Abstract：In order to discuss the torsional behavior of single pile in nonhomogeneous single-layer subsoil，based on the balance principle，the shear displacement method and power function distribution model of the subsoil shear modulus，the load-deformation control equation for the pile shaft and surrounding subsoil under pure torsional load was first set up，in which the non-zero subsoil shear modulus at the ground surface (on the contrary，zero value was assumed by almost all available other methods) and the nonlinear limit friction resistance along the pile-soil interface were considered as well. Then，elastic，elastic-plastic and plastic analytical solutions for the inner forces (torque) and deformation (torsion angle) of the pile shaft under various bearing states were deduced respectively. Based on the obtained solutions，a parameter analysis was carried out to find out the influencing factors and rules for torsional piles. The results show that，the non-zero subsoil shear modulus factor of ?g at the ground surface will influence the transmission efficiency of torque along the pile shaft. Furthermore，pile head stiffness will gradually decrease with the plastic zone development depth in the subsoil. When the plastic zone reaches a depth of 0.3 times of pile length，the pile head stiffness will reduce by 60%，i.e.，plastic failure in the surface soil layers plays a leading role for the decreasing of pile head stiffness. Therefore，reinforcing the surface subsoil is an effective way to improve the performance of torsional piles in practice.
2015, Vol. 34 
