Vibration Testing of Full-Scale Pile Group

* 9617613 Rollins基础桩和群桩的横向承载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，目前只有三个群桩测试可用于指导工程师关于群桩行为，特别是在动态载荷下。 由于试验数据的缺乏，群桩分析的计算机程序还没有得到充分的验证，经验方法在其应用中受到极大的限制。 当涉及到地震等动态载荷时尤其如此。 因此，设计师被迫保守，这导致改造和新建筑的成本增加。 杨百翰大学正在对盐湖国际机场软粘土中的全尺寸群桩进行一系列横向载荷试验。 该测试包括大应变水平下的静态和动态测试。 该行动的目的是支持对桩群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。 由于桩组已经就位，土壤勘探也已完成，因此与所获得的信息相比，进行这些额外测试的增量成本很小。 由于原始测试计划的时间限制，有必要加快低应变测试计划：一旦完成大应变测试，就不可能获得有意义的小应变结果。 低应变振动测试是用安装在桩帽顶部的偏心质量振动台进行的。 试验可以获得桩土系统的固有频率，以及在低应变水平下的刚度和阻尼。 这些参数与大应变参数相结合，提供了一个很好的案例历史，研究人员可以使用它来验证静态和动态条件下的计算机代码。

*** 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.***