1. Hardness tests for rock characteristics;Atkinson,1993
2. A systematic determination of engineering criteria for rocks;Aufmuth;Bull. Assoc. Eng. Geol.,1973
3. Rock Mechanics Class Notes;Cording,1996
4. Engineering classification and index properties for intact rock;Deere,1966
5. Physical properties of typical American rocks;Griffith;Iowa Engineering Experiment Station Bulletin,1937