Rock mechanics aspects related to cutting efficiency of mechanical excavators, 25 years of experience in Istanbul

The mechanical excavation of utility tunnels in Istanbul started in 1985 with roadheaders and impact hammers. The first TBM application was started for a sewerage tunnel in 1990. Since then, more than 60 km of tunnels including metro tunnels were excavated with mechanical excavators. A large amount of data was collected continuously by researchers in the Mining Engineering Department of Istanbul Technical University. Rock mechanics and engineering geological aspects of the rock formations affecting the efficiency of the mechanized excavation systems were also carefully recorded; the performance prediction models were developed and modified continuously for impact hammers, roadheaders and TBMs. This paper will summarize briefly the works done in these respects emphasizing specially on the concept of in situ specific energy when using TBMs. A numerical example showing how to calculate net production rate of a TBM is given based on the model developed in a complex geology.