Keshavarz, Mohammadreza (2018-11). Model Scale Experiment and Full-Scale Numerical Simulations of Geothermal Piles for Cooling Dominated Climate. Doctoral Dissertation.
Thesis
The objective of this research is to investigate the soil behavior surrounding a typical fullscale pile foundation of a large building under cyclic thermal loading from the application of geothermal foundation technology in a high plastic clay with shrink-swell problems. The current state of knowledge on the application of energy foundations has been challenged by potential users in the U.S.; specifically, in the southern regions with the high demand of cooling loads for their buildings. The key outcome of this study should provide preliminary answers to the uncertainties about the implementation of a full-scale geothermal foundation system. The focus will be on the effect of geothermal foundation on soil behavior including short and long-term foundation movement, distortion, and soil thermal pollution. First, the research background including current published literatures in the form of journal papers, manuals, and government issued guidelines and incentives are presented. Then, the performance of the modified full-scale geothermal pile under the Liberal Arts and Humanities (LAAH) building at the Texas A&M University campus, College Station, Texas, is analyzed. Findings of the LAAH building's system showed the propagation of thermal flux from the energy pile to the surrounding soil mass. The third step discusses the design and execution of a model-scale laboratory test. This test includes running long-term mechanical and cyclic thermal loading on a compacted native clay soil. Extensive long-term creep (i.e. over 24 hrs.), shrink-swell, and heat propagation testing was done. The water content sampling results showed that cyclic thermal loading will not have major effect on the shrink-swell concern within the soil. Creep movement results showed that the "n" value is increased by heating process compared to the mechanical loading only. The cooling cycle poses a lesser threat in changing the "n" value comparing to the heating. The fourth step includes numerical simulation work by using one of the most common numerical simulation software in Geotechnical Engineering, FLAC3D v.6.0. First, the mechanical model calibration for FLAC3D was done by the load tests performed by Briaud (1999). Then, series of sensitivity analysis was performed to design the proper numerical structure script for the more complicated and complex problems. After the sensitivity analysis part, the thermal, fluid, and mechanical modules were calibrated coupled with the data published by Akrouch et al. (2014). Then, the hypothetical study on a typical foundation footprint with various affecting parameters was done. We called this part "design recommendation" study. This aimed to propose some preliminary design guidelines for the engineers who deal with the challenges of designing a thermo-active foundation under a super structure. According to the findings, the thermal pollution of a full-scale geothermal pile system is affected mainly by pile spacing. Pile length found to be the factor with most impact on the productivity level of the system toward meeting the thermal load demand. Additionally, it was found that a gap between the surface of the load bearing soil and structural slab prevents development of large tension loads in the piles. As a test to our findings in the design recommendation part, the LAAH building was used as a case history to demonstrate its performance and pile-foundation behavior for a two-year cyclic operation of full-scale geothermal foundation system. Finally, for the economic analysis work, several operational guidelines were recommended based on the findings in the numerical simulation section and existing literatures.
