A non-classical alternative was adopted for the foundation system of a thirty-storey building in Beirut, Lebanon. The subsurface strata included a thick layer of highly weathered marls and/marly limestone overlying the karstic limestone base stratum. Ground improvement by rigid inclusions/mortar columns was proposed, analyzed, designed and successfully executed. 2D & 3D Finite element simulations were conducted to assess the degree of improvement, and then used to perform/finalize the design of the foundation system. The paper discusses the conducted analyses & presents some parametric studies & recommendations.