Project C991 is Singapore MRT Downtown Line 2 Extension which will extend a total of about 4 kilometers northwest from the existing Bukit Panjang Station to connect with the North-South Line (NSL). This project includes the construction of the main tunnel structure along with supporting new and renovation works related to the Gali Batu Depot. The project follows shield tunneling and cut-and-cover structure, of which the section constructed in shield tunneling needs to traverse the composite strata of granite and soft soil, in close proximity to existing infrastructure.