dry mixtures resulting in more slump.  In the real world, that means wet stuff is going to push laterally a lot more and a lot harder.  It's logarithmic loading too, so the deeper you cut, the forces grow exponentially.  It is a big structural concern. 

And subsurface conditions make a difference.  Think like my mountain work; Bedrock down about 8-15'.  The surface of that rock below has fissures, valleys, etc. It's seldom level or flat just like the mountain.  The top soil is gravel.  So there's a ton more water running along the top of the bedrock than there is at the surface (we've actually done several subsurface intercept drains up hill too).  And now you just cut a big ole hole in it.  Water is going to want to fill that hole.  Clays work like that too since water won't penetrate.  You essentially created a bathtub with the foundation excavation, but it's a 'bad thing' to ever allow it to fill up.

Wanna get real nasty?  I've done some projects where I've got 24% (not a typo) expansive soils with hydrocollapsable pockets/viens of gypsum.  Ever see a house rip in half?  I have... very pretty magazine cover home too. 

Miles JaffeMiles Jaffe
Feb 19, 14 6:13 pm

My inclination would be to *not* build basements in the conditions you describe.

mightyaa
Feb 19, 14 7:19 pm

lol... and not build in half the US because the subsurface conditions aren't ideal :P.

Actually around here most stuff is walk out basement conditions.  Clay soils are the worst since they don't easily allow water to infiltrate.  Most our stuff at least drains.  Lots of areas where basements are a really bad idea.  But here, it's common even in most commercial. 

If you know how to deal with it, and know what you are dealing with, you can design around it.  It just has to be considered both architecturally and structurally and understanding the options and risks.  Like that magazine cover home; Architect put a pond in the middle when there are hydrocollapsable soils (they dissipate when wet).  Didn't seem worried about it.  Terrible multi-million dollar mistake.  Really cool award winning design.. bad execution.  Ever have to design and install a whole new foundation and re-level a building AFTER the building is built? It's not cheap... Saving a few thousand by not getting an adequate geotech report exploring the subsurface conditions can destroy you in the long run. 

Miles JaffeMiles Jaffe
Feb 19, 14 7:50 pm

In NY you would be in court for a decade over that.

How much dissipation over what area?

Apurimac
Feb 19, 14 10:43 pm

LOL @ 24% expansive soil.  That has to be clay, clay is crap.

As another NYer, I think the approach I'm most familiar with is drain and add waterproofing.  I've never heard of hydro expansion being so bad its preferable to actually bring water into the building to release hydrostatic pressure.  Learn something new every day.
 

mightyaa
Feb 20, 14 2:18 pm

Claystone actually... super dry region that is essentially mesas and scrub brush like how you might picture Arizona desert.  It looks like shale (flaky like that), but red.  But get it wet and it's clay.  You kind of almost wonder if the mesa's were formed more like how mud looks after it dries out...  that's the Grand Junction region near Colorado and Utah.

It's also fascinating to me how thought and thinking changes so rapidly over the years when it comes to expansive soils and the depths needed to get below it.  In the '80's, a 20' deep pier was generally accepted (18" diameter).  '90's, was 30' and 12-16" dia.. now I'm seeing studies where the wetting and expansion is expected to take place down 50' and 24" sleeved piers.  So spread footings are coming back.

And it isn't just upwards lift.  Tilted plate rock formations that form the mountains, so there is lateral too.  Saw a 'cool one' where piers where snapped in half due to the subsurface lateral forces.  So with width of piers has also changed over time to resist those subsurface lateral loads..  I've seen helical piers corkscrew themselves to create inconsistent heave (or so the theory goes).  I've seen pinned slabs to the foundation tear off the top of the foundation stem wall; know how much force it takes to shear a 8" reinforced concrete wall? 

Basically, pay a lot of attention to sub-surface conditions and don't just rely on your engineer.  It really needs to be discussed because if a foundation fails, you have a very expensive problem. 

Miles JaffeMiles Jaffe
Feb 20, 14 6:43 pm

Amazing that someone would actually build a pond in such a climate. They must have had an autofill pumping constantly.

Every pond I've seen built has been with a liner.

mightyaa
Feb 21, 14 10:08 am

Worse Miles...  graded and re-routed a gulley (that drained I think the report said 1500 acres) between two mountains to flow into this.  Also created a series of waterfalls between two man made ponds.  One pump was to pump it under the driveway which acted like a dam when the water level reached a certain point (this is the one they deducted in-leu of massively undersized culverts). And to feed the upper pond so there'd always be water flowing down that series of waterfalls like a massive water feature since the area is usually pretty dry.  

There were also water features on the interior that played nicely into the aesthetic. It was a really was a truly beautiful and high design house...  too bad the architect just ordered a pit test for the geotechnical report and ignored within that report the plea to conduct deeper exploration given the soils conditions in the area.  He also made a whole series of other mistakes where he chose aesthetics over 'things that work' like watershed and weather barrier concepts.

"If only he'd ____" is something I end up saying a lot. I respect and admire the design quite a lot.  The execution though was terrible and pretty much condemned this building.   

Miles JaffeMiles Jaffe
Feb 21, 14 11:13 am

I have a hard time admiring dysfunctional design, but do enjoy the comeuppance that occasionally comes to such hubris. 

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