Experimental Study on Frost Heave, Thaw Settlement and Thermal Properties of Foundation Soils along China-Russia Crude Oil Pipeline

The China-Russia crude oil pipeline is one of the strategic energy channels of China. The pipeline passes through the permafrost region of the Da Hinggan Mountains, where the engineering geological conditions are very complex, especially near the Yilehuli Mountains, and frost heave and thaw settlement seriously affect the normal operation of the pipeline. Experiments were therefore conducted on soils in this area to study their properties of frost heave, thaw settlement and thermal conductivity, and the test data were subjected to the regression analysis and influencing factors analysis. Results show that when the plasticity of fine-grained soils is less than 10, the frost heave ratio of soils does not necessarily increase with an increase in the initial water content. Thus, gravel and breakstone should be used as cushion and filling materials, and waterproof and drainage measures should be taken. Meanwhile, the coefficient of thaw settlement increases with water content and decreases with dry density. The silt is very sensitive to the thawing action, hence not suitable for pipe foundation, and fine gravel is the best frozen soil foundation. Besides, the thermal conductivity increases with the increase of total water content and dry density. The thermal conductivity of coarse-grained soil is higher than that of fine-grained soil, and the thermal conductivity of frozen soil is higher than that of thawed soil. However, when the water content is less than 10%, the thermal conductivity of the thawed soil is higher than that of the frozen soil. In addition, the results of thermal conductivity obtained by different test methods are significantly different. Generally, the thermal conductivity of disturbed coarse-grained soil sample should be measured by heat flow meter method, that of disturbed fine-grained soil sample should be measured by hot wire method, and that of undisturbed sample should be measured by comparison method.