Abstract: Comments are made on the cover thickness of Metro works, with No. 3 line of Qingdao Metro as an example. The coverspan ratio of Metro tunnels is calculated according to different codes and theories and a rational quantitative theoretical value is obtained by means of comparison and analysis. Qualitative analysis is made on the cover thickness of Metro tunnels located in granite strata in terms of construction technology, environmental influence, engineering economical efficiency, functional requirements and entrance/exit arrangement. Recommendations are made on the subsequent construction of other lines of Qingdao Metro, so as to overcome the construction difficulties, minimize the influence on the surrounding environment and reduce the cost.

Key words: Qingdao Metro, cover, coverspan ratio, granite, mining method