Study on the Evolution Law of Fracture Field in Full-Mechanized Caving Mining of Double System and Extrathick Coal Seam

Table 1

Simulated height of overburden.

No.	Lithology	Thickness (m)	Key strata type
1	Fine-grained sandstone	6.4	Far-field key stratum 1
2	Siltstone	8.2
3	Coal 14	2.9
4	Siltstone	8.6
5	Sandy mudstone	6.5
6	Medium-grained sandstone	4.3
7	Mudstone	4.2
8	Coarse-grained sandstone	3.6
9	Medium-grained sandstone	3.4
10	Mudstone	9.1
11	Fine-grained sandstone	1.6
12	Mudstone	2.0
13	Fine-grained sandstone	4.3
14	Mudstone	17.3
15	Fine-grained sandstone	5.3
16	Siltstone	27.7	Far-field key stratum 2
17	Fine-grained sandstone	2.6
18	Siltstone	11.7	Far-field key stratum 3
19	Sandy mudstone	7.3
20	Fine-grained sandstone	3.0
21	Sandy mudstone	2.0
22	Coarse-grained sandstone	6.4
23	Coarse sandstone with gravel	4.6
24	Coarse-grained sandstone	3.2
25	Coarse sandstone with gravel	2.8
26	Coarse-grained sandstone	5.5
27	Coarse sandstone with gravel	12.7	Near-field key strata
28	Coarse-grained sandstone	5.8
29	Coarse sandstone with gravel	7.0
30	Mudstone	5.2
31	Sandy mudstone	3.6
32	Coarse-grained sandstone	6.2
33	Sandy mudstone	4.1
34	Medium-grained sandstone	2.4
35	Coarse-grained sandstone	2.4
36	Sandy mudstone	5.9
37	Coarse-grained sandstone	3.1
38	Mudstone	6.7
39	Sandy mudstone	1.9
40	Coarse-grained sandstone	5.3
41	Sandy mudstone	1.6
42	Coals 3–5	14.1