Monitoring ground temperature and deformation of the cast-in-place footings in permafrost regions on the Qinghai-Tibet Plateau

The long-term stability of the cast-in-place footings in permafrost regions has received much attention due to its climate sensitivity.The current research lacks long-term data validation,especially in the context of climate change.Based on the 13-year(2011-2023)temperature and deformation monitoring data from the Qinghai-Tibet Power Transmission Line,this study investigates the characteristics of permafrost variation and its impact on the stability of tower footings under the cooling effect from thermosyphons.The results reveal that the thermosyphons effectively reduce the ground temperature around the footings.After the first freeze-thaw cycle,the soil around the tower footings completed refreezing and maintained a frozen state.In the following 13 years,the ground temperature continued to decrease due to the cooling effect of thermosyphons.The duration notably exceeded the previously predicted 5 years.The temperature reduction at the base of the footings cor-responded well with the frost jacking of the tower footings and could be divided into three distinct phases.In phase 1,the ground temperature around the footings rapidly reduced,approaching that of the natural field,while the footings experienced pronounced deformation.In phase 2,the ground temperature decreased at a faster rate,and the deformation rate of the footings slowed down.In phase 3,the frost jacking of the footings gradually retarded with the decrease in base temperature.Additionally,the ground temperature differences of over 1 C were observed among different tower footings,which may lead to the differential deformation among the tower footings.The ground temperature differen-tiation is attributed to the difference in solar radiation intensity,which is shaded by the tower structure from different directions.This study provides theoretical support and empirical accumulation for the construction and maintenance of tower footings in permafrost regions.

实际接地系统的冲击特性试验研究(英文)

In this work,the results of an experimental study of the impulse characteristic of practical ground electrodes consisting of horizontal conductors of various lengths and full-scale tower footings were reported.These electrodes were installed at an outdoor test site having nonuniform soil,with equipment facilities for generating low-and high-magnitude impulse currents.The tests on the horizontal electrode were used to determine the effective length,the voltage and current distribution along the electrode length and the effect of the injection point along the electrode.The tests on the tower footings were used to determine impulse resistance and demonstrate its non-linear variation with current magnitude.Computer simulations of the test electrodes using the electromagnetic field method showed good agreement with the measured result.