Investigation of Dynamic behaviors of soils of Shashemene Town

Abstract

The nature and distribution of earthquake damage is strongly influenced by the response of soils to cyclic loading. The better understanding of the dynamic properties of some particular natural soil such as the Mexico City clays or the San Francisco Bay mud, together with the actual ground motion measurements during the Michoacan-1985 and the Loma-Prieta earthquakes, have been greatly contribute to show off the importance of local site conditions and dynamic properties of natural soils. Of those dynamic properties, the shear modulus and damping characteristics of cyclically loaded soils are critical to the evaluation of geotechnical engineering problems. Generally, soil is a nonlinear material which causes nonlinear seismic loading responses of grounds especially for earthquake ground motions corresponding to strain level (ɤ≥ 0.01%). The general objective of this research is to investigate the dynamic properties of soils found in Shashemene town. In this thesis, the shear modulus and damping ratio values of soils commonly found in Shashemene were determined using cyclic simple shear testing machine on remolded samples. 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 test results revealed that the shear modulus reduction values are in good agreement with curves of local soils but slightly lower than other established literature value at the highest strain level (ɤ >0.1 %). The damping ratio value of the tests are generally in acceptable range with curves of local soils but slightly lower than the other literature values. This indicates that, the testing conditions appear to have significant effect on the damping ratio values but little effect on the shear modulus reduction values. The cyclic simple shear test machine, currently functional in the laboratory, is capable of reproducing earthquake stress condition accurately. Moreover, the index properties of the soil are determined for characterization of the soil in the town to setup schedules of dynamic property investigations in this research.