Assessment of oyster shells and bottom ash for improvement of coastal saline soil through empirical tests

Abstract

Coastal soils have high salt concentration and poor drainage, which is unfavorable to the growth of crops. To utilize these soils effectively, salt removal is essential, and this can be achieved by improving the drainage properties of the soil. Oyster shells and bottom ash, which have large particles and high permeability, can enhance the soil's drainage when mixed, by improving particle size distribution. Furthermore, this approach provides an environmentally friendly solution for managing oyster shells and bottom ash, which often cause environmental issues when discarded. In this study, experiments were conducted to improve coastal saline soils using oyster shells and bottom ash. The desalinization performance was evaluated through leaching tests, while resalinization was assessed through capillary tests. Based on the results of these tests, optimal application methods for oyster shells and bottom ash were determined, and soil tank experiments simulating real-ground conditions were performed to assess practical applicability. The leaching test results indicated that mixing coarse-grained materials with soil significantly enhanced the leaching rate, with an increase of up to 20 times compared to the original soil. Meanwhile, the desalinization rate was more pronounced in soils mixed with oyster shells. Specifically, soil mixed with 40 % coarsely ground oyster shell reached a concentration equivalent to 20 % of the original salt concentration in approximately 28 min, demonstrating excellent desalinization performance. In the capillary test, it was observed that the capillary rise rate increased in the mixed soils, and a capillary barrier layer using bottom ash particles larger than 1 mm was found to effectively address this issue. In the soil tank tests, both desalinization and resalinization prevention were successfully achieved using coarsely ground oyster shells and bottom ash, along with a capillary barrier layer.