Artificial ground freezing of fully saturated mucky clay: Thawing problem by centrifuge modeling

Abstract

In the construction of cross passages in subway tunnels in soft soils having high water content and large void ratio, Artificial Ground Freezing (AGF) has been preferred due to its unique advantages as both a structural support and a water barrier. Compared to the freeze process, the thaw response is much more complicated and less research work has been documented, particularly in applicably predicting long-term settlement. It is mainly because of the variability in the redistribution of water released from melting ice crystals and the re-consolidation or over-consolidation circumstances during freeze. This paper is based on centrifuge modeling experiments to investigate the thaw settlement of the saturated mucky clay surrounding the subway tunnel. The experimental results demonstrated the significance of replicating the prototype self-weight stress condition in a model to evaluate the thaw settlement of Shanghai mucky clay after artificial ground freezing. The water content profiles of model soils presents that there was still serious water content re-distribution even after freeze–thaw. It indicates the potential reason of differential settlement along subway tunnel around AFG construction site. Great increase in permeability of mucky clay also makes clear sense for additional large thaw settlement after artificial ground freezing. More importantly, field self-weight stress condition extended the influence area of moisture migration and aggravated the pore size to be concentrated in coarser field. All the discussion revealed that the advantages of centrifugal modeling in thaw problem by providing field self-weight. Additionally in the further computation model development, large strain thaw consolidation theory should be applied to prognosticate the long-term settlement of thick soft mucky clay after artificial ground freezing construction. Finally the scaling laws generally used in thaw processes were also checked in this paper in consideration of lacking references on thaw problem in centrifuge models.