Macro-mesoscopic Study On Mechanical Response Of Buried Pipelines Reinforced By Geogrids

With the rapid growth of underground pipelines network construction area and the increase in demand for cost reduction,efficiency improvement and safety assurance,the research on the performance protection of buried pipelines has become more and more a hot topic.As an excellent reinforcement material,geogrid are widely used in geotechnical engineering.This thesis aims to apply geogrid to the reinforcement protection of buried pipelines and explore the reliability of geogrid reinforcement on the protection of buried pipelines.Through the determination of material parameters in the early stage,a model test of geogrid reinforced protected buried pipelines was established.By calibrating the macroscopic mechanical properties of the test materials,a discrete element model of geogrid reinforced buried pipelines was established.Based on model test and discrete element simulation analysis,the protective effect of geogrid on buried pipelines performance was explored from the macroscopic level.The protection effect of geogrid on pipelines is determined by the loading plate load settlement curve,the soil pressure distribution law around the pipe and the pipe ring strain during the vertical graded load loading process in the model test.The force chain distribution and particle displacement distribution in discrete element simulation are used to reveal the internal load transfer and deformation laws of the model.These research results can provide theoretical support for the application of geogrid to actual pipelines protection projects.The main research contents and results are as follows:(1)By using a loading plate with width B above the buried pipeline for vertical load loading,and changing the buried depth of the pipeline H,the geogrid reinforcement buried depth u,the reinforcement length l of the geogrid and the number of reinforcement layers n,it is found that when the buried pipeline is not reinforced,the buried depth of the pipeline under the same level of load is larger,the ultimate bearing capacity of the model is larger,the earth pressure around the pipe is smaller,the pipe ring direction should be changed less,but the filling settlement amount above the pipeline is greater.After the single-layer geogrid is reinforced above the pipeline,the ultimate bearing capacity of the model decreases with the decrease of the buried depth of the grid,and increases with the increase of the reinforcement length l.At the same time,when the buried depth of the geogrid is u/B=0.25 and the reinforcement length l/D is increased to 5,the vertical earth pressure distributed in the horizontal direction of the pipe top is the smallest,the soil pressure distribution around the pipe is the most reasonable,and the pipe ring strain value decreases the most obviously.When the length of reinforcement continues to increase to l/D=6,the protective effect of the pipeline is not greatly improved.(2)When the number of reinforcement layers n is increased from 1 layer to 2layers,the reinforcement effect is not obvious,and the reinforcement effect is best after the number of reinforcement layers n is increased to 3 layers,but considering economic factors,it is believed that the buried depth of the geogrid is u/B=0.25 when the single layer is reinforced,and the reinforcement length is l/D=5 when the reinforcement length is the best reinforcement scheme.(3)The results show that the discrete element numerical simulation and model test results have the same change trend in terms of ultimate bearing capacity and loading plate settlement,the numerical value of the model is larger,the failure mode of the model is the overall shear failure,and after the reinforcement above the pipeline,the stress concentration between the soil particles can be effectively reduced,the soil settlement under the same level of load can be reduced,and the compressive deformation of the buried pipeline can be reduced.(4)When the compaction degree of backfill soil above the pipeline is insufficient,the bearing capacity is low,and the reinforcement can significantly improve its ultimate bearing capacity.Compared with the reinforced condition when the backfill soil is fully compacted,the geogrid plays a more obvious role,and the integrity of the backfill soil above the pipeline is enhanced.At the same time,the deformation of the pipeline is reduced compared with that without reinforcement.