With the economic development of Western China, engineering construction has just been unfolding in cold regions. But as the global warming and construction disturbance, the mean annual ground temperature is increasing and the permafrost is degenerating. Some engineering diseases such as frost-heave and thaw-settlement become common phenomena. In order to ensure the stability and normal working of structure on frozen ground, some engineering and technical measures must be taken to guarantee the engineering foundation stability. Considering pile foundation has preferable load-carrying properties relative to the other foundation, it is widely used in the cold regions building [Orlando B. Andersland and Branko Landanyi, 1994]. However, due to the ground warming effect caused by atmospheric temperature increase and human disturbance will change the relationship of pile-soil interaction, which will further bring about the pile-soil interface adfreezing force decline, and at last, lead to the pile foundation settlement. In turn, this interfacial shear sinking process exacerbated the interface temperature increasing, which will bring about the pile skin friction distributed unevenly along pile skin, and produce an excessive downdrag to pile. This downdrag force is named negative skin friction produced by subsoil thawing settlement. With regard to negative skin friction in civil engineering, there has progressively gained attentions from the engineering profession after many foundation failures due to excessive downdrag. They suggest that there are six probable, but not limited to, reasons of existence of negative skin friction, namely, self-weight of unconsolidated recent fill, surcharge-induced consolidation settlement, consolidation settlement after dissipation of excess pore pressure induced by pile driving, lowering of groundwater level, collapse settlements due to wetting of unsaturated fill, and crushing of crushable subsoil under sustained loading, causing subsoil settlement [Shi Peidong 2008]. However, the settlement induced by subsoil thawing will not be motioned. But in cold region, the influence of the freeze-thaw transfer has to be considered as it will produce froze-heave or thaw settlement of soil around pile. This will change the way of pile-soil interaction and lead the structure damage. This paper investigate the influence of frozen soil temperature, pile section shape, load on soil layer, and cryostructure on pile skin friction by a series of model experiments. Meanwhile, by making use of the indoor model test (Fig. 1), this paper has also discussed that, the relationship between pile skin resistance and soil temperature, the relationship between pile axial stress and soil temperature, and the relationship between pile skin resistance and pile-soil relative displacement during the thawing process of frozen soil. At last, contrasted theoretical pile axial stress with pile axial stress measured by experiment in the pile, it is found that, the theoretical pile axial stress basically agreed with the measured pile axial stress. The following main conclusions have been obtained according to research.
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