Laboratory studies of the soil erosion and alluvium processes in the area of bridge supports

Abstract

The results of experimental studies of the process of bottom erosion during the construction of bridge supports under the protection of a sheet pile structure are presented. To protect the sheet piling box from the influence of ice floes during the period of ice drift, it is planned to install an ice-cutting protective device located upstream of the sheet piling box. In the process of conducting research, the principles of modeling the processes of river sediment transport taking into account the size of transported particles, non-erosive velocities and channel slopes are substantiated. Laboratory studies of the processes of forming erosion and alluvium are carried out for two cycles of parameters. At the same time, the influence of the ice-cutting device position relative to the sheet piling box on the amount of erosion and alluvium is studied. Experiments were carried out for various options of the ice cutter position relative to the sheet piling box; the ice cutter moved upstream along the axis of the tray with a step of 0.1 m (5 m for natural conditions). Based on measurements of bottom surface marks, two-dimensional erosion plans are constructed. For several options for the location of structures, the trajectories and directions of flow movement are determined by photographing the movement of surface floats, which makes it possible to create a grid of streamlines and determine the values of surface current velocities. An analysis of the velocity distribution over the surface and in the flow volume has shown that a horseshoe-shaped vortex is formed around the structure, with riffles and ridges appearing along its wings. A stagnation zone is established inside the “horseshoe”; in this zone the bottom remains relatively smooth. In the absence of an ice cutter, the main zones of soil erosion arise in the vicinity of the corners of the front face of the box, and alluviums form in the rear part of the structure. When installing an ice-cutting device in the shape of a triangle in front of the box, directed at an acute angle towards the oncoming flow, the erosion zones move to the vicinity of the corners lying at the base of the triangular ice cutter facing the box. The absolute values of erosion depth and alluvium height are reduced compared to the option without the ice cutter. When the ice cutter moves upstream relative to the box, a washout zone appears in the gap between the ice cutter and the box. The maximum values of erosion and alluvium occur in the absence of ice cutter and when placing the ice cutter at a distance of 200–300 mm from the box. The minimum values of erosion and alluvium are recorded when the ice cutter is placed close to the support box. With increasing flow rates and depths, the values of erosion and alluvium increase. Installing the ice-cutting device improves the hydraulic conditions of flow around the sheet piling box structure, which leads to a decrease in washout depths.