For the extension of the Shatin to Central Link metro line, contract no. 1128, connecting the New Territories in the north to the business district of the town centre, the Mass Transit Railway Corporation entrusted Dragages Hong Kong and Bouygues Travaux Publics with the construction works of 2 x 2 tunnels. To excavate close to the surface under a dense urban environment and cope with a complex geology, a variable density TBM was used — a first in Hong Kong. This new type of tunnel boring machine combines the advantages of traditional slurry pressure and earth pressure balance TBMs. It enables material density at the cutting face to be adjusted and to deal with a wide variety of ground conditions.