Design of fly ash dyke for seepage and stability analysis

Abstract

In India, due to progressively increase in number and capacity of coal based thermal power plant huge amount of fly ash is generated. In current scenario only 40-50% fly ash are used and rest of the fly ash is disposed of and restored in ash pond with dyke to reduce the land wastage. The failure rate of ash dykes are much higher than that of dams because seepage analysis is not taken into account while design of the former. So, construction of safe ash dyke becomes a top priority for engineers as its occasional failure creates havoc in safety of surrounding people. It causes economic losses as well as environmental and water pollution which is dangerous for both human and aquatic life. There is no well-defined design procedure and codal provision for design and maintenance of fly ash dam in India. This project describes about the design of ash dyke in various stages constructed in various methods with the help of finite element package PLAXIS considering various parameters representing varied environmental conditions. A laboratory model has been developed and it is found that the phreatic line is fairly matching with our numerical analysis result. Due to limited time, practical model variation could but made but numerical analysis are made for different heights of water at top of fill side, different rates of rapid drawdown, providing different width of vertical sand drains. The steady seepage analysis is done using PLAXFLOW module of PLAXIS and it is found that factor of safety is less compared to that of dry condition. Based on laboratory investigation it was observed that fly ash is dispersible. Further phreatic line does not remain within body of dyke when sand drains and toe filters are not provided, which may lead to its leakage. Then by using vertical sand filters of varying widths, dykes are analyzed and the one having minimum deformation is chosen.