Alleviating perimeter drain water
Techventurer
| Posted in GBA Pro Help on
We have a sump system with the perimeter perforated corrugated 4″ drain tiling flowing into the sump from a connection under our 6″ thick concrete floor.
If I put a liner into the sump allowing the drains to penetrate and also covered and sealed this liner with a top and installed a 1-1/2″ dia. ABS pipe extending out the top, sealed all floor drains, would the pressure of the perimeter drains build up enough while trying to drain into the sump now enclosed be enough to force the water up and out of the 1-1/2″ ABS pipe to a height of 60 inches? The 1-1/2 pipe now being the route of least resistance to allow the water to escape.
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Replies
Murray,
No, the pressure in the drains is inconsequential. You need something called a sump pump.
Martin
I have had a sump pump for 45 years eliminating the water.
Why do so say the pressure in the drains is inconsequential? When the power fails and the pump is working the pressure is not inconsequential!!
Please provide the basis of your statement with calculations why my theory/question is possible or not possible.
Murray,
Let's imagine that your basement is a wooden coffin the size of a room, and the wooden coffin is in a very big swimming pool. If the wooden coffin is submerged (by putting in some rocks) so that the water is almost up to the top lip of the coffin, and if you punch a hole in one of the walls, the water will rise inside the coffin to the level of the swimming pool. So I'll concede that it's possible.
However, you won't have that much hydrostatic pressure around your concrete basement unless you live in New Orleans and the city is experiencing a Katrina-style flood. It's possible, but when it happens it is evidence of an ongoing catastrophe.
imagine a horseshoe shaped tube. "pretend" that one end of the tube is water outside of your home/basement, the bottom of the tube is the sump pump pit, and the top of the tube, opposite end is your abs relief pipe running through your house. In your case, the top of the tube is 60" above the bottom. Now, fill one end of the tube up with water, and watch the opposite side, always in equilibrium. In order for your 60" height outlet to function, the water on the outside of the wall will need to be also at 60" height in order to "push" the water through. This is hydraulic head.
Hydrostatic pressures increase when the ground water level is higher than a restricted outlet, think about pinching the bottom of the tube as your pour the water in. Now the incoming water side rises higher, causing a hydraulic head and pressure, 5' of head is approximately 2psi.
Slightly offtopic; but restricted outlet doesnt necessarily mean pipe, it could also be the backfill material, preventing the ground water even reaching your weepers. That's why in new construction its good to go with a double layer drainage board (geosynthetic + HDPE membrain), that drains down into the clear stone surround of the weeping tile. The weeping tile should be wrapped in geosynthetic to prevent the migration of fines which can clog the pipe.
Martin & Ryan
Thank you for your input. I fully understand your examples
Now take the coffin if fully sealed on the top will not sink in the swimming pool water if it is full of air and wants to remain buoyant.
If a hole is put into the sealed top and an ABS pipe is sealed into the hole and at the same time an inlet has been cut into the side of the coffin with a corrugated pipe sealed in and the end of this pipe is above the level of the swimming pool and the coffin is then forced down to the bottom by the necessary force we then have a casket under water pressure (hydrostatic) sitting on the bottom with only the atmospheric pressure of 14.7 psi acting on the 1-1/2" dia. ABS pipe with a 1.78 sq. inches into the coffin top. This would have a force of 26.2 lbs. If we allow the tube into the side to be filled with water by pushing it down below the pool surface the 4" dia. has an area of 12.68 sq. inches generating a force of 14.7 atmospheric psi x 12.68 sq. in. = 186.4 lbs.
Therefore water would rise in the 1-1/2" pipe located in the top of the coffin to a height that would finally equal the force of the water coming into the 4" corrugated pipe.
The question comes back around to the hydrostatic force generated in the horizontal perimeter drains flowing into a sump if contained will the pressure increase in the sealed sump to the point of being able to push up the sump water to an equalization of the force from the 4" flow in and thus out of the 1-1/2 pipe??
Would it not be the same as the U-tube example had one side as a smaller diameter the level of water in the smaller dia. side would rise higher then the side with the larger diameter.
The water level in the pipe will always be equal as long as both ends of the pipe are open the same air pressure. The diameter of the pipe only changes how fast the water level equalizes.
Without a pump the only way to drain the sump is a sloped pipe leading to day light.
Walta
But the purpose of footing drains is not just to remove water, they should also relieve all pressure. Because a basement isn't a well sealed boat/coffin and will leak if there is any pressure (caused by standing water outside of it).
The standing water contained in the soil outside the house foundation will flow into the perimeter drains and will build up pressure as they completely fill. When filled the water will build up back-pressure in the soil being drained.
When the drain pressure builds to the maximum from being completely full and then released into a sump, the pressure decreases in the drains.
My original theory/question put forth is this - If the sump allowing the drains to run freely is sealed with the sealed sump allowing the drains in, and the top of the sealed sump has a small diameter ABS pipe inserted and sealed becoming a pathway for the pressurized drain water to escape as a path of least resistance, why would the drain water not continue to rise up the sump pipe as long as the pressure pushing from the perimeter drains is greater then the column pressure created by the increasing weight of the rising water and the atmospheric pressure on the surface of the vertical sump pipe ? I haven't seen a complete convincing answer to this date.
Murray,
I think we all understood your question. The answer is that the pressure never builds up to the point you anticipate. For one thing, the water would start coming through the cracks between your foundation walls and the footing, as well as small cracks in your foundation wall. For another, the pressure just isn't great enough -- which is why sump pump manufacturers are still in business.
Lots of people have sumps with airtight and watertight lids, along with pipes to remove water. These airtight sumps all have pumps.
You don't have to believe us, though. Buy a sump with an airtight lid, install it without a pump, and let us know how things work out.
Martin
The part of your last answer is probably all I was looking for," the pressure just isn't great enough".
Now how do you calculate this pressure?
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If you have 2 feet of standing water behind the lower portion of your basement walls, then you have ~2 feet of H2O of water pressure. This pressure will lift water to any height less than 2' above the bottom of the basement wall.
If you have 2 feet of water behind your walls and you turn off the pump a few hours later the water level inside the wall and outside will be the same as your floor to wall joint is not watertight.
Walta
In theory, if your basement walls and floor are watertight and my above scenario is in place, as the water builds up outside, the water in the ABS pipe on top of the sump enclosure will also climb to the level of outside water as the water flows into the sealed sump case.
Let's assume the outside water build up reaches 6 ft,. the distance from the basement floor to ground level.
If an outside sump drain is taking the water away and the opening is at ground level ( 6 ft, above the basement floor) and is buried at least 6 ft. horizontally draining to a creek behind the house and you tap into this corrugated drain below ground level, say 5ft. down and near the foundation and install a vertical perforated pipe into the sump drain line, the build up pressure of the ground water should not happen as the vertical pipe should act as a pressure relief route for the ground water.
I'm not sure if all the groundwater around the perimeter would be drained and certainly in all probability water would still have a tendency to flow down to the existing perimeter drains but greatly reduced.