Figure 1 shows the how the unconfined strength of one coal behaves for a wide range of top size and shows both the decreasing unconfined strength with decreasing top size for the large top sizes and more rapid increase unconfined strength with further reduction in top size.  The differing behaviour when coarse coal is removed and when fine coal is added was also found in the ACARP project 15070 .

As shown in Figure 2, all parameters relating to the size distribution of the coal have a significant influence of the maximum unconfined strength. One must remember for a fixed top size, whether 19mm as for Figure 2 or for normal product top size of 40 to 50mm, all these sizing parameters are closely related.

The Rosin Rammler “n” and the fines content have the best linear fit to maximum unconfined strength with r squared’s of 0.66 and 0.63 respectively.