Construction on three major contracts started recently for the 17km stretch of Circle Line Four and Five. These are the last parts of the overall project: 13 stations are to be built in total, one in advance and two as shells only.
'These will be completed when the demand rises with new housing, ' explains overall project director P Sripathy.
He says contracts have been kept fairly large to 'gain the benefits of economy of scale'.
The LTA has also specified minimum standards for the TBMs to be used, aware of difficulties faced by tunnellers on Singapore's Deep Tunnel Sewerage System recently.
'And we do go quite deep in places, enough to go under the DTSS at one point.' LTA staff worked with TBM manufacturers to devise a set of criteria for the machines.
Soon there will be 11 working, six bentonite slurry face and five earth pressure balance.
As with all projects in Singapore, the contracts have been given extra scrutiny in the wake of the Nicoll Highway collapse.
Sripathy says: 'We always looked at the contractor's temporary works proposals and validated them but now there is an independent set of calculations done for them by an outside consultant.' Contractors are required to use an outside consultant for work in design and build contracts rather than inhouse staff as previously.
Unusually, he says, the project will have outsourced supervision - by Maunsell - 'because our own manpower is stretched on phases 1, 2 and 3'. LTA remains responsible for project management.
Sripathy adds that finding geotechnical staff in general is a problem at present.