Shear Modulus and Damping Ratio Values of Soils Commonly Found in Hawassa
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Date
2012-06
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Addis Ababa University
Abstract
The nature and distribution of earthquake damage is strongly influenced by the response of soils
to cyclic loading. Design of geotechnical engineering problems that involve dynamic loading of
soils and soil-structure interaction systems requires the determination of dynamic soil properties.
The response of soil to cyclic loading is determined mainly by the shear modulus and damping
characteristics of the soil. In Ethiopia, areas close to the Ethiopian rift valley are prone to
damaging earthquakes. However, little experimental work has so far been done in assessing the
dynamic properties of soils and only two researchers have attempted to experimentally measure
dynamic properties of red clay soils found in Addis Ababa.
In this thesis, the shear modulus and damping ratio values of soils commonly found in Hawassa
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 100 kPa, 250 kPa and 400 kPa. The test results revealed that the shear
modulus reduction values are in good agreement with well established literature values except at
the lowest strain level (0.01 %). The damping ratio values of the tests are generally lower than
the literature values except at the lowest strain level (0.01 %). 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. Using the test results, the computed maximum shear modulus,
Gmax, values for the soils considered in this work are within the range of 31,734 kPa to 98,084
kPa, which is acceptable for this soil type based on the literature.
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Keywords
soils, Damping ratio, Shear