Does a concrete floor provide any resistance to ground water? 1

[vikkid]

An addition (residence) that was constructed to extend a house 8 years back that has quite a large basement room. Unfortunately, this room does not have a concrete floor and has a dirt floor with about 2' of crushed stone on top; a perimeter drain and a sump pump is also installed. Just to give some context, this dirt floor is about 17" lower than the finished concrete floors in the older basement rooms and when pouring a floor I'm considering coming up another 8"(4"crushed stone+4"concrete).

In the last 4 years there have been a few incidents where the sump pump has failed(variuos reasons from stones clogging the impeller to broken pumps). The room floods in the rainy/thaw seasons(not when the ground is saturated). The waterlevel in the room can be as high as 12" from the dirt floor. We all know that water takes the path of least resistance, so my question is if adding a concrete floor with a moisture barrier(eg: poly) below the floor provide enough resistance so the water travels elsewhere? My thought is that adding the floor will be enough to prevent the room from flooding in the future if the pumps were to fail say in case of a power failure. Rest assure I'm planning to run the pumps, but just worried for those unforeseen failures.

 

[thaidavid40]

Do you have a way to install a perforated underdrain system, and then drain it by gravity flow to daylight? Or to an exterior source, such as a manhole. Taking the pumps out of the equation would seem to help greatly. Keep them for emergency backup. I wouldn't count on the concrete stopping the water flow. In any event, it could float the basement out of the ground, if the level gets high enough, quickly enough.

Thaidavid

 

[Ron]

The concrete will not stop the water but will slow it down to seepage rather than flowing. Edge details are important in waterproofing a basement floor and made all the more important since this is an infill slab, not one that supports the walls.

I agree with David that a gravity system would be great, but you might not have an outfall for a gravity system unless you are on a hillside or similar elevation relief.

 

[vikkid]

Thank you for the thoughtful assistance.

 

[msquared48]

For this to work, you would need a minimum of the following:

1. The slab would have to be reinforced structurally;
2. The slab would have to be waterproofed on the underside
2. There could be no joints in the slab
4. There would have to be a water seal between the peripheral walls and slab.
5. The structure would not float at a high water table.

Your best bet is to invest in a backup sump pump, and a generator/deep cycle battery bank with an inverter for auxiliary power when you do lose power.



Mike McCann, PE, SE (WA)