EVALUATION OF STRIP FOOTING BEHAVIOR RESTING ON GEOGRID-REINFORCED SOILS

improvement is essential. In cases where weak soil is improved by a replacing method, the improvement depth, due to the stress distribution pattern, is of great importance. However, in some cases, it is very dicult or too expensive to provide enough improvement depth. Hence, additional bearing capacity or other improvement methods are required. Using a geogrid to reinforce soil is an eective alternative way to improve the bearing capacity more eectively and economically. In this paper, the eect of replacing a loose layer by a dense one on the bearing capacity and settlement of a strip footing has initially been investigated. Then, the in uence of a geogrid layer placed on the interface of loose and dense layers is analyzed and investigated using nite dierence FLAC  software. The numerical model is veried and calibrated using experimental data from a physical model developed in the Soil Laboratory of Amirkabir University. Analyses results show that increasing the depth of compacted soil layer by more than  times the width of the foundation, does not have a considerable eect on the ultimate bearing capacity of strip footings, and only settlements will decrease. Using a geogrid layer between loose and compacted soil will improve the bearing capacity greatly, for a modied depth less than  times the width of the foundation 'The most ecient improvement in this method is when the geogrid layer is placed on the boundary of loose and dense layers at a depth of  the foundation width. The eciency of reinforcement is reduced by increasing the improvement depth. Using a reinforced layer with a width of less than  times the foundation width is not recommended.