IN-SITU WALL CONCRETE QUALITY USING VELOCITY FIELD-DEPENDENT MIGRATION IN ZIGANA AND TORUL TUNNELS

Authors : Işıl SARIÇİÇEK, Aysel ŞEREN

Pages : 979-993

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Publication Date : 2021-06-01

Article Type : Research Paper

Abstract :In the scope of this study, the old Zigana and newly-built Torul Tunnels on an important transportation route were selected as the study areas. As the main purpose, monitoring of the distortions in the sidewall concrete lining of the Zigana and Torul tunnels were evaluated by using Diffraction 2D-velocity and Kirchhoff 2D-velocity migrations. Firstly, an artificial radargram was created based on the Finite Difference Time Domain method by taking the model of a tunnel wall structure. Then, for the results obtained from the model, a single velocity value was defined and the migration results were compared. However, as known to all, the outcome of migration by defining a single velocity value from radargrams with too many reflections do not give accurate results. Therefore, the Diffraction 2D-velocity and Kirchhoff 2D-velocity migrations were applied to these radargrams based on the velocity fields and their results were compared. Thus, we suggested that Diffraction 2D-velocity migration gives better results than those of the other in terms of focusing and resolution. When the amplitude slice maps obtained after applying Diffraction 2D-velocity were evaluated, it was observed that deteriorations in the structure continued up to a depth of 75 cm. However, the other type of migration is not very successful to move the distortions to their correct positions after a depth of 37 cm. Thus, in order to apply the migration results correctly, it is recommended to use velocity field.
Keywords : GPR, Zigana and Torul tunnels, 2D velocity field, two migrations types, amplitude slice maps

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