Seismic bearing capacity factor of dry cohesionless soil under surficial strip footing

Abstract

The modified pseudo-dynamic method is used to calculate the seismic bearing capacity factor Nγe for dry cohesionless soil underlying a surficial strip footing. This new method is used to estimate the seismic accelerations and thus estimate the seismic force more accurately than the commonly used but approximate pseudo-static method. This study shows that Nγe is significantly affected by both the horizontal and vertical seismic accelerations, and soil friction angle, whereas the soil damping ratio and width of the footing have negligible effect. Nγe decreased by about 86% as compared to static case for kh = 0.1 and if an additional kv = 0.1 acts, the value of Nγe further reduced by about 13%. When the soil friction angle was decreased from 40 o to 25 o , Nγe was decreased by about 79%. Amplification factor was also found to strongly influence the value of Nγe. If the seismic acceleration was in phase all along the depth up to the failure surface, drastic reduction in Nγe was observed as compared to the condition where it was out of phase. These outputs highlight the importance of using the modified pseudo-dynamic method compared to conventional pseudo-static method for estimation of Nγe, which can be used for design of shallow strip footings under earthquake conditions.