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

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 200 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 $H_{\mathrm{br}}$, maximum resistance $H_{\max }$, and residual resistance $H_{\mathrm{re}}$. Experimental data indicate that lateral soil resistance depends on the soil passive pressure and berm resistance ahead of the pipe and that $H_{\mathrm{br}}$ is strongly coupled with $H_{\max }$ and $H_{\mathrm{re}}$ in deeper embedments. An observational test was conducted to study the mechanism of breakout resistance $H_{\mathrm{br}}$. Simplifying $H_{\mathrm{br}}$ as the ultimate bearing capacity problem of a shallowly embedded cylindrical foundation under an inclined load, an upper-bound solution is proposed to calculate $H_{\mathrm{br}}$, 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 $H_{\mathrm{br}}$ of pipeline in Bohai Gulf.