According to modern seismic codes, the use of shallow foundations on liquefiable soils is only acceptable after proper ground improvement underneath and around the foundation. Still, there are no widely acceptable guidelines for choosing the required thickness and extent of the improved ground, as well as for computing foundation settlements. This problem is investigated herein numerically, through fully coupled non-linear 2-D analyses with the Finite Difference code FLAC, using the Critical State Plasticity constitutive model NTUA-SAND [Andrianopoulos et al. (2010)] to simulate the cyclic response and liquefaction of the sand. The parametric investigation initially focuses upon the reference case of ground improvement with "infinite" lateral extent (the improved zone extends to the lateral grid boundaries). Subsequently, the width of ground improvement (L_(imp)) is progressively reduced to nearly the width of the footing itself. The numerical predictions are organized into design charts and empirical relations, while conclusions are drawn regarding the optimum (from a cost-benefit point of view) extent of ground improvement.
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