Optimizing geothermal foundations in soft clay for urban buildings
Researchers use advanced modeling and simulations for simplified design of geothermal heat-exchanging foundations (energy piles)
Shibaura Institute of Technology
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Researchers develop a simplified model to design efficient energy pile foundations for geothermal temperature regulations in buildings.
view moreCredit: Prof. Shinya Inazumi from Shibaura Institute of Technology, Japan Source Link: https://www.sciencedirect.com/science/article/pii/S2214157X25008317?via%3Dihub
As urbanization increases and climate changes accelerate, there is an urgent need for sustainable and space-efficient solutions for heating and cooling in buildings. One promising solution is to use energy piles—concrete foundation systems that also serve as heat exchangers using geothermal energy. However, in high-density cities like Tokyo, Bangkok, and Manila, where buildings are often constructed on soft clay foundations, engineers face unique challenges in designing these energy piles.
In this context, a research team led by Professor Shinya Inazumi from the College of Engineering, Shibaura Institute of Technology, Japan, has come up with an innovative framework to improve the design and performance of energy piles, especially in soft clay soils. This study was made available online on June 27, 2025, and was published in Volume 73 of the journal Case Studies in Thermal Engineering in September 2025.
Energy piles are concrete foundation elements with embedded U-shaped pipes that circulate heat transfer fluids within them. These heat transfer fluids exchange thermal energy with the surrounding ground. When these elements are connected to ground source heat pumps (GSHPs), they can efficiently heat and cool buildings by using the stable underground temperatures. GSHPs are known to maintain high performance even in fluctuating surface temperatures, unlike conventional air-source heat pumps, which are less efficient in extreme weather—making GSHPs an ideal solution for extreme temperature climates.
While GSHPs increase efficiency, energy pile systems encounter several challenges. In most cities, soft clay soils are used for construction; these soils are characterized by low permeability (resistance to water flow) and low thermal conductivity (difficulty in transferring heat). In such cases, the accumulation of heat over time can lead to a phenomenon called thermal interference that reduces the efficiency of the entire system.
To encounter this, the researchers used a combined computational and experimental approach and developed a three-dimensional heat transfer model. Using finite element models (FEM) via COMSOL Multiphysics, a physics-based simulation software, the researchers modeled heat transfer around energy piles embedded in soft clay. These simulations were then calibrated using real-world data obtained from a test site in Bangkok. The model analyzed several pile groupings ranging from one to nine piles, which operated under various daily time cycles (8 to 24 hours).
“We developed a simplified prediction model to help engineers improve energy pile design without the need for expensive computational resources or specialized expertise,” says Prof. Inazumi.
The results revealed several insights on the performances of the energy piles. Firstly, the grouped configurations exhibited measurable thermal interference, with soil temperatures rising from 2.18% to 15.43% around the closely spaced piles. Estimating this interference at the design stage was considered critical as it can diminish the system’s efficiency.
“To simplify the process, we introduced practical multiplier factors that allow engineers to predict thermal behavior using single-pile simulations,” explains Prof. Inazumi.
The multiplier factors range from 1.6498 to 2.9119 and could be applied to the results obtained from single-pile simulations, allowing engineers to predict the performance of larger pile groups without the need for complex three-dimensional models. This dramatically reduces the need for full-scale FEM runs, offering a quick, accessible method for thermal performance estimation.
The study also noted that reducing operational hours could delay the temperature saturation (when the soil becomes too warm to absorb more heat) by 103 hours. Additionally, reducing the operational hours also decreased the peak soil temperatures by 29% over 5 years. Another critical finding was that the piles at the center get hotter in comparison to those at the edge, suggesting the effect of crowding. These insights suggest that the design of energy pile groups can be optimized by using the provided multipliers and temperature maps. This optimization strategy can help maintain structural integrity and extend the system's lifespan.
The model has significant potential for real-world applications. It is essentially relevant for engineers working in rapidly urbanizing cities built on soft soils, where traditional heating, ventilation, and air conditioning systems are both energy-intensive and climate-vulnerable. By offering easy-to-use simulation shortcuts validated with real-world data, this research lowers the entry barrier for adopting geothermal systems in Southeast Asia and beyond, paving the way for a cleaner, and sustainable future.
“Our study, by demonstrating the viability and affordability of geothermal energy systems for dense urban environments, addresses the challenges in regional development, contributing to the global climate agenda,” concludes Prof. Inazumi.
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Reference
DOI: 10.1016/j.csite.2025.106571
About Shibaura Institute of Technology (SIT), Japan
Shibaura Institute of Technology (SIT) is a private university with campuses in Tokyo and Saitama. Since the establishment of its predecessor, Tokyo Higher School of Industry and Commerce, in 1927, it has maintained “learning through practice” as its philosophy in the education of engineers. SIT was the only private science and engineering university selected for the Top Global University Project sponsored by the Ministry of Education, Culture, Sports, Science and Technology and had received support from the ministry for 10 years starting from the 2014 academic year. Its motto, “Nurturing engineers who learn from society and contribute to society,” reflects its mission of fostering scientists and engineers who can contribute to the sustainable growth of the world by exposing their over 9,500 students to culturally diverse environments, where they learn to cope, collaborate, and relate with fellow students from around the world.
Website: https://www.shibaura-it.ac.jp/en/
About Professor Shinya Inazumi from SIT, Japan
Dr. Shinya Inazumi is a Professor at the College of Engineering, Shibaura Institute of Technology, Japan. He has expertise in civil and environmental engineering, with a strong focus on geotechnical engineering. With over 300 scholarly publications on topics such as particle-method simulations, sustainable geopolymer materials, and AI-driven urban-resilience mapping, he is recognized as a leading geotechnical researcher. He has been honored with multiple awards, including the MEXT Young Scientists’ Prize (2015), ICE Publishing Environmental Geotechnics Prize (2020), ISSN Outstanding Researcher & Golden Research Awards (2020), and a Best Paper Award at the 14th International Conference on Geotechnique, Construction Materials and Environment (2024).
Journal
Case Studies in Thermal Engineering
Method of Research
Computational simulation/modeling
Subject of Research
Not applicable
Article Title
Integrated computational and experimental evaluation of thermal optimization in energy pile groups in soft clay
Article Publication Date
27-Jul-2025
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