考虑地基土剪切模量非线性分布的基桩受扭分析

为了探讨非均质单层地基中单桩受扭承载特性,基于平衡原理和剪切位移法,考虑地基土剪切模量在地面处为非零值且随深度呈幂函数分布模式,以及桩侧极限摩阻力沿深度非线性变化,建立纯受扭桩桩身与桩周土的扭转控制方程,进而推导出桩周土分别处于弹性、部分塑性及完全塑性受力状态时桩身的扭矩–扭转角解析解。由此进行的参数分析表明:剪切模量地面处非零因子ɑg的取值将影响桩身扭矩的传递效率,且桩顶刚度随桩周土塑性区深度的开展呈递减变化,当桩周土塑性区开展深度距离桩顶达0.3倍桩长时,桩顶刚度降低60%,即近地面土层的塑性破坏对桩顶刚度的降低起主导作用,工程实际中加固桩周地表土层可有效提高基桩抗扭性能。

ANALYSIS OF TORSIONAL PILES CONSIDERING THE NONLINEAR DISTRIBUTION OF SUBSOIL SHEAR MODULUS

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.