考虑孔壁粗糙体退化的灌注桩竖向荷载传递

研究剪切面粗糙体退化对桩岩界面剪切过程中荷载传递机理的影响.将桩身混凝土与钻孔地层之间的粗糙面抽象为一系列相同的等腰三角形,并用半波长和剪胀角定义单个粗糙体的尺寸,引入Patton模型来描述粗糙体的宏观剪切响应与相对剪切位移之间的关系,并考虑到孔壁地层与桩身混凝土的相对刚度比,基于能量原理,引入了一个粗糙体退化系数来定义在剪切过程中所产生的粗糙体表面磨损及体积压缩的行为.据此,修正了经典的Patton模型,进而推导了考虑孔壁粗糙体退化的灌注桩竖向荷载传递方程,该方程不仅可以考虑剪切面的粗糙程度(半波长及剪胀角)对桩身荷载传递行为的影响,而且该解答中所包含的参数物理意义明确.采用有限差分法对荷载传递方程进行求解,并与工程实例进行了对比验证.结果表明,本文理论预测方法的结果与现场实测结果吻合较好,对灌注桩的初步设计有一定参考价值.

Vertical Load Transfer Behavior of Cast-in-place Piles Considering Hole Wall Asperity Degradations

The influence of degradation of shear surface asperity on the load transfer mechanism of the pile-rock interface in the shear process is studied. Firstly, the rough surface between concrete of the pile and bored stratum is abstracted as a series of identical isosceles triangles, and the size of a single rough body is defined by half-wavelength and dilatancy angle. Secondly, the Patton model is introduced to describe the relationship between macroscopic shear responses of the rough body and relative shear displacement. Considering the relative stiffness ratio between the hole wall stratum and the pile body concrete, based on the energy principle, a rough body degradation coefficient is introduced to define the behavior of the rough body surface wear and volume compression generated during the shearing process. Accordingly, the classic Patton model was then improved. On this basis, the vertical load transfer equation of cast-in-place piles considering the degradation of the hole wall roughness is derived. This equation can not only consider the influence of the shear surface roughness (half wave length and dilatancy angle) on the load transfer behavior of piles, but the physical meaning of parameters included in the solution is also clear. Finally, the finite difference method is used to solve the load transfer equation, which is compared and verified by engineering examples. The results show that the theoretical predictions in this paper are in good agreement with the field measured results, and have a certain reference value for the preliminary design of cast-in-place piles.