DEM Analyses of an Uplift Failure Mechanism with Pipe Buried in Cemented Granular Ground

Abstract

The uplift failure mechanism of buried pipe and its linked soil resistance are key concerns in pipe design. Although the uplift responses of pipe buried in remolded backfill have been discussed extensively, little effort has been spent on pipes buried in cemented ground, a situation that could emerge in practical engineering. This paper aims to eliminate this deficiency through a comprehensive, two-dimensional distinct element method (DEM) study on the failure mechanisms of uplifting pipe buried in loose cemented sand ground with respect to soil bond strength and pipe cover ratio. Two forms of failure mode are identified, namely the global slide failure mechanism and the local flow failure mechanism. Three stages are identified for the global failure mechanism: (1) full mobilization of uplift resistance, (2) postpeak softening with full development of the crack zone, and (3) continual growth of the trapezoid zone with further softening. The local failure mechanism presents with the opposite flow of soils around the pipe, with soils above and below the pipe flowing upward and soils from the two lateral sides of the pipe to the far field flowing downward. With the soil bond strength decreasing or the pipe cover ratio increasing, the failure mechanism gradually changes from the global failure mode found in relatively strongly cemented cases to the local failure mode commonly found in weakly cemented or uncemented cases. A new dimensionless parameter r incorporating both the effects of bond strength and the cover ratio is proposed to identify the uplifting failure modes.