Study on Ultrasonic Response to Mechanical Structure of Coal under Loading and Unloading Condition

Table 1

The coal type and composition.

Coal sample	Ad/%	Vadf/%	Mad/%	St.d/%	Hardness	Type
Sanhejian	8.78–32.41	36.43–42.69	0.60–3.89	0.39–1.02	2-3	Gas coal