Very interesting work from Nick Sitar at UC Berkeley regarding Earthquake Induced Earth Pressure. Sitar states that Mononobe Okabe is reasonable for a 5 foot high wall retaining loose sand, but not applicible to higher walls with well compacted soil. For higher walls with well compacted soil (medium dense sand), his centrifuge testing found that there was very little or no additional increment of earth pressure due to earthquakes. Another recent study found similar results (Nakamura (sp?), 2006).
His prelim. reports can be found on the PEER website below. All of his conclusions are not in this report but will be coming out in the next couple weeks on the PEER website. He hopes to do more studies with cohesive soils and tie-back/reinforced wall.
A summary of the talk I attended is copied below:
Methods for evaluating the seismically induced lateral earth pressures gradually evolved from the
seminal Japanese work performed in the 1920’s. The resulting design procedures suggest large dynamic
loads during strong ground motion. However field evidence from recent major earthquakes fails to show
any significant problems with the performance of retaining structures designed for static earth pressures
only. The results of a series of centrifuge experiments performed by the authors indicate that seismically
induced lateral earth pressures are significantly less than those estimated using the most current design
methods based on the Mononobe-Okabe assumptions. Specifically, the data show that the earth pressure
distribution remains roughly triangular, increasing with depth, and the maximum dynamic moments on
the retaining structure are to a large extent caused by the moment of inertia of the structures themselves.
Therefore, a new approach based on direct consideration of the inertial forces due to the mass of the
structure and a limited contribution by dynamic earth pressures is being proposed.
His prelim. reports can be found on the PEER website below. All of his conclusions are not in this report but will be coming out in the next couple weeks on the PEER website. He hopes to do more studies with cohesive soils and tie-back/reinforced wall.
A summary of the talk I attended is copied below:
Methods for evaluating the seismically induced lateral earth pressures gradually evolved from the
seminal Japanese work performed in the 1920’s. The resulting design procedures suggest large dynamic
loads during strong ground motion. However field evidence from recent major earthquakes fails to show
any significant problems with the performance of retaining structures designed for static earth pressures
only. The results of a series of centrifuge experiments performed by the authors indicate that seismically
induced lateral earth pressures are significantly less than those estimated using the most current design
methods based on the Mononobe-Okabe assumptions. Specifically, the data show that the earth pressure
distribution remains roughly triangular, increasing with depth, and the maximum dynamic moments on
the retaining structure are to a large extent caused by the moment of inertia of the structures themselves.
Therefore, a new approach based on direct consideration of the inertial forces due to the mass of the
structure and a limited contribution by dynamic earth pressures is being proposed.
