Method for extracting and grading sand

US 6,499,239 B1
Method for extracting and grading sand
Hendrikus Van Berk, Bunnik (Netherlands); and Sjerp Zeldenrust, Winsum (Netherlands)
Assigned to De Groot Nijkerk Machinefabriek BV, Nijkerk (Netherlands)
Filed on 28-Feb-2001, as Appl. No. De Groot Nijkerk Machinefabriek BV, Nijkerk (Netherlands)
Int. Cl.7E02F 1/00

US 6,499,239 B1 Method for extracting and grading sand Hendrikus Van Berk, Bunnik (Netherlands); and Sjerp Zeldenrust, Winsum (Netherlands) Assigned to De Groot Nijkerk Machinefabriek BV, Nijkerk (Netherlands) Appl. No. 9/554,551PCT Filed Nov. 17, 1998, PCT No. PCT/NL98/00661PCT Pub. No. WO99/25932, PCT Pub. Date May 27, 1999. Claims priority of application No. 1007551 (NL), filed on Nov. 17, 1997. Int. Cl.7E02F 1/00 U.S. Cl. 378212;314 3 Claims 1. A method for extracting and grading or sizing sand, gravel or a mixture thereof, from a pit formed in untouched ground, comprising spraying a liquid into the ground, resulting in a fluidized state in the said 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, in which a pit is formed in the ground which contains fluidized sand or gravel, in such a manner that a layered state is obtained, sucking out the layer of sand or gravel with a specific relative density and/or size, while the remaining fluidized material remains behind in order to stabilize the wall of the pit, and feeding the material which has been sucked out to a grading device or sizing device.