Centrifuge experimental study of thaw settlement characteristics of mucky clay after artificial ground freezing

Abstract

Artificial ground freezing (AGF) plays a significant role in the construction of subway tunnel cross passages, underground commercial streets and underground pumping stations, etc. especially under adverse hydro-geological conditions. Associated with the properties of high water content and large void ratio in saturated Shanghai mucky clay, large thaw settlement has arisen after AGF construction. The thawing response is much more complicated compared to freezing and less research work has been documented in the AGF method partly due to the long-period and variability in the redistribution of water released from melting ice crystals and the rewetting of the soil aggregates in clay. This paper presented a series of centrifuge model tests to derive the thawing function development and predict the thaw settlement. The results show that the thawing rate was distinct and larger than the conventional results of small sample tests without stress acting. The thawing front advanced much faster compare to the development in natural frozen soil. An improved gray prediction model emphasizes that a simple analytical result with new thaw front function is much consistent with the experimental and prediction results. All the discussions demonstrate that small scale specimen thaw test at 1g is not capable to directly apply into full scale prediction of the thaw settlement in thick soft saturated clay after artificial ground freezing construction, in which self-weight dominates the process of consolidation. This could motivate, in the near future of computation model development, that the large strain thaw consolidation theory should be applied to prognosticate the long-term settlement of thick soft mucky clay after artificial ground freezing construction.