Influence of In-situ Cryogenic Freezing on Thermal and Mechanical Characteristics of Korean Marine Clay
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pISSN 1226-7988, eISSN 1976-3808 www.springer.com/12205
DOI 10.1007/s12205-020-0457-8
Tunnel Engineering
Influence of In-situ Cryogenic Freezing on Thermal and Mechanical Characteristics of Korean Marine Clay Hyun-Jun Choi
a
, Dongseop Lee
b
, Jongmuk Won
c
, Hyobum Lee
d
, and Hangseok Choi
e
a
Member, Research Institute, Dongmyeong Engineering Consultants & Architecture, Seoul 02589, Korea Steel Structure Research Group, POSCO, Incheon 21985, Korea c Member, Dept. of Civil and Environmental Engineering, University of Ulsan, Ulsan 44610, Korea d School of Civil, Environmental & Architectural Engineering, Korea University, Seoul 02841, Korea e Member, School of Civil, Environmental & Architectural Engineering, Korea University, Seoul 02841, Korea b
ARTICLE HISTORY
ABSTRACT
Received 12 March 2020 Revised 17 May 2020 Accepted 29 June 2020 Published Online 10 September 2020
The artificial ground freezing (AGF) method has been used in many geotechnical engineering applications such as temporary excavation support, underpinning and groundwater cutoff. The AGF method utilizes a refrigerant such as liquid nitrogen or brine, circulating through embedded freezing pipes in order to freeze the ground. In this paper, two in-situ cryogenic freezing experiments (i.e., single freezing-pipe test and frozen-wall formation test) were performed using liquid nitrogen to simulate the AGF in a Korean marine clay deposit, in which the freezing rate was evaluated. The thermal conductivity of frozen and unfrozen marine clay was evaluated by performing typical laboratory experiments. In addition, the strength and stiffness of frozen-thawed deposits were comparatively measured by sounding tests (i.e., piezocone penetration test and lateral loading test). The freezing rate of the frozen-wall formation test in the Korean marine clay deposit was approximately twice as high as that of the single freezing pipe test. Compared to the original marine clay deposit, the frozen-thawed marine clay showed a significant reduction in strength and stiffness.
KEYWORDS Marine clay Artificial ground freezing method Liquid nitrogen Cryogenic freezing Freezing rate
1. Introduction The artificial ground freezing (AGF) method conducts the freezing process by employing a refrigerant circulating through a set of embedded freezing pipes to form frozen walls that can be utilized as excavation supports and cutoff walls. Freezing using the AGF method is a reversible process with no environmental impact to improve the hydro-mechanical properties (strength, stiffness and permeability) of the ground and to provide a closed arch of the frozen wall around an excavated zone. In other words, the freezing process fuses soil particles together, significantly increasing soil strength, and making it impervious (Pimentel et al., 2012). The AGF method has been adopted in many geotechnical engineering applications such as temporary excavation support, underpinning and groundwater cutoff (Manassero et al., 2008; Crippa and Manassero, 2012; Pimentel et al., 2012; Ru
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