Soil Friction Restraint of Oblique Pipelines in Loose Sand

This paper presents the soil friction restraint on oblique pipelines in loose sand. A series of experimental tests are conducted in a prefabricated large-scale drag box with dimensions 1.83 m × 1.83 m × 1.22 m. Model pipes 0.61 m long with diameters of 152.4, 228.6, and 304.8 mm are obliquely moved from an axial-longitudinal to lateral-transversal direction in the drag box to study the associated soil restraints of the oblique pipes with various shallow embedded depths. All the test results indicate that for the axial pipes, the longitudinal soil restraint could be estimated as the product of the average of the vertical and horizontal earth pressures at the centerline of the pipe and the tangent value of soil-pipe friction angle, whereas for the lateral pipes, the transversal soil restraint could be predicted by using the limit equilibrium model with the assumption of the planar sliding failure surface. The longitudinal and transversal soil restraints of the oblique pipes could geometrically be obtained by multiplying the corresponding cosine and sine values of the oblique angle with the associated longitudinal soil restraint of axial pipe and the transversal soil restraint of the lateral pipe, respectively. The findings also indicate that the scale effects are not significant for the size of the pipes tested herein.