Full-Scale Testing of Large Diameter Steel Pipes under Soil Compaction and External Load
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Abstract
Pipes are buried as the safest method of transporting natural resources, such as oil and gas. 86% of the existing pipes buried in Alberta, Canada are made from steel. Large diameter pipes are designed and buried to replace the old ones and improve the oil transportation capacity. For buried pipes, heavy truck load is considered as one of the most important factors influencing the pipe behavior. Soil compaction during the pipe installation has been proven to affect the pipe behavior. The main objective of this study is to investigate the buried pipe behavior under soil compaction and truck load. The study is performed in three parts, i.e., laboratory soil tests, full-scale prototype tests on two Grade X52 steel pipes, and development and validation of a new semi-empirical method to predict pipe deformation.Firstly, the laboratory soil test results indicate that the soil modulus decreases with increasing water content, while it tends to increase slightly with confining pressure. The undrained shear strength of compacted silty sand increases with decreasing water content and increasing confining pressure. Secondly, the prototype test results illustrate that, during the soil compaction, the so-called peaking effect is detected on both pipes mainly due to the compaction pressure at the pipe sides. After that, the pipe is vertically compressed under overburden. The measured pipe strains increase with increasing applied load and decreasing cover depth. Perforation in pipe would induce stress concentration near the opening, thereby increasing the pipe strain. Increasing water content decreases the soil stiffness. As a result, a higher percentage of the applied load is taken by the pipe, and the pipe deformation is magnified. Compared to a static loading condition, pipe behavior under dynamic load is more complicated, and affected by factors including road roughness, cover depth, truck load, and truck moving speed.Thirdly, based on the results from the prototype tests, a semi-empirical method is proposed to predict the pipe stress and deflection in two steps. Pipe deformation is mainly attributed to the peaking effect and the overburden.