Study On Structural Characteristics Of Double-river In Small Watersheds Of Mountainous Cities

Before the urbanization of small watershed in mountainous area,ravines are deep and terrain is undulating.In the urbanization process,river facilities are usually built from the downstream to the upstream.The design is based on multiple objectives such as flood control,drainage and water ecology,and a double-layer river construction scheme is proposed.At present,there is no relevant research and regulation on the double-layer in theory and code.In the design stage,it is customary to consider the upper open channel and the lower box culvert separately,but its whole actual structural characteristics are more complex.In view of the above problems,this paper combines the existing seepage analysis of embankment slope,stress analysis of underground frame structure and theoretical analysis of fluid-solid coupling calculation,and uses the large-scale finite element software Abaqus to conduct fluid-solid coupling analysis of the structural characteristics of double-layer river in small watershed in mountainous areas under different working conditions,and obtains the following conclusions:(1)under the condition of static water level and water level falling,the height of the model's escape point is basically unchanged;The distribution of pore pressure infiltration line in static water level and water level drop condition is similar,but the distribution of pore pressure infiltration line in rainfall infiltration condition is different.(2)Under various working conditions,the maximum flow rate occurs at the location of the geomembrane of the bank slope and the location of the drainage hole of the box culvert,and there is a risk of contact scouring and osmotic damage.(3)Under various working conditions,the stress distribution of soil and rock mass of the box culvert roof is similar.On the whole,the intermediate stress value of the box culvert roof is smaller than that at both ends,and there is a phenomenon of stress concentration at both ends of the culvert roof.At the same time,there is a serious phenomenon of stress concentration in the soil mass not far from the culvert side.Under rainfall infiltration condition,plastic deformation of culvert side soil may occur.The maximum vertical stress of box culvert occurs at 3m static water level.The faster the water level drops,the bigger the maximum vertical stress of box culvert increases.(4)Under each water condition,the maximum settlement occurs in the upper leftand right corner of the model.The maximum horizontal displacement occurs at the water-side of the bank slope.(5)Under various working conditions,the maximum bending moment of the box culvert occurs at the midspan position of the bottom plate,and the maximum axial force occurs at the bottom of the side wall.The water level drop of the upper channel has certain influence on the internal force of the lower box culvert structure.In the whole process of rainfall infiltration,the increment of bending moment and axial force is very small,and the rainfall infiltration of upper river has little influence on the internal force of lower box culvert structure.(6)Internal force of the box culvert standard empirical formula calculation results and the calculated results,it is concluded that: standard empirical formula calculating the bearing capacity limit is numerical simulation,the control values of 1.2 ~ 4.01 times that in the similar engineering(mountain city watershed double channel,separate structure,buried depth is larger)box culvert design,the standard empirical formula calculation results safe enough.