ABSTRACT:

Experimental and theoretical studies on the soil resistance of obliquely loaded pipelines in loose sand are presented. A series of experimental tests were conducted in a prefabricated large scale drag box with dimensions of 1.83 m ´1.83 m ´ 1.22 m to study both effects of pipe velocity and oblique angle on the soil resistance of the pipelines. Model pipes with 1.22 m long and diameters of 38.1 and 76.2 mm were obliquely pushed down into the sand to determine the ultimate soil resistance on the pipes. All the test results indicate that the ultimate resistance of the pipeline increases with the inclination angle of pipeline movement. Most of the increase in the resistance is associated with the oblique angles in the range between 45° and 90°. The implicit limit equilibrium model with the assumption of the rupture surface of logarithmic spiral arc was used in the analysis. The trial wedge method was then applied and successfully predicted the ultimate soil resistance of the pipeline. It was also found that the soil resistance slightly increases with the pipe velocity for the smaller oblique angle pipes. However, for the larger oblique angle pipes, the resistance gradually decreases with the pipe velocity to a minimum value between 1 ´ 10–3 dia./sec. and 5 ´ 10–3 dia./sec. and then the higher values occur elsewhere. This finding is consistent with the work done by Vesic et al., in which the dynamic bearing capacity of footing reaches a minimum value approximately at the velocity of 5.08 ´ 10–3 cm/sec., and then continues to increase.

INTRODUCTION

Underground pipelines are extensively used to carry oil and gas from their deposit to the consumption places. An understanding of soil resistance against pipelines due to the soil-pipe relative movement is important for the pipeline designers.

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