Study On Dynamic Characteristics Of Saturated Silty Clay In Zhengdong New Area Under Cyclic Traffic Load

With the continuous development of economic construction in our country,more and more transportation facilities have been put into use.While these transportation facilities provide convenience,more and more engineering problems have gradually emerged,such as ground settlement and road cracking caused by long-term foundation instability.Aiming at the cyclic traffic load,this paper takes the subway planned in Zhengdong New District as the research background,and the original saturated silty clay as the research object.Laboratory soil tests and dynamic triaxial tests were carried out on the undisturbed silty clay to study the dynamic characteristics of saturated silty clay under different frequencies,confining pressures and dynamic stresses.Through a series of laboratory soil tests,including water content test,density test,specific gravity test,particle analysis test,boundary water content test,direct shear test and compression test,the basic physical properties of the undisturbed saturated silty clay were determined.The selection of test parameters provided a basis for dynamic triaxial tests.By designing a dynamic triaxial test program suitable for the area,processing the result data of the single-stage loading test,the development laws of dynamic pore pressure,dynamic deformation and dynamic strength under different frequency,dynamic stress and confining pressure conditions are studied.The development of dynamic pore pressure and dynamic deformation have experienced three stages of acceleration,deceleration and constant velocity.Dynamic deformation has three development modes:destructive,critical and stable.The dynamic strength gradually decreases with the increase of vibration frequency,and gradually increases with the increase of confining pressure.By processing the result data of the multi-stage loading test,drawing the hysteresis loop and the dynamic backbone curve,the relationship between the dynamic modulus,damping ratio,etc.of the important parameters in the dynamic stress-strain relationship and the consolidation confining pressure is analyzed,and the maximum dynamic elastic modulus is calculated.The value of the maximum dynamic shear modulus,the fitting formula of E_d-e_d under different confining pressures is obtained.Both the dynamic elastic modulus and the dynamic shear modulus gradually decrease with the increase of strain,and the decrease rate undergoes a change from large to small.As the confining pressure increases,the dynamic elastic modulus and dynamic shear modulus both increase.According to Hardin’s empirical formula,the fitting formula of the relationship of G_d/G_dmax-γ_d andλ-γ_d under different confining pressures is obtained.The hyperbolic curves of G_d G_dmax-γ_d and λ-γ_d are drawn and compared with the standard value.The result is consistent with the rule of the standard value.However,the values of G_d/G_dmaxunder different confining pressure in this area are all smaller than the normative values,which shows that the calculated dynamic response value is too large,and the result is biased towards safety.The damping ratios are all larger than the normative values,which shows that the calculated dynamic response value is too small and the result is not safe.Therefore,considering G_d/G_dmax and the damping ratio,the calculation result is not much different from the recommended value of the specification.