Weight of Rock Structure on Bond Beam

kaseyray2July 20, 2010

I have differing opinions from 2 different pool builders, on our massive rock structure (8 feet high, approx. 30-40 feet long). Builder#1 (who uses all faux, hand-sculpted concrete), would keep all the rock out of the pool,and set next to the bond beam, so as not to weight down the bond beam. Builder #2 uses a mix of real boulders and faux work, would have the faux rocks partially submerged and the weight of the structure would be engineered to be on the bond beam. He says the dirt next to the bond beam could settle, and Builder #1's method will put pressure on the pool wall anyway. Both say they will get "special engineering". I am worried about the integrity of the pool! Are both methods feasible? Thank you so much for your response!

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It's good to see that you recognize there's some serious weight issues that need to be address.

Setting that size load on a regular sized bond beam or right behind it will cause problems. On the beam, the beam gets crushed. Behind the beam, the load will settle, pressing the earth into the shell sufficiently to cause a cracked shell.

The beam and the ground behind it will need some significant beefing up. Larger rebar, thicker gunite and a thick, reinforced footer will be needed.

How much? I can't say. I am not a builder or engineer. Depending on the materials used, I would guess it could be from 20 to 50 tons, maybe more ,spread over a stretch of land several feet wide running the length desired.

I used to work on a few pools with 3' plastic pipe slides running through their waterfalls. I got to see them first when construction was almost done.

I am sure the builders, like just-a-be, huskyridor, womanowned, etc... could give us more specifics about the kind of reinforcements to expect.


    Bookmark   July 20, 2010 at 11:23PM
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Thank you so much, Scott. Can anyone else offer an opinion, or what I should look out for? Thanks!

    Bookmark   July 23, 2010 at 12:14PM
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Have the PB's define "special engineering". There is a difference between the PB adding a little steel and gunite and calling it "special Engineering" and actually using a Structural Engineer to make the calculations and provide the necessary drawings. Most PB's would charge extra for hiring a licensed engineer to provide specific drawings. It could cost $500 to $1,500 for the engineering and this could translate to construction costs also.
I would suggest that you ask the PB's who is doing the Engineering work and how much extra it will cost. Sometimes the permitting entity will require the engineering, but not always.
I have standard engineered drawings for various common sized rock waterfalls, but large specialty rock features require additional engineered calculations. Good Luck.

    Bookmark   July 23, 2010 at 1:08PM
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Rack Etear

Most of the time, the "special engineering" money is wasted by telling the builders to add more steel and concrete (which they were going to do anyways).

    Bookmark   July 24, 2010 at 2:02PM
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My PB said that the faux rocks are hollow and do not have the weight of real rock and do not need structural engineering. ????????

    Bookmark   August 5, 2010 at 8:52PM
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If they are made of gunite, hollow or not, they're going to weigh a lot. The base is usually at least 4" to 6" thick plus the "rocks" need to be formed thick enough to provide the strength for people to jump off (they will, especially kids).

They will, if a reinforced footer for it isn't made, it's weight will compress the soil and the pool shell's outside below ground. The shell is expecting pressure from inside from the water in the pool, not coming from the opposite direction.

The base will distribute the weight more evenly, preventing the problems with settlement over the heavier and larger sections. This is especially important if there is a slope behind the water feature, as often is the case.


    Bookmark   August 5, 2010 at 10:20PM
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I need to correct my earlier post about my PB saying that I did not need structural engineering for faux rock. i felt uncomfortable about risking this so decided to insist on building permits which then necessitated a structural engineer's calculations. I AM GLAD I DID THIS. All of that weight (I am doing extensive rock work) would have been too much. To support all of the rocks, they are installing more rebar and gunite inside and outside of my old pool that would otherwise had not been done.

    Bookmark   November 20, 2010 at 3:12PM
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The typical add to "engineering" is just another page on the permit that says the engineer saw the add on and provided the blue print page for the plan check department. The inspector will enforce the job. It should be $50 more for "engineering" in reality. Done right, that extra page dictates what is done on the wall that carries the load. It's no different than putting a patio cover close to a pool wall as it adds surcharge to the nearby wall. That wall needs extra steel. Or, putting a wall into a hillside or creating a high wall. It's just more steel and gunite and typically puts the bars on 6" centers rather than 12" and beefs it up to 1/2" depending on the load.

    Bookmark   November 24, 2010 at 9:45PM
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