Chatswood to Epping near finish

In Sydney, the two Robbins TBMs on the 25km long tunnelled Chatswood to Epping Rail Link have reached the Lane Cove River crossing marking the start of the final leg of tunnelling.

TBM 1 broke through into the Lane Cove cut and cover tunnel on 4 February. It was "walked" through the 150m long river crossing and recommenced boring on the far side on 9 February. T&TI was told the second TBM reached the Lane Cove crossing section on 6 March, where it also took five days to be pulled through the cut and cover tunnel, allowing it to recommence boring on 11 March.

The completion of TBM excavation on the US$663M scheme (formerly known as the Paramatta Rail Link Project) is expected by June this year. To date TBM 1 has cut 9.2km of 7.2m diameter tunnel, with its sister machine, TBM 2, having cut an 8km length of similar diameter. Both machines were procured on an optional buy back agreement and were refurbished under Robbins supervision.

When T&TI visited the site at the end of 2003, (T&TI, February 2004, p14), the contractor, Thiess / HochtiefJV (THJV), was excavating through the alignment's Hawkesbury Sandstone at up to 200m per week. Just over a year later, the average excavation rate remains an impressive 40m per day, with a best shift advance of 66m.The TBMs are operated on six 11 hour nightshifts and five 11 hour dayshifts per week.

The depth of TBM excavation on this final leg of the route varies from 56m to just 11m clearance to the tunnel soffit. The rock formations and grade restrictions for the trains that will ultimately run through the tunnels, meant that the Lane River crossing had to be set high in the sandstone and go through the paleo channel. The TBMs could not excavate through the alluvial soils deposited there so a 9m x 9m cut and cover tunnel was formed over a 150m length for the TBMs to pass through. With an internal diameter of 7.2m, the crossing was built as a three stage coffer dam by THJV, with design by GHD. Environmental impact was minimised by the design allowing the river to flow at all times.