Abstract: To evaluate the effect of the strain-softening of structured clays on the vertical bearing capacity of the spudcan foundations, firstly, the VUSDFLD subroutine was used to define the relationship between the undrained shear strength and accumulated absolute plastic shear strain , so that the coupled Eulerian-Lagrangian (CEL) numerical analysis method can simulate the strain-softening effect of structured clays. Then, based on the improved CEL numerical analysis method, the effects of soil sensitivity , soil strain-softening parameter , and soil brittleness parameter on the soil backflow above the spudcan as well as on the vertical bearing characteristics of spudcan foundations were analyzed. The results show that soil sensitivity , soil strain-softening parameter and soil brittleness parameter all have impacts on the soil backflow and on the vertical bearing capacity of spudcans, in which the effect of the brittleness parameter is most significant. Also, compared with the situation without considering the strain-softening effect, the bearing capacity factor of spudcan foundations and limiting cavity depth considering the strain-softening effect of structured clay are dramatically lower. Finally, the prediction expressions of the normalized limiting cavity height and vertical bearing capacity of spudcan foundations in structured marine clay were established, and the prediction results are reasonable. The research results of this paper can be used to assess the bearing capacity and penetration depth of spudcan foundations in practical engineering.

Key words: structured clay, strain-softening effect, limiting cavity height, vertical bearing capacity, coupled Eulerian-Lagrangian method