| Subsea pipeline is the most effective way of transporting hydrocarbons,typically operated under high-temperature and pressure.These can cause expansion and shrink-age along the routine.When the soil resistance provided by seabed soil is insufficient,the instability of pipeline will occur,i.e.global lateral buckling and axial walking etc.The former is mainly attributed to insufficient lateral resistance,and the latter is caused by the cumulative axial displacement accompanying the heating and cooling operations.The existing guideline for geotechnical design of subsea pipelines proposed a set of methods for evaluating the stability of pipelines based on the pipe-soil interaction mechanism.Yet,the bearing mechanism of the pipeline segment under the complex loading state is not understood well,and the assessment method of pipeline still needs to be improved.This study focused on the failure mechanism of subsea pipeline seg-ments under multi-directional loadings in place.The embedded pipeline segment is subjected to multi-degree-of-freedoms loadings(V-H_L-H_A-H_M,where V means vertical load,the letter H_L means lateral load,the letter H_A means axial load and the letter H_Mmeans moment load.)in the clay and sandy seabed by finite element and physical mod-elling analyses.The main work and innovations of this paper include:(1)The instrumentation of small-scale physical modelling is designed to obtain V-H_L failure envelope of the embedded pipeline segment in clay,compared with numeri-cal modelling results.(2)The numerical model of pipe-soil interaction in clay is established,which can truly reflect the detachment state of the pipe-soil interface under the multi-directional loadings in clay.Considered the distribution of undrained shear strength,the pipeline embedment,and the friction properties of pipe-soil interface,the geotechnical capaci-ties of embedded pipeline segments under multi-directional loadings are explored,in-vestigating the failure envelope of the pipeline under the combined V-H_L,V-H_A,V-H_L-H_A,V-H_M,V-H_M-H_A,V-H_L-H_M loadings,with the estimating method proposed accord-ingly.(3)The numerical model of pipe-soil interaction in sand is established,which can reflect the detachment behavior alone the pipe-soil interface under the multi-directional loadings.Considered the pipeline embedment,and the friction properties of the pipe-soil interface,the geotechnical capacities of pipeline segments are examined,investigating failure envelopes of the pipeline in sand under the combined V-H_L,V-H_A,V-H_L-H_A,V-H_M,V-H_M-H_A,V-H_L-H_M loadings,with the evaluating method proposed accordingly. |
