两段变直径桩的解析分析及工程应用

桩在水平荷载作用下的内力与位移计算，桩基设计规范推荐使用m法。m法的缺点是，当为了显著增大桩的水平承载力而在靠近承台的区域将土进行换填时，该处的土实际的刚度与其假定相距甚远。采用2K法进行水平荷载作用下桩的内力与变形分析，重点把握土的两个侧向弹簧刚度。2K法在工程中的应用是广泛的:承台附近土换填或加固，或将桩顶附近弯矩较大的桩身部分设为更大的直径，上段桩土弹簧刚度将增大，在一定的水平荷载作用下，桩顶位移将减小，桩的水平承载力得到提高而节省工程造价；如果在计算模型中未建立桩单元而欲求得桩顶反力，则采用变直径桩解析分析获得的位移函数和内力函数可计算桩的内力用于配筋；对于箱型基础、大型筏板基础，可较为精确地考虑其对桩顶的嵌固作用而提高桩的水平承载力；上部结构的刚度使得桩顶部有侧向支撑，桩身弯矩变小，也可优化桩基设计；对于桩基上的动力机器和块式基础，可以认为块式或承台是上段大直径桩，由此获得的上段桩侧向土弹簧刚度将非常可观，可用于优化桩基设计。如果考虑将桩建入计算模型，可以通过本方法得出的四个刚度参数输入到弹簧支座刚度矩阵中，能够节省桩建模及其内部单元带来的大自由度，计算模型更容易维护，其这也是一体化建模发展过程中的一个重要里程碑。

Analytical Analysis and Practice of Two-segment Variable Diameter Pile

The internal force and displacement of piles under horizontal load are calculated, and the m method is recommended for the design of pile foundation. The disadvantage of m method is that the stiffness of the soil is very far from the assumption that the soil is replaced by the soil in the region near the cap when the horizontal bearing capacity of the piles is significantly increased. In this paper, 2K method is used to analyze the internal force and deformation of piles under horizontal load, and the two lateral spring stiffness of the soil. The application of 2K method in engineering is widely: the pile foundation near the soil for filling or reinforcement, the larger diameter of the pile body, the upper part of the pile body is set to increase, the pile foundation displacement will be reduced, and the pile's bearing capacity can be improved, and the internal force of pile can be calculated, It can be more accurate to consider its effect on the pile top, the horizontal bearing capacity of piles, the pile bending moment of the pile top, the bending moment of piles, the pile bending moment, the pile body bending moment, the pile body bending moment, and the pile foundation design. If the pile is built into the calculation model, the four stiffness parameters can be obtained by this method, and it can save the large degree of freedom of the pile modeling and its internal unit. The model is more easy to maintain, and this is an important milestone in the development of integrated modeling.