Cyclic Stress-Strain Characteristics of EPS GeoFoam

EPS GeoFoam 的循环应力-应变特性

• 批准号: 0926042
• 负责人: Aurelian Trandafir
• 金额: $ 6.15万
• 依托单位: University of Utah
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-01 至 2010-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0926042&HistoricalAwards=false
• 关键词: Cyclic; Stress; Strain; Characteristics; EPS

This award is funded under the American Recovery and Reinvestment Act of 2009(Public Law 111-5).Block-molded expanded polystyrene (EPS) geofoam is a type of cellular geosynthetic with a long history of successful applications in geotechnical engineering. Characterized by an extremely low density, EPS geofoam has become the material of choice in a variety of geotechnical problems requiring lightweight fill for slope stabilization, embankments on soft soils, earth retaining structures, bridge approaches, bridge abutments, and buried pipes. During recent years, increasing consideration has been given to the compressible inclusion function of EPS geofoam associated with its low stiffness, which makes geofoam an ideal material for reducing the seismic lateral earth pressures against rigid non-yielding retaining structures (e.g., below grade building walls, bridge abutments, or restrained walls). Vertical EPS panels installed against such structures may act as seismic buffers reducing the seismic wall thrust during an earthquake. Recent findings from numerical simulations and physical shaking table tests addressing the seismic behavior of buried structure walls with EPS buffer are quite promising indicating significant reduction in the dynamic wall thrust compared to the rigid case with no geofoam inclusion. Although the behavior of EPS geofoam under monotonic loading conditions has been extensively studied in the laboratory using triaxial compression tests, little research has been done until present on the cyclic stress-strain behavior of this material. Currently published dynamic properties of EPS geofoam obtained from strain-controlled resonant column and cyclic uniaxial tests, and commonly employed by investigators in numerical seismic analyses, are characterized by degradation of dynamic shear modulus and increase in damping ratio with increasing cyclic shear strain amplitude. However, results from a preliminary laboratory study based on stress-controlled cyclic uniaxial tests indicate a logarithmic decrease in the damping ratio of EPS geofoam with increasing axial strain amplitude. Furthermore, for cyclic axial strain amplitudes greater than about 0.8%, the material seems to exhibit a visco-elasto-plastic behavior associated with the occurrence of permanent plastic strains. These experimental outcomes demonstrate that the cyclic stress-strain characteristics of EPS geofoam are currently poorly understood. In this context, the main objective of this research is to use laboratory triaxial tests to investigate in detail the behavior of geofoam under cyclic loading. This experimental investigation will be based on stress-controlled cyclic triaxial tests, and will focus on non-elasticized EPS materials commonly used in geotechnical applications. Particular emphasis will be placed on the influence of the following parameters: confining pressure, initial (static) deviator stress, cyclic deviator stress amplitude, loading frequency, EPS density, and specimen size. Intellectual Merit: This research will provide a better understanding of the fundamental stress-strain behavior of EPS geofoam under cyclic loading that is invaluable in optimizing the seismic buffer function of this material in geotechnical earthquake engineering applications. Specific questions to be addressed include: 1) What is the threshold cyclic axial strain amplitude for the onset of the elasto-plastic stress-strain behavior? 2) How are the dynamic properties of EPS geofoam affected by the confining pressure and initial deviator stress? 3) In what manner the permanent plastic strains accumulate with increasing number of loading cycles? 4) How does the specimen size influence the cyclic stress-strain behavior of EPS geofoam?Broader Impacts: This project will significantly expand our knowledge on the cyclic stress-strain behavior of EPS geofoam for a variety of material densities, initial stress conditions, and loading frequencies commonly encountered in practice. A reference website summarizing the geofoam dynamic properties obtained from the proposed laboratory work will be developed and advertised to the investigators involved with the assessment of the seismic behavior of EPS geofoam in various geotechnical earthquake engineering applications. The project will provide a University of Utah graduate student with training experience in laboratory triaxial testing and will expose an undergraduate student to various geotechnical research activities.

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。块状成型发泡聚苯乙烯（EPS）土工泡沫是一种多孔土工合成材料，在岩土工程中有着悠久的成功应用历史。 EPS土工泡沫的特点是密度极低，已成为各种岩土工程问题的首选材料，这些问题需要轻质填料进行边坡稳定、软土加固、挡土结构、桥梁引道、桥台和埋管。 近年来，人们越来越多地考虑与其低刚度相关的EPS土工泡沫的可压缩包含功能，这使得土工泡沫成为用于降低刚性非屈服挡土结构（例如，低于地面的建筑墙、桥台或约束墙）。 安装在这种结构上的垂直EPS板可以作为地震缓冲器，减少地震期间的抗震墙推力。 从数值模拟和物理振动台试验解决的EPS缓冲器的埋地结构墙的抗震性能的最新研究结果是非常有前途的动态墙推力显着减少相比，刚性的情况下，没有土工泡沫夹杂物。 虽然EPS土工泡沫在单调加载条件下的行为已经在实验室中使用三轴压缩试验进行了广泛的研究，但迄今为止对这种材料的循环应力-应变行为的研究很少。 目前公布的动态性能的EPS土工泡沫获得的应变控制共振柱和循环单轴试验，并普遍采用的研究人员在数值地震分析，其特征在于动态剪切模量的退化和阻尼比的增加，增加循环剪切应变振幅。 然而，基于应力控制循环单轴试验的初步实验室研究结果表明，随着轴向应变幅值的增加，EPS土工泡沫的阻尼比呈对数下降。 此外，对于大于约0.8%的循环轴向应变幅度，材料似乎表现出与永久塑性应变的发生相关的粘弹塑性行为。 这些实验结果表明，EPS土工泡沫的循环应力-应变特性目前知之甚少。 在此背景下，本研究的主要目的是使用室内三轴试验，详细调查在循环荷载下的土工泡沫的行为。 本实验调查将基于应力控制的循环三轴试验，并将重点放在岩土工程应用中常用的非弹性EPS材料。 将特别强调以下参数的影响：围压，初始（静态）偏应力，循环偏应力振幅，加载频率，EPS密度和试样尺寸。 智力优势：这项研究将提供一个更好地了解基本的应力-应变行为的EPS土工泡沫在循环荷载下，这是非常宝贵的优化地震缓冲功能，这种材料在岩土地震工程应用。 具体问题包括：1）什么是临界循环轴向应变幅的弹塑性应力-应变行为的开始？2)围压和初始偏应力对EPS土工泡沫动力特性的影响如何？3)随着加载循环次数的增加，永久塑性应变以何种方式累积？4)试件尺寸如何影响EPS土工泡沫的循环应力-应变行为？更广泛的影响：该项目将大大扩展我们对EPS土工泡沫在各种材料密度、初始应力条件和实际中常见的加载频率下的循环应力-应变行为的了解。 将开发一个参考网站，总结从拟议的实验室工作中获得的土工泡沫动态特性，并向参与评估EPS土工泡沫在各种岩土地震工程应用中的抗震性能的调查人员进行宣传。 该项目将为犹他州大学的一名研究生提供实验室三轴试验方面的培训经验，并将使一名本科生接触各种岩土工程研究活动。