Estimation of Active Earth Pressure Acting on a Retaining Wall During an Earthquake by Logarithmic Spiral Method

In 2016 Kumamoto Earthquake, many retaining walls, such as aged masonry retaining walls collapsed. Many of the existing retaining walls still have high potential for collapse during a future earthquake event in Japan, so that they need to be reinforced. It is necessary to know how those collapsed retaining walls perform during the earthquake loading. However, it is difficult to estimate the seismic capacity of existing retaining walls and appropriate reinforcement method has not yet been established. The Ministry of Land, Infrastructure, Transport and Tourism has been studying on establishing methods for reinforcing existing retaining walls and estimating their seismic resiliency. The purpose of this study is to establish a method for estimating the seismic capacity of existing retaining walls. Linear slip is often used in the stability analysis of retaining walls, but it could be less consistent with the actual situation. Logarithmic spiral slip is considered more realistic than linear slip, but the accuracy is not known due to lack of examples of calculations using it. In this manuscript, therefore, the logarithmic spiral method was used to calculate active earth pressures acting on retaining walls and slip lines to check the accuracy. Calculations were performed under different conditions and results are compared to those obtained by other theories, such as Coulomb’s earth pressure theory. The results showed differences in magnitude of active earth pressures and shape of slip lines. From this, it was found that the logarithmic spiral method is as accurate as or more accurate than Coulomb’s theory.