Investigation of Pore Pressure Migration During Piezocone Tests

压电锥测试过程中孔隙压力迁移的研究

• 批准号: 1927557
• 负责人: Diane Moug
• 金额: $ 8.56万
• 依托单位: Portland State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-09-15 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1927557&HistoricalAwards=false
• 关键词: Investigation; Pore; Pressure; Migration; During

The piezocone dissipation test, where an instrumented cone is advanced through the soil column, is used throughout geotechnical engineering, environmental engineering, and other groundwater-related fields. The test is routinely used to characterize how easily water seeps through soil (i.e. soil permeability) which is necessary for engineering analyses such as predicting rate of soil consolidation settlements or predicting contaminant transport by groundwater seepage. However, methods for interpreting these tests are limited due to several major simplifying assumptions. The test is performed by advancing the cone through the soil column and measuring porewater pressures at the cone shoulder, then pausing penetration and recording how porewater pressures change. Soil deformations around the penetrating cone induce an excess porewater pressure field in saturated soil. Then when penetration is paused, excess porewater pressures are recorded over time as they dissipate to hydrostatic conditions in a dissipation curve. Available methods to interpret soil permeability from dissipation curves assume that: (i) excess porewater pressure migration is horizontal, and (ii) measured porewater pressure decay to hydrostatic conditions is monotonic. However, there is a significant dataset of non-monotonic piezocone dissipation tests, where measured excess porewater pressure initially increases then decreases to hydrostatic conditions, which may be due to vertical excess porewater pressure migration. This project will investigate and characterize the causes of non-monotonic piezocone dissipation tests, which will lead to improved piezocone dissipation interpretation methods and more accurate characterization of soil permeability from the test data. The project also includes demonstrations at K-12 engineering outreach events to increase the engagement of Portland, Oregon grade school students with civil engineering concepts.The objective of this project is to characterize the mechanisms that contribute to non-monotonic piezocone dissipation curves with a numerical piezocone model. This project hypothesizes that vertical and horizontal excess porewater pressure migration contribute to non-monotonic piezocone dissipation curves. It is also hypothesized that those contributions are affected by soil stress history (i.e. over-consolidation ratio), soil properties, hydraulic conductivity anisotropy, and penetration drainage conditions. These hypotheses will be tested with numerical simulations of piezocone dissipation in saturated clay using a direct axisymmetric penetration model and the MIT-S1 constitutive model. The simulations will investigate: (i) the role of soil stress history and soil properties on excess porewater pressure distribution around the penetrating cone and subsequent dissipation curves, (ii) the role of vertical and horizontal porewater pressure migration on dissipation curves, (iii) the impact of hydraulic conductivity anisotropy on vertical and horizontal porewater pressure migration, and (iv) how the above factors are affected by partial drainage conditions during penetration. The results of these analyses will be synthesized to suggest interpretation methods for non-monotonic dissipation tests and to re-interpret existing non-monotonic dissipation tests.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

压电锥耗散测试，其中一个仪器锥通过土柱前进，是用于整个岩土工程，环境工程，和其他地下水相关领域。该测试通常用于表征水渗透土壤的难易程度（即土壤渗透性），这对于工程分析是必要的，例如预测土壤固结沉降率或预测地下水渗透引起的污染物迁移。然而，由于几个主要的简化假设，解释这些测试的方法是有限的。试验是通过推进锥体穿过土柱并测量锥体肩处的孔隙水压力，然后暂停贯入并记录孔隙水压力的变化来进行的。渗透锥周围土体的变形在饱和土体中产生超孔隙水压力场。然后，当渗透暂停时，随着时间的推移记录多余的孔隙水压力，因为它们消散到静水条件的耗散曲线。从耗散曲线解释土壤渗透性的现有方法假设：（i）超孔隙水压力迁移是水平的，和（ii）测得的孔隙水压力衰减到静水条件是单调的。然而，有一个重要的数据集的非单调piezocone耗散测试，测得的超孔隙水压力最初增加，然后减少到静水条件下，这可能是由于垂直超孔隙水压力迁移。本项目将调查和表征非单调压锥耗散测试的原因，这将导致改进的压锥耗散解释方法和更准确的表征土壤渗透性的测试数据。该项目还包括在K-12工程推广活动中的演示，以增加俄勒冈州波特兰小学生对土木工程概念的参与。该项目的目标是用数值压锥模型表征有助于非单调压锥耗散曲线的机制。本计画假设垂直及水平超孔隙水压力迁移对非单调压锥消散曲线有贡献。还假设这些贡献受土壤应力历史（即超固结比）、土壤性质、水力传导系数各向异性和渗透排水条件的影响。这些假设将进行测试，在饱和粘土中使用直接轴对称渗透模型和MIT-S1本构模型的压锥耗散的数值模拟。模拟将调查：（i）土壤应力历史和土壤性质对渗透锥周围的超孔隙水压力分布和随后的消散曲线的作用，（ii）垂直和水平孔隙水压力迁移对消散曲线的作用，（iii）水力传导率各向异性对垂直和水平孔隙水压力迁移的影响，及（iv）上述因素如何受贯入过程中的局部排水条件影响。这些分析的结果将被综合，以建议非单调耗散测试的解释方法，并重新解释现有的非单调耗散tests.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。