An experimental investigation on liquefaction potential and post-liquefaction shear strength of impounded fly ash

Liquefaction resistance and post-liquefaction shear strength of impounded Class F fly ash are investigated using laboratory experiments. The study was aimed to evaluate liquefaction potential of a 45 ha impoundment proposed as a base for a utility monofill. The evaluation included cyclic triaxial tests performed on reconstituted fly ash specimens with various densities at different confining stresses and cyclic stress ratios representative of the impounded material and the seismic environment. The results are presented in the form of design charts. Post-liquefaction strengths were measured by reconsolidating the specimens at the initial effective confining stress and performing consolidated undrained triaxial tests. The measured cyclic strength was compared with the seismically induced stresses in the profile using a one-dimensional wave propagation method. The cyclic loadings imposed on the ash by the design earthquakes were found to be lower than the measured cyclic strength of the material. The post liquefaction shear strengths showed some scatter; however, they were typically higher than the initial shear strengths before exposure of the material to cyclic load.