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Thread: Bedrock Question

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    Bedrock Question

    Hello everyone, I am so thankful to have found this site and for all of your helpful information. We are hopefully going to get started on our DIY inground pool build soon. We are planning a 36x18 sport pool, and are thinking of doing it at 4x6x4 for depth. We have a question for the more expierenced before committing and ordering a kit. We have done a lot of previous soil work and know that we will hit limestone bedrock at 2-3'. We have a jackhammer and excavater lined up and ready to work.

    My question:

    How do we stabilize and level the cracks and voids that will be left in the bedrock bottom to prepare it for the pool bottom? We will be using a vermiculite and Portland mix.

    Thank you in advance for your help.

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    Re: Bedrock Question

    Are you saying the rock is not a horizontal layer that you will penetrate but will be solid rock from 2-3' down?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Bedrock Question

    Yes we anticipate solid bedrock starting at 2-3' and will continue all the way down. It does break up in horizontal layers, but knowing that a jackhammer is not a precision instrument we anticipate cracking, voids and jagged edges.

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    needsajet's Avatar
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    Re: Bedrock Question

    There's some awesome experts here who will give much better information than me. But from other construction experience, being on solid rock is a good thing! It's quite normal to prepare rock under concrete with the jackhammer. When they dig a pool here, they put the jackhammer on the excavator and shape the hole. When the concrete is shot, it molds to fit the irregularities, locking it in.

    The pool shell is fully reinforced and well-spec'd concrete which should be engineered. So it will bridge gaps if there was anything significant, which there wouldn't be in rock. There would be other gaps and potentially soft spots, for example where there's fill around a main drain or in-floor cleaning pipes, easily bridged by a properly designed shell.

    The trickiest situation down here is part rock and part soil. In that case, piers are installed down to bedrock through the soil, so the pool is similarly supported throughout. Piers for our pool were at a maximum of 3.3' (1 metre) centers, although I only needed them for the wide parts of the deck that were poured with the pool shell.

    This is a trite example in a sense, but might be of interest. The photo below shows an example of how incredibly strong the reinforced gunite is. This was at a coastal location after a massive storm and wind/king-tide surge recently in Sydney. The pool was on sand, piered down to bedrock. The storm was enough to easily snap the reinforced piers, but the pool is remarkably intact.

    Gunite pool after storm.jpg
    Photo provided as a courtesy, from this link: Sydney storms: Collaroy houses flooded, damaged by insane weather | Photos
    12k IG salt; glass beads in plaster; K-2006C, K-1766, CCL, and Aussie 4in1 (HTH); Pentair Eco800 1.2HP VS; Zodiac SWC 1.3 lb/day (25 g/hr); 25" filter recycled glass; OKU solar panels; 1/2 HP solar pump; Rebel (Warrior) pool cleaner; FlowViz; prior pool AG 10k | Read Before Posting to get the best possible advice | ... and this helped me a lot!: TFPC for Beginners

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    Re: Bedrock Question

    Thank you for your thorough response. I should have also mentioned that it will be a vinyl lined pool. I was wondering if we would have to over dig and then backfill with something to create the contour for the bottom of the pool to put the vermiculite and Portland on.

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    Re: Bedrock Question

    You'll have to overdig a bit and then fill and level the bottom with something like #57 rock. It will rake out really smooth, needs no compaction and will readily accept the poolcrete.

    It's the same rock you see commonly under a concrete pour.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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