Hello all. I started building a block wall pool recently. I first dug the hole, poured a concrete slab bottom. Then, had bricklayers lay a seven course wall (16'x25') with 8x8x16 cinder block with a rod in each block. There is a 1-2.5' space between the block wall and the earth. The block was laid yesterday. Today it rained cats and dogs (2-3") and the space between the wall and the earth filled with water and eventally pushed down one of the long sections of the wall (i was not there to observe this). Finally the question; if i pump out the water and rebuild the wall, will backfilling the space between the earth and the wall with dirt push the wall down again. I would of course backfill slowly and be careful not to put too much pressure on the wall. Any advice would be greathly appreciated. Thanks blaise

Wow... sorry you had this problem. I'm no expert on pool construction but it sounds like you had a couple issues that contributed to the problem.

Your masons probably put the steel into the block and then solid filled the blocks with mortar or concrete. The portland cement probably did not cure before the rain storm hit so no bond between the steel and concrete was really formed yet. It takes 7 days to get to a reasonable strength in cement mixes so you may have had some wash out as well as a wall that wasn't even close to it's final design strength. You will need to check all portions of the wall to make sure that you don't have a wash out of your cement in other places. Last thing you want is to have a near failure situation to be left in place and then fail later. (The wall should have been covered if conditions called for rain)

The other thing is that any wall that isn't backfilled should have been shored up. This means that those masons should have thrown some framing members across the wall and supported it down to the slab... they will hopefully not be charging you to rebuild this portion of wall? (Protecting installed work is generally the responsibility of each trade and it's pretty standard practice to shore up a wall that isn't finished yet)

If your wall is designed properly then when it is backfilled it should work out for you. Sometimes in retaining wall construction ties are placed back into the fill to hold the wall from heaving. Ask your contractor about this? It depends on regional soil and climate conditions so the people nearby with experience in your area are really the best resource.

Did the masons or concrete contractor put in any bolts or ties between the concrete slab and the wall? Sometimes this is done with a "key"... this basically means that the concrete is slotted to receive the masonry. They reason for this is that some sort of tie between the slab and the wall will prevent the wall from kicking inward or slipping out at the bottom.

Final question... if you are in LA, the amount of water saturation there makes the hydrostatic pressure a significant issue against any subterranean wall. Personally, I haven't worked in such conditions so I can't advise you too much but it seems likely that the amount of pressure against your wall could be pretty great when the ground is totally saturated. Ask a contractor if drainage of the soil behind the wall is necessary. Here we tend to use gravel against walls to allow water to flow down to drain tile and not build up pressure against the wall.

Are you working with a pool contractor? or a builder/architect?

First, thanks for the reply. I sort of figured the main reason the wall failed was because I had not yet filled the hollow portion of the cinder block with concrete. This means the rebar anchored to the slab wasn't yet attached to the block. I'm going to drain the pool, redo the few rebar that are broken or unusable, rebuild the wall and quickly have the holes filled with concrete of some sort. I will also either leave a block out or install a few 2" pvc pipes to relieve the hydraulic pressure by letting water flow to both sides of the wall. I'll latter cap the pvc pipes after the wall is properly backfilled. Again thanks for the reply. I'm not a pool contractor by any means. Just a guy wanting a pool and not wanting to pay $25K blaise

To be honest, I don’t believe I have ever seen a pool build out of concrete block. I would think the hydraulic pressure from the pool water would be too great.

What I would at least do is install a perforated drain line around the pool below the bottom slab and back fill with gravel. This should be piped to a drain or sump pump basin. This will keep the ground water from collecting from around the outside of the pool.

I have a friend that decided it was time to clean and paint his pool. So he drained his pool. The next morning he found his pool had floated out of the ground at one end about 6 inch breaking all of the piping. He had to turn it into a garden.