Rock dust and rough rocks are used in a foundation.After completion of earth work excavation (deapth of the foundation will be min 1.5 feet to 3 feet max)rock dust put into the foundation for 1.5 to 2 feets and should be well consolidate before the next step.

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Then first layer of rock rocks are laid in to the foundation and the gaps are filled with small rock stones.And then rock dust is filled in the foundation without voids by using water

then do the same for next layer.no of layers are depending on the deapth of the foundation.