Best way to fill in an old swimming pool with high water table :(

[Lee Nowell]

Hi All,

A friend has an old indoor swimming pool which he got converted into a playroom. They removed the inner lining and constructed a deck over the pool enabling him to use the old pool below as a good storage area. This worked a treat until the winter rains came and it transpired that the water table is very high and the pool was not tanked on the outside. Net result water is seeping into the storage area and stinks!!

Ordinarily, he would fill it all in then finish with a DPM and concrete slab but this is going to cost a fortune - mainly because of access/ distance issues to transport the gear to the pool. As a cheaper option, a builder has suggested dropping the timber deck 100mm adding some DPM/ sealant on top of it and pouring a 100mm slab of reinforced concrete. I guess he would have to dig some of the edging away to ensure the slab sits on the pool side walls. Would this approach work?

My initial thoughts were...

1. water will still come in below the decking as normal but in theory, you won't smell it if the slab is fully sealed - seems likely to fail in the future.
2. during the wet months, water will come in from the "force" of the surrounding water table. Will this go away in the drier months or just sit there? The side walls are made of concrete blocks. Even if it does seep back into the soil, won't it leave a horrible slimy residue?

I would love to hear your thoughts on this approach and whether you can think of any other option? He did look at tanking it (in the same way as you would a cellar) but again this was too expensive.

thanks

Lee.

[Andrew Gabriel]

For a few years, until the timber went rotten and it all caved in one day when the kids were playing on it.

The other thing is that the walls were probably not built to withstand the static pressure of the soil long term without static pressure of the water in the pool to compensate. They might start collapsing in, and that movement might affect the building's foundations. You really need a structural engineer to advise, but if this is the case, you either have to turn it back into a pool, or backfill with rubble. Structural engineer might advise if you could use permanent horizontal props between opposing walls instead, as is temporarily done when trenching. If the walls are string enough to hold the static soil pressure, then you can probably get them tanked, or lined and use a sump pump as is done in cellars below the water table.

[Lee Nowell]

Hi Andrew - good points thank you. I will check on the wall construction...

What do you think about the water hanging around during the wet months?

[Phil L]

No. The timber wouldn't last more than a few years, no ventilation, constantly damp from the pool water etc, and when it rots away, the slab above is spanning the entire pool without support

I think he needs to decide whether he wants to keep this as a storage space or just cover it up once and for all and forget about it. If the former, he'll either have to pay out for tanking, or put up with the water ingress and associated smells, etc, if the latter, and he can't afford to get it filled, he'll have to cover it up properly. Concreting over wood is useless for the reasons mentioned earlier, steel is slightly better but also liable to rot / expand / both. His other option is to use concrete beams laid from one side to the other with blocks inbetween (block and beam*) and then concrete over this, you don't mention the size of the pool, but he may need to build a wall in the centre of the span to hold up the concrete beams, although this may well work out more expensive than having it tanked.

[Jim K]

just re-read this - by "stinks" what do you mean? sewage? or mouldy "cellar" smell?

Jim K

[Lee Nowell]

It is a stagnant water stench ......

[Andrew Mawson]

storage

It is a stagnant water stench ......

You can hire sections of conveyor belt intended for moving spoil quite cheaply, and in urban situations people seem desperate to give away rubble to avoid skip fees, so it should be perfectly possible to rubble fill it relatively easily and cheaply despite the distance. Then a proper concrete floor can be installed delivering the concrete by the same conveyor.

AWEM

[Sidney Endon-Lee]

In some countries (I don't know if it applies to the UK), the local authority requires unused swimming pools to be completely removed - you can't just simply leave them in the ground. If that is a requirement where you live, then if the LA has records, filling it with concrete could turn out to be expensive when you are required to remove the pool and concrete (or reinstate the pool).

This happened to someone I know in Denmark - he didn't fill his pool with concrete, but did have to remove the old pool, which was a long and expensive operation.

Sid

[Andrew Gabriel]

So, how do you remove a hole in the ground, other than by filling it?

I'm guessing this is because a hole in the ground, when no longer maintained full of water, is an inherently unstable structure - it's just waiting to collapse in.

[Jim K]

google "miniveyor"

- not cheap to buy or hire IIRC but once you have amassed sufficient s**te to fill the hole, undoubtedly a good way of moving it quickly and easily - you just shovel it on at one end and eventually it falls off the other end - hopefully exactly where you want it, spread around and compact, repeat as necess.

CHeers Jim K

[dennis]

Expanding foam is light and could be removed if he wants a pool back.

[Jim K]

erm.... if he made the newer pool smaller it could certainly be nicely insulated!! er at some cost obvioushly....

Jim K

[Chris J Dixon]

Or float out?

Chris

[Martin Bonner]

But he should read about canoes on the wiki FIRST!

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "dennis@home" saying something like:

A whole swimming pool's worth of foam? How much would that cost? I suppose it could be sliced out in sections and used for roof/wall insulation if the pool is wanted later.