Study On Dynamic Characteristics Of Mozigou Debris Flow And Its Impact On Bridge Pier Of Wenma Expressway

For the sake of the promotion of the"One Belt and One Road"construction better and faster and the implementation of the strategy of developing the western region in depth,and give full play to the advantages of the western region in terms of resources,minerals and tourism,the expressway-based rapid transit network in the western region has entered rapid construction period.However,be limited to the complex and varied topography,it is inevitable that the road will be routed through the debris flow activity area,road debris flow disasters occurs from time to time.The destruction of the road by mudslides is point-like and the roads are linear,while the affected areas are fragmented,and the economic losses caused by them are enormous.Therefore,it is imperative to study the development characteristics,prevention and control of road debris flow and the protection and design of related highway buildings.Based on the study of the basic characteristics and dynamic characteristics of the Mozigou and combined with the basic theories of computational fluid dynamics and fluid-solid coupling.This study selects the Keku Super Bridge through the debris flow and the mouth of the K56 Mozigou in Wenma Expressway as the research object.The appropriate mathematical model and simulation parameters are selected,and the external 3D modeling software and ANSYS Workbench are combined to complete the3D flow field numerical simulation of the Mozigou accumulation area at different frequencies and the Mozigou debris flow impact on the Kekute Super Bridge pier.The dynamic response of the fluid-solid coupling numerical simulation.The main conclusions are:(1)According to the field geological survey,aerial photography and indoor analysis,the basic data such as the geomorphology,geological structure,geological lithology,meteorological hydrology and social environment characteristics of Mozigou are obtained,and based on this,from the development characteristics and development trend of the outburst flow in the debris flow of Mozigou are analyzed in the next three aspects:characteristics,provenance and water source characteristics.The dynamic characteristic parameters of the debris flow in the Mozigou are obtained by the combination of field investigation,experiment and formula calculation.(2)Through investigation,it is found that the debris flow of Mozigou is a large-scale low-frequency transitional viscous debris flow in the storm gully.The debris flow is in the development stage,with the strong intensity of the debris flow and the easy-to-issue degree.The dynamic reserve of the source in the Mozigou ditch is 783,300 m~3,which is mainly controlled by the H3 landslide in the ditch.Through on-the-spot investigation,it is found that the current H3 landslide is in the stage of creep deformation,and the trailing edge crack has been trapped,and it has been destroyed under special conditions such as heavy rain or earthquake,which causes mudslide.(3)By combining AutoCAD,Rhino and ANSYS ICEM CFD to establish a three-dimensional geological model,and using ANSYS CFX computational fluid dynamics general simulation software,the three-dimensional flow field numerical simulation of the grouting trench accumulation zone at different frequencies was carried out,and the simulation was verified.The rationality of the method,and based on the numerical simulation results,the risk range of debris flow in different debris flow bursts is predicted.(4)By setting the monitoring points in the flow field,it is concluded that the bridge pier with the greatest impact on the debris flow is K56+304.The existing basic theory is used to simplify the mechanics of the debris flow impact pier,and based on fluid-solid coupling numerical simulation,The volume distribution map,the velocity streamline distribution map and the pressure distribution map of the pier surface and the bottom of the pier are obtained at different times in the flow field of the debris flow under different burst frequencies.The dynamic characteristics of the process of the debris flow impacting the pier are completely demonstrated.At the same time,the dynamic response analysis(displacement,stress and strain)of the pier under impact is also analyzed.The results of the analysis guide the construction and design of the protection project of the pier with the impact of debris flow.(5)The Mozigou debris flow has the possibility of exploding debris flow.It is necessary to set up a rainfall monitoring station upstream of the Mozigou watershed.In order to guide the early warning work,the maximum principal stress and displacement under each working condition will be simulated.The maximum rainfall corresponding to the design of different outbreak frequencies corresponds to the maximum rainfall.It is found that the principal stress and displacement increase exponentially with the increase of rainfall,and the corresponding damage caused by the debris flow of the Mozigou to the Keku Super Bridge is obtained.Alert level rainfall threshold and hazard level rainfall threshold.