1. The strength of coal in mine pillars;Holland,1964
2. A study of the strength of coal pillars;Salamon;Jl S. Afr. Inst. Min. Metall.,1967
3. A review of coal pillar strength formulas;Hustrulid;Rock Mech.,1976
4. A review of coal pillar strength formulas by W. A. Hustrulid;Bieniawski;Rock Mech.,1977
5. In situ coal pillar strength study;Wang,1977