A model for evaluating settlement of clay subjected to freeze-thaw under overburden pressure

Abstract

The settlement after freeze-thaw (F-T) is of great concern when artificial ground freezing is applied in soft soils. This paper focuses on the assessment of the post-freeze settlement of saturated clay under overburden pressure. First presented was laboratory data including temperature and deformation of specimens subjected to unidirectional F-T with or without overburden pressure in an open system. It then discusses the variation of the compressibility of specimens in terms of pre-consolidation pressure, compression index, and swell index along the specimen height. It is concluded that the thaw process can be decoupled from the consolidation process for post-freeze settlement evaluation since the time required for the frozen soil to thaw is much shorter than needed to consolidate. Variation of the effective stress and void ratio during thaw and consolidation processes in the frozen region was found to be very different from that in the unfrozen region, which is illustrated by detailed stress paths. A model is proposed for assessing the post-freeze settlement, which consists of the settlement induced by phase and soil structural change due to thaw without overburden pressure and the settlement caused by consolidation under overburden pressure. This model hinges on the residual stress in the frozen region when thawed without overburden pressure. The residual stress back-calculated based on the laboratory experimental settlement results agrees well with previous studies, which serves as an indirect validation of the proposed model. In the end, an example is provided to demonstrate how to apply the proposed model in a subway cross-passage constructed by artificial ground freezing.