Research On Physical And Mechanical Properties Of Permafrost In Mohe Region

This project comes from the 220kV Tahe - Mohe new construction of transmission lines. It is for the China-Russia oil pipeline's running to provide the necessary electrical equipment. For transmission lines, wind load along the wire causes the horizontal bending moment. So, the pile foundation is subjected to uplift. Interface type permafrost provides excellent resistance to uplift but freezing and thawing disease control is the key to carrying capacity. Therefore, the study of the site based on soil bearing capacity of the foundation of the transmission tower is necessary.The main investigation contents: First, 101 soil samples are collected from Tahe - Mohe transmission lines field in permafrost to determine physical and mechanical indicators, including the test of density of the frozen soil, water content, particle analysis, the initial freezing temperature, thermal conductivity, frost-heave coefficient, thawing settlement coefficient and uniaxial compressive strength of 87 soil samples from eight experiments. Experimental results show that theâ‘¡clay breccia (including gravel) layer and theâ‘¡1 silt clay mixed breccia layer of the Tahe - Mohe transmission lines site have the greatest impact on the bearing capacity of the foundation of the transmission towers. This is mainly in the form of representation of that when the density in the soil is the same, the water content of soil layers is much greater, so during the pile-soil interaction section, the layer which belongs to particularly strong frost, strong thaw frozen saturated soil will have a greater frost-heave amount and thermal amount to impact on the bearing capacity of the foundation. Thus, for bearing capacity of the foundations, special consideration should be given to theâ‘¡1 layer of silt clay soil mixed breccia layer with thaw characteristics, causing strong negative friction. Pile tip locatedâ‘¢mixed layer clay breccia layer is more favorable than theâ‘£layer of clay mixed with gravel layer.Secondly, the introduction of the British origin of nuclear magnetic resonance, and the research of matching refrigeration equipment, used to simulate the low temperature; under the ice melting, solid ice, bound water, liquid water can attenuate at different rates and have different relaxation time; determination of unfrozen water content of frozen soil with the NMR. It solves that problem of the difficulty and poor accuracy of the detection of the unfrozen water content; It also obtained unfrozen water content influence law by test analysis of the temperature of the frozen soil.