Experimental Study On The Influence Of Geogrid Reinforcement On The Erosion Process Of Subgrade Soil By Transparent Soil Material Test

In recent years,ground collapse accidents caused by the fracture and damage of different underground hydraulic pipelines have occurred frequently,and their suddenness and complexity have great hidden dangers to pedestrians and vehicles.Exploring the mechanism of ground collapse caused by fracture and damage of groundwater pipelines and how to alleviate ground collapse has become an urgent goal for many scholars.In this paper,transparent soil test technology is used to analyze and study the influence process of subgrade soil erosion caused by pipeline fracture and leakage under different hydraulic conditions and the setting of geogrid reinforcement in appropriate areas.In this experiment,the scale model test is used,the model size is 300 * 300 * 300 mm,and the model is made of transparent soil,so that the whole test process can be visualized.The development process of erosion cavity,the shape and size of erosion pit and the development time of erosion cavity caused by water leakage erosion in the experiment were observed and recorded.The particle movement in collapse was analyzed by difference method,and the depth,size and particle movement under different hydraulic conditions were compared.The appropriate area of geogrid reinforcement arrangement is determined,and it is verified that geogrid reinforcement can effectively alleviate the erosion collapse phenomenon in the test.It provides a basis for practical engineering to solve how to alleviate roadbed collapse accidents.The main work is as follows :(1)The visual model of internal erosion test is designed independently.The transparent soil with good sample preparation is loaded into the model for test.The speckle is generated by laser irradiation,and the internal overall erosion process can be clearly observed to realize the whole visualization.Through seven groups of indoor model tests,the effects of different hydraulic conditions,different pipeline fracture mouth sizes,and whether geogrid reinforcement is arranged on the development process,size,depth and development time of erosion pits were studied.(2)Through the difference analysis and comparison of the test pictures,the soil erosion range caused by pipeline fracture under different hydraulic conditions is mainly in the area directly above the fracture mouth.The soil is subjected to hydraulic erosion and the gravity of the soil itself to produce erosion pits.There is particle movement near the erosion pit.The level of particle movement in different regions is different.The whole soil can be divided into subsidence area,loose area,erosion area an d stable area.(3)According to the erosion results,geogrid reinforcement should be arranged.The reinforced area should cross the subsidence area and the loose area,and a certain pull-out area should be retained in the stable area,which can effectively alleviate the subsidence and settlement of subgrade soil.Especially under the pressure of half-pipe flow,the interlocking effect of geogrid on subgrade soil can effectively eliminate the secondary collapse of soil,improve the overall stability,and effectively reduce the loose area of soil.The layout of geogrid reinforcement at the fracture can also effectively reduce the occurrence of erosion areas.(4)When the pipeline is under the condition of no pressure,the erosion development is more uniform,and the whole collapse pit is conical column;setting geogrids can slow down the development of erosion pits.(5)When the flow in the pipeline is half-pipe flow,the erosion develops rapidly and is accompanied by secondary collapse.The final shape of the entire collapse cavity is similar to an ellipsoid,and there is a small erosion area at the nozzle fracture.The setting of geogrid can reduce the development of erosion pits to a certain extent,effectively eliminate the secondary collapse of soil,and inhibit erosion around the fracture mouth.(6)When the pipeline is full of pressure flow,the erosion develops rapidly and is accompanied by secondary collapse.Finally,the soil collapse cavity is shaped like a red wine cup,and there is a large erosion a rea at the pipe mouth fracture.Setting geogrid can make the whole test smoothly,effectively delay the development of erosion pit,and significantly reduce the formation of erosion area.(7)Through the comparison of test results,it is found that under different hydraulic conditions,the final erosion pit development is different.With the change of time,the erosion depth speed under the condition of half pipe flow is faster than that under the condition of full pipe flow and no pressure flow,but the final depth of half pipe flow and full pipe flow is almost the same and both are greater than that of no pressure flow;the stronger the hydraulic conditions,the larger the final size of the erosion pit.