MORE than 150 metres has been excavated on the Cheung Ching tunnels' project, engineers from the French-owned Dragages company said. Work on the ''pilot galleries'' is expected to begin this week. These will form the main working area as the twin three-lane tunnels are bored through 1.5 km of Tsing Yi island's solid granite. Work is progressing about four metres a day from both east and west. The breakthrough is expected in March 1995. The finished tunnel is expected to be handed over to the Highways Department in November 1996. At its peak, the Cheung Ching tunnel project is expected to employ 200 people. The tunnel's project manager is Jean-Pierre Barral. Dragages, the Hong Kong branch of the Bouygues Group, will begin work on October 15 on the $670 million Rambler Channel bridge project. The contract was won with an alternative design using ''external pre-stressing'', the commercial director of Dragages, Paul Ravelli, said. External pre-stressing involves placing reinforcing stabilisers that can be changed or tightened, under the box sections of the bridge carriageway. Dragages leads the consortium building the bridge. It includes the Bachy Soletanche Group and Penta-Ocean Construction Company Ltd. Mr Ravelli said the Bouygues group was most competitive in such large projects because it kept its engineers on a tight schedule. They were sent from France to projects only for the time they were needed before leaving for the next job. This was particularly effective on high-tech projects, such as the detailed design of the Rambler Channel bridge, Mr Ravelli said. ''With those highly trained engineers coming in, we are building up a good local group,'' Mr Ravelli said. The Rambler Channel bridge is scheduled to be finished in June 1996. Dragages is also one of two bidders for the Central Reclamation Project. Although the Government called Central Reclamation tenders on September 2 last year, the stalled Sino-British talks had stopped the contract from being awarded, Mr Ravelli said. The two tenderers had, as a result, been submitting extensions of tender validity, he said. They were now presenting to the Government the effect on their prices of extending their tenders since the beginning of this year. The Bouygues group has more than 80,000 employees worldwide. Dragages employs about 3,000 people.