Operation & Maintenance of Tailings Earth En Dam Specially For Disposal of Fly Ash from Thermal Power Stations
Several tailings earthen dams have failed during monsoon. Due to failure of tailings dam, stored tailings waste gets release in downstream area causing environmental hazard. Ash produced by combustion of coal in thermal power stations are stored in ash pond. No well-defined provision of operation and maintenance exists for ash pond. Therefore, this paper describes various issues related to operation and maintenance of ash pond.
DENSIFICATION OF DEPOSITED ASH SLURRY
In India, ash content in coal is usually high and percentage utilization for construction is limited. As a result, about 90 to 95 percentage of the ash generated has to be deposited in ash pond. The present ash generation is about 75 million tonnes and it is likely to exceed I 00 million tonnes by the end of this century. During the last decade, several laboratory studies have been made on densification of deposited ash slurry by vibration, application of vacuum, electro osmosis, etc. In last few years, with assistance from Department of Science and Technology, field experiments have been carried out to densify the deposit by vtbro flotation technique and also by explosives. This paper describes brief literature review on the subject andsummary of compaction achieved in field by vibroflotation as well as explosives. Based on the study canied out so far, it appears that densification in ash pond is very effective for rehabilitation of the area for housing or other use. It also eliminates chan~ Qf liquefaction during earthquake.
Compaction of alluvial sands by deep blasting
The Jebba Hydroelectric Development, Nigeria, presently under construction, features a 42 m high zoned rockfill embankment founded on river alluvium up to 70 m in depth. The riverbed alluvium comprises fine- to medium- to coarse-grained, quartzitic sands with traces of gravel. The relative densities of the sands vary appreciably in both the vertical and horizontal directions. During the dam design it was found that it would be necessary to densify the loose to medium dense portion of the river sands to maintain settlements within acceptable limits and to withstand design earthquake forces. The top 25 m of the river alluvium is densified by the vibrocompaction method, and below this level down to depths of 40 m the alluvium is densified by blasting. There is no precedent found in the literature for densification by blasting at such depth. This paper presents details of a test program and the production work. Test results conclusively show increases in static cone penetration resistance in loose sand layers...