The co-disposal of coal waste rock with fine benign waste can potentially aid in the prevention of acid rock drainage (ARD) by restricting the access of oxygen and water to sulfide bearing rock surfaces. However, in prevention studies, optimising the packing density of waste rock dumps remains a challenge. Large voids between the waste rocks are prevalent. This low degree of particle-particle interlocking reduces the packing strength that results in high seepage rates that contribute to oxidative weathering of the sulfide bearing rocks. Well-developed material placement protocols are therefore needed to ensure the long-term success of ARD co-disposal prevention methods. To aid in this design, particle packing models were explored to improve the packing performance of coal waste rock and coal fine waste. Consistency in packing was initially evaluated for the dry material using slump tests and thereafter extended to wetted fractions to maximise the solid concentration in the packed bed. An improvement in packed bed stability and a reduction in void content was significant under wet conditions relative to dry conditions as evidenced by the high packing density and low voidage. This refined packing indicates the potential for long-term ARD prevention by restricting access of natural oxidants to acid generating waste rock surfaces.