Numerical Simulations of the Fourth Avenue Landslide Considering Cyclic Softening

Abstract

Cyclic softening of fine grained soils has led to significant infrastructure damage in previous earthquakes. Despite this, methods to evaluate the potential deformations due to cyclic softening are not as well developed as methods to evaluate potential deformations due to earthquake induced liquefaction. This is especially true for numerical analyses where clayey soils are often modeled using a single undrained strength without considering the potential for strength loss. When strain softening is considered, the solution may become mesh dependent leading to unreliable results. This paper explores the use of two separate constitutive models to model the cyclic softening behavior of a mildly sensitive clay. The first constitutive model studied is a total stress based strain softening model with a softening-scaling based regularized implemented to provide an approximately mesh insensitive solution. The second constitutive model investigated is a critical state compatible effective-stress model which has been modified to model structural degradation of a sensitive soil. The Fourth Avenue landslide, which was initiated by the 1964 Great Alaska Earthquake, is used for this numerical evaluation. Deformation patterns and magnitudes from numerical simulations are compared to site observations. Uncertainty due to the choice of the input ground motion and the material properties are explored along with the effects of changing the density of the mesh. Practical implications of each model are discussed as well as potential limitations.