What 50 years of Erosion looks like- just sharing our amazement

[CallMeIshmael]

This weekend, we broke ground to explore a settling corner beneath the pool at the rear of our lot. This year's heavy rains literally doubled the drop (previously 2 1/2 inches) of the pool deck towards the southwest corner to 5 inches.
This is on the downslope side of a 20,000 gallon concrete pool. The coping was discovered to leak, in an older pool without proper controls for water level, so that may be the source of the moisture underneath. (No other leaks known- no noticeable disappearance of water) Here's what we found:

Looking towards settling corner:

Below Remaining Pool Deck:

Hard to gauge scale in a photo, but that void is a good 4 ft wide & 5 ft deep!
Another View Below:


Since it's been there 50 years, we knew the pool deck was going to be a big project, but that kind of erosion, and the cavern it created, pretty much amazed us! The soil engineer has been added to our call list... then it'll be time to call in the Caterpillars!

[FlashRedGLS1.8T]

Holy cow, that's a cavern.

[imfignewton]

Is the water getting inbetween the coping and the pool deck where the expansion joint should be? Does the pool deck slope towards the pool?

[CallMeIshmael]

The coping appears to be one of the main culprits- water was coming in both on the pool side (under the hairline-cracked mortar) & on the deck side of the coping. The deck actually sloped strongly away from the pool (past tense- the concrete deck is gone now!), but inside coping leak was the killer during the record rains of last year....

Our big question today was Where did all that dirt go?! The engineer's theory is that it tunneled about 15 feet down to slide right underneath the retaining walls that run 12 feet down.

Today's discovery: There is, so far, one hairline crack (top to bottom, 1/16" right in line with the main drain!) on the outside face of the pool wall now that it's exposed, but still no sign of an active leak... As for reinforcing that crack, two pool contractors are telling us to talk to the engineer, and the engineer is telling us to talk to the pool builder.... Hmm. The most popular idea seems to be short bolts epoxied into the pool wall & a concrete pillar that ties the two sides together. It seems a good idea, but I wonder what would happen if water did start coming through there. Hmmmm.
If we can solve the source, the drainage, and the soil outlet, I think we'll be okay.... Then we can go back to our plans for the Ipe view deck... Somehow that part was much more fun- LOL.
PS- Any ideas I can throw into the mix for the crack repair? I may have to put feelers out for more eyes on this... Any recommendations for SF Bay Area pool contractors/builders?

[bimmerboy]

As far as crack repair... they have a injected epoxy they use for basement wall crack repair and other structural repairs like bridge piling supports. They actually inject an epoxy into the crack that is supposedly stronger then concrete. Just a thought.

Here's a link I found on Google... http://www.emecole.com/

[ariasc]

Just following up on the comment from 'imfignewton'. My guess is that this pool is probably 10 years old... Just replaced the motor, but I have a concern regarding the sloping wall towards the pool. It's probably in the same shape as the pictures here!! You can see the thread I started here:

http://www.poolforum.com/pf2/showthread.php?t=1930

If you look at the attachment, the wall leans towards the pool on the right hand side of the picture.... Is time to call in the engineers?

[CallMeIshmael]

As far as crack repair... they have a injected epoxy they use for basement wall crack repair and other structural repairs like bridge piling supports. They actually inject an epoxy into the crack that is supposedly stronger then concrete. Just a thought.

Here's a link I found on Google... http://www.emecole.com/

Thanks Bimmer,
That's the kind of epoxy I meant for the bolted band. It's good stuff. We may still do a small concrete/cemented patch, as the engineer feels this would keep that crack from spidering off elsewhere.

And Ariasc, umm... in a word... YES :-> especially the last picture shows a huge drop in grade, and may be even more fun than ours! Consider it a great time to look into some upgrades in that area of the deck.

We are ending up completely removing 2/3 of the pool deck, and adding a lot of drainage, retainers, etc. The upside is that we can access things that were concreted in since we moved in 5 years ago. So in the process we'll be:
-Relocating the return (previously an unthreaded 1/2- 3/4 inch pipe!)
-Upsizing the return line (The old piping is 1"!),
-New light fixture/ wiring (has never worked- turns out it's both unwired & leaking- LOL)
-Solar heating panels with controllers
&
-A new view deck above the new retaining walls.

These benefits actually have me excited about this project now, though it's a lot bigger than we first planned. That first couple days was something else though!!