Vacuum consolidation of soda-ash tailings

The Solvay process, widely used in industrial production of soda ash, generates a large quantity of tailings. The tailings consist of fine solids suspended in alkaline water that remain in a loose state, causing environmental concerns. An alternative solution for the management of sodaash tailings is presented in this paper, that is, the use of a vacuum pre-loading technique to consolidate the tailings so that they can be used as a foundation material in industrial sites. This paper presents the procedure and results of vacuum pre-loading consolidation of soda-ash tailings in a field trial. A vacuum pressure of approximately 90 kPa was applied to a 45 × 45 m area to a depth of 8 m via prefabricated vertical drains. The results showed that after 66 days of vacuum pre-loading treatment, the water content of the soda-ash tailings was reduced by 12·3% to 42·4%. Also, densification was shown by changes in void ratio, unit weight and settlement. The tailings were consolidated to a material with the undrained shear strength ranging from 22·3 to 34·4 kPa, compared with the initial value of 7·1–14·5 kPa. The allowable bearing capacity of the tailings reached 120 kPa as tested from the static loading plate test. The vacuum pre-loading method has shown to be a fast, effective and economically feasible alternative for in situ consolidation of soda-ash tailings.