The effect of EPB face pressure on TBM performance parameters in different geological formations of Istanbul

This study summarizes the effect of EPB pressure varying from 0.5 bar to 4 bar, on TBM performance i.e., on thrust force, torque, penetration, and specific energy. 6511 data points were analyzed, each representing mean values attributed to different segments of 1.5 m in length, in four different fractured hard rock formations, in a transition/weathered complex zone, and in silty-clayey sand. From this study, it emerges that thrust and torque values almost increase up to 2.2 and 1.7 times with EPB face pressure changing from 0.5 to 4 bar in all formations studied except for torque in silty-clayey sand. However, after 2 bar of face pressure, the effect of EPB pressure on penetration and specific energy is more remarkable than the other parameters. Specific energy increases almost 2-2.5 times in silty-clayey sand and up to 4 times in a transition/weathered zone. To contribute to understanding better the factors affecting TBM performance in fractured hard rock, the effects of geological and geotechnical parameters are also discussed briefly. We think the results will serve as a basis to understand better the effect of EPB face pressures on TBM performance, to design more efficient EPB-TBMs, and to help to develop new performance prediction models for EPB-TBMs working in fractured hard rock formations and in soft ground if some correction coefficients as will be developed later, are added to previously published models. However, it is strongly recommended to use the results of this article for tunnels having similar geological conditions as in Istanbul.