| 摘要 |
A method for extracting and grading or sizing sand, gravel or a mixture thereof, from a pit formed in untouched ground. Liquid is sprayed into the ground, resulting in a fluidized state in the ground, in which state sand or gravel with a relatively high relative density and/or relatively large dimensions moves downwards, and sand or gravel material with a relatively low relative density and/or relatively small dimensions moves upwards. Thus a pit is formed in the ground which contains fluidized sand or gravel, in such a manner that a layered state is obtained. The layer of sand or gravel with a specific relative density and/or size is sucked out, while the remaining fluidized material remains behind in order to stabilize the wall of the pit. The material which has been sucked out is fed to a grading device or sizing device. |
