非均质地基中单桩受扭弹塑性分析

Torsional elasto-plastic analysis of single piles in heterogeneous ground

基于平衡原理和剪切位移法,考虑桩周非均质地基土剪切模量在地面处为非零值（已有方法多假定为零）且随深度呈指数和幂函数两种分布模式,以及桩-土接触面上的位移非协调性,建立出纯受扭桩桩身与桩周土的扭转控制方程,进而导出桩周土分别处于弹性、弹塑性及塑性受力状态下的桩身扭矩~扭转角解析解。由此进行的参数分析结果表明：随土体剪切模量指数分布函数中非线性系数m值的减小和地面处桩土剪切模量比μ值的增大,桩顶扭矩的传递深度、桩顶及桩身的扭转角均表现为增大的特性;幂函数分布模式中地面处剪切模量非零因子αg的取值将影响桩身扭矩的传递效率,并导致扭矩分布呈现凹、凸两种不同形状。此外,桩身扭矩的传递存在一临界深度,当桩身长径比L/D≥50时,桩顶扭矩的破坏值与弹塑性临界值之比ζ趋于稳定。

Based on the equilibrium principle and the shear displacement method,the torsion governing equations for pile shaft and surrounding subsoil under the action of pure torsion were proposed in consideration of the incoordination of deformation at the pile-soil interface and two distribution models for subsoil shear modulus,which is assumed to be nonzero at the ground surface,but may increase in exponential function and in power function,respectively. Furthermore,analytical solutions for the torque and torsion angle of pile shaft under elastic, elasto-plastic and plastic states,respectively,were derived. The parameter analysis was carried out,and the results show that,with the decrease of coefficient m in the exponential distribution function for subsoil shear modulus and with the increase of the shear modulus ratio μ of pile shaft to surrounding subsoil,the transferring depth and the torsion angles at the pile top or along the pile shaft will increase accordingly. When the power distribution function is assumed,the non-zero αgvalue of subsoil shear modulus at the ground surface will influence the transmission efficiency of torque and lead to the distribution shape of the torque either in concave pattern or in convex pattern. In addition,a critical depth can be found for the transferring of torque along pile shaft. When the aspect ratio L / D is greater than 50,the ratio ζ of torque failure value and elasto-plastic critical value at the pile top becomes stable.