#Thegreatpoolpondconversion - 200112
First the routine update:
After we did what’s explained below, we backfilled for a while. You know that story, shovel sand into the cart. Drive the cart to the pool. Shovel sand into the wheelbarrow. Barrow over to the pool and dump. Repeat till cart is empty. Spread out the piles of sand with a hoe. Pound it all flat and compact. Rinse, repeat.
Here’s what it looks like now:
We guesstimate about two more days of back filling and that’s the end of it.
On to the major story; the water.
Take say a quart glass jar with a wide mouth. Put 3 inches of sand in it. Now pour in 5 inches of water slowly so as not to disturb the sand. You know what happens. The water starts to seep down into the sand, pushing out the air which you can see as escaping bubbles. After it settles you can look through the side of the jar and see that the water level is higher than the sand and that the water has also percolated down to the bottom of the jar; ‘in’ and ‘under’ the sand.
Do it again. 3 inches of sand. 2 inches of water. This time, after it settles you can look through the side of the jar and see that the water level is below the top of the sand.
You all remember this from days at the beach or high school physics, or it’s just kind of obvious.
We started with that first situation. Water standing on top of the sand. So we bailed and bailed and eventually, no more water to bail. We know there’s more water under the sand; it’s intuitive right? Also we can see it and feel it in the soggy sand we’re walking on.
Now we’re in the second situation. We have to get the water out. (We assume this. It’s possible we could just leave it there and our project would be fine. Something tells us no. Remember filling a pail of sand at the beach and turning it over? Too little water and sand won’t hold a shape. Too much and it won’t either. Just enough - the middle way or Goldilocks amount and it’s much stronger.)
If we just start digging a hole to get at the water, we’d be digging below the water line, as it were. The wet sandy sides would just cave right in and then eventually the walls would follow.
So we came up with an idea. Nothing brilliant. You’ve probably seen something like it at road construction projects (though they have pumps and we have a bucket and coffee can). Since we can’t pound down dozens of feet, we needed something to hold the wood in place. We cut the bottom out of a rubber horse tub feeder. Then we jammed it into the sand as far as it would go and used it to frame the wood slats so they wouldnt collapse in because of the soup-like sand. This took a lot of awkward sledgehammering because we couldnt get a proper overhead swing. it was all arms and wrists and two days later we still feel it. After we got the wood in, we jammed the rubber ring down as far as we could. Then we dug till we hit water. And here’s what we got:
It started to fill up almost immediately because the sand level in the hole is eight inches below the sand outside the hole.
A good four inches seeped in during the hour or so we backfilled (so we bailed it out):
We opened up the tarp on Monday and there was a lot of water in the thing:
There was so much water we could actually bail with the bucket and took out two full loads. then back to the coffee can for another bucket or so.
Tuesday, another 5 inches of water - you can just see the depth of the trowel and its up to the coffee can lid:
Hopefully we can empty it twice a day and let it refill.
We bail, then wait for it to seep / refill. Each time it should refill just a bit less than last time because we removed another 2 buckets of water from the whole system. When we get close to the sand in the center, we dig more, cause the entire water table is now lower and water seeks it’s own level.
The wood prevents the walls from caving in, while letting the water seep by. However the planks we had on hand werent long enough to reach the actual bottom of the pool. next sunday we’re gonna pound in another set of longer ones behind these and all the way down. We figure three feet to the bottom.
More on damage:
Our thinking right now is there was some ‘erosion’ we can’t see. The water poured in at the shallow end, percolated down, then traveled along the slope of the original bottom to where it settled in the deep end where we are digging. The sandbag walls themselves are compact and tight and seem stable. At the deep end we built the wall on a sand base. We never figured something like this would happen. Had we started the walls at the actual bottom of the pool, it would have been way more bags, way less sand leveling etc, but the end result would have been much the same and it would have taken longer and been way more work. (And used just as much sand of course, just some of it bagged.)
So our thinking out loud is that we don’t think there are any actual ‘voids’. Where would the sand have gone or shifted to? This is a closed system (jar). Maybe a little of it shifted with the ‘flowing’ water. Not much, because there was no real way for it to ‘move’. So when it’s dry, we’ll check and re-tamp some of the backfill spots if we have to. When we’re done bailing and the ‘floor’ and the hole dries up, we’ll put the sand back and pound it down. Nothing’s gonna move once it’s all filled and under tons of water.
we lost half a day building this frame thing.
we’ll be bailing once or twice a day almost every day. that’s no big deal. 10 minutes each time. no effect on the schedule.
we may need up to a day to clean it up and check the backfill
All in all very little, almost no time lost.