In the theory of Mononobe and Okabe, the distribution of unit seismic earth pressure is linear and the location of application point of total seismic earth pressure is at H/3 from the base of retaining wall, which is different from test results. Based on the assumption of planar sliding surface in Coulomb's earth pressure theory and the moment equilibrium of sliding soil behind retaining wall, the seismic amplification factor is introduced, the method determining the application point of total seismic earth pressure is presented, the effective formula of unit seismic earth pressure is proposed and the effects of seismic amplification factor on seismic earth pressure and its distribution are analyzed. The results show that the total seismic earth pressure without seismic amplification factor is identical with those from Mononobe theory, which indicates that the latter is a special case of the proposed method; the location of application point of total seismic earth pressure is at 0.40H~0.50H from the base of retaining wall, which is identical with Sherif's experiments and proves that the proposed method is a further supplement of Mononobe's theory; the distribution of unit seismic earth pressure along the wall is non-linear and approaches to a parabola, and the maximum value is not at the base, which shall be paid attention during the stability design of retaining wall.
It has been more than 200 years for the study on retaining wall's earth pressure, but the study on seismic earth pressure started in 1920s. After the big earthquakes in Tokyo and Yokohama of Japan, Mononobe and Okabe firstly proposed an effective method of seismic earth pressure on the basis of Coulomb's theory, which assumed that seismic earth pressure results from the triangular sliding soil behind retaining wall.
Additionally, under the action of earthquake, the entire soil is regarded as a rigid body with same acceleration and the action is applied as an inertial force on the centroid of sliding soil. Then, the total seismic earth pressure is obtained from the limit equilibrium of sliding soil and the distribution of unit earth pressure is triangle along the wall. Therefore, the location of application point of total seismic earth pressure is at H/3 from the base of retaining wall.
However, subsequent theoretical and experimental studies show that the obtained total earth pressure of Mononobe method is close to test results but the location of application point is totally different from the observation. For example, Wood found that it is in the middle of the wall, Seed and Whitman recommended that the static and kinetic part are at H/3 and 0.60H respectively, Prakash suggested that it is at 0.45H for rigid walls and 0.55H for flexible walls, Wang Liqiang proposed that it is at 0.42H~0.46H and Xu Limin proved that it is at 0.40H. Consequently, the location of application point of seismic earth pressure and the distribution of unit seismic earth pressure still need further research.
