• A_A@lemmy.world
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    2 days ago

    Perfect guess ! (afaik) ρ(concrete) ≈ 2.5 tons/m³
    so full sphere ≈ (2.5 x 382) tons = 955 tons
    they have 400 t so the cavity removes :
    955 - 400 = 555 t … so 7.51m diam. cavity
    … so, yes 3/4m thick wall 😌👍 !

    • Cocodapuf@lemmy.world
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      1 day ago

      That’s exactly the way I would have calculated it, glad someone beat me to it though. Thanks!