Case study: footing load test using stone columns in Port Fouad-Egypt

Installation of stone columns is an efficient technique to improve very soft to soft clay deposits that exist at shallow depths in many coastal areas in Egypt. The stone columns provide vertical stiff permeable members in the deposit to be improved. Upon loading, the presence of stiff columns reduces settlement, and increases the overall shear strength of the deposit, thus bearing capacity. Further, the high permeability of the columns provides drainage boundary that accelerates the dissipation of excess water pressure and thus increases the consolidation time rate of the soft soil. This paper presents analysis of a case history of footing load test founded on soft clay improved by stone columns for a project in Port Fouad, Egypt. The stone columns are of end-bearing type. The footing is analyzed using 3D finite element method. The analysis aims to; (1) show the importance of increased post-column installation coefficient of lateral earth pressure in light of the pre-shearing effect (Mesri and Hayat in Can Geotech J 30:647–666, 1993), (2) show the importance of considering the time-dependent settlement in evaluation either of the improvement technique and/or the design method, and (3) use the field measurements to evaluate and compare between the FEA method and the other published methods of estimating the settlement improvement ratio.