THE Circle Line MRT project could take up to 2012 to complete, and the escalated cost of sand and granite will inflate the $6.8 billion budget.

"We have decided to compensate the contractors for 75 per cent of the cost increase in sand and aggregate," Land Transport Authority deputy chief executive Lim Bok Ngam said.

He said he does not expect the higher cost in the two raw materials to push the Circle Line budget beyond a single-digit percentage, as "concrete works make up only 20-30 per cent of total cost".

But Mr Lim said additional costs from more stringent design and engineering requirements after the Nicoll Highway accident in 2004 "have not been worked out".

For instance, the Farrer Road Station being built now has retaining walls that are 1.2m thick - 50 per cent thicker than the failed walls at the Nicoll Highway station.

Even so, it had so many steel struts holding the walls in place that it was impossible to see right to the bottom of the excavation.

The LTA said this is because the station is very close to HDB blocks on one side and a major road (Farrer Road) on the other.

The LTA would not be pinned down on the exact date of opening nor the eventual cost of the line, but admitted that tougher engineering and design requirements after the Nicoll Highway tragedy will add to cost.

But at a progress report on Friday, it indicated that a stretch measuring about 8km - with seven stations between MacPherson and Marymount - was in advance stages of completion.

And the Circle Line's train depot is along this stretch (at Kim Chuan), it is feasible to open it, as early as first-half 2010.

Mr Lim said this stretch should be ready by 2010 Stage 3 - a 5.7km stretch linking Bartley to Marymount.