Liquefaction Evaluations of Finely Interlayered Sands, Silts and Clays

最近的地震，包括2010-2011年新西兰坎特伯雷地震序列(CES)，已经表明，当前的工程方法有一种强烈的趋势，即过度预测薄层间砂土、粉土和粘土沉积物的液化效应。这是在新西兰克赖斯特彻奇的里卡顿地区观察到的，那里的破坏最小，但各种工程分析预测，2010-11年的CES事件中，至少有一次应该是由于1到10米深的土壤液化而造成的地表重大破坏。对这些类型矿床的液化影响的过度预测是世界各地工程实践中的一个主要问题，因为它导致可能不必要的和昂贵的地基改善或结构加固工作。这项研究将有助于消除当前液化评估程序中的这种偏差，解决与以下基本限制有关的问题：(1)锥形贯入仪测量的地层分辨率不足，(2)中间土类型的液化触发模型存在偏差，以及(3)用于估计地面变形的分析模型中没有充分考虑空间变异性。改进的圆锥贯入测量解释方法和地质可变性解释方法的发展对岩土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利用规划。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成果，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土木工程对女孩的接触，我们研究生团队的加强指导将培养更多样化和参与的行业和学术领袖。这项研究将解决目前液化评估程序的一个主要局限性，试图消除对细小夹层砂土、粉土和粘土沉积物中过度预测液化影响的强烈偏见。第一项任务将使用土工离心机上的物理模型和锥体贯入过程的轴对称数值模拟，以完善使用锥体贯入测试(CPT)数据来划定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，该模型具有针对中间土壤类型的改进的基于力学的函数形式。第三项任务将使用地下地层学的空间相关地统计学实现的非线性动态分析，以检查一维液化易损性指数，其固有的水平分层假设，如何偏向于过度预测这些类型的沉积物中地震引起的地面变形。第四项任务将使用任务一至任务三的调查结果，重新评估里卡顿地区在2010-11年CES中的表现，并评估这些调查结果在多大程度上解决了里卡顿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，这项研究将整合实验、理论和案例研究结果，以解决影响液化评估的基本问题，以及更广泛的关于细层间土壤中圆锥贯入试验数据的解释和地面变形模型中空间变异性的表示也可能对一般实践产生重大影响的发现。

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.