中文摘要：

为探讨双层非均质地基中单桩的受扭承载特性,基于单层土体剪切模量呈幂函数分布的假定,考虑桩–土接触面上极限摩阻力随深度非线性变化,建立出桩顶扭矩作用下的桩身扭转控制方程,进而导得桩顶及桩身的扭矩（T）与扭转角（Φ）等解答,并将其退化为单层非均质及双层均质地基后与已有成果进行了对比验证。同时,桩顶T–Φ曲线参数分析结果表明：增加桩体剪切模量G_p有利于控制桩顶扭转角;桩径r0增加一倍,相同扭转角下桩顶能承受的扭矩值增大4～6倍;随地面处土体剪切模量μ_1和模量分布函数中非线性系数α_1,α_2的增加,桩身受扭性能得到显著改善。此外,桩顶扭转影响因子I_Φ的对比分析表明：桩身在ζL〈0.2和ζL〉5.0时分别表现为刚性桩和柔性桩,且后者传至桩底的扭矩极小而可忽略;当ζL〉5且上下土层顶部剪切模量比μ_1/μ_2〉1时,0.2倍桩长（L）范围内的上部土层对桩身受扭性能影响较大;当ζL〉10且μ_1/μ_2〈1时,桩身受扭能力主要源自0.4L的表层土。

英文摘要：

To discuss the torsional behavior of a single pile in double-layered non-homogeneous subsoil, assuming the shear modulus of each single layer as the power function distribution and considering a nonlinear variation of the limit friction resistance along the pile-soil interface, the governing differential equation for the pile shaft under torque is established. Then, the internal forces（torque T） and deformations（torsion angle Φ） at the pile top and along the pile shaft are obtained respectively. By simplifying the solutions to single-layered non-homogeneous or double-layered homogeneous subsoil, good agreements are found between the calculated results and the available achievements. Besides, a parameter analysis of pile top T–Φ curve shows that increasing the shear modulus of pile shaft G_p helps to control the torsional angle at pile top. And a double value of pile radius r0 will result in an increase of 4~6 times the torsional resistance at pile top. Similarly, the performance of torsional piles can be improved by greater values of the nonlinear coefficients α_1 and α_2 and the surface modulus μ_1. Besides, comparative analysis results of torsional influence factors at pile top I_Φ show that the pile shaft can be seen as a rigid body for ζL0.2, while a value of ζL5.0 will cause a flexible pile with the torque transferred to the pile tip small enough to be ignored. Moreover, for a combined value of ζL5.0 and shear modulus ratio of upper to lower layers μ_1/μ_21.0, the main contribution to torque resistance comes from the 0.2L surface subsoil, while the 0.4L surface soil layer will determine the torsional behavior of pile shaft for ζL10 and μ_1/μ_21.0.