STABILITY STUDY OF ASH DYKES 4- THROUGH STONE COLUMN

Abstract

n India, due to continuous increase in number and capacity of coal based thermal power plants huge amount of fly ash is generated year by year. In current scenario only 40 to 50% of fly ash content is utilized and rest of the fly ash is dumped or disposed of and restored in ash pond with dyke structure to optimize the land wastage. So construction of safe ash dyke becomes a top priority as its occasional failure creates big problem in safety of surrounding people and plant itself. As we know that the performance of the structure is mainly based on the safety and serviceability requirement of foundations i.e. required bearing capacity and settlement. For the mega projects, it is necessary to adopt the innovations of using non-conventional methods when the characteristics of unsuitable soil or ground may impair the integrity, safety and serviceability of the structures. In such situations, the natural condition of poor ground needs to be altered or enhanced to meet the basic requirements, is termed as ground improvement. Stone column is one of the widely adopted ground improvement technique. The stone column (granular pile) is nothing but a vertical column element formed below the ground level with compacted and non-cemented stone chips. fragments or gravels. When the stone column is subjected to vertical axial loading, it undergoes significant vertical compression caused by the lateral straining or bulging of the aggregates. As the column simultaneously bulges and moves downward, the granular material presses into the surrounding soil and transfers stress to the soil through shear. On the basis of modeling performed with help of software PLAXIS, it is concluded that the bulging of the column increases the lateral stress within the fly ash which provides certain amount of additional confinement for the stone material. The effect of bulging is reduced by applying geosynthetic encasement material around the column which resists the lateral movement of stones towards the surrounding soil. Load capacity and confinement of the stone column mainly depend upon the stiffness modulus of the encasement and also upon the area of applying vertical load on the column alone or along with the surrounding soil.