Mechanism and effective design of generating bearing capacity of group piles by statnamic load test

近十年来，动态载荷试验作为最经济的桩基载荷测试方法之一，受到了打桩界的广泛关注。然而，几乎所有的研究和开发都是基于现场试验的数据。由于地面的不确定性和复杂性，利用这些数据很难实现一致的解释。为了克服这一不足，本研究的第一个目标是开发一种可以在一个恒定条件下进行静态载荷试验的系统。研制了一种用于模型试验的小型静态加载装置，该装置使用预压缩空气代替爆炸气体。在这项研究中，两种类型的桩，即摩擦桩和ENC承力桩，分别承受两种水平的力，即小荷载和大荷载。前者用于确定桩的初始刚度，后者用于确定极限承载力。这项研究的第二个目标是开发一个可以分析各种类型载荷的三维有限元程序。对于动力分析，通过在时间域中直接积分来确定解。实验结果表明，可以产生与原始静态载荷试验相似的载荷曲线。分析还表明，静力荷载作用下桩体内的受力分布与静力荷载作用下的相似。

During the past ten years, the Statnamic load test has drawn attention from the piling community as one of the most economical methods for pile load testing. However, almost all of the research and development have been based on data from field tests. A consistent interpretation is difficult to achieve with such data due to the uncertainty and the complexity of the ground. To overcome this deficiency, the first objective of this research is to develop a system whereby Statnamic load tests can be performed under one constant condition. A small-scale Statnamic loading device for model tests has been developed whereby pre-compressed air is applied instead of gas from an explosion. In this study, two types of piles, friction piles and enc bearing piles, are modeled and are loaded with two levels of forces, namely, small loads and large loads. The former loads are for determining the initial stiffness of piles and the latter for determining the ultimate capacity. The second objective of this study is to develop a 3D-FEM program that can analyze various types of loading. For a dynamic analysis, the solution is determined by the direct integration in time domain. The experimental results show the possibility of producing a loading curve similar to that in the original Statnamic load test. The analysis also shows that the force distributions in piles under Statnamic loading are similar to those under static loading.