GOALI: Strength Loss in Clays During Earthquake and Other Cyclic Loading

地震引起的边坡破坏对强震区边坡和挡土系统的设计产生了重大影响。 例如，在1964年阿拉斯加地震期间，在天然粘土地层中发生了几次大规模山体滑坡，造成了生命损失，并对安克雷奇的基础设施和私人财产造成了重大经济损失。 因此，在此事件后开发的抗震稳定性设计方法采取了过于保守的方法，即假设适合于完全扰动粘土的强度值较小，导致设计系统地忽略了扰动和天然粘土行为的实质性差异。 这种过分保守的做法导致设计比考虑天然粘土的实际行为的设计要昂贵得多。 基于这项研究结果的设计将更经济，但对公众来说，安全系数足够。 因此，这项研究将有利于美国的经济和社会。 拟议研究的社会和教育影响是广泛的，因为其结果将影响预测自然灾害发生和开发可持续岩土工程设计所需的基础科学。 本研究涉及工程力学、岩土工程、地震工程和工程地质等多个方面。 研究的多学科方面将有助于扩大代表性不足的群体在研究中的参与，并对工程教育产生积极影响。这个学术与工业联络（GOALI）研究的资助机会是工业和工业之间的合作，它具有研究成果快速应用于实践的好处。 本研究为定量研究循环荷载作用下天然粘土的强度退化和破坏提供了一种新的方法。 它将结合联合收割机的实验和理论研究结果来预测地震引起的天然粘土沉积物的破坏。实验将在不同敏感度的Bootlegger Cove地层的高质量样品上进行。 这一地层中非常敏感的粘土引发了1964年安克雷奇地震期间发生的灾难性滑坡。 西北大学将与地球工程师公司合作进行这项研究，负责协调生物浓缩物样本的钻孔和取样工作。 实验计划将包括对完整和复溶样品的单调和循环试验。实验将阐明增量非线性，应力路径，固结历史和循环荷载的作用。建模活动将使用这一证据来制定增量非线性本构模型，再现孔隙压力累积和周期性破坏中的破坏效应。 虽然已经提出了几种模型来科普天然粘土的复杂力学，这些模型往往忽略了丰富多样的可能的破坏模式。流体饱和土壤的工程力学理论提供了见解，但为了捕捉地震震动过程中发生的复杂过程，这些理论必须得到加强，以适应周期性衰减的刚度和强度过程。 该方法将包括制定具体的分叉标准，用于评估作为应力条件和循环次数函数的循环强度退化。 该模型将在计算机程序中进行数值实现，用于岩土问题的耦合动力分析。

Slope failures caused by earthquakes have had a significant impact on the design of slopes and earth retention systems in areas of strong seismicity. For example, several massive landslides occurred within natural clay soil formations during the 1964 Alaskan earthquake that caused loss of life and significant financial loss to infrastructure and private property in Anchorage. Consequently, design methods for seismic stability developed after this event take an overly conservative approach by assuming small values of strength that are appropriate for fully disturbed clay, resulting in designs that systematically ignore the substantial differences the behavior of the disturbed and the natural clay soil. This over conservatism results in designs that are significantly more expensive than one which accounts for actual behavior of the natural clays. Designs based on the results of this research will be more economical yet result in adequate margins of safety for the public. Therefore, this research will benefit the U.S. economy and society. The societal and educational impacts of the proposed research are broad, because its results will impact the basic science needed for predicting the occurrence of natural hazards and for developing a sustainable geotechnical design. This research involves aspects of engineering mechanics, geotechnical engineering, earthquake engineering and engineering geology. The multi-disciplinary facets of the research will help broaden participation of underrepresented groups in research and positively impact engineering education. This Grant Opportunity for Academic Liaison with Industry (GOALI) research is a collaboration between industry and academe, which has the benefit of rapid application of research results to practice. This research will develop a new approach for quantifying the strength degradation and destructuration of natural clays exposed to cyclic loading. It will combine experimental and theoretical findings to predict the onset of seismically-induced failure in natural clay deposits. The experiments will be conducted on high quality samples of Bootlegger Cove Formation of varying degrees of sensitivity. Very sensitive clays in this formation triggered the catastrophic slides that took place in Anchorage during the 1964 earthquake. Northwestern University will collaborate in this research with GeoEngineers, Inc., who will coordinate drilling and sampling of BCF specimens. The experimental program will include monotonic and cyclic tests on intact and reconstituted samples. The experiments will elucidate the role of incremental nonlinearity, stress-paths, consolidation history and cyclic loading. The modeling activities will use this evidence to formulate an incrementally non-linear constitutive model reproducing the effect of destructuration in pore pressure build-up and cyclically generated failure. Although several models have been proposed to cope with the complex mechanics of natural clays, such models often ignore the rich variety of possible failure modes. Engineering mechanics theories for fluid-saturated soils provide insights, but to capture the complex processes taking place during seismic shaking, these theories must be enhanced to accommodate cyclically-decaying stiffness and strength processes. The approach will include the development of specific bifurcation criteria for assessing the cyclic strength degradation as a function of stress conditions and number of cycles. The model will be numerically implemented in computer programs for coupled dynamic analysis of geotechnical problems.