Swimming Pool Wall With Surcharge from Retaining Wall

[homajo]

I need to design an in-ground shotcrete pool wall the long side of which will be next to a sloping retaining wall, the water will be 3' from the retaining wall.

The retaining wall is 1' thick reinforced concrete cantilevered with the heel under grade and is 9' high at the shallow end of the pool. It has 4" perf drainage pipe as well as weep holes, and slopes down to 4' high 18' laterally from the shallow end of the pool.

The retaining wall footing on the pool side extends toward the pool 1' laterally, and the footing bottom is 2' below grade. The undisturbed clayey sand seems to have an unconfined compressive strength of about 4K psf. Assuming a standard angle of repose 45 deg and a 1' radius where the vertical pool wall transitions to the pool bottom, the area of influence doesn't intrude into the pool (shotcrete pool walls are installed against undisturbed soil).

Ten feet or so from the shallow end the pool depth will begin transition from 4' to 6' over another ~10'.

To handle the surcharge as the pool deepens and intrudes into the footing influence we should be good with guidelines like these in sheet 1 and 2 that show the surcharge condition and table 1 schedule D:

http://www.pooleng.com/Standard-Pool-Structural-Plan/av-53.aspx.

Because of the 2'-6" min radius transition from vertical wall to floor on the deep end the intrusion is 1' or less.

For simplicity we have consulted to recommend a 1' thick pool wall with #3 rebar 6" O.C. each direction next to the retaining wall.

Since the owner is stressing over cost I see only a need to reinforce the pool wall next to the retaining wall, and then transition to standard pool wall sections (6" thick) after the radius reaches the bottom.

Anyone see considerations I missed or does someone have other good ideas? (see drawings - not necessarily to scale):

 

[FixedEarth]

When you make a 6 ft excavation adjacent to the footing, you are removing the passive resistance of the soil. Have a soils firm do a slope stability study and determine the stability of the cut. You will most likely need shoring piles to retain the soils prior to excavating for the pool.

Also the adjacent footing load should be modeled as a strip load instead of a line load. I have seen few designers model a wall with a footing as a line load. Expansive soils may also be present which increases lateral stresses. You may discover 8" thick with #3@4" may work or your proportions may also work.

Someone also needs to ensure there is a separation between the shoring wall and the pool shell - something like a compressible EPS. For such a complex loading conditions, why not just hire Pool Engineering? This pool when designed and constructed will not be inexpensive.

http://www.soilstructure.com/

 

[hokie66]

homajo,
You seem to be only considering vertical pressures, while as FixedEarth has pointed out, you must consider horizontal forces as well. If you excavate for the pool as shown, you risk causing the retaining wall to slide.

The lateral force from the retaining wall footing must be resisted by the pool wall AND base, so I would expect the base thickness for some distance will have to match the wall thickness.

 

[homajo]

Thanks a lot for the advice, seems we needed a check on things. We met with an engineer who has designed many residential and commercial pools including challenging situations similar to ours (along with many more things over 30 years). He is comfortable tackling this so we plan to hire him to spell everything out.

From what I've read here so far, this seems like the sort of thing this site is for.