Chemical injection is a process that enhances sand strength and its water-sealing capacity, making sandy soil suitable for various applications in construction. However, a unified understanding of how this process results in increased strength remains elusive. Some studies in the past have suggested that chemical injection separates soil particles, which causes volume expansion. This creates pockets of vacuum, resulting in "negative pressure," which pulls soil particles together and strengthens it. Increased tensile strength (which determines the load the soil can endure) is also thought to influence this behavior. Other studies have proposed that shrinkage of hydrogels (water-retaining polymeric structures) leads to soil particle compression and confinement, imparting strength to the soil. However, there is still a lack of clear understanding of the underlying mechanism behind strength development of sandy soils.
Now, a team of scientists from Japan, led by Professor Shinya Inazumi from the Department of Civil Engineering at Shibaura Institute of Technology, has conducted a thorough investigation into the behavior of chemically injected sandy soil. Talking about the motivation behind this study, Prof. Inazumi says, "We were driven by a passion for sustainable development and the desire to contribute to safer and more efficient construction practices, particularly in the context of climate change and increasing urbanization." Additionally, the researchers were also motivated by the goal of advancing geotechnical engineering, with the hope that it can have implications for public safety, by enabling the development of technologies that mitigate the risk of natural disasters. Their work was published in the journal Gels on 27 October, 2023.
In this study, the researchers first chemically injected sand-gel and hydrogel mixtures with an acidic solution, and conducted various tests. This included the consolidation drainage triaxial compression tests which isolate and measure the "cohesive strength" and the "angle of internal friction" in chemically enhanced soils. This testing method was chosen for its ability to provide accurate insights into soil behavior under static conditions, which is crucial for the safety and reliability of construction soil.
Additional techniques for mechanistic and structural analysis included unconfined compression tests, small-angle X-ray scattering, volume shrinkage studies, and theoretical modeling. Notably, this study marks the first instance of independent examination of the effects of dilatancy and hydrogel shrinkage on soil strength development. This distinction holds significance for the field, offering the potential to guide more targeted and efficient soil treatment methods.
The experiments revealed that the enhancement of strength in chemically treated sandy soil can be attributed to increased cohesion and the internal friction angle of the soil particles. Moreover, this improvement exhibits no long-term strength loss, and interestingly, the initial weakness of untreated sandy soil can be traced back to the hydrogel itself.
This understanding of hydrogels at the molecular level holds immense potential in civil engineering and environmental management. For example, this breakthrough can be used in earthquake-prone regions to enhance building safety, impart seismic resilience, and diminish soil liquefaction risks. Furthermore, flood-prone areas also stand to benefit from this new understanding as the water-sealing properties of these treated soils can mitigate floods and safeguard human settlements and agriculture. In the long term, this technology can also protect coastal communities against rising sea levels, storm surges, and saltwater intrusion.
By stabilizing soil and increasing its water retention capacity, the present work yields numerous advantages across various other domains as well. This includes land reclamation, which is crucial for global food security, and pollution mitigation, which is important for curbing leaching into water bodies from landfills. Furthermore, it can also enhance the structural durability of civic infrastructure and ensure mining safety by preventing landslides. As Prof. Inazumi explains, "Our research promises to fill critical knowledge gaps in soil treatment, which can be translated into more efficient and durable construction practices, and ultimately benefit a wide range of industries."
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Reference
Title of original paper: Strength Assessment of Water–Glass Sand Mixtures
Journal: Gels
DOI: https://doi.org/10.3390/gels9110850
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 will receive 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 8,000 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 Inazumi from SIT, Japan
Professor Shinya Inazumi is a faculty member at The College of Engineering, Shibaura Institute of Technology in Tokyo, Japan. He earned his Ph.D. from Kyoto University and has an extensive academic record with over 105 publications and 350 citations. Prof. Inazumi specializes in civil, geotechnical, and environmental engineering and has earned several prestigious awards, including the "ICE Publishing Awards 2020 (Environmental Geotechnics Prize)" from the Institution of Civil Engineers, the "International Research Award" from the International Society for Scientific Network Awards, and the "MEXT Young Scientists' Prize" from the Ministry of Education, Culture, Sports, Science and Technology in 2015.
Funding Information
This research received no external funding.
