In-situ stabilization of sedimented ash deposit by partial penetrating chemical columns.

This paper highlights the efficacy of partial penetrating chemical columns of sodium hydroxide (NaOH) in improving the geo-engineering and leaching characteristics of sedimented ash deposits through a comprehensive laboratory model testing program. Sedimented ash beds were formed in cylindrical tanks and treated with centrally installed chemical columns of either 9M or 18M concentration. After specified curing periods the in-situ moisture content, dry density, unconfined compressive strength (UCS), hydraulic conductivity, pH and concentration of major and trace elements were measured at different locations. Bell-shaped stabilized zones were found to develop around the columns with different magnitudes of strength. A series of sodium based geopolymeric compounds and calcium-based hydration products were identified in the treated ash specimens. Formation of these compounds is primarily responsible for modifying the geo-engineering properties of the sedimented ash deposits. The leaching of different elements from the ash bed is expressed in terms of contamination potential ratio (CPR), which is influenced by the reaction products, the pH of pore fluid and hydraulic conductivity. Test results indicate that chemical columns are quite effective in increasing the strength, reducing the hydraulic conductivity and leachability of elements along with modifying other parameters like in-situ water content and dry density.