Control of surface settlements with umbrella arch method in second stage excavations of Istanbul Metro

In metro tunnel excavations, it is important to control surface settlements observed before and after excavation, causing damages to the surface structures. Otherwise, metro tunnel cannot perform the task expected and the advantages of metro tunnel are lost. For this purpose, second stage excavation of Istanbul Metro between Unkapani and Yenikapi was studied. Geology in this section is composed of clay, claystone, sand and marl. New Austrian tunnelling method (NATM) was used in tunnels having cross-section of 36 m2. In this study surface settlements are compared for NATM and umbrella arch method (UAM) in sensitive regions. As a result of this study, it was found out that surface deformations especially in clay bearing formations could be controlled efficiently by using the UAM.