The effect of variation of soil conditions along the pipeline in the fault-crossing zone

Abstract

In the paper, buried steel pipelines crossing strike-slip and normal-slip faults are considered within analytical and numerical approaches. The effect of variation of the backfill soil properties along the pipeline in the fault-crossing zone on the stress-strain state of the pipeline is analyzed.The analytical model developed in the previous publications is substantially reworked to take into account the variation of soil conditions along the pipeline length and the effect of internal pressure on the deformed pipe geometry. A complete set of analytical solutions for the axial pipeline-soil interaction force taking into account two zones along the pipeline length with different soil conditions, plastic behavior of the pipeline and soil, initial stress in the pipeline has been derived and introduced into the model.The effect of special (loose sand) backfill segment length on the pipeline response under strike-slip and normal-slip fault actions is studied. It is shown that the extension of the special backfill length has an advantageous effect in case of substantial axial fault displacement component. In this case, the reduction of soil constraining effect on a larger distance substantially reduces the maximal tensile strains in the pipeline. In contrast, under bending-dominant behavior of the pipeline, the elongation of the special backfill zone has no positive effect on the maximal strains.