Simplified analytical solution of bell-spigot jointed ductile iron pipelines crossing normal faults

Abstract

Bell-spigot jointed ductile iron pipelines are increasingly used, which are highly susceptible to permanent ground deformation. It is necessary to predict their responses under normal fault conditions. This investigation presents an analytical approach that simplifies the pipeline as a beam-type structure resting on discrete Winkler foundation comprising discrete springs, connected by shear and torsional springs at the bell-spigot joints, which is solved by the finite difference method. Comparisons of pipe deflection and joint rotation with the results from two full-scale experiments confirm the effectiveness of this method. Parametric analysis is conducted with respect to soil modulus, location of peak curvature, burial condition, pipe diameter, and joint rotational stiffness. It is found that increase in soil modulus can deteriorate the deformation of pipe bodies. Concentration of shear zones intensifies the responses of both pipeline segments and bell-spigot joints. For deeply buried jointed pipelines, less compacted backfills can reduce the soil-pipe interaction forces, mitigating the detrimental impact of fault rupture. A concept of relative joint-pipe stiffness ratio, R, is introduced to describe different joint rotational stiffness, identifying the threshold of R = 10 % for transition between jointed and continuous pipelines. Considering different failure limits, joint rotation failure always occurs earlier than pipe bending failure.