1. ACI 336.3R-72 (Reef. 1980);ACI Committee 336,1980
2. ACI 336.1-79 (Rev. 1985);ACI Committee 336,1985
3. ADSC: The International Association of Foundation Drilling (1987), Standards and Specifications for the Foundation Drilling Industry, ADSC, Dallas, Texas.
4. Report EL-5323;JF Beech,1987
5. Bishop, A. W. (1966), The strength of soils as engineering materials Geotechnique 16 No. 2, pp. 91–130.