Assessment of twin tunnel induced ground deformation by empirical and numerical analyses (Eurasia tunnel: NATM part, Istanbul, Turkey)

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2019
Ağbay, Ebru
Pre-support systems become very important for inner-city shallow tunnels especially while applying New Austrian Tunneling Method (NATM) which requires some deformation to relieve the stress. Previous studies about assessing the magnitude of surface displacements caused by twin tunneling do not include the effects of presupport system and stress release by deformation. Moreover, most of the established empirical equations were obtained by using data from tunnel passing through clayey soil. Objective of this thesis is to introduce a detailed procedure for obtaining modification factor including the effects of pre-support system and of rock mass quality and which can be used as a reduction ratio in prediction methods used for twin tunnel induced surface settlement. Twin tunnel induced surface settlement data comes from Asian side of the Eurasia Tunnel excavated by using NATM method and supported by forepoling and umbrella arch method. The steps that need to be completed in order to achieve the determined objective are; i) performing numerical analysis on the selected 12 cross section lines along tunnel route to update the geological profile at which there is no borehole drilled and to approximate the results of numerical models to actual field measurement in terms of maximum surface settlement, ii) conducting parameter study in which the distance between pipes in the pre-support systems was used as a variable, iii) obtaining a statistical formula that presents the decreasing effect of pre-support system on maximum surface settlement. It was concluded that twin tunnel-induced surface settlement mainly depends on deformation modulus of the geo-materials around tunnel. Deformation modulus was obtained by evaluating rock mass quality which is controlled by fracturing and surface weathering. A new formula predicting twin tunnel induced ground deformation is proposed as a modification factor of Herzog’s equation.

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Citation Formats
E. Ağbay, “Assessment of twin tunnel induced ground deformation by empirical and numerical analyses (Eurasia tunnel: NATM part, Istanbul, Turkey),” Ph.D. - Doctoral Program, Middle East Technical University, 2019.