打桩锤击模型的解析算法

ANALYTICAL SOLUTION FOR MODEL OF PILE HAMMER IMPACT

桩的可打性研究需要模拟桩的锤击,计算出桩顶的应力波。该应力波可由数值或解析方法研究获得。针对桩锤、桩帽、锤垫、桩垫组成的锤击系统,提出了一种新的解析模型。该模型分别用不同的集中质量块表示桩锤、桩帽,用一并联的弹簧、阻尼器表示锤垫,用一弹簧表示桩垫,同时用一阻尼器表示桩,建立平衡方程,利用拉普拉斯变换推导出锤击力的解析解。该解析解均用无量纲量表示,可用来研究桩垫层材料的参数、桩帽与桩锤质量之比对锤击力的影响,并利用室内试验确定出桩垫材料的刚性系数,将理论计算值与实测值进行对比,理论值与实测值吻合较好,故该解析模型可用来研究参数的组合对锤击性能的影响。

The drivability study of piling requires modeling of the hammer impact to calculate the input force wave at the pile head. This force wave can be computed numerically or by simple analytical solutions. Analytical solutions are presented for hammer impact considering a model which uses lumped mass for the ram and anvil, a spring and a dashpot for the anvil cushion, and another spring for the cap cushion on the top of a pile. The pile is modeled as a dashpot. The solutions account for the separation of the anvil mass from the pile cap cushion as well as the separation of the ram mass from the anvil cushion. The developed solutions are used to perform a parametric study to show the influence of the pile cushion and the mass ratio of pile cap to pile hammer on the maximum force transmitted to the pile head. The parameters of pile cap cushion are achieved by laboratory static test. Force-time responses derived from the analytical model are compared with field data, which indicate well consistent with each other.