Hydrodynamic analysis of an unsteady pressureless filtration flow in earth cofferdams

Hydraulics and Engineering Hydrology
Authors:
Vitaliy Sergeev Evgeny Kotov Svyatoslav Horobrov Mohanad Muayad Sabri Darya Nemova
Abstract:

Non-pressure filtration flows with a free surface, on which the fluid pressure is a constant and equal to the external atmospheric pressure, are essential characteristic of groundwater filtration through such hydraulic structures as, dams, water drawdowns, drains, foundations, and pits during their drain. The problems of fluid filtration in porous media are distinguished by a variety of boundary conditions for the desired complex filtration potential, geometric and physical characteristics of the filtration flow. Solving such problems by analytical methods becomes significantly more complicated due to the nonlinearity of the equation describing the filtration movement, the presence of a free surface and the geometry of the slopes of the structure. An alternative to their solution is the use of numerical methods for estimating unsteady free-flow filtration flows. This research is dedicated to developing a hydrodynamic analysis approach of the process of unsteady filtration by the methods of computational fluid dynamics on the example of a rectangular cofferdam of various configurations to apply the results in the design of hydraulic structures. Numerical modeling of an unsteady free-flow filtration in a rectangular cofferdam using the finite volume URANS method (ANSYS FLUENT) and finite-element method (PLAXIS 2D) was carried out. The depression curve evolution through time was obtained. Also, numerical results have been compared both with the experimental results and classical theoretical assumptions. Was found that the constructed models both for finite-volume and finite-element methods are consistent enough with the experimental data, and on the other hand, theoretical assumptions don’t agree with experimental and numerical data. Further, the filtration patterns in rectangular cofferdams with different drain positions were obtained using the developed calculation model, which allows to choose the most effective drain position for different purposes.