Table 1 Pearson correlation coefficients...

Table 1

Pearson correlation coefficients between drilling parameters and surrounding rock class

Drilling parameter	Average value of the drilling parameter $\bar{x}$	Average value of the surrounding rock class $\bar{y}$	Pearson correlation coefficient $ϒ$
Feed speed /(m·min⁻¹)	2.914 7	3.775 9	0.806 8
Impact pressure /bar	118.185 1	3.775 9	−0.898 4
Propulsion pressure /bar	67.267 9	3.775 9	−0.441 0
Rotation pressure /bar	85.787 2	3.775 9	−0.684 8

Drilling parameter	Average value of the drilling parameter $\bar{x}$	Average value of the surrounding rock class $\bar{y}$	Pearson correlation coefficient $ϒ$
Feed speed/(m·min⁻¹)	2.914 7	3.775 9	0.806 8
Impact pressure/bar	118.185 1	3.775 9	−0.898 4
Propulsion pressure/bar	67.267 9	3.775 9	−0.441 0
Rotation pressure/bar	85.787 2	3.775 9	−0.684 8