This paper presents the results of an in situ lateral load test on a caisson-type foundation of the old Niu-Dou Bridge in Ilan County, Taiwan. The caisson was 12 m long and had circular cross-sections whose diameters were 5 m in the upper portion and 4 m in the lower portion. The test site was located on soil with a high gravel content. A site investigation, including laboratory and field tests, was carried out. A six-component Winkler-beam model was applied to simulate the caisson response in the lateral load test. To determine the nonlinear properties of the Winkler springs, a method based on large-scale geotechnical field testing was proposed. With this method, the soil springs could be properly set and the Winkler-beam model could reasonably capture the lateral behavior of the caisson foundation.

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Shaking-table tests on plane-strain geosynthetic-reinforced model slopes using stepwise intensified sinusoidal pulse loads with specific frequencies were conducted to investigate the influence of peak ground accelerations, wave frequencies and plastic slope displacements on the horizontal acceleration response of the slope. A comparative study on the crest response behavior suggested that the tests using pulse loads give useful insights into the dynamic behavior of soil structures subjected to earthquake loads. Test results indicate that both the horizontal acceleration response at the crest and the lateral slope displacement are influenced by the horizontal peak ground acceleration, the wave frequency, and the cumulative permanent displacement of the slope. Amplification factors at the crest of the slope are functions of input wave frequencies; they decrease exponentially with increasing input horizontal peak ground acceleration. Transitions from an amplification state to a de-amplification state at the slope crest occur at certain levels of input ground accelerations, which are associated with the development of major slip planes in the slope mass (or with noticeable slope displacement). It was found that a ratio between the plastic slope displacement and the total slope height (Dmax/Ht) of the order of 0.42–5.9 × 10−2 is relevant to this amplification–deamplification transition. A practical implication of these observations is that the resonance acceleration of the slope is a major factor that needs to be considered in seismic stability analyses of reinforced slopes with a small plastic slope displacement of Dmax/Ht ≈ 2.5 × 10−3; it does not need to be considered in the seismic stability evaluation for reinforced slopes with plastic slope displacements of Dmax/Ht = 5.0–5.9 × 10−2.

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