Abstract:In order to evaluate the stability of roadbed in frozen soil area, the dynamic shear modulus and damping ratio of fill along Qinghai—Tibet railway are analyzed by means of laboratory test and theoretical analysis. Firstly, the long-term consolidation undrained cyclic triaxial tests were carried out to analyze the effects of different negative temperature and cyclic stress ratio on dynamic shear modulus and damping ratio of subgrade silty clay and foundation sand. The results show that for subgrade silty clay, the dynamic shear modulus is negatively correlated with temperature, and increases with the increase of cyclic stress ratio, and the damping ratio decreases with the increase of dynamic shear modulus. For foundation sand, the dynamic shear modulus and damping ratio show the same trend under the influence of temperature as that of silty clay, but the value of dynamic shear modulus is about 110 MPa higher than that of damping ratio under the condition of -10 ℃ temperature and cyclic stress ratio of 0.2, which is 1.22 times, and the damping ratio is 0.66 times. It is worth noting that the dynamic shear modulus of sand responds to the peak value when the cyclic stress ratio is about 1, which means that when the dynamic stress amplitude reaches the confining pressure, the dynamic shear modulus tends to decrease while the damping ratio tends to increase with the increase of the cyclic stress ratio. Then, based on the high cycle model proposed by Wichtmann, the prediction model of dynamic shear modulus was established, which can well reflect the response law of dynamic shear modulus with vibration number under the influence of temperature and cyclic stress ratio. The fitting parameter w₀ reflects the law of dynamic shear modulus increasing first and then decreasing with cyclic stress ratio. The fitted mathematical relationship shows that the dynamic response law of soil changes significantly when the number of long-term vibrations is about 13000 or the vibration duration is more than 8 minutes. Finally, based on Hardin-Drnevich hyperbolic model, the experimental results of dynamic shear modulus and damping ratio were fitted, and the functional relationship between dynamic shear modulus and damping ratio was obtained, so as to roughly predict the trend and range of damping ratio with the change of dynamic shear modulus. With the increase of normalized shear modulus, the damping ratio tended to decrease.