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

在地震、船舶碰撞等横向动力循环荷载作用下的桩基设计，仍然需要一种合理的分析方法。近年来，人们对非线性温克勒地基梁法（BNWF）的适用性进行了研究。BNWF方法已被证明可以很好地解决涉及静态单调加载的问题。在尝试将静态BNWF扩展到动态问题时，会出现许多困难。其中，选择合适的阻尼模型（串联或并联）及其对应的阻尼值、选择合适的循环孔压累积计算方法、选择合理的桩土间隙计算方法的困难最为突出。解决这些困难的一种方法是进行适当的现场试验，监测其行为，并根据现场数据反算所需参数。近年来的研究表明，静力试验装置可用于桩侧荷载试验。静态装置产生单脉冲负载。我们已经解析地确定，如果通过包含质量和弹簧的单自由度振子施加荷载，而不是直接在桩头上施加荷载，则桩头的运动变为循环运动。本研究的目的是开发一种直接从单桩动态循环横向荷载试验中获得的一组现场数据反演p-y乘数和阻尼参数的方法。为了实现这一目标，将在FHWA的特纳-费尔班克公路研究中心（TFHRC）的试验场进行一系列现场试验。其中一些测试将在18英尺深的测试坑中进行，在不同密度的湿砂、饱和砂和粉砂上进行，其他测试将在坑外的天然粘土中进行。将对桩和周围的土壤进行充分的测量，以测量所需的数量。现有的基于p-y曲线的分析方法将进行修改，以考虑孔压效应和桩土间隙。并对九桩群进行实验，探索利用单桩数据分析群桩的方法。该研究将由一名博士生进行，并由PI监督。该博士生已经花了一年多的时间进行研究的分析部分，并基于现有的基于p-y曲线的方法开发了计算机代码。对分析方法的修改和实验工作将在两年内完成。

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.