Importance of Sand Fabric Anisotropy on the Bearing Capacity of Footings

Conventional design methods estimate the bearing capacity of shallow foundations by considering the soil as an isotropic elasto-plastic medium with an associated flow rule. State-of-the-art numerical analyses of such foundations employ constitutive models that consider strain softening and a non-associated flow rule if the soil is granular. Such analyses lead to increased accuracy over the conventional design methods, i.e. relatively lower bearing capacity, yet they do not consider the effect of soil fabric anisotropy. In order to investigate this effect, analyses of the bearing capacity of shallow foundations are carried out, by means of the finite difference method using the SANISAND-FR constitutive model that is fabric-based and verified against element and centrifuge test results. A comparison is made here between the analyses with this model and its variant that does not consider fabric effects, after their calibration to give identical results in the usually available triaxial compression tests. The comparison shows that neglecting sand fabric anisotropy, along with model calibration on triaxial compression tests, lead to an overestimation of the bearing capacity of footings, i.e. to un-conservative design.