Experimental Investigation of Longitudinal Bending of Buried Steel Pipes Pulled through Dense Sand

North America is traversed by many high-pressure oil and gas transmission pipes and the stability of that essential buried infrastructure must be maintained under a variety of earth-loading conditions. In the research reported in this paper, a series of pipe-bending experiments have been conducted on 105-mm (4.1-in.) outside diameter and 1,830-mm (6-ft) long steel pipes buried in dense sand placed in a $\mathrm{4,000}\times \mathrm{2,000}\times \mathrm{2,000}\text{-}\mathrm{mm}$ ($157.5\times 78.7\times 74.7\text{-}\mathrm{in.}$) test pit. The pipe ends were pulled by two parallel cables attached to a spreader beam outside the test region, which was pulled by a hydraulic actuator. The research reported in this paper investigated burial depth-to-diameter ratios of 3, 5, and 7 as well as two horizontal extents for the soil behind the pipe distances of $3D$ and $9.5D$. Special consideration was made to assess the influence of friction between the pulling-cables and soil. This friction is significant and may contribute about 20% of the maximum pulling load for the case of a depth-to-diameter ratio of 3. Consistency of results was established using four test repetitions for some cases. Whereas the horizontal extent of soil behind the pipe tested in the research reported in this paper had an insignificant influence on the pulling forces, the burial depths significantly influenced the ultimate pulling forces for the system. The failure mechanism controlling the limiting pulling force in these tests was consistently governed by the soil and the pipe remained elastic.