Guangzhou Metro Line 21 is one of lines under construction, roughly east-to-west. It is approximately 61.6 kilometers long, of which about 40.1 kilometers is the bottom line; 6.8 km tunnel through a mountain; 14.7 kilometers of overhead lines. It would be set up 21 stations, including 17 underground stations, 4 skyline stations, and 7 transfer stations. The average station spacing is 3.685 km, and the maximum station spacing is 7.325 km with a total construction area of 485,452.5 square meters and total demolition area of 193,476.8 square meters across the board.
February 2014, the feasibility study of Guangzhou Metro Line 21 got the official approval form the provincial Development and Reform Commission, expected to be built and opened to traffic by the end of 2017.
The biggest obstacle about Guangzhou line 21: sand, silt layer, sandstone, granite and huge boulders. Complex geological conditions became a major test for line 21. To ensure the smooth progress of the project, it is suggested to choose Metis self drilling bolt
and also choose different drill bits according kinds of geological conditions, which can play the role of supporting broken rocks and firming foundations.