Cooling principle is adopted in roadbed constructions in permafrost regions on the Qinghai-Tibet Plateau for protecting the underlying permafrost. One way is to use duct-ventilated emban kment. Based on ground temperature data collected along experimental emban kments in Beiluhe section of the Qinghai-Tibet Railway, engineering effects of duct-ventilation for protection of the permafrost beneath the emban kment were studied. Analyses of ground temperature changes and heat inlux indicate that ventilation ducts effectively cool the soils surrounding the ducts in the emban kment and that yearly heat collection of the ambient soils appears as heat release. Permafrost behaviour beneath conventional emban kment and test emban kments with ducts installed at a high and low positions were studied to determine temperature-changing tendency during three years. Where the permafrost under the conventional emban kment and the duct high-positioned emban kment decreasingly absorbs heat during the period. The ground temperature of the permafrost under the conventional emban kment rises and that under the high-positioned emban kment decreases slightly. The temperature of the permafrost under the duct low-positioned emban kment decreased remarkable due to release of heat. These findings demonstrate that ventilated emban kments with low-positioned ducts produce beneficial temperature-controlling effects that actively cool the roadbed soils and keep the roadbed thermally stable. Accordingly, they were strongly recommended for use in the construction of emban kments in the permafrost regions on the plateau.
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