The Study Of Dynamic Properties Of Soils In Bishoftu Area

Abstract

The responses of soils to earth quake is influenced by the dynamic properties of soils namely: shear modulus and damping ratio, site response of soil deposits under cyclic loading and soil-structure interaction.In this study,an attempt has been made to determine the shear modulus and damping ratio of Bishoftu town soils.The soil samples were collected from Bishoftu town at four different locations, namely; Adis Safar (Keble 01), Around TVET (Keble 02), Babugaya (Keble 09) and Babugaya (Keble 15). The grain size analysis test result showed dominant proportion of soil particle in the research area is low to high plasticity silt soil. The tests were conducted as a function of cyclic strain amplitude of 0.01 %, 0.1 %, 1 %, 2.5 %, and 5 % under the axial pressures of 100kPa, 200kPa, 300kPa and 400kPa. The value of shear modules was in the range of 0.51 to 16.78MPa and damping ratio values range between 6.05 to 29.35 %. The influences of some important factors on dynamic soil properties were also discussed. 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 values of maximum shear modulus, Gmax, ranges from 13.47 to 47.21 MPa, normalized shear modulus, G⁄Gmax, ranges from 0.04 to 0.48 and the specimen having high void ratio have lower maximum shear modulus ,Gmax, and the void ratio has no significance influenced on damping ratio at any strain amplitude levels. The normalized shear modulus and damping ratio values of the investigated soils found to be similar with those previously developed in the literature. [3], [5], [30] & [31].