Failure Mechanism Analysis and Support Design for Deep Composite Soft Rock Roadway: A Case Study of the Yangcheng Coal Mine in China

Table 1

Classification criterion of rock quality by the RQD [26, 27].

RQD (%)	Classification	Rock quality
<25	V	Very poor
25–50	IV	Poor
50–75	III	Fine
75–90	II	Good
90–100	I	Excellent