Vibration Testing of Full-Scale Pile Group

*9617613滚动基桩和群桩的水平承载能力是减轻地震灾害的关键考虑因素。由于全尺寸测试的成本和后勤困难，目前只有三种群桩测试可用于指导工程师关于群桩行为，特别是在动态荷载下的群桩行为。由于缺乏试验数据，群桩分析的计算机程序还没有得到充分的验证，经验方法的应用也受到极大的限制。当涉及到地震等动态加载时，这一点尤其正确。因此，设计师被迫保守，这导致了翻新和新建筑成本的增加。杨百翰大学正在盐湖国际机场对软粘土中的全尺寸群桩进行一系列横向载荷测试。这种测试包括大应变水平下的静态测试和动态测试。这一行动的目的是支持对群桩进行额外的低应变振动测试，从而为校准和验证计算机模型提供数据。由于群桩已经就位，土壤勘探已经完成，与要获得的信息相比，执行这些额外测试的增量成本很小。由于原试验计划的时间限制，有必要加快低应变试验的进度：一旦完成大应变试验，就不可能获得有意义的小应变结果。采用安装在承台顶部的偏心质量振动器进行低应变振动试验。通过试验可以得到桩-土体系的固有频率，以及在低应变水平下的刚度和阻尼值。这些参数与大应变参数相结合，提供了一个很好的病历，研究人员可以使用这些病历来验证他们的计算机代码在静态和动态条件下的有效性。

*** 9617613 Rollins The lateral load capacity of foundation piles and pile groups is a key consideration in earthquake hazard mitigation. Because of the cost and logistical difficulties of full-scale testing, only three pile group tests are currently available to guide engineers regarding pile group behavior, especially under dynamic loading. Due to the dearth of experimental data, computer programs for analyzing pile groups have not been thoroughly validated, and empirical methods are extremely restricted in their application. This is particularly true when it comes to dynamic loading such as earthquakes. As a result, designers are forced to be conservative and this leads to increased costs for retrofits as well as new construction. Brigham Young University is performing a series of lateral load tests on a full-scale pile group in soft clay at the Salt Lake International Airport. This testing involves both static and dynamic testing at large strain levels. The objective of this action is to support additional low-strain vibration testing of the pile group, thereby providing data for calibrating and validating computer models. Since the pile group is already in place, and soil exploration is completed, the incremental cost of performing these additional tests is small in comparison to the information to be gained. Due to time constraints on the original test schedule, it is necessary to expedite the schedule for the low strain testing: once the large-strain testing is completed, it is impossible to obtain meaningful small strain results. The low-strain vibration testing is conducted with an eccentric mass shaker which is mounted on top of a pile cap. The testing makes it possible to obtain the natural frequency of the pile-soil system, as well as the stiffness and damping at low strain levels. These parameters, in combination with the large-strain parameters, provide an excellent case history which researchers can use to validate their computer codes for both static and dyna mic conditions.***