Study On Settlement Early Warning Quantity Of Composite Reinforced Pipeline Base On Interface Specimen Test

Buried pipeline is an important part of long-distance pipeline and has become an important support for china's economic development.Buried pipeline needs to be connected by welding technology in segments.Because of the difficulty of controlling the environmental humidity at the construction site and the inadequate preheating and insulation measures,all kinds of defects are easy to occur in the weld of the pipe.Once soil settlement occurs,buried pipelines are liable to fracture at weld defects.In recent years,high-strength and lightweight composite materials have been widely used to reinforce defective pipelines.The reinforcing effect of composites mainly depends on the load transfer of the composite/pipeline steel interface.Once the interface fails in a large area,the reinforcing effect of composites will be seriously affected.Therefore,it is of great significance to study the interface failure evolution process of pipelines with composite reinforcement defects under load,and to provide the load warning value of pipelines with composite reinforcement and the settlement warning value of buried pipelines.The composite/pipeline steel interface mechanical properties and failure processes are studied in detail by means of specimen test and finite element simulation,and the reinforcing effect of composite material for repairing defective pipelines is discussed in depth,the specific research content is as follows:The specimens test and finite element simulation of bimaterial composite/pipeline steel interface were carried out,including the tensile test of interface fracture DCB specimens of type ? and interface fracture double lap bonded joint specimens of type ?.The relationship curve between test force and displacement was obtained by DCB specimens tensile test,the critical energy release rate under load conditions of type I was calculated,and the R curve was drawn.Based on the tensile test of double lap bonded joint specimens,the strain variation law of composite material was measured,and the bond-slip curve of interface was calculated and depicted.By calculating the area enclosed by bond-slip curve,the critical energy release rate under type II load condition was obtained,and the effective lap length and maximum tensile force were calculated.Finite element studies include: basing on the contact element with cohesive force model to simulate the interaction of composite/pipeline steel interface,the finite element model of DCB specimens test and double lap bonded joint specimens test were established.The correctness of the simulation method was verified by comparing the simulation results with the experimental data.At the same time,the rationality of applying the simulation method to the model of composite reinforced pipeline was explained.In addition,the effect of anchorage depth on the maximum interfacial tension and failure modes was analyzed by changing the anchorage depth of the base surface with different processes.The full-scale pipeline failure test of unreinforced/composite reinforcement with circumferential welds cracks were carried out.By monitoring axial strain and CMOD evolution at weld crack,it could get curves between bending moment?internal pressure and axial strain?CMOD.By establishing the relationship curve between CMOD and axial strain,the reinforcing effect of composite materials for pipelines with circumferential weld cracks was evaluated.The finite element model of composite reinforcement pipeline was established by using contact element with bilinear cohesive force model.The finite element simulation result was compared with the experimental data to verify the correctness of the finite element simulation method and the accuracy of the data.The bending moment and axial force were applied to the finite element model of composite reinforced pipeline.The relationship curves between bending moment?axial force and interface damage length?CMOD could be obtained.The damage evolution law of weld crack interface under the action of bending moment and axial force was analyzed,the CMOD warning value was determined,and the load warning curve of composite reinforced pipeline under the combined action of bending moment and axial force was drawn.Using the pipe-soil interaction model,the finite element model of pipeline under uneven settlement of foundation was established.The mechanical response of buried pipeline under vertical settlement and axial movement of soil was analyzed,and the settlement warning curve of buried pipeline under different buried depth was drawn.