Effects of crest improvement on the seismic stability of small earth dams

Abstract

Crest improvement has been conducted to improve the seismic resistance of small earth dams, which are widely distributed in Asian regions with high seismic activity. This method increases the apparent cohesion of the crest. Although circular slip analysis has revealed that the safety factor increases, the effect of partial improvement on the seismic resistance of the entire embankment is yet to be investigated. In this study, we conducted a centrifuge model experiment on a small earth dam embankment that had undergone crest improvement, and we evaluated the effect of crest improvement on the seismic stability of the small earth dam embankment and the issues involved. The results revealed that crest improvement suppressed the settlement of the embankment. At a seismic acceleration of 1.5 m/s², the settlement of the small earth dam embankment with crest improvement was below 0.1 m. Under a seismic acceleration of 4.5 m/s², the settlement was suppressed to 25% of that observed without countermeasures, with the greatest reduction achieved when crest improvement was applied to the upper 30% of the embankment height. Furthermore, amplification of the response acceleration, and increase in the excess pore water pressure ratio were also suppressed with crest improvement. However, in cases where crest improvement was implemented, the application of strong seismic motion led to separation at the boundary between the embankment and the cement-stabilized soil. This separation poses a risk of water leakage and potential erosion along the downstream slope, and its impact is expected to be more pronounced when the section of crest improvement is located below the full water level. Future research should focus on mitigating boundary separation and cracking, enhancing resistance to bending and tensile stresses, and preventing brittle fracture in cement-stabilized soil.