Applicability of coal bottom ash for the rehabilitation of clay mines: Potential as a backfill material

The higher cost associated with the restoration of clay mines and shortage of suitable filling materials have created many abandoned clay mines in Sri Lanka, which leads to many environmental and health issues. Coal bottom ash (CBA) generated during the coal combustion process as a by-product is a potential fill material. Currently, most of the CBA is open dumped into nearby lands creating environmental pollution and utilizing CBA as a fill material for clay mine restoration will be a suitable solution for these problems. Therefore, main objective of this study is to investigate the applicability of CBA as a partial or full replacement of the existing fill materials for clay mine rehabilitation. CBA produced from Lakvijaya coal power plant, Sri Lanka was used and the basic properties, shear strength parameters, compressibility characteristics and heavy metal leachability of CBA were investigated. According to results, CBA behaves as a poorly graded and non-cohesive material with a friction angle of 35. Further, CBA can be considered as a free draining material with low compressibility. The highly porous structure of CBA caused a lower dry density (975 kg/m3). However, it can be improved using 10 – 25% of soil to CBA. Further, the leachability potential of trace metals in CBA does not exceed the allowable limits. Thus, CBA would be a suitable fill material for clay mines restoration or similar uses.