Abstract
Artificial freezing methods can help highlight the mechanical properties of marine clay. The construction of cross passages in metro tunnels employs the freezing method. Freeze–thaw circulation, which is part of the process, affects the engineering properties of clay and produces differential settling. This paper describes the percentages of specific diameters of frozen–thawed soil under different freezing temperatures, measured with the help of nuclear magnetic resonance (NMR). In response to the experimental results, a weakening effect of freezing temperature and speed on soft soil is proposed. All sizes of undisturbed soil pores tend to increase under various freezing temperatures. Owing to differences in free water content, the water in medium pores freezes quicker than that in tiny pores. The quicker the freezing, the greater the resulting void ratio. Finally, potential reasons for changes in pore size under different freezing conditions are explained from a microcosmic perspective.
Highlights
Artificial ground freezing (AGF) [1] was employed to stabilize and waterproof passageways constructed under seawater and offshore engineering
Because the freeze–thaw cycle destroys the internal structure of the soil skeleton, weakening its structure and reducing its dynamic characteristics [2], tunnels using AGF settle much more than others do [3]
A limitation of the nuclear magnetic resonance (NMR) test was fixed error; to minimize this, the analysis focused on the change in pore size distribution
Summary
Artificial ground freezing (AGF) [1] was employed to stabilize and waterproof passageways constructed under seawater and offshore engineering. Several models have been proposed with which to predict changes in soil after freezing. Reference [17], for example, gives a soil freezing characteristic curve for unfrozen water, and a method for calculating the unfrozen water content of silty clay is given in [18]. Finding a way of accurately measuring changes of frozen water in soil becomes the most pressing problem. Introduced to civil engineering [21] only recently, it uses an NMR signal to calculate soil water content and pore diameters [22]. A few NMR-based tests of frozen soft soil have been proposed, changes to percentages of specific diameters in frozen–thawed marine soft soil under various freezing temperatures remain unclear. Several important conclusions are drawn to supplement the theoretical basis for uneven settling in freeze–thaw construction
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