The engineering geology of Gebze-Kosekoy 3. railway line-T5-1 tunnel route

In this thesis, it is aimed to evaluate the study area with the principals of engineering geology by using field measurements and experiments with laboratory data, which is planned to be constructed 3rd Railway line between Gebze-Köseköy, and to examine the T5-1 in terms of tunneling. To be able to evaluate the study area in terms of engineering geology, total of 36 exploration drillings with an average depth of 30 meters along the route and 83 observation pits with an average depth of 4 meters were opened, field and laboratory tests were performed on the data obtained from the drillings. The literature review was carried out to obtain additional data about the T5-1 Tunnel which will pass through between P2 and P3 feet of Osmangazi Bridge North Approach Viaduct. The engineering geology map is prepared by placing the engineering geology parameters (drillings, formation boundaries, fault, etc.) in the topography map of the tunnel area. Tunnel cover thickness is approximately 26 meters. The first 120 meters of the tunnel in this area will be excavated in the limestones with massive, light gray colored, thick bedded, karst cavities belonging to the Lower - Middle Triassic aged Hereke Formation and the next 110 meters with thin - bedded, fractured conglomerate limestone belonging to the Upper Triassic Tepecik formation. It was understood from the field observation that these two formations were cut by a normal fault having K30B,75 KD orientation. Units to be encountered in tunnel were evaluated in terms of RMR, Q and GSI rock mass classification then these assessments were correlated together with ÖNORM-B (NATM) classification system, tunnel excavation support type was determined as B3. Most critical sections of tunnel were analyzed for deformations by using a finite element method Phase (RS2). As a boundary condition, the existing T-6 tunnel which is parallel to T5-1 Tunnel, 14 meters from the P2 foot, was considered to be rigid in the modeling as it is far from the T5-1 tunnel excavation (45 meters). The design of T5-1 tunnel was carried out considering of the loads acting on the piles under the P2 and P3 feet. In order to determine the geological situation, 12 borehole in the study area were taken into account. The tunnel section was first examined in terms of maximum deformations that would occur in case of excavation without support. As a result of the design, the maximum deformation resulting from the tunnel excavation is 1.78 mm, so there would be no problems during excavation of the tunnel. Additionally, according to the support elements proposed in the B3 excavation support type, deformations that will occur after supporting of underground opening are evaluated. In this case, the deformation decreases to 1.76 mm. In last stage, a seismic analysis was repeated to carry out the effect of an earthquake on tunnel stability. In this analysis, maksimum deformation is approximately 3 mm. To understand relation between T5-1 Tunnel and the fault, another two dimentional numerical modal at 10 meters ahead of the first section was evaluated similarly. The maksimum deformation for this cross-section is 3,6 mm. As a result of these study, it was understood that during construction of T5-1 Tunnel, there will be no unstability problem effecting the feet of the viaduct of the Osmangazi Bridge.