Pool on Soft/Weak Soils and High Water Table
Pool on Soft/Weak Soils and High Water Table
(OP)
We have a situation where our client would like to construct a pool however the soils are weak and the water table appears to be only a couple feet below grade. It would be an all concrete pool
I beleive there are 2 issues - soil strength and buoyancy force:
Soil strength. This does not seem to very 'important' to me as we are taking soil out (say 100pcf) and replacing it with water which is lighter (62.5pcf). If the pool is concrete and made rigid there maybe some settlement but it should not be differential as the surcharge is uniform (water).
Buoyancy force. If the water table is above the bottom of the pool the buoyancy pressure will tend to lift the pool out of the ground if it is not filled with water. Also constructability may be an issue as water must be pumped during construction.
In talking to the contractor they were not very concerned with the water or buoyancy force. They were more concerned with the pore soils supporting the pool. In talking with a geotech, he was more concerned with the buoyancy pressure than soil strength. In researching the subject it seems most pool installers are only concerned with keeping the hole dry for construction as they do not mention buoyancy.
Is buoyancy a big issue or I'm I making too much out of it?
Solutions:
Soil strength - over excavate backfill possibly a concrete slab to work on. Or provide piers with slab.
Water - Determine water table elevation - Place pool above it. Pump water out. Hold pool down.
Am I on the right track?
I beleive there are 2 issues - soil strength and buoyancy force:
Soil strength. This does not seem to very 'important' to me as we are taking soil out (say 100pcf) and replacing it with water which is lighter (62.5pcf). If the pool is concrete and made rigid there maybe some settlement but it should not be differential as the surcharge is uniform (water).
Buoyancy force. If the water table is above the bottom of the pool the buoyancy pressure will tend to lift the pool out of the ground if it is not filled with water. Also constructability may be an issue as water must be pumped during construction.
In talking to the contractor they were not very concerned with the water or buoyancy force. They were more concerned with the pore soils supporting the pool. In talking with a geotech, he was more concerned with the buoyancy pressure than soil strength. In researching the subject it seems most pool installers are only concerned with keeping the hole dry for construction as they do not mention buoyancy.
Is buoyancy a big issue or I'm I making too much out of it?
Solutions:
Soil strength - over excavate backfill possibly a concrete slab to work on. Or provide piers with slab.
Water - Determine water table elevation - Place pool above it. Pump water out. Hold pool down.
Am I on the right track?






RE: Pool on Soft/Weak Soils and High Water Table
Brad
RE: Pool on Soft/Weak Soils and High Water Table
RE: Pool on Soft/Weak Soils and High Water Table
RE: Pool on Soft/Weak Soils and High Water Table
The pool will not be constant depth. 6' deep in one end 3.5' or so in the other.
EIT
www.HowToEngineer.com
RE: Pool on Soft/Weak Soils and High Water Table
Consider the use of drain pipes and thick gravel below the pool mat such that any rising water is intercepeted and carried away from the pool. You can route it to a dry circular well backfilled with crushed rock. Keep us posted.
RE: Pool on Soft/Weak Soils and High Water Table
Agree with the others that piles will be required if soil conditions are poor (to support gravity loads and resist uplift). Your geotech should be giving you clear guidance, if they have been retained to perform an soils investigation (often not the case for residential pools).
RE: Pool on Soft/Weak Soils and High Water Table