Study on Fracture and Stress Evolution Characteristics of Ultra-Thick Hard Sandstone Roof in the Fully Mechanized Mining Face with Large Mining Height: A Case Study of Xiaojihan Coal Mine in Western China

Figure 3

SEM images at different resolutions in the main roof: (a) 100X; (b) 250X; (c) 350X; (d) 500X; (e) 800X; (f) 1000X.

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