The two 6.68m diameter NFM TBMs being used to drive the Shiraz metro in Iran (T&TI, February, p10) have broken through to the second station on their alignment after both achieving drive rates of up to 12 rings, or 17m, in a day.

This first stretch of tunnel was 770m long. TBM 1 was launched from Allah Square on 1 October last year. The machine performance quickly picked up, after six weeks a second shift was added and the effects of this are readily apparent when the progress curves (below) are scrutinised.

Thierry Strohl, a representative of NFM, told T&TI that the geology comprised soft clay throughout, apart for a short section of gravel after 350m. This coincided with the machine being stopped for final installation works in the portal. The performance did not seem to diminish because of the stoppage. In fact one week after restarting the best weekly advance of 55 rings, or 77m, was recorded for TBM 1.

By 28 February, TBM 1 recorded its peak performance so far, with 12 rings, or 17m of advance in 24 hours.

The two month delay from mid-March to mid-May was due to non availability of the civil works in the station No. 2 said Strohl. He said that if this period was discounted, together with the time when dummy rings were removed and switches installed, it gave an advance of 770m in 20 weeks, to give an average performance of 39m per week.

Strohl speculated that with the maintenance carried out as the station was crossed, together with a trained and experienced crew, 70m per week advances could be possible for the next 650m section to No. 3 station.

TBM 2 was launched 10 weeks after TBM 1 and followed a similar performance curve. Marked gains were seen with the addition of a second shift, followed by a period of inactivity as the portal installation took place. A delay of nearly three weeks occurred to TBM 2 as work was carried out on the gangways and bridge connecting the shield and the backup. In the final metres before breakthrough to the station, TBM 2 beat its sister machine with a best weekly performance of 59 rings, or 82m.

Current plans call for TBM 1 to be launched for the second section of tunnel by mid-July.

Related Files
Performance curves for the two NFM machines on their initial drives