Study On Scour Mechanism And Prevention Methods Of Roadbed Along Rivers In Mountain Areas

In western regions, highway is always located along rivers, and the roadbed is seriously scoured by water flow. For example, the water scour for Sichuan-Tibet Highway often leads to the road disruption. So, it is very necessary to study on the scour theory of water flow and prevention methods. The problem is studied in this paper based on the S&T projects of traffic construction in China's West, MOC: "Research of Control technology and hydrology Simulation of Roadbed along Rivers" (No.2001 318 792 57).Based on brief and commentary on local flow field around roadbed along river, scour mechanism and simulation, sediment motion characteristics in mountain rivers are analyzed, and the critical velocity of non-uniform sediment is discussed. Local flow condition, scour types, scour mechanism and factors influencing the scour depth are analyzed, then the model of roadbed stability analysis is deprived, considering such factors as water flow scour and water level change etc. Experiment study about water scour is undertaken, and scour depth with different factors about water discharge, flow depth, velocity, sediment and radius of concave bank is studied. Experiment study is also undertaken about the effect of the apron decreasing the scour depth of prevention wall. Hydraulic characteristics and scour mechanism of local flow field around spur dike is studied, and the simulating methods of the maximum scour depth and recirculation flow length around the spur dike is discussed.In the paper, a computing method of critical velocity for non-uniform sediment is discussed, which considers the non-uniform characteristics, the riverbed coarsening and interaction between coarse particles and fine ones. The model of roadbed stability analysis is deprived, and it can reflect on the changing progress of the stability coefficient during a flood, then it can help us to see whether the roadbed is safe and where is the most dangerous surface. Through the method of theoretical analysis and experiment study, the formula of the maximum scour depth of prevention wall in concave bank is put forward, and a parameter, which indicates the non-uniform sediment factor and formulate for calculating, is firstly proposed. The existing experiment data about the scour of spur dike is collected. Considering various influencing factors, the method of dimensional theory and regression analysis is used to deprive the formula for calculating the maximum scour depth around the spur dike, and the formula is applicable for non-uniform sediment river in mountain areas. As for the practice of prevention methods, a serious scour section in Sichuan-Tibet Highway is introduced as an example.