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2. Soil dynamics in tillage and traction;Gill,1968
3. The calculation of passive pressure in two-dimensional soil failure;Hettiaratchi;J. agric. Engng Res.,1966
4. Symmetrical three-dimensional soil failure;Hettiaratchi;J. Terramech.,1967
5. Cleavage of soil by tined implements;O'Callaghan;J. agric. Engng Res.,1964