Prediction is the first step to prevent and control coal outburst geological disasters. Generally, both limits and disadvantages are generated for the traditional prediction methods of drill cuttings from a Phi 42 mm borehole with increased mining depths. To investigate the discharge law of drill cuttings and improve the prediction index, briquettes were drilled with different borehole diameters under various side stresses. All the briquettes were loaded by a tri-axial experimental system to simulate the side stress of coal rock, and acoustic emission (AE) was used to monitor the AE events and record their characteristics during the separate drilling processes. The results showed that a larger borehole diameter and higher surrounding rock stress caused an increase in the quantity of drill cuttings (S). A power function relationship between S and the borehole diameter was found under the same side stress, and S was positively correlated to the side stress of a certain borehole diameter. Incremental drill cutting quantity (Delta S) was proposed to be the prediction index and the relationship between Delta S and the borehole diameter was fitted as a power function with a fitting coefficient of more than 0.99. The coupled values of Delta S and AE energies measured from a Phi 85 mm borehole were more sensitive than those of a Phi 35 mm borehole. In addition, the peak stress area using the larger drill bit was delayed by approximately 40 mm compared to that of the Phi 35 mm drill bit. Larger diameter boreholes are preferable for larger regions of stress relief and outburst removal; as a result, the use of larger diameter boreholes provides technological support to improve mine safety and increase production efficiency. (C) 2017 Elsevier B.V. All rights reserved.