Environmental effects of tunnel excavation in soft and shallow ground with EPBM: the case of Istanbul

Abstract

In metro tunnel excavations, it is important to control surface settlements observed before and after excavation, which may cause damage to surface structures. Otherwise, the metro tunnel cannot perform the task expected, and the advantages of the tunnel are lost. In this study, short-term surface settlements and their effect on buildings are examined in three zones for twin tunnels, which have been excavated between the Otogar and Kirazlı 1 stations of the Istanbul Metro line, and are 5.8 km in length. Geology in the study area is composed of fill, stiff clay, dense sand, very dense sand, and hard clay, respectively, starting from the surface. Tunnels are excavated by using two Earth Pressure Balance Tunnel Boring Machines (EPBMs) with a 6.5 m diameter as twin tubes with 14 m distance from center to center. The EPBM in the right tube is followed about 100 m behind the other tube. Segmental lining with 1.4 m of length is currently employed as final support. The results of this study indicate that, with EPBM excavation method in shallow depths and soft grounds, the damage done to the environment prolonged project costs up to 15.8% more. In addition, tunnel conditions prolonged the project schedule to 29.3%.

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.…”

“…Whereas according to literature, tail void from excavation diameter-external shield diameter is 6,564 mm -6,300 mm = 264 mm for lovat and 6,500 mm -6,300 mm = 200 mm for Herrenknecht. Additionally, with accepting of tunnel diameter as 6.500 and 6.564 m (Ocak 2009;Ocak and Bilgin 2009), some minor changes will occur in Table 3 and Table 4 like…”

Damage zone propagation and support pressure estimation around two access tunnels of the Barapukuria coalmine in Bangladesh: a two-dimensional numerical modeling approach

“…The presence of mines or metro tunnels disturbs the in-situ state of stress (Yavuz 2006). The excavation method, face supports pressure, excavation rate, stiffness of support system, and excavation sequence has dramatic effects on ground deformations that occur due to tunneling operations (Ocak 2009). Stress redistribution and deformation of the rock start occurring ahead of the opening face (Yavuz 2006 Ocak 2009).…”

“…The excavation method, face supports pressure, excavation rate, stiffness of support system, and excavation sequence has dramatic effects on ground deformations that occur due to tunneling operations (Ocak 2009). Stress redistribution and deformation of the rock start occurring ahead of the opening face (Yavuz 2006 Ocak 2009). Before the development of mine access tunnels, technical parameters include tunnel depth and geometry, tunnel diameter, single or double track lines, and neighboring geological structures.…”

“…Before the development of mine access tunnels, technical parameters include tunnel depth and geometry, tunnel diameter, single or double track lines, and neighboring geological structures. Construction method, which leads a safe and economic project, should be planned so that ground movements will be limited to an acceptable level (Ocak 2009). Estimation of stress and deformation in the ground due to the excavation of tunnel (Bobet 2009) is a significant task for developing coalmines in Bangladesh (Fig.1).…”