Uplift resistance of pipelines embedded in stiff soils and rocks: Effect of backfilled trench shape and dimensions

Abstract

The paper presents the results of a numerical study regarding the effects of trench dimensions on the development of the ultimate peak uplift resistance of pipelines embedded in stiff soil or rock formations. The numerical methodology is calibrated against small-scale experiments and then applied to an extensive parametric investigation for different backfill densities, embedment depths and trench dimensions. It is, thus, shown that commonly excavated trenches are not adequately wide to accommodate the mobilized failure surface associated with ultimate peak soil resistance and consequently soil reaction to pipeline uplift may increase significantly. The numerical results are further interpreted to establish correction factors for the increase of the ultimate soil reaction and the associated yield displacement relative to the reference values for an “infinitely” extending sand backfill which are provided by analytical methodologies. In addition, an optimized trapezoidal trench geometry is proposed, which envelopes the unobstructed failure surface, so that the effects of the trench dimensions can be effectively eliminated with reduced trench excavation and backfill volume. The importance of lateral trench dimension in pipeline design is demonstrated through a typical example of a steel pipeline verification against normal fault rupture.