Askari - Assoc. Prof., International Institute of Earthquake Engineering and Seismology, IIEES
Farzaneh - Prof. of Civil Eng. Dept., Faculty of Engineering, Tehran University
Moghadam Rad - M.Sc. of Civil Eng., Islamic Azad Univ

Calculation of earth pressure coefficients has been extensively studied by geotechnical engineers. Although a large number of investigations have been performed to estimate the earth pressure for the static case, limited results are available in seismic state. Earthquake has the unfavorable effect of reducing passive lateral earth pressures. Hence, the assessment of seismic lateral earth pressures is of practical significance in design of retaining walls. In this paper, the effect of seismic forces on retaining walls has been studied by the method of characteristics lines. While earlier studies were carried out mainly for sands, in the present study the seismic passive pressure coefficient due to cohesion, Kpc, were obtained in addition to Kp. (due to soil unit weight). In general, passive earth pressure coefficient due to the component of soil unit weight (Kp.) and due to cohesion (Kpc) have been found to decrease and not to be changed with an increase in the magnitude of horizontal earthquake acceleration respectively. The computed passive earth pressure coefficients were found to be the lowest when compared to the previous solutions available in the literature.