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Geomechanics and Engineering Volume 27, Number 5, December10 2021 , pages 433-445 DOI: https://doi.org/10.12989/gae.2021.27.5.433 |
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Experimental and numerical investigation of closure time during artificial ground freezing with vertical flow |
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Hyunwoo Jin, Gyu-Hyun Go, Byung Hyun Ryu and Jangguen Lee
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| Abstract | ||
| Artificial ground freezing (AGF) is a commonly used geotechnical support technique that can be applied in any soil type and has low environmental impact. Experimental and numerical investigations have been conducted to optimize AGF for application in diverse scenarios. Precise simulation of groundwater flow is crucial to improving the reliability these investigations' results. Previous experimental research has mostly considered horizontal seepage flow, which does not allow accurate calculation of the groundwater flow velocity due to spatial variation of the piezometric head. This study adopted vertical seepage flow-which can maintain a constant cross-sectional area-to eliminate the limitations of using horizontal seepage flow. The closure time is a measure of the time taken for an impermeable layer to begin to form, this being the time for a frozen soil-ice wall to start forming adjacent to the freeze pipes; this is of great importance to applied AGF. This study reports verification of the reliability of our experimental apparatus and measurement system using only water, because temperature data could be measured while freezing was observed visually. Subsequent experimental AFG tests with saturated sandy soil were also performed. From the experimental results, a method of estimating closure time is proposed using the inflection point in the thermal conductivity difference between pore water and pore ice. It is expected that this estimation method will be highly applicable in the field. A further parametric study assessed factors influencing the closure time using a two-dimensional coupled thermo-hydraulic numerical analysis model that can simulate the AGF of saturated sandy soil considering groundwater flow. It shows that the closure time is affected by factors such as hydraulic gradient, unfrozen permeability, particle thermal conductivity, and freezing temperature. Among these factors, changes in the unfrozen permeability and particle thermal conductivity have less effect on the formation of frozen soil–ice walls when the freezing temperature is sufficiently low. | ||
| Key Words | ||
| artificial ground freezing; closure time; groundwater; model test; parametric study; vertical flow | ||
| Address | ||
| Hyunwoo Jin:Department of Future and Smart Construction Research, KICT, 283, Goyang daero, Ilsanseo gu, Goyang si, Gyeonggi do, Republic of Korea Gyu-Hyun Go:Department of Civil Engineering, Kumoh National Institute of Tech., 61, Daehak-ro, Gumi-si, Gyeongsangbuk-do, Republic of Korea Byung Hyun Ryu:Department of Future and Smart Construction Research, KICT, 283, Goyang daero, Ilsanseo gu, Goyang si, Gyeonggi do, Republic of Korea Jangguen Lee:1Department of Future and Smart Construction Research, KICT, 283, Goyang daero, Ilsanseo gu, Goyang si, Gyeonggi do, Republic of Korea | ||