Field Method for Back-calculation of Dynamic p-y Multipliers and Damping

承受地震、船舶碰撞等横向动态循环荷载的桩基设计，仍然需要一种理性的分析方法。 近年来，非线性Winkler地基梁（BNWF）法在此类问题中的适用性得到了研究。BNWF方法已被证明适用于涉及静态单调加载的问题。 当试图将静态BNWF扩展到动态问题时，会出现一些困难。 其中，选择合适的阻尼模型（串联或并联）和相应的阻尼值，一个合适的方法来考虑循环孔隙水压力的建立，和一个合理的方法来考虑桩土间隙的困难最为突出。 解决这些困难的一种方法是进行适当的现场实验，监测行为并从现场数据反算所需的参数。 近年来的研究表明，静力试验装置可用于进行桩的横向载荷试验。 Statnamic器械产生单脉冲加载。我们已经分析确定，而不是直接施加在桩头上的负载，如果它是通过一个单一的自由度振荡器，包括一个质量和弹簧，桩头的运动成为循环。 建议的研究的目的是开发一种方法，反计算的p-y乘子和阻尼参数直接从一组现场数据来自单桩动态循环横向载荷试验。 为了实现这些目标，将在FHWA的Turner-Fairbank公路研究中心（TFHRC）的试验场进行一系列现场试验。 其中一些测试将在18英尺深的测试坑中在不同密度的湿饱和砂和粉砂上进行，而其他测试将在坑外的天然土壤（粘土）中进行。 桩体和周围土壤将配备足够的仪器，以测量所需的数量。 现有的基于p-y曲线的分析方法将被修改，以考虑孔隙压力效应和桩土间隙。 此外，还将对一个九桩群桩进行试验，并探索将单桩数据应用于群桩分析的方法。 本研究将由一名博士生进行，并由PI监督。 这位博士生已经花了一年多的时间进行研究的分析部分，并根据现有的基于p-y曲线的方法开发了计算机代码。 对分析方法和实验工作的拟议修改将在两年内完成。

The design of pile foundations subjected to lateral dynamic cyclic loading such as caused by earthquakes, ship collision, etc., is still in need of a rational analysis method. In recent years, the applicability of the Beam on Nonlinear Winkler Foundation (BNWF) method for these problems has been studied. The BNWF method has been proven to work well for problems involving static, monotonic loading. A number of difficulties occur when trying to extend the static BNWF to dynamic problems. Among these, the difficulties of selecting a suitable damping model (series or parallel) and the corresponding damping values, a suitable method for accounting for the cyclic pore pressure build up, and a rational method for accounting for the pile-soil gapping stand out the most. One method of addressing these difficulties is to conduct a suitable field experiment, monitor the behavior and back-calculate the needed parameters from the field data. Recent studies indicate that the Statnamic testing device might be used for conducting lateral pile load tests. The Statnamic device produces a single pulse loading. We have analytically determined that, instead of applying the loading directly on the pile head, if it is applied through a single degree-of-freedom oscillator involving a mass and a spring, the motion of the pile head becomes cyclic. The objective of the proposed study is to develop a method of back-calculating the p-y multipliers and damping parameters directly from a set of field data derived from a dynamic cyclic lateral load test on single piles. In achieving the objectives, a series of field tests will be conducted at the test site of Turner-Fairbank Highway Research Center (TFHRC) of FHWA. Some of the tests will be conducted in a 18-foot deep test pit on wet and saturated sands and silty sands of different densities, and the others outside the pit in the natural soil which is clay. The pile and the surrounding soil will be adequately instrumented for measuring the needed quantities. Existing p-y curves based analysis methods will be modified to account for pore pressure effects and pile-soil gapping. Also, experiments will be conducted on a nine-pile group, and methods of applying the single pile data to analyze pile groups will be explored. The study will be conducted by a doctoral student and supervised by the PI. The doctoral student has already spent over an year on the analysis portion of the study and developed computer codes based on existing p-y curves based methods. The proposed modifications to the analysis method and experimental work will be completed in a period of two years.