Attenuation Mechanisms and Measurements

摘要/ ABSTRACT摘要：颗粒材料（如土壤）对动力载荷的响应是通过频率范围内的速度和衰减谱来表征的。先前对土壤沉积物近地表特征的研究强调对速度的研究，部分原因是在实验室和现场测量衰减的困难。然而，衰减数据可以用来更充分地表征近地表土壤对动力荷载的响应。土壤的颗粒性以及几何扩散和波动现象导致的衰减增加了评估土壤中物质衰减损失机制的复杂性。本研究计划的目的是增进对近地表土壤流失机制的了解，并制定健全的评估程序。这个问题是从两个极端尺度来解决的：在微观尺度上澄清潜在的物理过程和发展适当的现场（即宏观尺度）测量方法。这些是朝着制定实验室和现场测量程序迈出的初步步骤，这些程序反映了对损失机制的详细了解。研究任务包括双层能量损失的研究（微观水平模拟和实验研究），根据新的现象学假设（实验研究）重新评估低应变下的滞后损失，以及开发主动和被动现场测试程序（分析，模型和现场研究）。专门的设备，新的实验室和现场测量程序，和独特的模拟软件和算法的使用。对损失机制的更好理解和新的评估方法的发展将增强表征近地表材料的能力（例如，老化，化学效应，饱和度），并改进基于波的地球过程监测（例如，原位应力状态的反演，液化空间演化的评估，以及系统对动态激励的响应）。对物质损失机制的进一步了解和实地评估方法的进步也将有利于减轻地震灾害的现场特征。

ABSTRACT: CMS-9616013, Glenn Rix, Georgia Tech The response of particulate materials such as soils to dynamic loads is characterized by the velocity and attenuation spectra over a range of frequencies. Prior research on the near-surface characterization of soil deposits has emphasized the study of velocity, due in part to difficulties in measuring attenuation in the laboratory and field. However attenuation data can be uniquely used to more fully characterize the response of near-surface soils to dynamic loads. The particulate nature of soil and the attenuation due to geometric spreading and wave-phenomena add to the complexity of evaluating the loss mechanisms for material attenuation in soil. The objectives of this research program are to enhance the understanding of loss mechanisms in near-surface soils and to develop robust assessment procedures. The problem is approached from two extreme scales: the clarification of underlying physical processes at the microscale and the development of adequate methods for field (i.e., macroscale) measurement. These are initial steps toward developing laboratory and field measurement procedures which reflect a detailed understanding of the loss mechanisms. Research tasks include the study of energy losses in double layers (micro-level simulations and experimental studies), reassessment of hysteretic losses at low strain in light of new phenomenological hypotheses (experimental studies), and development of active and passive field testing procedures (analytical, model, and field studies). Specialized devices, new laboratory and field measurement procedures, and unique simulation software and algorithms are used. An improved understanding of loss mechanisms and the development of new methods of assessment will enhance the ability to characterize near-surface materials (e.g., aging, chemical effects, saturation), and improve the wave-based monitoring of geoprocesses (e.g., inversion of state of stress in situ, assess ment of the spatial evolution of liquefaction, and response of systems to dynamic excitation). The improved understanding of material loss mechanisms and advances in field assessment methods will also benefit site characterization for earthquake hazard mitigation.