Research On Damage Mechanism And Structure Design Of Culvert In Active Region Of Debris Flow

Debris flow is one of the most typical geological disaster along highway,and it seriously threats the roads,bridges,culverts and their structures in the southern mountain area.As the China-proposed Belt and Road Initiative gradually implemented and the Great Western Development Strategy in-deep continuously promoted in new period,Dong Chuan area is located in Xiaojiang activity fault zone,where the complicated topographical features and geological conditions has offered a favorable condition for frequently suffering of debris flows,especially the expending of human activities.At this exact moment,it is an urgent issue for highway traffic construction to solve problems of culverts eroded and damaged in the regions of debris flows along highways.Based on field studies,the condition of the broken culverts and the growth characteristic of debris flow disasters has been analyzed,the dissertation mainly focus on debris flow gully of Heishui River,damage mechanism of culverts were impacted and eroded by debris flows were studied by combination of theoretical analysis and field tests and numerical calculation and finite element simulation from impacting and excavating of debris flows,U-shaped culvert was designed,the integrated techniques ware analyzed and put forward.The main achievements on the research are as follows:(1)Time-space distribution characteristics for debris flow gully development was studied.There are 122 strips debris flow gullies in Xiaojiang basin,as the linear distributed density is 0.81 strips per km from Gong Shan to its estuary,and The linear density from Gong Shan to Dong Chuan is 1.25 strips per kilometers.(2)The main reason of culverts damaged was caused by debris flows constantly scouring and abrading,the rate of breakage is about 51%,the planned highway area of Dongchuan region has the largest number of slab culvert,slab culvert accounts for 53%,the rate of slab culvert's breakage is about 49% of culvert damaged culverts,circular culvert has the highest rate,reached to 68% of culverts damaged.(3)Deformation stage of debris flow directly impacting mainly includes arrangement stage for the load of debris flow rushing up,repeat stage of debris flow impact and dragging stage.The main stresses are concentrating in the foot of culvert pier which two-dimensional stress and displacement are analysizing when debris flows directly impact pier of the culvert entrance,and the maximum stress value is 0.91 MPa,and The maximum displacement value of 3.93 mm.Fluctuation of debris flow make stress and displacement of culvert change obviously,with the emergence of impact and erosion peak of debris flow,stresses of culvert's inside become more and more concentrated.The lower right side of the pier feet appears the maximum stress,the maximum stress is 0.718 MPa.(4)Three dimensional(3D)stress field and displacement field had been analyzed when debris flow was getting through the culvert,downside region of culvert body and culvert foundation where are the largest stress concentration,in which reflect the most serious damage by debris flow impacting and eroding and excavating,and the maximum stress value is 0.718 MPa,and and The maximum horizontal displacement value is 48.22 mm,3D model could have been presenting to the variation of debris flow's flow pattern and the process damage of culvert,in which could has been seeing more detailed and more comprehensive and in-depth then 2D model.Both 3D model and 2D model could have been reflecting the damage process,of which is a process from eroded impacted to excavated to abraded to damage,at the same time,it's a process from micro-scale deformations to macro widespread damages.(5)Hydraulics factors of the culverts that are included rectangular bad and horizontal bed and round-bottomed bed and half elliptical foundation bed and V-sharped bed and ladder bed have been explicitly calculated or measured.Taking the constructi on technology and quality control into consideration sufficiently the comprehensive assessment that half elliptical foundation bed of culvert is the optimal hydraulicsection,thickness of the foundation bed is 0.6m.At last,U-sharped culvert has been designed by make extensive use of half elliptical foundation bed.(6)With the presence of the impacting and eroding peak debris of flow debris,flow debris fluidize a most constantly changing,at the same time,the stress of culvert foundation up-bottom and downside region of culvert wall and joints are place where are most concentrated,Later then,the biggest changes are about to happen in displacement,the corner that is stress concentration will be stripped from the adhesion of culvert.As a whole,there is significant positive correlation between the variation of culvert's stress and displacement and impact value of flow debris.Debris flow,vehicle load,earthquake can respectively change stress field and displacement field of U-shaped culvert.the change of culvert's stress and displacement can be exacerbated by vehicle load and earthquake when debris flow acts on culvert.Compare stress and displacement of mud-rock flow erosion type rectangular and horizontal bed culverts and U-shaped bed culvert,the degree of stress concentration and the maximal displacement peak decrease obviously.It significantly proved that U-shaped culvert can effectively alleviate the damage degree of culvert.(7)By comparing three kinds of energy dissipation type that are mainly include common type,wave type and ski-jump type,the ratio of dissipation of ski-jump type is best.It can promote the property of cracking resistance and toughness when hydraulic concrete are mixed with steel fibers and steel bars.Mud sandy suitable for the buffer layer between the foundation and foundationTime-space distribution characteristics and dynamic characteristics of Dong chuan debris flow were analyzed systematically.By further researching on damage mechanism culverts,stress field characteristics of new type culvert under the condition of multiple load was explored.It will not only contribute to deeper understanding the flow variation of debris flow and the changing rules of the displacements and stresses of culvert,What is more important is that a reasonable scheme for crossing the middle and small scale debris flow gully is in applicability provided that the U-shaped culvert was systematically designed.And especially the results provide theoretical basis and technical supports for design and research of new culverts in regions of debris flows along highways.