Controlled Roof Collapse during Secondary Mining in Coal Mines

Table 1

Critical length 𝐿_𝑐.

h(m)	𝐻 = 120 m; 𝐿𝑐(m)	𝐻 = 500 m; 𝐿𝑐(m)
0.1	9.26	4.54
0.2	18.53	9.08
0.3	27.80	13.62
0.4	37.06	18.16
0.5	46.33	22.7
0.6	55.60	27.23
0.7	64.86	31.77
0.8	74.12	36.31
0.9	83.39	40.85
1	92.65	45.39