Abstract: When the direction of soil principal stress rotates during the shearing process, there is a non-coaxial phenomenon between the direction of principal strain rate and principal stress; but the conventional elastoplastic constitutive model could not take this phenomenon into consideration. In order to reflect the non-coaxial phenomenon, a non-coaxial plastic strain rate term is added to the tangential direction of conventional constitutive model’s yield surface. The non-coaxial model is numerically implemented into the finite element analysis of suction bucket foundation bearing capacity with automatic substepping scheme and explicit integral algorithm; and then the relation between non-coaxial model and some factors, such as flow rule, friction angle and dilation angle, is researched. The results show that this model could obtain reasonable convergence accuracy with FEM software’s default allowable error; and it is available to the associated and non-associated flow rule. The influence of different flow rules on the numerical result could be neglected when the conventional coaxial model is used into the numerical analysis. But there is difference between the results of different flow rules when the non-coaxial model is used. The non-coaxial phenomenon has a softening effect on the bearing capacity-vertical displacement curve; and this softening effect would be more apparent when the non-associated flow rule is used.

Key words: bearing capacity, non-coaxial, numerical integration, constitutive model