Attenuation Mechanisms and Measurements

摘要：CMS-9616013，Glenn Rix，格鲁吉亚理工学院 颗粒材料（如土壤）对动荷载的响应可通过在一定频率范围内的速度谱和衰减谱来表征。以前对土壤沉积物近地表特性的研究强调了速度的研究，部分原因是在实验室和现场测量衰减的困难。然而，衰减数据可以唯一地用于更全面地表征近地表土壤对动态载荷的响应。 土壤的颗粒性质以及由于几何传播和波动现象引起的衰减增加了评估土壤中材料衰减的损失机制的复杂性。该研究计划的目标是加强对近地表土壤损失机制的理解，并制定可靠的评估程序。这个问题是从两个极端的尺度来处理的：在微观尺度上澄清基本的物理过程和发展适当的方法来进行现场（即，宏观尺度）测量。这些都是初步的步骤，发展实验室和现场测量程序，反映了详细的了解损失机制。 研究任务包括双层能量损失的研究（微观模拟和实验研究），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）。使用专用设备、新的实验室和现场测量程序以及独特的模拟软件和算法。 更好地了解损失机制和开发新的评估方法将提高确定近地表物质特性的能力（例如，老化、化学效应、饱和度），并改进地质过程的基于波的监测（例如，原位应力状态的反演、液化空间演变的评估以及系统对动态激励的响应）。对物质损失机制的更好理解和实地评估方法的进步也将有利于减轻地震灾害的场地特征。

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.