In Hong Kong, 2 Bouygues Construction subsidiaries, Bouygues Travaux Publics and Dragages Hong Kong, won a contract to construct the 3.5-kilometre underground stretch of the railway linking Hong Kong to Guangzhou. In this very dense urban environment, numerous networks and deep-laid foundations of buildings made tunnelling operations for the two parallel tunnels, each 9 metres in diameter, a real challenge. During the site work, many measures were taken to minimise the nuisance caused to local residents, in particular the installation of 2 sound baffles, which reduced site noise by 49 decibels.