Numerical Modeling of Discrete Spatial Heterogeneity in Seismic Risk Analysis: Application To Treatment of Liquefied Soil Foundations

Abstract eng:
A binary mixture model is proposed to study the effects on liquefaction-induced settlement after soil improvement based on the consideration of the added spatial variability between the natural and the treated soil. A 2D finite element model of a structure founded on a shallow foundation was coupled with a binary random field. Nonlinear soil behavior is used for both materials and the model is tested for different mesh size and input motions. Historical evidence as well as physical and numerical modeling indicates that improved sites present less liquefaction and ground deformation. In most cases this improvement is modeled as homogeneous however, in-situ measurements evidence the high level of heterogeneity in the deposit. Inherent spatial variability in the soil and the application -transportation, mixing, permeation - of some soil improvement techniques such as biogrouting and Bentonite permeations will necessary introduce heterogeneity in the soil deposit shown as clusters of the treated material in the natural soil. Hence improvement zones are regarded as a two-phase mixture that will present a nonlinear relation due to the level of complexity of seismic liquefaction and the consequent settlement in a structure. This relation was shown to be in general independent to the sensibility with respect to the spatial discretization of the finite element model and the binary random field. However, it is greatly affected by the mechanical behavior of the soils used and the input motion. The effect on the latter can be efficiently related to the equivalent wave period.

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