Similar Material Simulation Study on Protection Effect of Steeply Inclined Upper Protective Layer Mining with Varying Interlayer Distances

Table 2

Levels of orthogonal design for similar materials.

Level number	Sand-binder ratio	Density (kg·m^−3)	Water content (%)
1	6	1550	5
2	8	1600	3
3	10	1650	2
4	12	1700	1