Study On Flow Characteristics Of Longitudinal Section Of Single Bend River In Mountainous Area

In the design of the Xihan Expressway,taking into account the protection of the ecological environment of the Qinling Mountains,longitudinal bridges were adopted in many sections along the river to replace the excavated and filled roadbed.The piers of the longitudinal bridge section are densely arranged along the river channel,especially in the sharply curved section where the flow velocity is large,the impact force of the current flow and the impact force carrying the rolling stones can threaten the substructure of the bridge.Aiming at the flow characteristics of longitudinal bridges in single-curved rivers,the effects of the spans and different layout patterns of longitudinal bridge piers in 70° bends on the flow velocity and pressure distribution characteristics of the bends are studied by means of indoor model tests and numerical simulations.On this basis,a numerical simulation was carried out on the K44+800 section of the Xihan Expressway,and protection suggestions were put forward.First of all,this paper analyzes the main factors that affect the flow pattern of the longitudinal bridge layout section.On this basis,indoor experiments with different spans(52cm,64 cm,80cm,120 cm,160cm)and different pier layout schemes(parallel layout,staggered layout)were designed and carried out.The test results show that:(1)The smaller the span of the pier,the greater the overall velocity of the flow field;the pressure change law of each working condition is similar.The pressure in front of the pier is the largest,and the negative pressure zone is on both sides and behind the pier.The pressure of the convex bank is less than that of the concave bank.The pressure of the concave bank gradually decreases along the way.The pressure of the convex bank first decreases to the beginning of the curve and begins to increase.(2)When the bridge piers are arranged in parallel,the flow velocity changes of the piers of the small and medium-span bridges are similar.The flow velocities on both sides of the bridge piers on the upstream side of the bend are larger.The piers of the cross section of the bridge piers in the middle and downstream of the curve are affected by the wakes around the piers.The velocity of the upper and lower velocities on both sides of the piers is small and the central velocities are large.The flow velocities on both sides of the bridge piers have increased.The flow velocities on both sides of the bridge piers near the concave bank increase significantly on the middle and downstream sections of the curve.(3)When the bridge piers are staggered,the flow velocity changes of the piers of medium and small span bridges are similar.The flow velocity on both sides of the first pier near the convex bank on the upstream of the bend increases significantly,and the first pier on the middle and downstream of the bend The lateral velocity is affected by the flow around the pier.The velocity in the middle of the two sides of the pier is greater than the upper and lower parts.The second pier has a similar change,but the velocity increase on both sides of the pier is less than the first one.The flow velocity on both sides of the second bridge pier near the concave bank located on the downstream side of the curved bridge is greater than that on the upstream;there is almost no effect between the rows of bridge piers of the large-span bridge.Increase.(4)Due to the influence of centrifugal force,the streamline between the first row of bridge piers and the concave bank wall and the first and second row of bridge piers is dense,and the streamline between the third row of bridge piers and the fourth row of bridges is sparse.Finally,the single-bend longitudinal bridge section of the K44+800 section of the Xihan Expressway is numerically simulated.The results show that the right side of the convex bank on the upstream of the bend and the right side of the bridge pier on the right side of the bend have a large velocity.In order to prevent erosion damage,the upstream convex bank slope and the two sides of the middle and downstream bridge pier should be protected.