Abstract：High-strength layer at the bottom of foundation is treated as rigid layer to determine ultimate bearing capacity of strip foundation. Failure modes of strip foundation under the action of ultimate load become extremely complex when it is restricted by the rigid layer at the bottom of foundation. Under this scenario，ultimate bearing capacity of foundation is derived using limit analysis，slip line or other numerical methods，which is less likely to obtain quantitative failure modes. In this paper，the finite element upper bound method with rigid translational motion element is adopted to conduct systematic analysis. The upper bound solution reflected by curves and the slip line failure modes for bearing capacity factor Nc related to the cohesion is mainly discussed. The related factors such as the thickness of soil layer，the internal friction angle of soil mass and the finite friction of foundation at the interface are studied. The results show that the changes in Nc and the correction Kc influenced by rigid layer are not prominent with varying friction angle and thickness of the soil layer when the thick foundation is above the rigid layer. However，for thinner soil layer，the Nc and Kc increase sharply with the increase of internal friction angle of soil mass and the decrease of soil thickness. Furthermore，for the thinner soil layer，the friction conditions of contact surface between strip footing and foundation has a significant influence on the failure modes. In other words，the decreasing roughness of the bottom of the foundation makes the Nc smaller. It is significantly different from the one free from the restriction of the bottom rigid layer. Finally，the conversion relationship between the ultimate bearing capacity coefficient of the foundation Nc and Nq is verified through the analysis using the finite element upper bound method with rigid translational motion element.
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2023, Vol. 42 
