The dissertation work presents a new solution to the topical issue concerning the method of forecasting general and maximum erosion at the floodplains in the area of bridge crossings, based on the positions of mechanics of heterogeneous environments.
The depths of the floodplain section of the opening of the bridge after smelting are determined by the non-motorized velocity for the soils constituting the section. The review of the work showed that, to date, there is no uniform approach to considering the influence of soil heterogeneity on the non-ozmic velocity, indicating the difficulty of evaluating the criterion of the maximum stability of a heterogeneous particle mixture, that make up the understanding. Presented analysis of the physical model of flood flux formation relative to sediment distribution during floods, flooding in the area affected by the bridge in the future made it possible to obtain an analytical approximation for determining the amount of erosion to the floodplain, taking into account the distribution of velocity within the layer of plants.
These equations are derived from the general three-dimensional hydrodynamics equations by integrating the latter along the flow depth. As a result, a law was defined for the vertical distribution of the average hydrostatic pressure. In the case of fixed motion, taking into account the estimation of the order of terms and dependencies for turbulent stresses, after transformation, stable equations of the two-dimensional currents of the grasslands with the vegetation, taking into account the force factors were obtained. Force factors cause resistance to the flow of vegetation in floodplains, to the erosion of fine-grained soils and to the resistance to the flow of bridge supports.
To obtain an unambiguous solution of the considered problem, boundary and initial conditions were added to the presented closed system of original equations. These conditions make it possible to determine the level of a free surface of flow and the zone of influence of a bridge crossing at different stages of the estimated flood.The proposed approach is based on a change in the properties of the central stream of the river in the area of the artificial influence of the bridge structure. In order to implement the discrete analogues of the main transport equations in the compression and vegetation zones, the following parameters have been provisionally determined: transformation coefficients of the expenditure of the channel flow, the flow rate of the flood streams, the dynamic speed of the catchments, coefficient taking into account the uneven distribution of speeds by vertical, the universal parameter of the shape of the river flow, the turbulent exchange coefficient, the mean turbidity vertically, the resistance coefficients of the elements of vegetation, Resistance to the removal of soil grain in the bottom region, resistance to the flow of bridge supports. Based on finite-difference analogs of transfer equations, the distribution of velocities and depths in estimated sections was calculated. By iteration, the longitudinal velocity in a flood flow with vegetation elements was determined, according to the distribution of the mud and the resistance when the bridge supports are rounded.
The results of the calculation of washout on floodplain areas of a sub-bridge watercourse of the lowland river Siversky Donets on the T-05-14 road in the Donetsk region were obtained. It has been established that the development of common channel deformations in the bed and at the floodplains takes place on a stretch from 1,195 m to 2,144 m long. The distribution of river depth is obtained, which increases from 0,58 m to 2.17 m. The boundaries of the areas of compression and growing according to the change in the slope of the water surface are defined. As river flows increase, the parameters of the compression zone also increase from 246 m to 1382 m, and the vegetation zones decrease from 949 m to 762 m. The depth of a flood flow after a washout was determined based on the ratios of actual and flood-free velocities. When compared with the initial bottom marks, the general washout of the larger floodplain is 0.96 m, that of the smaller floodplain – 1.28 m. The maximum washout depth at the higher floodplain is 2.75 m, and at the lower plain is 1.91 m, which is due to the effect of the drag on the fairing of bridge supports and the compression of the flow between them.
