Seismic Bearing Capacity of Rough Strip Footing Placed Over Geogrid-Reinforced Two-Layer Sands

The lower bound limit theorem in conjunction with finite elements is used to quantitatively estimate the pseudostatic bearing capacity of a rough strip footing placed on geogrid-reinforced sandy soil. The objective of this study is to show how the bearing capacity of the rough strip footing will be improved in seismic prone areas by (i) laying a stronger soil layer beneath the foundation and (ii) inserting geogrid reinforcement layers in the soil stratum. Both the soil mass and the foundation are subjected to horizontal and vertical seismic acceleration. Solutions are obtained for different combinations of (a) geometrical parameters [e.g., size of reinforcement, depth of reinforcement, top (dense) layer thickness], (b) sand properties, and (c) seismic loadings. The optimum width and the critical depth of the reinforcement corresponding to different soil conditions and seismic loadings are presented in the article. It is observed that when seismic loads are applied, the reinforcements are to be placed at a shallow depth to ensure maximum benefit. Failure patterns are also drawn for a few cases.