Collaborative Research: Critical Hydraulic Conditions for Piping in Sandy Soils, Laboratory Measurement and Numerical Simulation

本项目的目的是提供对管道现象的基本了解和管道关键水力条件的实用解决方案，这些条件包括：1)土壤特性(例如，级配、颗粒大小和颗粒形状)、2)流动方向、3)应力条件和4)出口表面条件。在目前的岩土工程实践中，通常没有考虑这些因素，并且假定临界水力坡度只是土壤浮力单位重量的函数。然而，最近的分析、实验室实验和现场观察表明，管道可以在比当前实践预测的值低得多的坡度处启动。因此，目前的做法在某些条件下可能是不保守的。项目目标将通过以下方式实现：1)使用专门为该项目设计的实验室设备，对具有不同土壤性质、流动方向和出口表面条件的土样的临界水力坡度进行实验测量，2)通过将离散单元法和光滑颗粒流体力学方法相结合，开发能够捕捉饱和颗粒土中管道机制的数值模型，以及3)通过提供经验的、基于机理的关系，将实验测试和验证的数值模拟的结果整合到当前的工程实践中，以考虑上述因素对临界水力坡度大小的影响。该项目将通过犹他州立大学和宾夕法尼亚州立大学的合作研究来完成。该项目的结果有可能改变实际中分析渗漏相关侵蚀的方式。新的方法不仅比现有的分析方法更准确，而且由于其基于机理的起源，还将具有应用于大量渗流条件的灵活性。这种改进的分析方法的社会效益不应被低估。美国各地的大坝和堤坝系统正在老化，在许多情况下，需要翻新或维修，以使其达到当前标准或满足不断变化的负荷要求。改进的分析方法预计将极大地提高管道潜力评估的准确性，提高公共安全，并允许更好地利用可用于翻新我国这一关键方面的资金-S基础设施。该项目还将提供大量的教育收益，包括培训硕士和博士生，并为本科生提供研究机会，特别是那些来自犹他州立大学和宾夕法尼亚州立大学传统上代表性不足的群体的学生。

The objective of this project is to provide fundamental understanding of the piping phenomenon and practical solutions to the critical hydraulic conditions for piping that account for: 1) soil properties (e.g., gradation, grain size, and grain shape), 2) direction of flow, 3) stress condition, and 4) exit face conditions. In current geotechnical engineering practice, these factors are generally not considered and the critical hydraulic gradient is assumed to be only a function of the soil buoyant unit weight. However, recent analyses, laboratory experiments, and field observations indicate that piping can be initiated at gradients much lower than the values predicted by the current practice. Therefore, the current practice may be unconservative under certain conditions. The project objectives will be achieved through: 1) experimental measurements of critical hydraulic gradients of soil specimens with varied soil properties, direction of flow, and exit face conditions, using laboratory devices designed specifically for this project, 2) development of a numerical model capable of capturing piping mechanisms in saturated granular soils by coupling the discrete element method and the smoothed particle hydrodynamics method, and 3) integration of the results from experimental testing and validated numerical modeling into current engineering practice by providing an empirical, but mechanism-based, relationship to account for the effects that the factors discussed above have on the magnitude of critical hydraulic gradients. This project will be accomplished through collaborative research between Utah State University and The Pennsylvania State University.Results of this project have the potential to transform the way that seepage-related erosion is analyzed in practice. The new approach will not only be more accurate than existing analysis methods, but will also have the flexibility to be applied to a vast array of seepage conditions due to its mechanism-based origin. The societal benefits of this improved analysis approach should not be underestimated. Dams and levee systems across the U.S. are aging and, in many cases, in need of retrofitting or repair to bring them up to current standards or meet changing load requirements. The improved analysis approach is expected to vastly improve the accuracy of the assessments of piping potential, increasing public safety and allowing for better utilization of funds available to renovate this critical aspect of our nation?s infrastructure. The project will also provide substantial educational benefits, including training M.S. and Ph.D. students and providing research opportunities for undergraduate students, particularly those from traditionally under-represented groups at both Utah State University and The Pennsylvania State University.