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Abstract
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In this thesis, the ultimate bearing capacity of ring foundation and strip footing located on heterogeneous soils have been studied. the stress characteristics method and Discontinuity Layout Optimization (DLO-LA) method is used to analysis for ring and strip footings, respectively.in this study 3 forms of base was considered for ring footings; 1) homogeneous adhesive-friction soils 2) heterogeneous soils by linear increasing in cohesive by depth 3) two clay layered soils. While just one form of base is considered for strip footing, layered sand-clay media. For all case of soils, the mohr-coulomb failure criterion is true. Bearing capacity, stress distribution beneath the footing and failure surface been investigated for ring footing. Increase the internal friction angle and increase cohesive of soil, result more increase in bearing capacity if opening of the ring footing decrease. by Increase in opening of ring footing, the bearing capacity decrease. for homogeneous soils, if rii<0.2 this reduction in bearing capacity has less gradient rather rii>0.2. in this study the failure zone inward to ring foundations been considered for the first time, that this cause reduction in the bearing capacity of ring footing. The failure surface shrink and bearing capacity increase, if the stronger clay layer located bottom the weak clay layer and participation in the failure surface. In the study of the strip footing, increase in the thickness and internal friction angle of the sand layer and decrease in the undrained shear strength of the clay layer cause increase in the improvement factor of the bearing capacity where the improvement factor is the ratio of bearing capacity with an overlaying sand layer to that for a footing lying directly over clayey strata. In this paper the seismic mode of strip footing on layered sand-clay media was studied for first time. In seismic mode, the bearing capacity decrease and failure surface is asymmetric.
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