GOALI: Dynamic Soil Properties - Effects of Construction-induced Stress Changes

通常，地震活跃区的项目必须考虑多个应变水平的条件。 在设计中，结构的稳定性和极限变形是在相对较高的应变水平进行评估。 在小应变水平的刚度的基础上，完成的结构上的地面震动的影响进行了评估。 这些吗？动态？然后呢？静电干扰？刚度是基于施工前进行的测试，因此仅反映结构施工前的应力条件。 然而，地震事件的影响通常会在结构建成后对其产生影响。 在土壤中的条件是改变从他们的初始条件，因此出现的问题，作为应力变化的影响？动态？受影响土壤的性质。 安克雷奇港扩建项目的设计和建设提供了一个测试平台，以评估这些概念，并扩展国家的最先进的。这个研究项目是西北大学和地球工程师公司之间的共同努力。位于华盛顿的雷德蒙，是该项目的岩土工程顾问。 扩建项目包括建造近2英里的新开放式码头设施。 90英尺高的码头将由一系列相互连接的板桩单元组成，这些板桩单元沿着表面形成一个连续的挡土墙，但是？开着吗在端部（陆侧）。 大型码头结构物的施工将极大地改变结构物下及向海地基土的应力，从而改变结构物的动力特性。 为了评估施工后适用于地基土的动力特性，必须明确考虑这些应力变化。 工作范围包括常规现场和实验室测试、现场跨孔地震测试、地震CPT探头、粘土薄壁管取样、轴向和径向变形内部测量的三轴应力探头测试以及三维弯曲元件剪切波速度同步测量。还将进行码头施工的有限元分析和设计地震事件的模拟。 码头施工的性能监测将允许将预测与全尺寸性能进行比较，并将进行参数研究，以确定何时这些施工影响重要。 最后，将制定一项测试协议，将常规的现场和实验室结果与详细的实验室结果联系起来。 这种合作提供了一个独特的机会，将现场调查期间收集的常规数据，研究质量应力应变数据和最先进的有限元模拟与地质结构的全尺寸性能相关联，以推进岩土地震工程的最先进水平。 特别是，在了解加载的增量非线性材料的波传播特性的影响的进展是相关的这一领域。 在这项研究中获得的信息将直接适用于所有其他有限元建模项目，在静态和地震荷载条件下的变形是重要的，特别是在静态问题的应用程序，其中重要的是包括本构响应非常小到更大的应变。 研究生和本科生都将在这项研究中发挥不可或缺的作用。 GeoEngineers，Inc.西北大学提供了一个令人兴奋的机会，让学生参与一个重大的设计和建设项目。 这项工作将是他们的优秀经验，无论他们选择追求学术/研究生涯，或在工程实践的职业生涯。

Frequently, a project in a seismically active zone must consider conditions at multiple strain levels. In design, the stability and limiting deformations for the structure are evaluated at relatively high strain levels. The effects of ground shaking on the completed structure are evaluated on the basis of stiffness at small strain levels. These ?dynamic? and ?static? stiffnesses are based on tests conducted prior to construction and thus only reflect the stress conditions prior to construction of the structure. However, the effects of a seismic event normally impact the structure after it has been constructed. Conditions in the soil are altered from their initial condition, and thus the question arises as to the effects of the stress changes on the ?dynamic? properties of the affected soil. The design and construction of the Port of Anchorage Expansion Project provides a test bed to evaluate these concepts and extend the state-of-the-art. This research project is a joint effort between Northwestern University and GeoEngineers, Inc. of Redmond, Washington, the geotechnical consultants for the project. The expansion project consists of constructing nearly 2 miles of a new open-cell wharf facility. The 90-ft-high wharf will consist of a series of interconnecting sheet pile cells that form a continuous retaining wall along the face but are ?open? at the ends (landside). Construction of the large wharf structure will greatly alter the stresses, and thus the dynamic properties, in the foundation soils beneath and seaward to the structure. To evaluate the dynamic properties applicable to the foundation soils after construction, these stress changes must be considered explicitly. The scope of work includes conventional field and laboratory testing, field cross-hole seismic testing, seismic CPT probes, thin-walled tube sampling of the clay, triaxial stress probe tests with internal measurements of axial and radial deformations and synchronous measurements of shear wave velocity with bender elements in 3-dimensions. Finite element analyses of wharf construction and simulation of the design seismic event will also be conducted. Performance monitoring of wharf construction will permit comparison of predictions with full-scale performance, and parametric studies will be conducted to define when these construction effects are important. Ultimately, a testing protocol will be developed to relate conventional field and laboratory results to detailed laboratory results. This collaboration provides a unique opportunity to relate conventional data collected during site investigation, research quality stress-strain data and state-of-the-art finite element simulation with full-scale performance of a geo-structure to advance the state-of-the-art in geotechnical earthquake engineering. In particular, advances in understanding the effects of loading on the wave propagation characteristics of incrementally-nonlinear materials are relevant to this field. Information gained in this research will directly apply to all other finite element modeling projects where deformations under static and seismic loading conditions are important, particularly in applications to static problems wherein it is important to include constitutive responses over very small to larger strains. Both graduate and undergraduate students will play an integral part in this research. The close collaboration between GeoEngineers, Inc. and Northwestern University provides an exciting opportunity for students to participate in a major design and construction project. This work will be excellent experience for them, whether they choose to pursue an academic/research career, or a career in engineering practice.