Prediction of Ultimate Bearing Capacity of Surface Footings with Regard to Size Effects

Abstract

A simplified prediction method based on Terzaghi’s bearing capacity formula for surface footing, with regard to size effects, is proposed. Clarification of size effects, which is indispensable for appropriate design of large foundations, may permit use of the results of small scaled loading tests and prevent increases in the construction costs of foundations. Size effects may be mainly attributed to stress-level effects on the shear strength of ground materials; stress-level effects are taken into account in the proposed method. The proposed method incorporates a method for determination of shear strength constants c and ϕ that should be applied to the bearing capacity formula. A nonlinear Finite Element Method which incorporates the confining stress dependent shear strength is used to calculate stress distribution in foundation grounds beneath the footings. It is shown that the effective mean principal stress σ m tends to range from 2 γB to 10 γB for strip footings and from 1 γB to 15 γB for circular footings; within this region the parameters c and ϕ are determined from the straight fitting line. The proposed method is verified with the results of some series of model surface footing loading tests on cohesionless and cohesive grounds reported by the authors and other researchers. This verification confirms the applicability of the proposed method to strip, circular and square footings on cohesive and cohesionless foundation grounds with sufficient accuracy for practical purposes.