Failure Mechanism Of Subgrade Retaining Wall In Curved Channel Section Under Mountain Flood Action

Due to the mountainous and hilly terrain in China,the construction of roads must rely on the topography of its mountainous areas.However,the terrain in mountainous areas is extremely complex and variable.When selecting road routes,it is often necessary to choose along the river or stream,and semi-cut and semi-fill roadbeds are often used due to the need for road construction.One side of the road along the river is the bank slope of the river channel.In some special cases,protective structures such as retaining walls are added to ensure the service life of the road along the river.However,the subgrade slope and the base sediment of the retaining wall are percolated and eroded by the river.The cohesion and internal friction of the soil decrease continuously,leading to the outbreak of floods during the rainy season in mountainous areas,and the water level in the riverbed rises significantly.A large amount of water flows into the main river,and the speed of the flow and the water level rise sharply,which increases the impact and erosion intensity on the roadbed along the river multiple times,thereby exacerbating the degree of erosion and damage to the roadbed in the concave bank section of the river bay,causing the retaining wall to slide and the road surface to sink,resulting in poor traffic in mountainous areas.Therefore,the study of erosion and damage to the roadbed in the curved river section of the road along the river in mountainous areas is particularly important.This article studies the factors related to the damage of riverbank roads caused by flash floods,including flow velocity,flow rate,river bend angle,initial water depth,and riverbed quality,through experiments on the erosion of roadbed slopes by flash floods.At the same time,Fluent simulation software is used to simulate the degree of erosion of the roadbed along the river under different working conditions,and further analyze the mechanism and process of damage to the retaining wall of the roadbed in the curved river section.The main research contents are as follows:1.Analyzed the flow characteristics of flash floods in curved river sections,the types of damage to along-river highways caused by water erosion,and the mechanisms of damage.It was concluded that the factors affecting the damage to along-river highways in mountainous areas can be roughly divided into external factors,internal factors,and time factors.Further exploration was conducted on the entire process of damage caused by flash floods,including erosion of the concave bank of the river bay,erosion of the foundation of the retaining wall,sliding damage of the roadbed retaining wall,sliding of the roadbed,and subsidence of the road surface.2.Established a mechanical model for analyzing the stability of retaining walls under flood erosion,and combined with engineering examples to analyze the stability of roadbed slopes and retaining walls after the dry season and flood peaks.It was calculated that the difference in water level before and after the flood peak increased,and the antisliding stability of the retaining wall decayed faster than the anti-overturning stability.3.Constructed a scaled experimental model of mountain flash flood erosion of roadbed slopes with the engineering background of National Highway 549 from Shimian to Jiulong section K39+150-K39+450.Based on the principle of a single variable,four different working conditions of a dynamic bed model were adopted,and a retaining wall was added on one side of the river bay to maximize the reproduction of the lateral and longitudinal erosion depth of the roadbed caused by flash floods in mountainous areas.The damage process of the roadbed retaining wall was further explored.4.Recorded the process of flood impact on retaining walls under different working conditions,and discovered the phenomenon of lateral circulation in curved sections and the cross-sectional phenomenon of "concave erosion and convex deposition" in the river channel.Under the same working conditions,the water depth of each section of the roadbed retaining wall of lightweight model sand was higher than that of natural sand.The distribution law of water depth and flow velocity of the roadbed retaining wall slope in curved river sections was analyzed,and the results showed that the water depth and flow velocity were the highest at the exit of the curved section.5.The experimental phenomena of the horizontal and vertical erosion of the water flow on the foundation of the retaining wall during the mountain flood scouring of the roadbed slope were recorded.The erosion rules of the retaining wall foundation in different working conditions were analyzed.According to the results,it was found that the degree of erosion of the retaining wall foundation in different sections of the bend was different,and the overall erosion degree was concluded to be(bend exit)>(bend top)>(bend entrance).This may be due to the increase in water flow velocity and the resulting greater erosion kinetic energy under the influence of the circulation at the bend exit,which leads to the enhancement of the undercutting stress of the retaining wall foundation at that location,causing more obvious erosion and easier damage to the retaining wall.6.A three-dimensional model of mountain flood scouring of the roadbed was established,and different working conditions were simulated and analyzed using Fluent software.The simulation results showed that:(1)the dynamic pressure and static pressure from the bend entrance to the bend top were convex bank greater than concave bank,but from the bend top to the bend exit,the dynamic pressure continuously moved towards the concave bank side.(2)Under the same working conditions,the higher the flow velocity,the stronger the erosion of the retaining wall foundation,and the faster the sliding and damage of the retaining wall,and the deeper the sliding depth.(3)When the flow velocity is constant,the increase in initial water depth and turning angle accelerates the erosion of the retaining wall foundation.(4)The impact pressure on each section of the retaining wall in the curved river section is the largest at the bend exit,followed by the bend top,and the smallest at the entrance.(5)The simulation results were consistent with the experimental results.