Excavation cave-in

[MLHinDFW]

After new build excavation but before rebar, we‘ve had heavy rain. The project manager covered the walls with tarps beforehand, but the wind and rain beat them up. One side of the pool’s length is 38 feet and curved, and on this curve will be a low wall with columns and fire bowls. The curved length currently shows as much as 18 inches of erosion in a couple of places. The project manager explained that the crew will put in a piece of plywood between the eroded part of the wall and where the rebar will go in, allowing enough gunite to fully surround the rebar. The gunite will hit the plywood instead of the dirt wall. I’m told this is a common practice in this situation.

My concern is this part: The project manager explained that the decking crew will fill the gap between the eroded wall and plywood with cement before laying the decking. However, I know that the plywood will eventually disintegrate, and a gap will be left in its place. Is this a valid concern, or should I simply let the PB handle it, since they are on the hook for the warranty?

I‘ve received the PB’s quote to expand the arc of the curved length, so that the final excavated wall is a smooth curve and doesn’t require the plywood/cement workaround. It adds $8,000 to the cost. I am sure they would love this, but I don’t want to spend the money unless my concern is valid. Warranty or not, I do not look forward to having rework done if a problem comes out of the plywood/cement workaround.

Your input and guidance about which route is better for me, the owner of this big hole, would be much appreciated! Thanks in advance!

 

[dschlic1]

Have them remove the plywood after the gunite is set. That should not be a big deal.

 

[Toxophilite]

The plywood will be removed after gunite is hardened. It's just a temporary form wall - the area is filled with dirt. No issue. It's common to have a large area that has to have an outer form wall and then filled back with dirt prior to decking or sod, as many times that area is where skidsteer ramps into and out of dig area. Don't worry about it.

 

[JoyfulNoise]

Agreed. Not a concern. Plywood will be removed. They can backfill the wall after the gunite has setup. Work with the PB and decking sub to come up with the best fill strategy. It may require some crusher run stones and then fill dirt. It’s up to the decking sub to make the base layer grade level and free from erosion.

 

[davecraze]

I had erosion/cave-ins much larger than that around huge parts of my excavation and rebar from the rains. We put hundreds of feet of tarp on the project before the storms started, but it did not make one bit of difference. It took like a week just to drain and "de-muck" (which they did by hand with little cups through the rebar openings) the pool before gunite. Also, the builder had his crew completely wall off the voids with plywood. Then, after gunite, they pulled the plywood and bracing forms off (that was a full day) and backfilled dirt in the remaining voids that abutted the gunite. I think you will be fine.

As an aside, the plywood likely saved me significant cost on the gunite as there were no gunite companies that were willing to give a fixed bid to my pool builder. They were not able to get comfortable estimating how much gunite would be required for the project, including excess/scrape off. Minimizing the voids beyond the rebar helped - still went over 8 grand (or around 20 percent) - but it could have been much worse.

 

[AQUA~HOLICS]

In my area drywall is used instead of plywood but is removed shortly after the Shotcrete is firmed up.

 

[MLHinDFW]

Thanks for the excellent input. I’m feeling much better about the outcome AND about not forking out more cash to get a cleaner line on the excavated wall.

 

[okpodo]

Glad to see the feedback in this thread. I'm due to start excavation next week and all the rain in Texas lately has me worried about the same issues.

 

[JoyfulNoise]

If it’s raining and the ground is saturated, the PB should reschedule the dig. Unfortunately, building pools in the winter time can be fraught with unpredictable weather. It doesn’t make sense to dig of storms are predicted.