Model Test Studies on Soil Restraint to Pipeline Buried in Bohai Soft Clay

Abstract

Under high thermal stress, buckling of submarine pipelines may occur to release the stresses accumulated in the walls of the pipelines. The likelihood that buckling occurs is largely determined by the capability of the soil to resist pipeline movements. Therefore, it is very important to determine the soil resistance in upheaval buckling when designing submarine pipelines. A series of large-scale model tests were carried out with soft clay chosen as the supporting medium in view of Bohai Sea geotechnical conditions. Pipe segments with diameters of 30, 50, and 80 mm were used. The pipes were buried in different depth-to-diameter ratios between 1 and 9. The uplift, lateral, and axial resistances were recorded during the tests. The test results have shown that the soil resistance depends on the pipe’s diameter and cover depth. According to the uplift test results, the load-displacement relationships with smaller depth of cover differ greatly from those with larger depth of cover. The results of the lateral sliding and axial pull-out tests have shown that the soil resistance initially increases before a peak value is reached. However, once the peak value is reached, the soil resistance will remain at approximately the same level. For the same cover depth, the lateral soil resistance is more than twice as much as that of the uplift. The observed data were compared with existing formulae, among which the best fit is selected. Meanwhile, the coefficients for the chosen formula were determined. These formulae and coefficients can be used in calculating the soil resistance in the Bohai Gulf.