Liquefaction Evaluations of Finely Interlayered Sands, Silts and Clays

最近的地震，包括2010-2011年新西兰的坎特伯雷地震序列（CES），已经表明，目前的工程程序有很强的倾向，过度预测薄层间砂、淤泥和粘土沉积物的液化效应。这是在新西兰基督城的Riccarton地区观察到的，那里的破坏最小，但各种工程分析预测，2010-11年的CES事件中至少有一次应该会造成严重的地表破坏，因为土壤在深度1到10米之间液化。对这类沉积物的液化效应的过度预测是世界范围内工程实践中的一个主要问题，因为它可能导致不必要的和昂贵的地面改善或结构加固工作。本研究将有助于消除当前液化评估程序中的这种偏差，解决以下基本限制：(1)锥贯仪测量的地层分辨率不足，(2)中间土壤类型的液化触发模型的偏差，以及(3)用于估计地面变形的分析模型中对空间变异性的考虑不足。开发改进的方法来解释锥突测量和计算地质变异性，对岩土工程专业具有广泛的适用性和益处。纠正液化程序中的过度预测偏差将有助于更现实的风险评估和改善社区的土地使用规划。与新西兰研究人员的合作将能够在克赖斯特彻奇地区直接实施结果，从而有助于更有效的重建工作。学生培训和模块开发将增加女生对土木工程的接触，我们研究生群体的加强指导将培养更多多样化和参与工业界和学术界的领导者。本研究将解决当前液化评估程序中的一个主要限制，通过寻求消除对细层间砂、淤泥和粘土沉积物中液化效应的过度预测的强烈偏见。第一项任务将使用岩土离心机的物理建模和轴对称锥体穿透过程的数值模拟，以改进使用锥体穿透测试（CPT）数据来描绘地层分层和材料类型的程序。第二项任务将使用新西兰最近的现场数据更新基于cpt的液化触发模型，并改进中间土壤类型的基于力学的功能形式。第三项任务将使用非线性动态分析和地下地层学的空间相关地质统计学实现，来研究一维液化脆弱性指数（其固有的水平分层假设）如何偏向于过度预测这类矿床中地震引起的地面变形。第四项任务将使用任务一到任务三的发现，重新评估2010-11年CES中Riccarton地区的表现，并评估这些发现在多大程度上解决了Riccarton地区在这些不同地震事件中的预测和观测表现之间的差异。因此，本研究将整合实验、理论和历史研究成果，以解决影响液化评估的基本问题，并在细层间土壤中解释锥体穿透试验数据和地表变形模型的空间变异性方面取得更广泛的发现，这些发现也可能对一般实践产生重大影响。

Recent earthquakes, including the 2010-2011 Canterbury Earthquake Sequence (CES) in New Zealand (NZ), have shown that current engineering procedures have a strong tendency to over-predict liquefaction effects in thinly interlayered sand, silt, and clay deposits. This was observed in the Riccarton area in Christchurch, NZ where minimal damage occurred, but various engineering analyses predicted that at least one of the 2010-11 CES events should have caused significant ground surface damage due to liquefaction of the soils between depths of 1 and 10 m. The over-prediction of liquefaction effects in these types of deposits is a major concern in engineering practice worldwide because it leads to potentially unnecessary and expensive ground improvement or structural strengthening efforts. This research will contribute to eliminating this bias in current liquefaction evaluation procedures by addressing fundamental limitations associated with: (1) insufficient stratigraphic resolution with cone penetrometer measurements, (2) biases in the liquefaction triggering models for intermediate soil types, and (3) insufficient accounting of spatial variability in the analysis models used to estimate ground deformations. The development of improved methods for interpreting cone penetration measurements and accounting for geologic variability has broad applicability and benefit to the geotechnical profession. The correction of over-prediction biases in liquefaction procedures will contribute to more realistic risk assessments and improved land use planning for communities. The collaboration with NZ researchers will enable direct implementation of results in the Christchurch area and thereby contribute to more efficient rebuilding efforts. The student training and module development will increase the exposure of civil engineering to girls and the enhanced mentoring of our graduate student group will foster more diverse and engaged leaders in industry and academia.This research will address a major limitation in current liquefaction evaluation procedures by seeking to eliminate the strong bias toward over-predicting liquefaction effects in finely interlayered sand, silt and clay deposits. The first task will use physical modeling on a geotechnical centrifuge and axisymmetric numerical simulations of the cone penetration process to refine procedures for using cone penetration test (CPT) data to delineate stratigraphic layering and material types. The second task will update a CPT-based liquefaction triggering model using recent field data from New Zealand with improved mechanics-based functional forms for intermediate soil types. The third task will use nonlinear dynamic analyses with spatially correlated geostatistical realizations of subsurface stratigraphy to examine how one-dimensional liquefaction vulnerability indices, with their inherent assumption of horizontal layering, are biased toward over-predicting earthquake-induced ground deformations in these types of deposits. The fourth task will reevaluate the performance of Riccarton sites in the 2010-11 CES using findings from tasks one through three, and evaluate the extent to which those findings resolve the differences between the predicted and observed performances of the Riccarton area in these different earthquake events. This research will thereby integrate experimental, theoretical, and case history findings toward resolving fundamental issues affecting liquefaction evaluations, with the broader findings regarding the interpretation of cone penetration test data in finely interlayered soils and the representation of spatial variability in ground deformation models also having potentially major impacts on general practice.