Experimental study on behavior of wood and steel single piles

The goal of this study is to investigate the friction between sandy soil and pile materials (wood and steel) in four different relative densities including 10%, 40%, 65% and 90%. It is also aimed to study the behavior and ultimate bearing capacity of the single model piles under axial loading for the same materials. Finite element method was also used in this research to study the behavior of the single model piles under axial loading. For this purpose thirty-six direct shear tests were performed to study the internal friction angle of the sand and skin friction angle between sand and pile materials in different relative densities mentioned above. Twelve direct shear tests were conducted to investigate the internal friction angle of the sand, and twenty-four interface shear tests were performed to study the skin friction angle between the sand and pile materials. In addition, the axial load tests for pile models were conducted in the laboratory to study the behavior and load-settlement curve of single mode piles under action of axial loading. The results from direct shear tests showed that the internal friction angle of the sand increases with increasing relative density. From the interface direct shear test, the skin friction angle between the sand and pile materials (wood and steel) increases with relative density up to 65% but in 90% relative density it started to decreases. Because in dense sand, the resisting shear stress increases with shear displacement until it reaches a failure stress, after failure stress is attained, the resisting shear stress gradually decreases as shear displacement increases until it finally reaches a constant value. Also the results from experimental pile model tests and Plaxis 3D finite element programs indicated that the ultimate bearing capacity of the model piles increases with increasing relative density, and there is a good agreement between experimental results with finite element programs results.