The mechanical excavation of utility tunnels in Istanbul started in 1985 with roadheaders and impact hammers. The first TBM application was started for a sewer-age 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 care-fully 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.
The geology of Istanbul is complex and some of the tunnels have been currently excavated in young Cenozoic formations and some of them in complex series of Paleozoic formations. The Paleozoic rock formations are cut frequently by andesite and diabase dykes, fracturing the main rock, decreasing the daily advance rates and increasing the tunneling cost tremendously. Sometimes in EPB (Earth Pressure Balance) TBM applications, excessive ground deformations may cause damages to the surrounding buildings like experienced in Otogar-Esenler metro tunnels which caused an extra cost of 35.6x106 $ to the project. The total length of the tunnels planned to be excavated in Istanbul in near future is 127 km for metro tunnels and 47 km for utility tunnels. Majority of the tunnels will be excavated with tunnel boring machines and the total cost of the operation is estimated to be around 10x109 Euros.
