Control of surface settlements with Earth pressure balance method (EPB) for Istanbul metro

Regarding urban development, metro tunnels are increasingly being excavated in soft ground conditions. In metro tunnel excavations, it is important to control surface settlements observed before and after excavation, which may cause damage to surface structures. Construction of tunnels induces a state of strain in the soil around the excavation that could cause damaging differential displacements in existing structures near the tunnel. This paper reports the results of a study carried out to estimate the values of the surface settlements induced by the excavation of twin tunnels, which have been excavated between the Otogar and Kirazlı stations of the Istanbul Metro line namely a length of 5.77 km. Authors of the paper have not carried out field studies at the tunnel; data related to tunnel were taken from Mahmutoğlu (2010), Ocak (2009) and Ercelebi et al (2010). In this paper only numerical modeling has been performed on obtained data. In particular, the purpose of this study has been to compare the vertical surface displacements monitored during the advancing excavation and the settlements estimated by using 3D Finite Difference model. For numerical analyses, FLAC3D program is used. Geology in the study area is composed of fill, stiff clay and dense sand and hard clay. Tunnels are excavated by using two Earth Pressure Balance Tunnel Boring Machines with a 6.5 m diameter as twin tubes with 14 m distance from center to center. Ground settlement results obtained by numerical modeling are in good agreement with field measurements

Keywords:

Numerical modeling , Surface settlement , Face pressure , FLAC 3D