Abstract
The purpose of this investigation is to determine quantitatively shear modulus G and damping ratio D which are needed for the dynamic response analysis of soil structures with a slope. A series of dynamic triaxial tests were conducted using actual earth fill dam materials: the first material is the random zone material, which is mainly located in the upper and lower slopes of the dam subjected to initial shear stress; and the other material is the core zone material, which is located the central part subjected to isotropic stress. Thus, in these tests, initial shear stress was applied to the random specimens prior to the dynamic stress application.
First, the following previous experimental results were confirmed from these test results of the random specimens subjected to initial shear stress, of which intensities were determined by static mobilized stress ratio MSR (MSR= 0.0, 0.1, 0.3 and 0.5):(1) The major effect of initial shear stress on the dynamic behavior of soils is the significant increase of plastic axial strain ;(2) Initial shear stress has a considerable influence on D but little on G.
Then, we obtained the following, conclusions as the result of considering the quantitative determination of G and D: Both shear modulus G and damping ratio D of the random material subjected to initial shear stress and the core material subjected to isotropic static stress could be determined by the following equations, which have been obtained by an investigation previously carried out by the authors.
For shear modulus
G, G/G0= [G/G0] p'=1·(p') m (γa)
For damping ratio D,
D= (a+b·G/G0)
In this investigation, quantitative functionG0, [G/G0] p'=1-γarelation m' (γa)-γarelation (for shear modulus G), parameter ‘a’ which decreases with the number of N cycles and parameter ‘b’ which is constant for the same material (for damping ratio D) are given.
