Robbins has claimed the fastest progress rate achieved with any of the 14 TBMs on Phase 2 of New Delhi metro – 168 rings, or 202m, in a week with the first of its two shields to complete excavation.

Being driven by JV contractor Continental Engineering Corp (CEC/Soma, the 6.52m diameter EPM completed its second 1km long bore, on which the high advance rate was achieved, on 5 March.

The JV is working on contract BC-16 between Udyog Bhavan and Green Park. The Robbins shields were built to an EPB design by Mitsubishi Heavy Industries (MHI) are undertaking half of the tunnelling required – the parallel tunnels between Jor Bagh in the middle of BC-16 and Udyog Bhavan at the contract boundary with BC-15.

On the other side of Jor Bagh, a pair of 6.54m diameter Herrenknecht shields (S-411, S-412) have been employed by the JV to drive twin tunnels. They were launched from INA box station.

Geology along the alignment comprises sandy silt, silty sand and gravels with groundwater pressures generally up to 2 bar. Cover is approximately 15m.

In early 2007 the JV was awarded a 40-month contract by Delhi Metro Rail Corp (DMRC) to design and build the tunnels, totalling approximately 4km in length.

The first Robbins TBM was launched from Jor Bagh station in May last year and finished the first 1km long drive with an intermediate breakthrough at Race Course station in late September. On that leg, the machine achieved up to 19 rings per day – more than expected – and with 90% availability, the JV commented, noting the contribution from electric motors in continuing the drives in mainly soft clays.

The sister shield, which achieved up to 118 rings, or 142m, in a week during its first 1km long drive which fully got underway when the five gantries were installed by October 2008. It has been relaunched from Race Course and is scheduled to complete excavation next month.

In total, the metro scheme involves approximately 16km of TBM bores as part of about 30km of underground works including box stations.

Earlier this year the last of the 14 TBMs required for the metro expansion was launched on the Airport Express Link part of the scheme (T&TI, February, p7).

Most TBM drives in Phase 2, though, are in the corridors from Central Secretariat (CS) to Badarpur and to Qutub Minar, the latter including BC-16. The 5.7m i.d. and 5.8 i.d. tubes on the scheme are lined with segmental rings (5+1) of 275mm thickness.

DMRC aims to have all tunnelling competed by December. New Delhi is hosting the Commonwealth Games next year.