CAREER: Thermo-Active Geotechnical Systems with Reinforced, Unsaturated Soils

这个教师早期职业发展（Career）项目的研究目标是了解在哪些条件下，来自建筑和工业的虚假热量可以用来改善涉及土工合成增强土的土工系统的性能。具体来说，在非饱和条件下，热诱导水流作为保持土填土压实的一种手段正在被研究，在这种情况下，更大的有效应力将导致强度和刚度的增强。一种在岩土系统内施加温度的新方法也正在研究中，该方法在施工过程中安装热交换器管和土工合成增强材料。目前正在使用单元尺度试验来权衡在非饱和条件下保持土壤所获得的好处与温度升高对加筋土的潜在负面影响。这些负面影响包括热体积变化产生的孔隙水压力、屈服面形状的热变化、土水保持曲线的热变化以及土工合成钢筋的蠕变变形。单元尺度试验的观测结果被合成为本构关系，可用于表征非饱和土-土工合成复合材料的热-水-力学行为。此外，在不同边界条件下，离心级热活动岩土系统的流动和变形行为被用于系统级验证这些本构关系。综合教育计划的目标是培养学生研究人员有效地将研究成果传播给具有不同技术专长水平的受众，并提高学生对其教育成功的个人参与。为了达到这些目标，将首先为学生研究人员开发一个交流研讨会，其中包括有效沟通技巧的讲座，使用书面案例陈述的指导演示计划，以及带有电影反馈分析的演示实践。然后，学生研究人员将向来自丹佛东高中的高中新生、CU BOLD中心内的各种学生组织、行业利益相关者和岩土工程公司做报告。教育项目的成功与否将通过比较观众的反馈和学生的书面案例陈述来评估。对温度对非饱和土影响的进一步了解有可能使目前在加筋土系统中无法使用的回填土得以使用，从而节省材料和运输成本。同时，热交换过程可用于提高建筑冷却系统的能源效率，或在不产生水蒸气（干冷却）的情况下消散工业过程中的虚假热量。从这项研究中吸取的经验教训付诸实践，可能会在岩土工程和土工合成工程领域形成一个新的市场部门，从而产生新的经济机会。作为这项工作的一部分，土工合成复合材料的本构模型将为实践者提供基于性能的生命周期成本评估工具，以评估他们在该领域的设计，提高该技术的可持续性和市场化。此外，参加综合沟通培训计划的学生将获得实用的策略，以有效地与具有不同技术专长水平的受众进行沟通，这将帮助他们在这个新的市场领域开始成功的领导者职业生涯。他们的报告将促进研究成果向实践工程师、利益相关者和公众传播。此外，在科罗拉多大学和高中课堂上对不同学生群体的演讲将有助于招募代表性不足的学生进入STEM领域。

The research objective of this Faculty Early Career Development (CAREER) project is to understand the conditions under which spurious heat from buildings and industry can be used to improve the performance of geotechnical systems involving geosynthetic-reinforced soils. Specifically, thermally induced water flow is being investigated as a means of maintaining compacted soil backfills in unsaturated conditions, in which case greater effective stresses will result in enhanced strength and stiffness. A novel approach for imposing temperatures within geotechnical system is also being investigated, in which heat exchanger tubing is installed along with geosynthetic reinforcements during construction. Element-scale tests are being used to weigh the benefits gained by maintaining soils in unsaturated conditions against potentially negative impacts of elevated temperatures on reinforced soils. These negative impacts include pore water pressure generation due to thermal volume change, thermal changes in the yield surface shape, thermal changes in the soil-water retention curve, and creep deformation of geosynthetic reinforcements. The observations from the element-scale tests are being synthesized into constitutive relationships which can be used to characterize the thermo-hydro-mechanical behavior of unsaturated soil-geosynthetic composites. Further, the flow and deformation behavior of centrifuge-scale thermo-active geotechnical systems under different boundary conditions are being used for system-level validation of these constitutive relationships. The goals of an integrated educational program are to train student researchers to effectively disseminate research results to audiences with varying levels of technical expertise, and to improve students' personal engagement in the success of their education. These goals will be reached by first developing a communication workshop for student researchers which incorporates lectures on effective communication skills, guided presentation planning using written case statements, and presentation practice with film feedback analysis. Student researchers will then make presentations to high school freshmen from Denver East High School, diverse student organizations housed within the CU BOLD center, industry stakeholders, and geotechnical engineering firms. The education program's success will be assessed by comparing audience feedback with students' written case statements. The improved understanding of temperature effects on unsaturated soils has potential to enable the use of backfill soils currently unusable in reinforced soil systems, leading to material and transport cost savings. At the same time, the heat exchange process can be used to improve the energy efficiency of building cooling systems, or to dissipate spurious heat from industrial processes without the generation of water vapor (dry cooling). Implementation of the lessons learned from this study into practice may form a new market sector in the fields of geotechnical and geosynthetics engineering, resulting in new economic opportunities. As part of this effort, the constitutive model for soil-geosynthetic composites will provide practitioners with tools for performance-based life-cycle cost assessments of their designs in this area, enhancing the sustainability and marketability of this technology. Further, students participating in the integrated communication training program will gain practical strategies to effectively communicate with audiences with varying levels of technical expertise, which will help them start successful careers as leaders in this new market sector. Their presentations will facilitate dissemination of research results to practicing engineers, stakeholders, and the public. Further, presentations to diverse student groups at CU and high school classes will help recruit underrepresented students into STEM fields.