Experimental And Numerical Analysis Of Mechanical Performance Of Flexible Buried Pipes Reinforced By Geogrids Under Cyclic Loading

As the important part of urban water supply,gas transportation and sewage system engineering,buried pipelines play a significant role in modern society.However,buried pipes are often influenced by upper traffic load due to the concealment of pipes.The normal use of pipelines has potential safety threat caused by frequent traffic load.It is overwhelmingly possible to affect normal operation of traffic light if buried pipes have accidents.More seriously,it can cause fatal disasters such as fire hazard,explosion,gas leak and all of these disasters are horribly harmful to human life and property safety.Therefore,it is more than important to study the protection of buried pipes.Currently,geogrids have been widely used in strengthening retaining structures,soft ground treatment and slope protection,and so on.All of those methods have achieved good effect.This paper is aimed at introducing the protection measure by use of the function of isolation and excellent load reduction of geogrids.The validation and mechanism of geogrids-reinforced flexible buried pipes were investigated on the basis of a series of laboratory tests and numerical analysis.The main research contents and conclusions are listed as follows:This paper firstly carried out a series of laboratory studies of geogrids-reinforced buried pipes during cyclic loading to analysis the optimal laying parameters of reinforcement when buried depth of pipes was 3D(D,external diameter of the pipe).The results showed that optimum embedment depth of the uppermost reinforcement,spacing of geogrid layers and length of reinforcement is 0.4B(B,width of load plate),0.5B and 5D,respectively.Secondly,according to the optimal parameters of reinforcement,the lab tests comprehensively analyzed the effect of buried depth of pipes(H),geogrid layers(N),load level(P)and load frequency(f)on mechanical and deformation performance of pipes.The deformation of pipes decrease and the settlements of loading plate increase when buried depth increases.Adding the numbers of layers of geogrids can significantly enhance the strength of soils and then reduce deformation of pipes and settlements of loading plate.It is pronounced that higher level of load or lower frequency can affect remarkably mechanical performance of buried pipe.Increasing level of cyclic loading or lowering frequency of loads can result in increase of radial deformation of pipes and settlements of load plate.The strains of reinforcement decrease with the increasing of distance away from the center of loading plate.In addition,with the increasing of cycles of loads,strains in the center of geogrid tend to increase firstly and then decrease.Moreover,higher load level or lower load frequency can make the strain of reinforcement higher.Finally,through the numerical analysis platform of software ABAQUS for two-dimensional modeling,this paper is aimed to analysis the mechanical behaviors of soil and pipes under cyclic load and compare results with physical model tests.In addition,the paper investigates the distribution of deformation of pipes and the soil under different reinforcement elasticity modulus.Simulation results show that the deformation law of structures by finite element model analysis is basically consistent with physical model,but the numerical results are smaller than the experimental value.The soil subsidence and pipeline deformation can be effectively reduced by appropriately increasing the modulus of reinforcement.