双层非均质地基中V-T联合受荷桩承载特性分析

为探讨近海环境双层非均质地基中预制型单桩基础在桩顶竖向荷载V和扭矩T联合作用下的承载特性,假定单层地基土体剪切模量随深度呈幂函数分布,考虑桩–土接触面上极限摩阻力沿深度的非线性变化,并计入桩–土接触面上的位移非协调性,基于剪切位移法和桩身荷载传递函数建立出桩身位移控制方程,由此导得不同加载顺序(V→T或T→V)和受力阶段下的桩身内力位移解答,进而获得桩身承载力包络图。通过与已有成果的对比分析,验证了模型与解答的合理性。最后,通过参数分析获得了桩身长径比(L/D)、加载顺序以及地基土剪切模量幂函数分布系数(m1,m2与n)等参数对桩身承载变形特性的影响规律:桩身承载力随L/D与n的增大而逐渐减小;V→T加载时m1的影响范围主要为z/L≤0.4,m2影响范围随Tt/Tult的增加而增大;T→V加载时m1基本无影响,而m2的影响范围为0.6≤z/L≤1.0;桩顶可承受的竖向力随扭矩增加不断减小而趋于零,且V→T加载时的承载力包络线始终处于T→V承载力包络线外侧。

Bearing behavior of a single pile in double-layered nonhomogeneous subsoil under V-T combined loads

To discuss the bearing behavior of a single pile under combined vertical load V and torque T in offshore double-layered nonhomogeneous subsoil, the shear modulus of each soil layer is assumed as an increasing distribution with the depth defined by a power function. Then, considering various loading sequences and the non-coordination deformation along the pile-soil interface, the governing equation for the pile shaft is first established by using the load transfer function and the shear displacement method. Subsequently, the analytical solutions are deduced to calculate the inner forces and deformations of the pile shaft under various bearing stages and loading sequences (V→T or T→V). Based on the results by the obtained solutions, the failure envelops for the bearing capacity of the pile shaft are plotted correspondingly. Through a comparative analysis of the results with the available achievements, the rationality of the proposed method is verified. Finally, a parameter analysis is carried out to discuss the influence laws by the key factors such as the slenderness ratio of pile shaft (L/D), loading sequences and constant coefficients determining the shear modulus distribution (m₁, m₂, n) of subsoil. The results show that the bearing capacity decreases with the increase of L/D and n. The main influence range of m₁ is z/L≤0.4 and the influence range of m₂ increases with the increase of T_t /T_ult under V→T loading path. The effect of m₁ can be ignored and the main influence range of m₂ is 0.6≤z/L≤1.0 under T→V loading path. To increase the value of torsion at the pile top will result in a decreasing vertical bearing capacity with a final zero value. Furthermore, the failure envelope under V→T loading path remains outside of that under T→V loading.