Simulation Analysis of the Refreezing Characteristics of Cast-in-Place Piles in Permafrost Regions on the Qinghai-Tibet Plateau

The stability of piles used for the Qinghai-Tibet Power Transmission Line (QTPTL) is important for the operation of the line because this type of foundation is generally used in areas with unfavorable geological conditions. Intensive heat influence of casting temperatures and hydration heat means that the refreezing of cast-in-place piles obviously affects the schedule and cost of the project. The refreezing process was simulated on a cast-in-place pile based at tower 1443 of QTPTL in the warm and ice-rich Touerjiu region, Qinghai-Tibet Plateau. The results show that the thermal energy, originating from the casting temperature and hydration heat of cement, dissipates mainly through lateral heat flux, resulting in the warming and thawing of surrounding soil. The stability of the pile will dramatically decrease during the process. It was also found that the dissipation of the thermal energy is affected by the heat conductivity and water/ice content of the surrounding soil. The refreezing process of a 1-m-diameter pile in Touerjiu region continues for about 67 days. The maximum thermal influence range is about 9.8 m for a single pile, and group pile effects exist for towers of QTPTL in Touerjiu region. The duration of the thermal impact of casting temperature and hydration heat of a single pile is about 630 days.