Upward Pipe-Soil Interaction for Shallowly Buried Pipelines in Dense Sand

Uplift resistance is a key parameter against upheaval buckling in the design of a buried pipeline. The mobilization of uplift resistance in dense sand is investigated in the present study based on finite-element (FE) analysis. The prepeak hardening, postpeak softening, density-dependent, and confining pressure-dependent soil behavior are implemented in FE analysis. The uplift resistance mobilizes with progressive formation of shear bands. The vertical inclination of the shear band is approximately equal to the maximum dilation angle at the peak and then decreases with upward displacement. The force-displacement curves can be divided into three segments: prepeak, quick postpeak softening, and gradual reduction of resistance at large displacements. Simplified equations are proposed for mobilization of uplift resistance. The results of FE analysis, simplified equations, and model tests are compared. The importance of postpeak degradation of uplift resistance to upheaval buckling is discussed.