Thermal characteristics of cast-in-place pile foundations in warm permafrost at Beiluhe on interior Qinghai-Tibet Plateau: Field observations and numerical simulations

Cast-in-place pile foundations are widely employed to support basic infrastructures on the Qinghai-Tibet Plateau (QTP). However, concrete hydration heat substantially affects the thermal stabilization of pile foundations in permafrost regions. In this paper, the thermal characteristics of a cast-in-place pile foundation in a warm (>-1 degrees C) permafrost region on the interior QTP were studied via field observations and numerical simulations. The temperature field observations showed that the peak temperature of the pile foundation occurred two days after the concrete was poured, and that positive temperatures of the pile foundation lasted 21 days. The temperatures at different depths of the pile foundation dropped below 0 degrees C 93 days after the concrete was poured. However, even 224 days after the concrete was poured, the temperatures in the pile foundation were still higher than that of the natural ground. Based on the observational data, three-dimensional numerical models were established to analyze the thermal disturbances and the freezing process. The results showed that the thickness of the thermal disturbance annulus around the pile foundation was 1.6 m, namely, twice the pile diameter. It would take approximately 420 days for the temperatures in the pile foundation to recover to approximately that of the natural ground. When the mean annual ground temperature (MAGT) decreased, the thickness of the thermal disturbance annulus around the pile foundation increased, and the freezeback time of the pile foundation decreased. (C) 2020 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.