3 ms·
Digging subway tunnel through rock costs about $100M per kilometer. On the one hand, these holes would be vertical, which is harder than horizontal I would hav
by cperciva 12y ago
Digging subway tunnel through rock costs about $100M per kilometer. On the one hand, these holes would be vertical, which is harder than horizontal
I would have thought that a better comparison would be oil wells, which cost about $500 per ft of depth, or $1.5M per km.
our total volume of mass will be about 25 m^2 1000 m = 25,000 cubic meters. If the weights are made from lead, that's a total mass of ~280,000 tons*
You seem to be assuming that the entire depth of the shaft is filled by weights. My impression was that the weight was much smaller than the shaft it fell down.
- msandford 12y agoOil wells are also only a foot in diameter. Makes the economics worse, really.
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- darkmighty 12y agoActually 1/2 the shaft filled by weights is optimal independently of material, considering only raw energy. (E=p A h(H-h), respectively density, area, payload height and shaft height, Eopt=p A H^2/2 ). Pretty surprising to me that the energy increases quadratically with depth.
- cperciva 12y agoYes, if you're considering only energy. But in practice there are other considerations, such as the cost of the weight, the strength (and thus cost) of the cables, the amount of torque which can be produced for lifting the weight, etc.
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