A general description of stone material to be used for stone columns is that it shall be clean, hard and inert. It can be sand gravel and crushed rock. There are other materials used such as crushed slag, well burnt plastic shale, concrete waste etc. All these materials shall be assessed with respect to the ground conditions that exist in a particular project.
Grading of all these materials is the key parameter considered for choosing them along with other strength related parameters. The grading of these infill materials will depend on methodology and equipment adopted for installation of stone columns. Following are recommended by various standards and codes of practice.
Top Feed:
1.    BRE – Dry Top Feed range 40mm to 75mm with fine contents not more than 5%
2.    BRE – Wet Top Feed: Range from 20mm to 50mm with fine contents not more than 5%
3.    ICE – Top Feed: Range from 20mm to 75mm
4.    EN 14731: Dry Top Feed: Range from 40mm to 75mm
5.    EN 14731: Wet Process: Range from 25mm to 75mm

Bottom Feed:
1.    BRE – Dry Bottom Feed: Range from 20mm to 50mm with fine contents not more than 5%
2.    EN 14731: Dry Bottom: 8mm to 50mm



A most common gradation range used and accepted by industry is given below for both top feed and bottom feed: