Research Upon Dynamic Response And Long-term Settlement Of Soft Clay Foundation Under Multi-frequency Dynamic Loading

Driven by large scale of infrastructure investment,a new round of rail transport facilities construction such as high-speed rails and subways has brought a series of geotechnical engineering problems.The soft clay has properties of high water content,high compressibility and low permeability.Under the long-term complex dynamic loading,soft clay produces great deformations and long-term settlement,which results in a threat to the safe operation of trains especially in the soft-clay coastal areas.It is of great theoretical and practical value to study systematically the dynamic response and long-term settlement of soft clay subjected to cyclic loading.In this work,a series of cyclic triaxial tests are carried out systematically on the soft clay under the effect of single frequencies and variable frequencies.The deformation of the soft clay is analyzed through cumulative axial strain,strain softening and stress-strain relationship.The factors of vibration frequency,vibration times and cyclic stress ratio on the deformation of soft clay are analyzed under the condition of variable frequency through the numerical simulation of ABAQUS.The characteristics of dynamic response and long-term settlement of soft clay are analyzed and the influences of vibration frequency and cyclic stress ratio on the ultimate settlement of soft clay are discussed.The results show that the hysteresis curves have a list to the strain axis obviously.The deformation of soft clay is greater than that under the effect of the single higher frequency and smaller than that under the effect of the single lower frequency.The number of vibration times has an obvious influence on the deformation of soft clay under the effect of variable frequencies.The effect of different ways of variable frequencies on the deformation is small.The deformation of soft clay increases in a ladder type under the effect of intermittent cyclic loading,considering frequency combination.The pore water pressure increment decreases with the increasing of vibration periods.When the number of vibration times is within a certain range,the relation between the long-term settlement and vibration frequency is nearly linear.When the cyclic stress ratio is 0.3,the pore water pressure increases instantaneously at the beginning of cyclic loading,reaches its peak value at the intermittent loading stage and dissipates afterwards.The effect of cyclic stress ratio on the long-term settlement of soft clay is obvious.However,the number of vibration times in a loading period has little impact on that.The long-term settlement of soft clay presents a stable trend.The empirical formula is given,which can reflect the developmental trend and values of the long-term settlement.