Experimental Study On Dynamic Shear Modulus And Damping Ratio Of Seasonal Frozen Soil

With the development of national economy, and launch of strategy “the Silk Road Economic Belt and the 21st-Century Maritime Silk Road”, construction of transportation network and housing in cold region increase progressively. For subgrade vibration analysis and earthquake disaster risk evaluation problems related to seasonal frost appear in the construction process, dynamics performance of frozen soil, which attracts less attention before, is gradually taken seriously. But in fact, restricted by research conditions, the reliability of frozen soil shear modulus and damping ratio, which are often tested by low temperature dynamic tri-axial apparatus in the past, need to be improved.Based on the firs low temperature resonant column apparatus in China, exploring experimental technique of low temperature resonant column test in this dissertation. A series of low temperature resonant column tests for clay, silt and sand specimens are conducted, which contain different negative temperature, moisture content and freezing-thawing cycles. The dynamic shear modulus and damping ratio evolution patterns and rules are summarized. Seismic response in class Ⅰ and Ⅱ ideal conditions, which contain seasonal frost, are preliminarily studied.Experimental technique starts with confining pressure medium. After scheme comparison, choose chloroprene rubber membrane and silicone oil as the confining pressure medium. Combining with the measured results and the predecessors’ achievements, freezing duration is set to 24 hours, and freezing temperature is set according to the soil type. In accordance with the technology of low temperature resonant column test, test results are tiny discrete and with high reliability.Depending on advancing reliable technology of low temperature resonant column test, study on basic model of three typical soils dynamic shear modulus and damping ratio under negative temperature. Also the concept and computation method of temperature correction factor are proposed. Results indicate that, to each type of soil, negative temperature has significant impact on initial shear modulus, shear modulus and damping ratio, while corresponding temperature correction coefficient change according to the combinatorial functions of Boltzmann and exponent. The change flatten out after rapidly change in 0 ℃ to-6 ℃,and the degree of change and parameters fitting the functions are related to soil type.Conduct a series of low temperature resonant column experiments for three typical soils under different moisture content and negative temperature, in order to research the influence, caused by moisture content and negative temperature, to the correction coefficient. Also, the concept of correction coefficient, considered moisture content, and its computing method are provided. Results show that, for some soil type, surface shape of bi-factor(moisture content and negative temperature) correction coefficient is mainly under the control of negative temperature parameter, while little influence is made by moisture content parameter. But for different soil types, surface shapes keep proximity, while their values are unequal.Conduct freezing-thawing cycle experiments for three types of soil specimens under confining pressure. Afterwards their dynamic shear modulus and damping ratio under low temperature are tested, and their correction coefficients are researched. The results indicate that, the changing rules of freezing thawing correction coefficients relate to soil type. And whatever the soil type, freezing thawing cycle weakens dynamic shear modulus and damping ratio of specimens. So it is necessary to take measures to alleviate this negative influence in engineering.Model classⅠ and classⅡ sites, which contain seasonal frozen soil layers. Then conduct computation by equivalent linearization program, which is widely used in China. Results show that, frozen soil layer weakens earthquake motion in most classⅠ and Ⅱ sites, and the thicker of the frozen layer, the more evident vibration-suppressed effectiveness can be observed. However in some class Ⅰ sites cases, when the inputting amplitudes are low, frozen layer aggravates earthquake motion, that is similar with earthquake damage phenomenon in Dedu earthquake swarm.