Experimental Study On Hydraulic Erosion Characteristics Of Subgrade Filler Of Highway Along The River In Mountainous Area

The problem of subgrade scouring of highway along the river is one of the main disasters threatening the safety of highway in mountainous areas.During the construction of highway projects in mountainous areas,the line is mostly extended in the form of mountain and river,and the subgrade is mostly in the form of half filling and half excavation.Therefore,the subgrade of highway along the river has been washed and eroded by the river for a long time,especially in the season of frequent mountain torrents.Therefore,the disaster of subgrade damage along the river caused by scouring often occurs.The scour performance of embankment slope geotechnical filling materials is very important to the study of anti scour,in which the scour rate and starting shear stress are the two main parameters to describe the anti scour performance of geotechnical materials.Relying on the Karakoram Highway(KKH)flood disaster treatment project,this paper studies the variation law,influencing factors and theoretical model parameters of scouring rate and starting shear stress of mixed soil samples with different compactness and clay content by using the methods of physical test,theoretical analysis and numerical simulation.Selecting typical subgrade fillers,the erosion test of mixed soil samples with different compactness and different clay content is carried out by using erosion function analyzer(EFA),the current determination method of starting shear stress is analyzed and summarized,the simulation of erosion performance of soil samples with different compactness and different clay content is carried out,and the medium coarse sand and According to the distribution form of clay and the scouring failure mode of mixed soil samples,the applicability of different scouring rate models is studied.The research results can provide a basis for the selection of subgrade filling materials and construction control along the river.The main work and research results of this paper are as follows:(1)According to the scouring test results of mixed soil samples,the filling form of particles in mixed soil samples with different clay content is closely related to the scouring failure mode of soil samples;Combined with the scouring rate curve,the method of selecting the starting shear stress of soil sample is determined;When the clay content of soil sample increases from 25% to 100%,the starting shear stress of soil sample increases from 2.4pa to 21.3pa;When the compactness of the soil sample increases from 90% to 96%,the starting shear stress of the corresponding soil sample increases from 7.1pa to 23.4pa,and its anti scouring performance is significantly improved.(2)When the content of cohesive soil in the mixed soil sample is 25%,the soil sample shows the characteristics of cohesionless scouring,and the scouring behavior is significantly affected by the cohesionless coarse sand.When the clay content is 50%,the mixed soil samples are mainly in the form of micro clusters composed of cohesionless coarse sand and clay.At this time,they show the characteristics of viscous scouring.With the increase of clay content,the viscous scouring characteristics of mixed soil samples become more and more obvious.(3)The critical clay content of the measured mixed soil samples in this study ranges from 25%to 50%.Combined with the soil skeleton theory,when the content of coarse sand in the soil sample is greater than 65%,the nature of the soil is determined by the skeleton of the coarse sand.When it is less than this value,the clay separates the coarse sand from each other and cannot effectively form the skeleton.The test results are in good agreement with the theoretical analysis,which verifies the reliability of the test results.(4)The applicability of over shear stress model,dimensionless over shear stress model,Wilson model and parameter dimensionless Wilson model to the scouring performance of mixed soil samples is evaluated.The fitting results show that the over shear stress model and dimensionless over shear stress model are more accurate than Wilson model and parameter dimensionless Wilson model in predicting the scouring rate of cohesionless mixed soil samples.Wilson model and parameter dimensionless Wilson model are more suitable for predicting the scouring rate of cohesionless mixed soil samples than dimensionless over shear stress model.(5)The applicability of Wenyu-Ergun mixed drag model is verified by simulating the filling scouring process with computational particle hydrodynamics software,and the motion characteristics of soil particles in the scouring failure process of soil sample are analyzed.Under the action of scouring flow,the failure of soil sample shows a multi starting point and progressive centripetal failure mode;The residual cohesion is used as the index to measure the scouring performance of each soil sample.When the clay content increases from 25% to 100%,the residual cohesion of the corresponding soil sample increases from 18.5k Pa to 82.3k Pa,which is increased by3.5 times;When the compactness of the soil sample increases from 90% to 96%,the residual cohesion of the corresponding soil sample increases from 6.5k Pa to 55.8k Pa,an increase of 7.6times.