Challenging Mixed Face Tunneling at India’s Sleemanabad Carrier Canal
India’s Sleemanabad Carrier Canal is a prime example of just how challenging mixed face conditions can be, although other examples exist. The water transfer tunnel is being bored using a 10 m diameter hybrid-type rock/EPB TBM. However, in 6.5 years of tunneling the machine had only advanced 1,600 m. Commercial issues for the original contractor stalled the project frequently, while ground conditions turned out to be even more difficult than predicted. Low overburden of between 10 and 14 m, combined with mixed face conditions, transition zones and a high water table restricted advance rates. The TBM manufacturer mobilized a team to refurbish the TBM and within a period of 6 weeks a team of 180 people had been deployed to take over all aspects of tunneling and support activities. Production rates improved dramatically as the TBM advanced more than 400 m in four months. This paper discusses the problems faced and the methodology that enabled good advance rates in highly variable mixed face conditions.
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