عنوان مقاله [English]
Shear modulus and damping ratio are two most important dynamic parameters for seismic design of structures. Several attempts have been made to determine and study these two dynamic parameters using field and laboratory experiments. Sample disturbance is one of the reasons for the discrepancy between laboratory and in situ dynamic parameters test results. Inattention to the effects of reconstituting on the dynamic parameters of soil, under dynamic laboratory tests and analysis may cause serious damage. Hence, it is necessary to recognize the dynamic behavior of materials by conducting dynamic tests on cored materials and comparing the results with those of reconstituted specimen.
In this research, the dynamic behavior of soil in small strains has been studied by performing a resonant column test on cored and reconstituted samples. The core sample which has been used in this study is clayey sand with high plasticity and the reconstitution of samples was carried out using wet tamping method. Then, core sample at dry condition and reconstituted samples at dry and moist conditions were subjected to resonant column test according to the standard under isotropic and anisotropic consolidated stresses of , , and KPa. The effect of consolidation stress, reconstitution, moisture and anisotropic consolidated stress condition was studied by using the shear modulus and damping ratio versus shear strain diagrams. Furthermore damping ratio of the samples was determined by both free vibration decay and half power bandwidth method and the effect of calculation method was studied as well. The results of the study indicate that, by increasing the consolidation stress, the shear modulus and damping ratio increase and decrease, respectively. Also, reconstituting reduces the shear modulus, but the variation of damping ratio versus shear strain for cored and reconstituted samples is negligible. Comparison of diagrams from dry and moist reconstituted samples, showed that moisture can significantly reduce the shear modulus but did not affect the damping ratio. Anisotropic condition may also cause increase in shear modulus. The damping ratio calculated from the half power bandwidth method is more than the damping ratio obtained from free vibration decay in all samples.