Investigation of the influence of extreme floods on the stability of protective dams (using the example of Hanoi city)

Abstract

According to the territorial development plans of the city of Hanoi, there is a need to build a new dam system to ensure the normal functioning of the riverside areas. Therefore, the solution of the problem of analyzing the causes of the loss of stability of the of dam slopes protecting the city from floods is of particular relevance. When assessing the possibility of dam failure as a result of a landslide process, the most important indicator is the appearance of cracks in the body of the dam. The possible mechanisms of loss of stability of the dam slopes as a result of changes in the hydrological situation are considered, their rationale based on the results of mathematical modeling is given. The studies used a “geotechnical” approach to estimating pore pressure values, which is new in Russian practice. This approach, without excluding the need to perform hydrogeological modeling, makes it possible to assess the stability of the dam slopes when the level of flood waters changes. The generalized engineering-geological model of the lithotechnical system (LTS) of the dam can be represented as the following scheme: at the base of the LTS lies an aquifer, represented by sands of various grain sizes and flowing sandy loams, which is overlapped by low-permeable loamy and clayey soils. Two scenarios for the violation of the stability of the dam slope are considered: when the groundwater level rises during the period of extreme flood; due to the rapid drawdown of the level of flood waters. By the methods of mathematical modeling it is proved that the decrease in the stability coefficient occurs in both cases. Thus, it is shown that the collapse of the dam slopes is possible both when the groundwater level rises during the flood period and during a sharp decrease after the end of the flood. At the same time, in the first case there will be a slide of the slopes falling in the direction “from the river”, and in the second — “to the river”. This fact must be taken into account when developing measures to strengthen the slopes of existing dams, as well as when designing a new dam system in Hanoicity.