Experimental and Upper-Bound Analysis of Lateral Soil Resistance for Shallow-Embedded Pipeline in Bohai Sand

Abstract

In the deep sea, pipelines can undergo penetration during the laying process; therefore, lateral soil resistance is of great importance for shallowly embedded pipelines to maintain stability under high-temperature and high-pressure conditions; in this case, a pipeline may buckle due to release of stress, with a large amplitude over several pipe diameters. This paper reports on a series of large-scale plane strain model tests to study the lateral pipe–soil behavior in large-displacement conditions, and a fine sand collected from Bohai Gulf is chosen in view of Bohai sea geotechnical conditions. A 2 mm diameter model pipe section is integrated into a lateral pipe–soil interaction testing system to study the lateral soil resistance response as influenced by pipe weight W and relative embedment z/D. From the test results, three characteristic soil resistances are identified, derived from the soil resistance curves, namely, breakout resistance Hbr, maximum resistance Hmax, and residual resistance Hre. Experimental data indicate that lateral soil resistance depends on the soil passive pressure and berm resistance ahead of the pipe and that Hbr is strongly coupled with Hmax and Hre in deeper embedments. An observational test was conducted to study the mechanism of breakout resistance Hbr. Simplifying Hbr as the ultimate bearing capacity problem of a shallowly embedded cylindrical foundation under an inclined load, an upper-bound solution is proposed to calculate Hbr, and both the failure mechanism and corresponding velocity are derived from experiments. Through comparison with existing calculation methods, the upper-bound solution is proven to provide an alternative prediction method for the breakout resistance Hbr of pipeline in Bohai Gulf.