Collaborative Research: Hydraulic Sustainability of Soil-Bentonite Cutoff Walls Subjected to Cyclic Wetting and Drying

这个研究项目是路易斯安那州立大学（LSU）和巴克内尔大学（BU）之间的合作努力，前者是一个研究机构，后者是一个主要的本科机构。本研究的总体目标是评估地下水位波动区域内土-膨润土防渗墙回填体水力性能退化的可能性。在大多数防渗墙应用中，防渗墙的某些部分位于地下水位波动区。这部分墙，当低于地下水位时，必须作为一个可混合的地下水污染物运输的屏障，尽管随着该区域地下水位的上升和下降，可能会发生循环润湿和干燥。然而，有限的现场和实验室研究结果表明，在循环润湿和干燥的干燥阶段，土-膨润土的水力导电性可能会不可逆地增加。该项目将通过制作一个模型土-膨润土回填体来完成，该模型土的成分和性质与现场展示的模型土和膨润土回填体具有代表性。模型充填体的试样将在受控的基质吸力下进行干燥循环。模型充填体的水力导电性将作为固结应力、干湿循环次数和干燥阶段施加的吸力的函数进行评估。此外，还将在三轴环境下测量模型充填体的保湿性和体积特性，并与基质吸力进行关联。最后，数据将使用目前应用的非饱和土壤行为模型进行分析和综合，并酌情修改模型以解释本研究中开发的数据。研究结果将对以下问题提供新的认识：(1)地下水位波动区土壤-膨润土防渗墙的行为；(2)该区域内水力传导率退化的可能性；(3)在设计和建造土壤-膨润土防渗墙时，需要将循环润湿和干燥行为作为一个因素，以可持续地长期保护人类健康和环境。这项研究的结果将在设计和建造用于就地遏制废物的土-膨润土防渗墙方面推进最先进的技术，以实现对人类健康和环境的更可持续的长期保护。除了项目的科学方面，路易斯安那州立大学和波士顿大学之间的合作促进了研究生和本科生的大量教学，培训和学习，从而对该专业产生长期影响。在波士顿大学，本科生参与研究提高了这些学生决定攻读更高学位的可能性。这项研究还为波士顿大学的研究人员提供了与路易斯安那州立大学的专业同事互动的机会，同时增加了路易斯安那州立大学的研究人员与波士顿州立大学潜在高质量研究生的接触。此外，在研究人员在学年期间安排的现场访问期间，该研究使许多学生接触到最新的研究。最后，研究结果将通过口头报告、经审阅的已发表论文和一个专门提供垂直屏障可持续性信息的网站向科学界和专业人士传播，该网站可供专业人士使用。

This research project is a collaborative effort between Louisiana State University (LSU), a Research I institution, and Bucknell University (BU), a predominantly undergraduate institution (PUI). The overall goal of the research is to evaluate the potential for degradation in hydraulic performance of soil-bentonite cutoff wall backfill within the zone of a fluctuating groundwater table. In most cutoff wall applications, some portion of the cutoff wall is in the zone of a fluctuating water table. This portion of the wall, when below the water table, must be sustainable as a barrier to transport of miscible groundwater pollutants despite the cyclic wetting and drying that may occur as the groundwater table rises and falls in this zone. However, limited results from field and laboratory studies suggest that an irreversible increase in the hydraulic conductivity of soil-bentonite backfill is possible during the drying phase of cyclic wetting and drying. This project will be accomplished by fabricating a model soil-bentonite backfill with composition and properties representative of those exhibited at field scale. Specimens of the model backfill will be subjected to drying cycles under controlled matric suction. Hydraulic conductivity of the model backfill will be evaluated as a function of consolidation stress, the number of wet-dry cycles, and the suction applied during the drying phase. In addition, moisture retention and volumetric behavior of the model backfill will be measured in a triaxial environment and correlated with matric suction. Finally, the data will be analyzed and synthesized using currently applied models of unsaturated soil behavior and, as appropriate, models revised to account for the data developed in this study. The results of the research will provide a new understanding of (1) the behavior of soil-bentonite cutoff walls in the zone of a fluctuating water table, (2) the potential for degradation in hydraulic conductivity within this zone, and (3) the need to consider cyclic wetting and drying behavior as a factor when designing and constructing soil-bentonite cutoff walls for sustainable long-term protection of human health and the environment. The results of the research will advance the state-of-the-art with respect to the design and construction of soil-bentonite cutoff walls for in situ waste containment to achieve more sustainable long-term protection of human health and the environment . In addition to the scientific aspects of the project, the collaboration between LSU and BU promotes substantial teaching, training, and learning of both graduate and undergraduate students resulting in long-term impacts on the profession. The involvement of undergraduate students in the research at BU enhances the probability that these students will decide to pursue advanced degrees. The research also provides opportunities for the investigators at BU to interact with professional colleagues at LSU, while enhancing the exposure of the investigator at LSU to a pool of potentially high quality graduate students at BU. Moreover, the research exposes numerous students to the latest research during the scheduled site visits by the investigators during the academic year. Finally, the results of the research will be disseminated to the scientific and professional communities through oral presentations, refereed published papers, and a web site devoted to providing information on sustainability of vertical barriers that is accessible by the practicing profession.