Research On Lateral Soil Resistance Of Shallow-embedded Submarine Pipeline In Sand

As the exploitation and extraction work of offshore oil and gas resources are extended into deeper water,the lateral buckling under HTHP condition for shallow-embedded pipeline in deep sea has become an issue can not be ignored.For the purpose of releasing the axial force accumulated in the pipeline and accomplishing the control of buckling,the lateral soil resistance to pipe is treated as an important parameters for buckling design,of which the mechanism and prediction method has gradually become the focus problem in ocean engineering.Based on the former researches,a serious model experiments of lateral soil resistance under large-displacement condition have been conducted.With combination of limit analysis theory and nonlinear numerical FEM method,a prediction formula of lateral soil resistance has been put forward.The main conclusions are summarized as follows:Based on the experimental results,the development of lateral soil resistance and the influences by pipe wight W and relative embedments z/D has been discussed.By the way of fitting,the empirical formula between breakout resistance F_br,the maximum resistance F_max,and residual resistance F_re is proposed.The experimental results is verified by FEM numerical method,with the mechanism of breakout is revealed as follows:The plastic zone is developing along with the motion of pipe,and a continuous slip face appears when breakout happens,the lateral resistance is breakout resistance F_br.By simplifying the breakout of a pipe as an ultimate bearing capacity problem of a partially embedded cylindrical foundation under an inclined load,integrated with the assumed failure mechanism and velocity fields,an upper-bound solution is proposed to calculate the breakout resistance Hbr.After verification by the former formulas,the upper-bound solution is proven to provide a relative precise prediction of the breakout resistance under various conditions.For the purpose of evaluating the on-bottom stability of pipelines under combined loading condition accurately,a FEM numerical method is adopted to study the V-H failure envelopes of shallow-embedded pipelines on sandy seabed.Fitting formulas are established to describe the parameters V_max and?₀ depend on?and z/D.In practice,applying the soil parameters and potential loading conditions to analysis,the on-bottom stability of pipeline can be determined.