Stability Analysis of Seismically Damaged Embankments

This paper describes a pseudo-static stability analysis of seismically damaged embankments during the 1983 Nihonkai-chubu earthquake (Japan). It places a great emphasis on the discussion of a dynamic shear strength of soils to be used in a seismic stability analysis of embankments. Several existing concepts of a dynamic strength are reviewed, which vary from each other with respect to loading patterns, drainage conditions and strength criteria in soil element tests. The main part of this paper is to apply some of the dynamic soil strengths discussed above to seismic stability analyses of three embankment sections, laid on loose sandy deposits which were damaged by the 1983 Nihonkai-chubu earthquake in Japan, and to evaluate the applicability of those strengths. Dynamic response analyses and pseudo-static stability analyses were performed on the basis of field and laboratory soil test data, such as SPT, shear wave logging, CPT, VCPT (vibratory cone penetration test) and cyclic triaxial compression test. The safety factors obtained from the analyses were compared with the settlements of respective embankment sections which would have possibly occurred during the earthquake. It was concluded that the dynamic shear strength, which is defined as a sum of static and dynamic shear stresses that can produce a certain value of cumulative shear strain in a certain number of stress cycles, is the most reasonable of them