Construction and Application of Mathematical Model of Stable Fracture Development Zone of Roof

Table 3

1201 drilling hole design and actual layout parameters of directional drilling field with return air downhole.

Hole number	Designed internal staggered distance to return air trough (m)	Designed distance to 1^# coal roof (m)	Hole depth (m)	Projection length of borehole (m)
1^#	40	15	255	246.72
2^#	20~25	14	267.6	257.04