LIQUEFACTION AND EMBANKMENT FAILURE CASE-HISTORIES, 1988 ARMENIA EARTHQUAKE

The 1988 M(s) almost-equal-to 6.8 earthquake in Armenia resulted in more than 40,000 human casualties and massive destruction of the northwestern region of Armenia. The effects of local geology and soil conditions upon the earthquake-induced damage were analyzed and reported by the writers in other publications in the ASCE Geotechnical Journal. This paper presents data and analysis of liquefaction and liquefaction-induced embankment failure case histories, the significance of which stems from the fact that the liquefied sands had a high gravel content (up to 50%). There are only a few well-documented field observations of liquefaction of gravels and gravelly sands, and the information presented in this paper augments this limited database. Our analyses lead to the conclusion that loose to medium-dense gravelly soil deposits that are not confined against drainage can withstand large (0. 5 g- 1.0 g) peak ground accelerations without liquefying. However, a mere 30 cm thick impermeable topsoil can impede drainage, thus causing liquefaction of such soils leading to significant deformations and lateral spreading. The residual shear strength of the gravelly soils investigated (with field SPT of almost-equal-to 36 blows/m (12 blows/ft)) was back-estimated to range between 5 to 13 kPa (100-260 psf), values comparable to the residual shear strength of loose clean sands. The observations and conclusions from liquefaction of gravelly soils in Armenia compare well with the well-documented cases from the 1983 Borah Peak, Idaho. earthquake.