The engineering geology of Istanbul Kaynarca-Sabiha Gokcen metro line and analysis of the critical areas in terms of tunnel engineering

Due to the rapid growth in Istanbul's population, construction industry has been accelerated in order to overcome the transportation problems. Within this context, large scale of metro projects are under construction for both improving connections and simplifying the transportation. With the Kaynarca-Sabiha Gökçen Metro Line, which is the continuation of the Kartal-Kaynarca Metro Line Project, it is aimed to connect Kadıköy to one of the most important location, airport, with an uninterrupted line. Within the scope of this study, the engineering geology of Kaynarca-Sabiha Gökçen Metro Line was examined and the boundary conditions in critical areas were numerically modelled and analyzed. As the geology of the alignment is examined, it is predicted that the tunnel excavation level will be encountered with units belonging to Kurtköy, Gözdağ, Dolayoba and Sultanbeyli Formations. According to the right line, the existence of an old stone quarry was determined between Ch:0+780 and Ch:1+080. This section is filled unrestrainedly and the existing filling has a heterogeneous structure. According to the right line again until Ch:4+920 Gözdağ and Dolayoba Formation, until Ch:6+220, Kurtköy Formation, until Ch:7+020 Sultanbeyli Formation and from Ch:7+020 to the end of the line Kurköy Formation are estimated that tunnel excavation will take place in these units. Kurtköy Station will be completely excavated in the Kurtköy Formation and towards the Sabiha Gökçen Station it is expected to be excavated again in the same formation consisting of intercalation of sandstone, mudstone-shale, and conglomerate and also the separated units upper this formation. Dolayoba Formation, which is located at a large proportion of the tunnel sections, has large voids as well as good rock quality. A large part of the Kaynarca-Sabiha Gökçen Metro Line is being drilled and blasted. Tunnel excavation is carried out using conventional methods in areas where rock quality is low or where drilling-explosion is not possible. The drilling-blasting or the tunnel opened by conventional methods are supported using the appropriate support system according to the rock class. According to the support system that the IBB has determined for urban metro tunnels, the excavation support class is between A1 and A5. This excavation support classification is used in the project. Within the scope of this study, the engineering geology of Kaynarca-Sabiha Gökçen Metro Line was investigated and boundary conditions in critical regions (Ch:0+300-0+600, Ch:0+ 850-0+980) were determined and numerically modeled and analyzed. In the scope of the this thesis, in order to determine the geology of the alignment and modelling the correct design for a safe excavation, drilling studies, field and laboratory experiments were carried out in the direction of the data obtained from these studies. Test results obtained from the design stage experiments were used in evaluations. The most common underground tunnel excavation issues such as; interaction of tunnel with the structure, the probability of stability problems due to lower overburden and thickness of the filling, and the probability of the water ingress inside the tunnels. As per the safety reasons and the possibility of causing damages on buildings due to tunnel excavations and the use of drilling-blasting method under the Ytong Factory, which is the oldest gas concrete production factory in Istanbul, has been investigated with a wide perpective. It has been determined from the excavation support systems that the rock mass quality is determined. The tunnel deformation remains at very low levels and that no damage will occur to the structure as a result of using the determined maximum explosive in critical areas. Suggestion monitoring techniques are also included in order to make the tunnel excavations more secure. The pilot tunnel application for approximately 130 meter along tunnel has been requested by the Project Designer because of the thick fill layer and the overburden of approximately 17 m from tunnel crown which will pass under the old stone quarry area. According to the analyzing the numerically modeled of this occasion, the necessity of the pilot tunnel was investigated. Due to the permeability of the mainland, the probability of water ingress in the tunnel was examined and limit values were obtained. In the calculations made according to the drilling data, which has the highest permeability value from the drilling, it is suggested to inject through the tunnel against the tunnel excavation but it would affect the excavation speed. In the same way, special patterns prepared by the university due to drilling-blasting excavation due to the stability of the rocks are included in this study. In addition, the problematic sections have been investigated in Şeyhli Station which is 180 m long, according to the right line reference between Ch:3+406 and Ch:3+586. In these area, collapse occurred in the stair tunnel excavations. According to the geological model which is based on the data obtained from the underground research, it was determined that the section composed of andesitic basalt continued horizontally. The limestones belonging to Dolayoba Formation and feldspar sandstones belonging to Gözdağ Formation are located at the tunnel section of the station. In addition, dike intrusions were identified in these areas. While the drilling data are evaluated and the geological profile is prepared, dykes are shown in the horizontal position at the tunnel crown. However, core trays have been reconsidered it has been found that the separated units of the Gözdağ Formation are located in the openings of the B3 type stair tunnels at the tunnel crown, where these dykes are located vertically in some regions that have not progressed horizontally. It was observed that the limestones belonging to Dolayoba Formation under Sultanbeyli Formation were located in a certain region during the excavations. These sections have reached the conclusion that stair tunnel face can be effective for long periods without support. Due to the weak unit, it is foreseen to apply the soil improvement application to the tunnel crown to the bedrock and the sample application pattern is included. On the other hand, it is thought that the interruption of the face excavations for a certain period of time (the unsupported face is kept waiting for a long time) is thought to be effective in the material coming from the tunnel crown.