Rebar Spacing

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markmac

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Jun 29, 2011
183
Texas
In reviewing my plans, the engineering seems to be calling for fairly tight vertical spacing. The plan is for (what I believe) a pretty standard geometric pool, 3.5’ to 6.5’ water depth, with a raised wall on one side. Build is in Texas, so land doesn’t get much more flat.

Looking at the plans, what seems to be driving it is the PCF value that correlates to equivalent fluid pressure?

the horizontals are simply 12” oc per the plan, but vertical spacing at 6” and 3” seems like pretty tight. Maybe I’m reading this wrong? D is water depth and H is D plus any raised wall height.

d1 and d2 are gunite specs.

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PCF is an abbreviation for pounds per cubic foot, so yes, that's pressure. Was the rebar spec'd from other builders at 8" OC also #3 (3/8")? The spacing requirement will vary depending on the size of the rebar, with large rebar having wider spacing. I'm the furthest thing from a pool expert, but deal with a lot of concrete, and if faced with rebar on 3" spacing I'd be looking what the required spacing would be using bigger rebar.

A lot of the flat parts of Texas have significant clay content in the soil, and higher clay content requires significantly more reinforcement. It's steep rocky terrain that doesn't require the concrete to be reinforced as well. Is there any mention of soil classification anywhere? Do you happen to know if your soil has some clay content?
 
Thanks. When I looked up expansive soil maps for Texas, everything around Dallas and Houston show Highly expansive soil. I know it’s a lot of clay.

the drawings state PCF of 60. In reading some pool engineering articles, seems like 60 is not really, really high, but above avg.

builders were stating #3 @ 8”
 
markmac said:
Thanks. When I looked up expansive soil maps for Texas, everything around Dallas and Houston show Highly expansive soil. I know it’s a lot of clay.

the drawings state PCF of 60. In reading some pool engineering articles, seems like 60 is not really, really high, but above avg.

builders were stating #3 @ 8”
Click to expand...

The 60 PCF per ft of depth equivalent fluid pressure is a pretty standard value used for "highly expansive soils". For simply "expansive soils" a value of 45 PCF is pretty standard. Whoever did the engineering either has some reason to believe the soil is highly expansive, or is unsure how expansive the soil is and is erring on the conservative side.

Is the issue that the builder thinks the engineering is overkill? If so, you could try to ask the engineer what they're basing the soil classification on, and ask the builder what evidence they have that it's not highly expansive soil. Is your property within one of the "highly expansive" soils areas on the maps you found? If so, that's likely where the engineer came up with that value. And a builder saying "we've always done it this way and never had a problem" isn't evidence that the soil in your particular yard isn't highly expansive.

Another option would be to contact a local soils lab and have them run some atterberg tests on a couple samples of soil from the pool excavation. A couple hundred dollars in testing could give you a definitive answer, and could potentially save you either thousands in unnecessary rebar work or 10's of thousands in repairs later on from issues caused by insufficient reinforcement.

And if you (or lab testing results) determine that the engineer is right about your soil, then you run into the issue of practicality. Using 3" rebar spacing is approaching the area where the cost of the materials and labor are impractical compared to simply using larger rebar on wider spacing to achieve the same level of reinforcement. Might not hurt to ask your builder what the cost difference would be for using #4 rebar on 8" spacing rather than what they quoted using #3 on 8" spacing.
 
I was thinking about getting a test run also. In the map of the state, yes, Houston is in the highly expansive area.
im also wondering if I’m reading the tables above correctly. And if the spacing of 3” is only in the area where depths reach beyond 6’. If that’s the case, it’s really only the last few feet and back wall that needs that density verticall.
 
Forgot to answer your question. It’s not a case of a builder telling be to go another way. I’m doing an OB and I’m now preparing a package to send out for quotes, and I suspect many will come back with cheaper options of Different spacing.

I‘ve sent the engineering company a request if they have a similar table for #4 at pcf 60.
 
markmac said:
im also wondering if I’m reading the tables above correctly. And if the spacing of 3” is only in the area where depths reach beyond 6’. If that’s the case, it’s really only the last few feet and back wall that needs that density verticall.
Click to expand...

Hard to say looking at the tables alone, but that's definitely a strong possibility. Water pressure and equivalent fluid pressure of soil are both depth dependent.
 
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