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 will discuss the problems faced and the methodology that enabled good advance rates in-highly variable mixed face conditions.