Study On Erosion Theory And Stability Of Subgrade Slope Along River Bend

The concave subgrade slope has been suffering from the erosion of the flow in river bend. Therefore, this paper discussed mechanisms of the circulation flow creation in a curved channel by the way of theoretical analysis and experimental verification. The computing formula of water surface super-elevation, circulation flow velocity and boundary shear stress on concave bank were verified by experimental and field data, and the computing and testing results were very similar.In this paper, with force analysis of a single sand particle on the concave bank-subgrade slope in river bend, the incipient motion conditions for non-cohesive and uniform sediment were firstly derived and tested by experimental field data. The calculating formula of the incipient motion velocity of sediment on concave bank slope was gained in the light of three threshold motion judgment criterions, such as weak, moderate and general motion, by the way of analyzing the threshold motion probability and average percentage. It was firstly found that the incipient motion of sediment on concave bank-subgrade slope be advanced in result from the increasing of affection coefficients that were the subgrade slope angle and the spire degree in continuous bottom circulation flow. According to the experimental observation of concave-bank subgrade slope deformation, It was affirmed that their main erosion process include circulation flow scouring and thier intermittent failure. Finally, the equations of anti-scouring steed slope angle were obtained, by means of creating and analyzing three-dimensional force model for single sand particle on concave bank-subgrade slope.On the other hand, it had be created a generalized typical model about the subgrade suffering from scouring and dilapidation. and then, the subgrade whole stability was discussed through analyzing some limitations that were water-surface elevations, phreatic-surface elevations, bank slope angle and lateral scouring distances. Further more, calculating methods about pore water and hydrostatic confining pressure were put forward. and it has been clear that the law of subgrade whole stability is readjusting by various limitations, according to computed results. Finally, protection measures for subgrade along river bend were discussed at the aspects of direct and indirect protection methods.