Influence of the air phase on water flow in dikes

Abstract

Abstract. Numerical models are often used to describe flow and deformation processes occurring in dikes during flood events. Modeling of such phenomena is a challenging task, due to the complexity of the system, consisting of three material phases: soil skeleton, pore water and pore air. Additional difficulties are transient loading caused by variable in time water levels, heterogeneity of the soil or air trapping. This paper presents a brief review of the influence of the air phase in soil on water flow and pore pressure generation, with focus on applications related to stability of dikes, earth dams and similar structures. Numerical simulations are carried out to investigate the differences between the Richards equation and the two-phase flow model, using an in-house code based on the finite volume method. A variety of boundary problems are considered, including seepage through flood dikes, dike overtopping and water level fluctuations. Special attention is paid to the problem of air trapping, which occurs when water flows over the top of a dike. Such a phenomenon occurred during experiments on model dikes reported in the literature, ultimately leading to development of cracks and damages in dike structure.

Simulations of air and water flow in a model dike during overflow experiments

“…During the overflow experiment on a model dike, a large amount of air was trapped which finally led to the formation of macropores and cracks. The general pattern of water infiltration observed in the experiment was in qualitative agreement with earlier numerical simulations for real-sized dikes [43,44]. In this work, an attempt was undertaken to reproduce the experimental results with numerical simulations based on a two-phase flow model with parameters estimated from the granulometric curve using the modified Kovacs method by [2].…”

“…Such a situation occurs when water infiltrates the domain from all sides, leaving no continuous path for air to escape. This occurs, for example, in flood dikes or earth dams during extreme flood events, when water flows over the top of the structure [43,44]. In order to investigate this phenomenon, a series of experiments were carried out in the Institute of Hydro-Engineering of the Polish Academy of Sciences in Gdańsk.…”

Numerical simulations of overflow experiments on a model dike

“…The statistics published in [1] showed that occurrence of the overflow caused approximately 40% of all dike failures. A number of authors have studied the mechanism of dike failures due to overflowing [2,3,4,5,6,7,8]. They are in agreement that fast raise of the water table level cause air trapping on pore and structural level.…”

“…mostly air-filled) area surrounded by the water-saturated material is created. Both phenomena are connected with the loss of macroscopic homogeneity which is particularly undesirable in dike structures [8,9,10,11]. This problem is difficult to investigate in-situ due to the lack of appropriate monitoring of the water saturation.…”