Investigation of buried pipes under axial tension and compression loadings

ABSTRACT: Buried pipes exposed to ground movements can experience soil loads in various scenarios. When the ground movement is parallel to the pipe axis, it experiences axial/longitudinal forces. The longitudinal force can be tension or compression depending upon the locations of the pipe to the moving ground. A downstream pipe segment experiences compression, while an upstream pipe experiences tension. Previous studies focused on investigating the pipe responses to tensile force using axial pullout tests. The compression loading, as well as loading-reloading effects, were not investigated well. The loading-reloading is expected when the pipeline is subjected to intermittent ground movements. This study investigates high-density polyethylene (HDPE) and ductile iron pipes subjected to tension and compression loadings and loading-reloading cycles. For tension loading, a pipe buried in a soil box was pulled axially. For compression loading, the soil box with the buried pipe was placed on a shaking table. Then, the shaking table was moved to push the pipe against a reaction frame. The test results revealed that the maximum axial force needed to mobilize the interface frictional resistance over the entire pipe sample length is the same for tension and compression loadings for the ductile iron pipe. However, for the HDPE pipe, the corresponding axial force was significantly higher for compression than for tension. The higher axial force for the flexible HDPE pipe during compression might be due to the increase in diameter. For the ductile iron and HDPE pipes, the axial force for mobilization of interface frictional resistance reduced with the loading cycle, likely due to the arching effect after releasing the interface bonding in the first cycle. The method recommended in the current design guidelines significantly underestimated the maximum pulling forces observed during the tests.