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

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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.