Overburden Migration and Failure Characteristics in Mining Shallow Buried Coal Seam with Thick Loose Layer

Table 2

Value of excavation disturbance parameter D.

Project disturbance	D
The rock mass is excellent, controlled blasting or rock excavation by machine	0
The rock mass quality is poor, manual prying or mechanical excavation	0
The tunnel is located in the squeezing stratum and has floor heave without invert	0.5
The blasting quality of hard rock tunnel is poor, and the influence depth of loosening is 2-3 m	0.8
The damage of surrounding rock is common and the blasting quality is poor in small-scale slope excavation	1.0
The damage of surrounding rock is general and the blasting quality is good in small-scale slope excavation	0.7
Large-scale production blasting, serious disturbance, production blasting	1.0
Large-scale production blasting, serious disturbance, mechanical excavation	0.7