The Effects of TBM Operational Parameters on Excavation Performances in Complex Geology when Driving Twin Tunnels in Istanbul
The geology of Istanbul is complex, changing frequently from very hard rock formation with different degrees of fracturing to soft ground in a short length. Twin tunnels which were excavated by an EPB-TBMs in Istanbul Metro Projects, gave the opportunity to investigate the effect of geotechnical properties, EPB pressures in virgin and disturbed zones by the excavation, on the performance of a TBM. This study gave also a unique opportunity also to develop a new prediction model of maximum surface settlements in a complex geology in İstanbul which will be discussed in other paper. There is quite limited number of research studies on predicting the performance of EPB TBMs in complex geology in twin tunnels especially in mixed faces, in fractured rocks, in transition zones and in disturbed zones etc. The problem of interaction between complex geology, EPB face pressure, TBM performance parameters were interactive which were needed to be studied. It was also noticed that this interactive problem affected the net production rates of TBMs. The performance of TBM is proved to be different in each line of twin tunnels. In rock, for the same thrust value, the advance rate of TBM in tunnel which is behind the first one is found 22% higher than the other tunnel. However, for stiff clay this is contrary, for the same thrust value the advance rate of TBM, which is behind, is 40% slower than the first one. At the other hand for the tunnel which is behind the other, the unit volume of rock is excavated with 10% less energy than. However, this is contrary for stiff clay, the excavation of the tunnel which is behind needs 10% higher energy than the tunnel which is in front. These results are believed to play important roles for scheduling the tunneling activities in the future in complex geology.