Surface settlement predictions for Istanbul Metro tunnels excavated by EPB-TBM

Abstract

In this study, short-term surface settlements are predicted for twin tunnels, which are to be excavated in the chainage of 0 ? 850 to 0 ? 900 m between the Esenler and Kirazlı stations of the Istanbul Metro line, which is 4 km in length. The total length of the excavation line is 21.2 km between Esenler and Basaksehir. Tunnels are excavated by employing two earth pressure balance (EPB) tunnel boring machines (TBMs) that have twin tubes of 6.5 m diameter and with 14 m distance from center to center. The TBM in the right tube follows about 100 m behind the other tube. Segmental lining of 1.4 m length is currently employed as the final support. Settlement predictions are performed with finite element method by using Plaxis finite element program. Excavation, ground support and face support steps in FEM analyses are simulated as applied in the field. Predictions are performed for a typical geological zone, which is considered as critical in terms of surface settlement. Geology in the study area is composed of fill, very stiff clay, dense sand, very dense sand and hard clay, respectively, starting from the surface. In addition to finite element modeling, the surface settlements are also predicted by using semi-theoretical (semi-empirical) and analytical methods. The results indicate that the FE model predicts well the short-term surface settlements for a given volume loss value. The results of semi-theoretical and analytical methods are found to be in good agreement with the FE model. The results of predictions are compared and verified by field measurements. It is suggested that grouting of the excavation void should be performed as fast as possible after excavation of a section as a precaution against surface settlements during excavation. Face pressure of the TBMs should be closely monitored and adjusted for different zones.

Discussion on article “Surface subsidence induced by twin subway tunneling in soft ground conditions in Istanbul” by Yılmaz Mahmutoğlu, Bulletin of Engineering Geology and the Environment, 2011 70(1):115–131

“…Generally, result of this study-both in terms of surface settlement and environmental effect-is in agreement with former studies published with regard to same project (Ocak 2009;Ocak and Bilgin 2009;Ercelebi et al 2011). But I would like to submit some minor contributions to paper.…”

Hydrogeological impact assessment by tunnelling at sites of high sensitivity

“…The second type of soil displacement was a long term movement, which may take between a 5 few months and a few years to reach a steady state (Ercelebi et al, 2011). This movement was 6 evaluated using the data between December and March 2011 (last measurement).…”

“…This period 7 is depicted by number 3 and an arrow in the upper plots of Figure 11. Long term movements 8 are generally associated with creep, stress redistribution and consolidation of the soil after 9 drainage of groundwater (dissipation of water pressure; Ercelebi et al, 2011). However, soil 10 consolidation due to the redistribution of the water pressure as a result of the interaction 11 between the aquifer and the tunnel (barrier effect) should also be considered.…”

Three-dimensional numerical simulation of mechanized twin stacked tunnels in soft ground

“…As far as the excavation of mechanized twin tunnels in close proximity is concerned, most cases reported in previous studies have focused on the interactions between two horizontally driven tunnels, using physical tests (Kim, 1996;Chapman et al, 2007;Choi and Lee, 2010;He et al, 2012;Ng et al, 2013;Ng, 2014;Ng and Lu, 2014), field measurements (Yamaguchi et al, 1998;Suwansawat and Einstein, 2007;Chen et al, 2011;Zhou et al, 2012;Ocak, 2013), empirical/analytical methods (Wang et al, 2003;Hunt, 2005;Suwansawat and Einstein, 2007;Yang and Wang, 2011), and numerical analyses (Yamaguchi et al, 1998;Hefny et al, 2004;Zheng and Qiu, 2005;Karakus et al, 2007;Hage Chehade and Shahrour, 2008;Afifipour et al, 2011;Chakeri et al, 2011;Ercelebi et al, 2011;Mahmutoğlu, 2011;Channabasavaraj and Vishwanath, 2012;Hasanpour et al, 2012;Li et al, 2012;Do et al, 2014b;2014d). However, less work has been devoted to the interactions between tunnels stacked over each other (Yamaguchi et al, 1998;Hefny et al, 2004;Suwansawat and Einstein, 2007;Hage Chehade and Shahrour, 2008;Liu et al, 2008;Channabasavaraj and Vishwanath, 2012;…”