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

本研究项目是路易斯安那州立大学（LSU），一个研究I机构，和巴克内尔大学（BU），一个主要的本科院校（PUI）之间的合作努力。研究的总体目标是评估地下水位波动区域内土壤膨润土防渗墙回填土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。当低于地下水位时，这部分墙必须是可持续的，作为可混溶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福尔斯的下降，可能会出现周期性的湿润和干燥。 然而，有限的现场和实验室研究结果表明，不可逆的增加土壤膨润土回填的水力传导率是可能的，在干燥阶段的循环润湿和干燥。 该项目将通过制作一个模型土壤膨润土回填，其组成和性能代表现场规模。 在受控基质吸力下，对模型回填土样本进行干燥循环。 将根据固结应力、干湿循环次数和干燥阶段施加的吸力对模型回填土的导水率进行评估。 此外，将在三轴环境中测量模型回填土的保水性和体积特性，并将其与基质吸力相关联。 最后，将使用当前应用的非饱和土行为模型对数据进行分析和合成，并酌情对模型进行修订，以解释本研究中开发的数据。 研究结果将为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）该区域内水力传导系数降低的可能性，以及（3）在设计和建造可持续的长期-长期保护人类健康和环境。研究结果将推动最先进的土壤-膨润土防渗墙的设计和施工，用于就地废物遏制，以实现对人类健康和环境的更可持续的长期保护。除了该项目的科学方面，路易斯安那州立大学和BU之间的合作促进了大量的教学，培训和研究生和本科生的学习，从而对该行业产生了长期影响。 在BU的研究本科生的参与提高了这些学生将决定追求高级学位的概率。 该研究还为BU的研究人员提供了与LSU专业同事互动的机会，同时提高了LSU研究人员对BU潜在高质量研究生的接触。 此外，该研究使许多学生在学年期间调查人员预定的实地访问期间了解最新研究。 最后，研究结果将通过口头介绍、经审阅的已发表论文和一个专门提供有关纵向壁垒可持续性的信息的网站向科学界和专业界传播，供从业人员查阅。

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.