Liquefaction of Completely Decomposed Granite

Abstract

Completely decomposed granite, which was regarded as a high quality fill material with little risk of liquefaction, was found to liquefy during the Hyogo-ken Nambu earthquake. In this paper, a series of monotonic triaxial compression and extension tests over a wide range of density and confining pressure were conducted to determine the critical state line and study the flow liquefaction behavior. Another series of cyclic triaxial tests were conducted to study both flow liquefaction and cyclic mobility behavior of completely decomposed granite. It is found that saturated decomposed granite behaves like clean sand during undrained shearing. The intrinsic behavior of completely decomposed granite could be described within critical state framework. Flow liquefaction can be triggered by monotonic loading when state parameter is 0.127 or cyclic loading when cyclic stress is 33% higher than steady state strength. Cyclic mobility occurs when cyclic stress is less than both tensile and compressive steady state strength. Liquefaction resistance of completely decomposed granite with 70% initial relative compaction is 0.17 under 100 kPa initial effective stress and 0.14 under 300 kPa initial effective stress. The results will be helpful for liquefaction evaluation and can be applied to remediation of fill slope or reclaimed land.