Investigation of Liquefaction Failure in Earthen Dams during Bhuj Earthquake

A Magnitude (MW) 7.6 earthquake occurred in Bhuj, India on January 26, 2001. A large number of water-retaining earthen dams were affected by the earthquake. This paper examines the nature of distress in seven relatively severely affected dams. The consequences of these problems were not very severe because of the fact that (a) the reservoirs in question were almost empty at the time of the earthquake and (b) the dams performed reasonably in spite of being shaken by free-field horizontal peak ground acceleration (PGA) as high as 0.5g. Some of the distress reportedly was due to the liquefaction of saturated alluvium soil in foundation. Also analyzed herein three relatively large dams, each undergoing free-field ground motion with a PGA of 0.52. One of these dams, Chang Dam, underwent severe slumping, whereas Fatehgadh Dam and Kaswati Dam were affected less severely. The limited amount of subsurface information that is available indicates that the liquefaction within the top 2.0 to 2.5 m depth of foundation soils was relatively widespread underneath Chang Dam. For Fatehgadh Dam and Kaswati Dam, on the other hand, liquefaction occurred within the top 2.0 to 2.5 m depth of foundation soils near the toe, while the same layer underneath the dam crest may have liquefied only to a limited extent. This appears to be the explanation for the basic difference in the observed performance of Chang Dam and those of Fatehgadh Dam and Kaswati Dam. Results of sliding block analysis for these structures were also found to be in general agreement with the observed deformations