ULTIMATE SEISMIC BEARING CAPACITY OF STRIP FOOTING USING MODIFIED KREY’S METHODS (FRICTION CIRCLE METHOD)

Abstract

In geotechnical investigation, determination oftheseismic bearing capacity of foundation soilconstitutes an important task. The bearing capacity of soil under static loading has been extensivelystudied since the early work of Prandtl (1921).Design of foundation in seismic areas needs specialconsiderations compared to the static case. The inadequate performance of structure during recentearthquake has motivated researches to revise existing methods and to develop new method forseismic resistant design. For foundation of structure built in seismic areas the demands to sustain loadand deformation during earthquake will probably be the severe in their design life. Due to seismicloading foundation may experience decreases in bearing capacity and increases in settlement. Twosource of loading must be taken into consideration inertial loading caused by lateral forces imposed onthe superstructure, kinematic loading caused by the ground movement developed during earthquake.Many techniques used for studying the effect of seismic forces on the soil bearing capacity such as, limitequilibrium method, kinematic approach of yield theory, a variational approach, and unified theory ofstress, which the shape of failure surface has been assumed. The seismic forces are considered as pseudostaticforces acting both on the footing and on the soil under the footing. However, finite element andstress characteristics methods shape of the failure is not required to be assumed.In the present paper, a theoretical analysis has been performed on the basis of Krey's method(friction circle method) with radius of friction circle equal to = 𝑟 sin (∅ − tan−1 𝑘ℎ1−𝑘𝑣)where r is theradius of the circle slip surface to determine the influence of the earthquake acceleration coefficientson the seismic bearing capacity of foundation with assisted by a computer program. The presentstudy is compared with the various theoretical solutions. The comparison of that the present studypredicted values of ultimate seismic bearing capacity of soil are less than others theories of ultimateseismic bearing capacity. In order facilitate the calculation of seismic bearing capacity, using theproposed equations. It is a function of (B, Rf, , tan ∅ , 𝑘ℎ and c)