Experimental Study On Dynamic Elasticity Modulus And Damping Ratio Of Coarse-Grained Soils

ABSTRACT:Coarse-grained soil have some good engineering properties, such as stable structure, high strength, high bearing capacity, small deformation and difficult to liquefy under dynamic loads. They have been applied widely as fillings in geotechnical structures. Study on static characteristics of coarse-grained soil are relatively sufficient compared with their dynamic characteristics under earthquake, traffic load and blasting. Basic data and parameters are very limited in the establishment of constitutive model and dynamic calculation. In order to decrease the deformation and prevent the instability of geotechnical structures using coarse-grained soil as main material, and reveal the dynamic characteristics of coarse-grain soil, it is necessary to carry out experimental investigations and dynamic analysis on coarse-grained soil.The TAJ-2000large-scale dynamic/static triaxial test platform was used to study the dynamic characteristics of typical coarse-grained soil fillings. Their dynamic elastic modulus and damping ratio were studied, and the influencing factors like confining pressure, vibration frequency and vibration cycle were analyzed. Experimental results indicate that, there is an obvious nonlinear relation between dynamic stress and dynamic strain. With the magnification of dynamic strain, dynamic modulus shows obvious strain softening feature, and1/Ed reduces linearly. The constructive relation of coarse-grained soil can be described with the hyperbolic model presented by Hardin, and then relevant parameters were obtained. With the increment of confining pressure, dynamic strain induced by the same dynamic decreases. With the increment of vibration frequency, dynamic strain induced by the same dynamic also decreases, the deformation becomes limited. With the increment of dynamic strain, dynamic modulus reduces nonlinearly while damping ratio increases nonlinearly. When dynamic strain exceeds0.1%, the dynamic modulus stay basically unchanged, and the Ed-εd curves of different confining pressure and vibration frequency are almost the same. Dynamic elastic modulus and damping ratio increase with the enlargement of confining pressure and vibration frequency. Under different dynamic stress level, with the increment of vibration cycle, the dynamic elastic modulus attenuates at different degrees. The smaller the vibration frequency is, the more significant the attenuation is.Based on test results, the maximum dynamic elastic modulus and the largest damping ratio were calculated, and then the influence of confining pressure and vibration frequency was analyzed. An empirical formula of the maximum dynamic elastic modulus with confining pressure and vibration frequency was put forward. Then the empirical attenuation formulas of dynamic elastic modulus and damping ratio with dynamic strain were also presented.The research results can provide basis for the seismic design and dynamic analysis of geotechnical buildings and structures, enrich the study on dynamic parameters of coarse-grained soil, and provide experimental data for theoretical analysis.