Buried Pipe Span Ovality Assessment

This paper evaluates field ovalization measurements of NPS 24 pipe using 3D continuum finite element analyses. The combination of the soil backfill weight and loose bedding material beneath the pipe near a tie-in concentrates stresses at the location where native undisturbed soil transitions to loose backfill along the trench bottom, which increases the ovality in the pipe cross section. The analysis indicated that at burial depth, transient surface loading temporarily increases the ovality in unpressurized pipe but the ovality is reduced to near normal levels when the transient surface loading is removed. The internal pressure reduces the elastic pipe ovality. This analysis method can be useful for a cost benefit analysis between using thicker pipe, versus the additional costs, such as intervention and/or padding/compacting of soil around the pipe (with inspections).