The method of characteristics is used to establish consistent factors for the vertical bearing capacity of circular and strip footings on soil which satisfies a linear (c, 4) Mohr-Coulomb strength criterion. This method of solution avoids the assumption of arbitrary slip surfaces, and produces zones within which equilibrium and plastic yield are simultaneously satisfied for given boundary stresses. Although similar solutions have previously been published for circular footings, their application has been hindered by errors and confusions over terminology. These are resolved, and the method of solution is explained. It is confirmed that Terzaghi's approach to the superposition of bearing terms containing N , N.,, and N, is both safe and sufficiently accurate for circular footings, as for strip footings. The values to be adopted are tabulated as functions of +. Differences between the factors applicable to circular and strip footings far exceed the allowances of the empirical shape factors in common use. Some new shape factors are suggested that better represent the relationship between the limiting equilibrium of circular and strip foundations. Some current shape factors attempt to allow simultaneously for the differences in equilibrium solutions and the differences in axisymmetric (triaxial) and plane strain soil parameters. This cannot succeed, since the relationship between strength parameters depends strongly on relative density. The new bearing factors facilitate a more rational approach in which soil parameters appropriate to the geometry can first be determined and then used to find appropriate bearing capacity factors.La mCthode des caractCristiques est utilisCe pour Ctablir des facteurs consistants de capacitC portante verticale de semelles circulaires et filantes sur un sol qui satisfait un critbre 1inCaire (c, +) de Mohr-Coulomb. Cette mCthode de solution Cvite l'hypothbse de surfaces de glissement arbitraires, et produit des zones I'intCrieur desquelles 1'Cquilibre et la dCformation plastique sont simultanCment satisfaites pour des contraintes aux frontibres donnCes. Quoique des solutions similaires aient Ct C publikes antkrieurement pour des semelles circulaires, leur application a CtC entravCe par des erreurs et des confusions sur la terminologie. Ces problbmes sont rCsolus et la mCthode de solution est expliquge. I1 est confirm6 que I'approche de Terzaghi ii la superposition des termes de portance contenant N,, N,, et N, est en m&me temps sCcuritaire et suffisamment prCcise pour les semelles circulaires, comme pour les semelles filantes. Les valeurs adopter sont mises en tableau en fonction de +. Les differences entre les facteurs applicables aux semelles circulaires et filantes dCpassent de beaucoup les tolirances des facteurs de forme empiriques d'usage courant. L'on suggbre de nouvaux facteurs de forme qui representent mieux la relation entre 1'Cquilibre limite des fondations circulaires et filantes. Des facteurs de forme courants tentent de tenir compte en m&me temps des diffkrences dans les sol...

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