ABSTRACT-The most important dynamic soil properties are shear modulus and damping ratio which plays a crucial role in prediction and analysis of soil responses in dynamic loadings. The behavior of soils subjected to dynamic loading is influenced by these soil properties. In this study an attempt was done to determine the shear modulus and damping ratio of Modjo town soils by giving emphasis to Modjo Dry Port. The soil samples were collected from Modjo town at four different locations, namely; Modjo dry port (MD), Teklehaymanot church (TK) and Shashemane road exit (SH) and Near minjar road (NMR).
Investigation of index properties of Modjo soils were done and classified using USCS and AASHTO soil classification system. Based on test results, the soil from MD, TK and SH were highly plastic silt soils and NMR was silty sand. The shear modulus and damping ratio values were determined using cyclic simple shear machine. Strain-controlled cyclic test were conducted at a cyclic loading frequency of 1Hz with a remoulded sample of 70mm diameter and 20mm hight. The tests were conducted as a function of cyclic strain amplitude of 0.01%, 0.1%, 1%, 3%, and 5% under axial stresses of 100kPa, 200kPa and 400kPa. The value of shear modulus was in the range of 0.11MPa to 22.98MPa and damping ratio values range between 0.25% and 25.63%.
This study systematically investigates the effect of cyclic shear strain amplitude, confining stress, number of loading cycles, void ratio and soil plasticity on the shear modulus (G) and damping ratio (D) values. As number of loading cycles and confining pressure increase, the shear modulus increases and damping ratio decreases. Shear modulus decreases and damping ratio increases with increase in cyclic shear strain amplitude. The shear modulus values of Modjo soils were normalized to compare with previously developed values in the literature.
Key words:- Cyclic loading, Shear modulus, Damping ratio, Normalized shear modulus and Cyclic simple shear test.
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