Comprehensive Analysis of Stability of Coal Seam Composite Roof Based on Analytic Hierarchy Process

Table 2

Comparison of bending strengths of combined models of different lithologies.

Layer number	Combination mode (mm) (from top to bottom)	Bending strength (MPa)		Comprehensive strength index	Comprehensive influence coefficient
		Noncohesive layer	Cohesive layer		Noncohesive layer	Cohesive layer
One layer	① Black 100	10.480	—	64.170	1.000	—
	② Yellow 100	5.460	—	36.670	0.570	—
Two layers	① Black 50 + 50	6.530	8.370	64.170	0.613	0.678
	② Black 50 + yellow 50	5.160	7.170	50.420	0.525	0.576
	③ Yellow 50 + black 50	4.490	5.910	50.420	0.547	0.598
	④ Yellow 50 + 50	3.860	5.760	36.670	0.390	0.427
Three layers	① Black 50 + 30 + 20	5.310	6.840	64.170	0.545	0.610
	② Black 50 + yellow 30 + black 20	5.190	6.650	55.920	0.534	0.591
	③ Yellow 50 + black 30 + 20	3.830	5.040	50.420	0.448	0.499
	④ Yellow 50 + 30+20	2.980	4.500	36.670	0.319	0.356
Four layers	① Black 30 + 20 + 30 + 20	4.880	6.260	64.170	0.503	0.568
	② Black 30 + yellow 20 + black 30 + 20	4.560	6.030	52.250	0.419	0.473
	③ Yellow 30 + black 20 + 30 + 20	4.300	5.830	52.250	0.426	0.479
	④ Yellow 30 + 20 + 30 + 20	2.560	3.820	36.670	0.287	0.324