Basement in Ground Water
Basement in Ground Water
(OP)
I have a client who wants to have his house constructed with a full basement in an area that after the excavation and boring it will be in at least in 2 feet of water. The area also has a few feet of dark grey peat and clay. Once it was excavated and water started getting in the standing water stabilized and in about two weeks the water almost turned green with a lot of algae. My questions are the following and would appreciate any advice or references:
1.How can we compact soil that is wet? Do I have to dewater the area first?
2.Is there any way to make a basement fully waterproof?
3.Should I suggest to replacing some of the clayey/silty material ( 2-6 blow counts) with RCA for good compaction?
4.Why would so much algae is growing in the water in such a short time? Does peat cause that?
1.How can we compact soil that is wet? Do I have to dewater the area first?
2.Is there any way to make a basement fully waterproof?
3.Should I suggest to replacing some of the clayey/silty material ( 2-6 blow counts) with RCA for good compaction?
4.Why would so much algae is growing in the water in such a short time? Does peat cause that?





RE: Basement in Ground Water
You definitely will have to dewater in order to construct the basement.
Theoretically, you can waterproof the basement. The membrane has to be on the outside, that is under the slab and on the earth side of the walls, and continuous. The effectiveness of waterproofing depends highly on the workmanship.
As to the algae, swimming pools do that if the chlorine level is not high enough, especially in warm weather.
RE: Basement in Ground Water
Mike McCann
MMC Engineering
RE: Basement in Ground Water
The advantage of a basement is that you might get through the peat layers and into something decent that you can then found on otherwise you will need to found deeper. Remember to design the base slab and walls for the water pressure which can be large forces. That often gives you quite a thick base which then acts nicely as a stiffened raft foundation.
Carl Bauer
www.bauerconsultbotswana.com
RE: Basement in Ground Water
That is not the scenario that I read here. If you cannot control the water by gravity, as power to run sump pumps is frequently lost during storms (auxiliary generator needed), I would still seriously consider raising the level of the basement floor and mporting fill to achieve the level of basement cover desired. Without doing that, you are looking at a long term maintenance problem.
Mike McCann
MMC Engineering
RE: Basement in Ground Water
I'm with Mike on the undesirability of relying on sump pumps. Unless the client wants a large indoor swimming pool.
DRG
RE: Basement in Ground Water
My big concern would be the layer of peat. The gray clay could be organic. Were soil borings done? Many jobs where I have seen peat near the surface, layers of peat and organic silt are also be found near the bottom of the basement elevation and have extended up to 50 feet below the surface. Is the house on or near a lake?
RE: Basement in Ground Water
By the OP's description, I don't think this soil is permeable.
RE: Basement in Ground Water
Even if it is held down, what sort of structural slab is needed to keep the slab from blowing up?
RE: Basement in Ground Water
RE: Basement in Ground Water
That's partof the reason why I want to raise the building!
Mike McCann
MMC Engineering
RE: Basement in Ground Water
RE: Basement in Ground Water
Can you imagine the Madison, WI engineers shock when Frank Lloyd Wright designed a large auditorium next to their lake in 1960 placing the main floor one foot below the elevation of the nearby lake at normal conditions. At flood times it would be a few feet higher.
If finally got built with some common sense.
RE: Basement in Ground Water
RE: Basement in Ground Water
Most clients are persuaded to do so by the significant costs and risks
associated with construction below the water table.
The client should be prepared to spend at least 2 to 3 times more for the subaqueous foundation system,
with no guarantee of future performance.
I think the more difficult cost analysis
will be the use of a pile and structural slab system vs. soil replacement.
RE: Basement in Ground Water
RE: Basement in Ground Water
Learn from New Orleans and think about the wisdom of constructing structures below copious amounts of water... You may perhaps win the battle against Mother Nature, but she will ultimately win the war.