Model Scale Experiment and Full-Scale Numerical Simulations of Geothermal Piles for Cooling Dominated Climate
Abstract
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.
Citation
Keshavarz, Mohammadreza (2018). Model Scale Experiment and Full-Scale Numerical Simulations of Geothermal Piles for Cooling Dominated Climate. Doctoral dissertation, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /174529.