考虑圆孔扩张理论的支盘桩荷载传递法

Load Transfer Method for Squeezed and Branch Piles Considering Cavity Expansion Theory

为求解出支盘桩受压时扩径体处相关力学性状,并预测桩基沉降,结合圆孔扩张理论求解出扩径端力与位移关系,并对支盘桩应用荷载传递法。将支盘桩在竖向受压扩径体向下挤土位移的过程,看作土体中的圆孔扩张课题,在合理假定的基础上,分析受压时扩径体与相邻土体的相对位移,推导出扩径体水平内压力与竖向位移的关系,对扩径体下侧面进行力学分析,得出桩土接触作用面A′C段的变化规律及扩径端阻力与竖向位移的关系,并对其进行参数研究。在此基础上,选择桩侧荷载传递函数为双曲线型,桩端为线弹性,对支盘桩应用荷载传递法,得到桩顶沉降曲线及桩体内力。研究结果表明:以圆孔扩张理论推导出扩径端阻力与竖向位移关系的方法,充分考虑了扩径体的几何构造特点和挤土效应,扩径端阻力能充分体现对挤扩角的敏感性,更加符合工程实际;扩径体水平内压力在倒圆台形下侧面呈现非线性分布,随着初始孔径的增大而逐渐减小,随着竖向位移的增加,水平内压力分布的非线性愈加明显;水平内压力值随着竖向位移的增大而增大,随着挤扩角的增大而减小;考虑圆孔扩张理论的支盘桩荷载传递法能有效地求解支盘桩沉降及相关力学性状,且对于支盘桩而言,挤扩角引起的扩径端阻力变化比单纯的侧阻变化更能影响最终承载力。相关方法和结论可以为工程设计提供参考。

To obtain the mechanics behavior at an enlarged-part and predict the pile settlement when a squeezed and branch pile was vertical loaded,the relationship between the force and displacement at the enlarged-part was solved by using the cavity expansion theory,and the load transfer method was applied to the squeezed and branch pile. When a pile is vertically compressed,the enlarged-part will squeeze the soil and move downward,which can be regarded as a cavity expansion problem.Based on a rational assumption,the relationship between the enlarged-part horizontal internal pressure and the vertical displacement was deduced.From the mechanical analysis on the subsurface,a varying pattern of the pile-soil contact surface,A′C,and relationship between the enlarged-part resistance and vertical displacement were confirmed,and some influential parameters were also researched.Based on the above,by applying a hyperbolicmodel and linear elastic model in the pile shaft and pile tip,respectively,the load transfer method was applied to the squeezed and branch pile to obtain the pile-head settlement curve and pile inner force.The research result shows that by using the cavity expansion theory,the approach for obtaining the relationship between the enlarged-part resistance and vertical displacement completely considers the soil squeezing effect and geometric construction features of the enlargedpart.The enlarged-part resistance is more sensitive to the squeezed angle,which is in more accordance with engineering practices.The enlarged-part horizontal internal pressure has a nonlinear distribution on the reversed-truncated cone-shaped subsurface and decreases with the increase in the initial radius,and the nonlinearity becomes more obvious as the vertical displacement increases.The value of the enlarged-part horizontal internal pressure increases as the vertical displacement increases,but decreases with the increase in the squeezed angle.The load transfer method for squeezed and branch piles considering the cavity expansion theory can determine the settlement and mechanics behavior effectively.Regarding the squeezed and branch piles,the variation in the enlarged-part resistance caused by the squeezed angle has a stronger effect on the final bearing capacity than the simple side-resistance variation.The relevant method and conclusions can provide references for engineering.