This paper reports on preliminary laboratory geotechnical investigations conducted to explore the compaction and unconfined compression strength (qu) behaviour of granular waste mixtures of coal wash (CW) and steel furnace slag (SFS). Compaction was conducted under relatively dry and submerged conditions. Proctor compaction test results show that the higher the SFS content, the greater the maximum dry density of mixtures, while the optimum moisture content (OMC) is rather constant. However, for mixtures compacted at their OMC, qu decreases with increasing SFS content. In contrast, for mixtures compacted under submergence and cured in seawater for up to 28 days, qu increases with both the SFS content and curing time. The preliminary findings suggest that CW-SFS mixtures have good potential as fill for port reclamation. However, two different mixtures, in terms of SFS content, should be used for dry and submerged fills.