Af­cons uses Rob­bins EPB TBM to Com­plete Third Bore for Chen­nai Metro Pro­ject


Con­trac­tor Af­cons In­fra­struc­ture Ltd used a 6.65 m (21.8 ft) di­am­e­ter Rob­bins EPB TBM to bore through in Chen­nai Metro, mak­ing it the con­trac­tor's third tun­nel to be bored by the ma­chine for the pro­ject. The three sep­a­rate bores for the EPB are part of an in­creas­ing trend as many Rob­bins EPBs have been used on mul­ti­ple tun­nel drives with good per­for­mance.

Rob­bins EPBs are built one third heav­ier than any other EPB in the mar­ket and are de­signed for 10,000 hours of us­able life, mak­ing them ideal for use over many kilo­me­ters. “Rob­bins is known for de­sign­ing re­silient machines,” says Mr. Gopal Dey, Af­cons Se­nior Man­ager. “For this pro­ject, we needed a ma­chine that was specif­i­cally tai­lored to pro­ject con­di­tions from soft clay to mixed ground with rock. Rob­bins EPB TBMs have unique de­sign fea­tures that op­ti­mize the ma­chine for the ge­ol­ogy.”

Af­ter com­plet­ing its orig­i­nal twin tun­nels, the EPB was re­fur­bished in prepa­ra­tion to bore its lat­est 1.8 km (1.1 mi) sec­tion. Dur­ing re­fur­bish­ment, the in­ner seal greas­ing sys­tem was changed from auto to man­ual mode, and the foam noz­zle sys­tem was mod­i­fied. These changes op­ti­mized the ma­chine for ex­ca­va­tion in the highly vari­able mixed face con­di­tions en­coun­tered in the first two tun­nels.

The EPB was launched on Fe­bru­ary 3, ear­lier this year. Ac­cord­ing to con­trac­tor Af­cons, the ma­chine faced a ma­jor chal­lenge right out of the gate. “When the TBM came out of the launch­ing shaft, a few rings were erected, and then the ma­chine had to cross a live rail­way track, which meant there would be a pos­si­bil­ity of ground set­tle­ment,” says Af­cons Di­rec­tor, Mr. Manivannan. “At this stage, we had to closely mon­i­tor TBM’s face pres­sure and ad­vance the ma­chine at a uni­form rate to en­sure proper pri­mary grout­ing.” The bore’s ge­ol­ogy mainly con­sisted clayey sand and about 60 me­ters (197 ft) of mixed ground.

Adds Mr. Dey, “We chose this ma­chine for this pro­ject due to the un­der­ground ge­ol­ogy in Chen­nai, which con­tin­u­ously changes from soil to mixed ground. We also liked that

On Tues­day, Oc­to­ber 31, 2017 a 6.65 m (21.8 ft) Rob­bins EPB made its third break­through at India’s Chen­nai Metro.

Rob­bins and con­trac­tor Af­cons cel­e­brate the break­through and good per­for­mance of the EPB, which achieved rates up to 80 mm (3 in) per minute in mixed ground con­di­tions.

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