Densification of Pond Ash by Blasting

Fly ash from thermal power plants is disposed, in huge quantities in ash ponds, which occupy large land areas otherwise useful for agriculture, housing, or other development. For effective rehabilitation of ash ponds, densification of the slurry deposit is essential to increase the bearing capacity and to improve its resistance to liquefication. Extensive field trials were carried out to evaluate the effectiveness of deep blasting for densification of deposited fly ash. Ninety explosions comprising 15 single blasts, with varying depths and quantities of charges, and 3 group blasts, each having 25 charges placed at various spacings, were carried out. The compaction achieved in terms of an increase in relative density was evaluated from surface settlement measurements. Extensive field monitoring was undertaken through pore-water pressure measurements, vibration measurements, penetration tests, and block vibration tests. For the average charge of 2–4 g of explosive per cubic meter of untreated deposit, the average relative density was found to improve from 50% to 56–58%. Analysis of the test results indicates that deep blasting may be an effective technique for modest compaction of loose fly ash deposits. The field testing program presented in this paper provides valuable information that can be used for planning blast densification of fly ash deposits.