Cyclic Soil Tests to Propose Appropriate Seismic Design Methods for Sliding Type and Slump Type Failures of Road Embankments

Abstract eng:
On October 23 in 2004, the Niigataken-chuetsu earthquake, of Magnitude 6.8, occurred in Japan. The maximum surface acceleration recorded at Kawaguchi town was 1722 Gals. Many railways including Shinkansen, roads, houses, pipelines and other structures were severely damaged. Similarly highway embankments were damaged. Especially, the damages in two areas: 1) between Horinouchi and Kawaguchi and 2) near Ojiya IC, were serious. In the first area, the highway road was constructed by cut and fill method on the slope of hill. Sliding of filled embankments occurred at several sites. On the contrary, in the second area, highway embankment was constructed by filling soils on lowland plain. Surface soil of the plane is gravel, sand or clay. The reason why the sliding of the embankment in the first area occurred may be due to inertia force and/or excess pore water pressure. Then the authors conducted many dynamic soil tests to study the detailed mechanism of the failures. Cyclic torsional shear tests were carried out to demonstrate the following items: a) cyclic strength of saturated soil, b) cyclic strength of unsaturated soil, and c) shear modulus of the soil after cyclic loading. Test results showed that cyclic strength and shear modulus of saturated soil was comparatively low. And, under high cyclic shear stress, failure occurred even though the sample was unsaturated. These test results contribute to appropriate seismic design methods of road embankments proposed for sliding type failure and slump type failure.

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