Browse Forums Pools & Spas 1 Dec 05, 2022 1:41 pm Hi, We've recently had the concrete shell of our pool installed. As the water table is very high (~700mm below soil surface) we've had some epic dewatering in order to excavate and get to this point. The finishing trades will return in a month to complete it (Xmas break). In the meantime, the dewatering spread has been packed up (except the spears, since we'll need to dewater again to finish) and there's an open pvc pipe preinstalled through the bottom of the shell as a conduit for groundwater inflow (to prevent upward force on the pool as water table rises back to normal level). Since stopping the dewatering, the water table in the soil immediately surrounding the pool has stabilised at 900mm below the top of the pool shell (measuring through the spears), yet the groundwater inflow to the pool has peaked at 1300mm below the edge of pool shell. I would expect this to equalise given enough time, yet it appears to have reached equilibrium. Does this differential between groundwater level and pool level sound normal? Thankfully the pool hasn't decided to float, though I'm nervous about the groundwater level continuing to rise back up to 700mm depth and causing issues. Note: We are near the Swan River (Perth) and according to Water Corp the groundwater level in this area is mainly dictated by tidal effects. Re: High water table - empty pool shell with relief pipe 4Dec 05, 2022 2:21 pm bad brains Note: We are near the Swan River (Perth) and according to Water Corp the groundwater level in this area is mainly dictated by tidal effects. OUCH, The swimming pool lifting may be the start of your problems. River tidal surges and stormwater back flows is sure to add to your woes This should have been sorted beforehand by you builder Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: High water table - empty pool shell with relief pipe 5Dec 05, 2022 3:05 pm StructuralBIMGuy bad brains Note: We are near the Swan River (Perth) and according to Water Corp the groundwater level in this area is mainly dictated by tidal effects. OUCH, The swimming pool lifting may be the start of your problems. River tidal surges and stormwater back flows is sure to add to your woes This should have been sorted beforehand by you builder To elaborate, when completely empty, the point at which buoyant force = pool shell mass (ignoring friction) is roughly when the water table is at its peak. And there's a couple of cubes of water in the shell at present, so should be ok. Though it is a little unnerving that the level in the pool is not equalising with surrounding water table. Is this to be expected? Can you please elaborate on issues you would expect from "tidal surges and stormwater backflows"? Would this only apply with the pool empty and no relief valve? Note the lower reaches of the Swan are technically an estuary with minimal flow restriction to the ocean, so tidal level does not differ appreciably from ocean tides, and I've not seen tidal effects on water table level more than a few cm in magnitude. Cheers! Re: High water table - empty pool shell with relief pipe 6Dec 05, 2022 3:51 pm Not withstanding swimming pool myths - see that thread (Urban Myths thread) - an empty pool can be forced up by pressure. Some have a valve for such things - or so I've been told. BUT - I would have thought if it is installed correctly it should be OK. If the water table is that high I'm surprised anything can be built on it. Re: High water table - empty pool shell with relief pipe 7Dec 06, 2022 8:44 am bad brains Can you please elaborate on issues you would expect from "tidal surges and stormwater backflows"? Would this only apply with the pool empty and no relief valve? Note the lower reaches of the Swan are technically an estuary with minimal flow restriction to the ocean, so tidal level does not differ appreciably from ocean tides, and I've not seen tidal effects on water table level more than a few cm in magnitude. Cheers! This is a problem around south perth and mt pleasant along the river foreshore. many a house has had to have their soakwells and paving redone after it's lifted Around middle sawn along the river it's recommended you lift the pool on a sand pad with retaining walls. Same goes with House pads Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Much a do about nothing. You can see the fall heading to the actual drains. Stormwater ingress will be minimal and it's far better to have the top sitting flush rather… 12 6257 DIY, Home Maintenance & Repair We have a hot water copper pipe that runs from our hot water unit on one side of our house under a concrete slab to our bathroom and laundry...old house so not ideal. The… 0 5124 Hi, Really struggling to find some consistency amongst Span Tables, can anyone help… 0 2671 |