Investigation of the factors affecting the design of tunnel structures

INVESTIGATION OF THE FACTORS AFFECTING DESIGN OF TUNNEL STRUCTURES SUMMARY In many places of the world tunnels are playing an essential role. Tunnels can connect two points directly under the ground. This feature makes tunnels unique. If we generalize the main uses of tunnel structure, tunnels can be designed for Electricalmechanical works, transportation, irrigation, drainage, service or military purposes etc. Design methods of tunnel structures vary. New approaches are including more information about the geological details and the effective forces. Many structures have been designed by using these methods. This study will investigate the different methods and the details of the design impact and how it is getting addressed in the design. Tunnel lining damages, the possible causes and damage mechanisms are investigated. The precautions and advices are explained. Tunnel structure resists to earth and water pressure, also the excavation machine pressure and vibrations. During the transportation to destination tunnel parts can be damaged. These damages or cracks can be visible or invisible but under loading conditions it has been observed that damages are getting more visible. To prevent damage mechanisms precautions must be unique for tunnel design. Loading on the segment plate's start at early stages and the compaction injection plays key role to minimize any damage. The geometry and production methods of the reinforced concrete elements used in the construction of tunnels vary according to the tunneling methods. The designer considering the economic conditions decides these methods. However, due to reasons not considered during the construction phases, the construction period is delayed and repair costs arise. It is forced to make repairs in the structure and a repaired structure is more costly and unsafe than a properly constructed structure. To minimize errors, design process should cover all parameters with correct values. For this purpose, in this publication, the design phases, the execution of these phases, the evaluations based on the errors that can occur are tried to be presented. As tunnels become more prevalent as subway structures, problems related to building tunnel interactions are also increasing in cities. In the last part, the effects that will be on the tunnel will be examined. In the first part, the purpose of the tunnels and the tunnel made in our country are examined. Tunneling methods and tunnel sections varying according to the purpose of use are given. The main national and international studies on tunnel design have been studied up to date. The second section summarizes how the design and production are shaped according to different tunneling methods. In this section, drill and blast method, open cover method, mechanical opening method and other methods are mentioned. Some ideas about which method would be more suitable for the purposes of production of the tunnels are given. Examples of the tunneling machines that produced for tunneling under different ground conditions are given. In the third part, the support xxviii structure account which is the subject of the design is provided with the necessary information in the account phase. The project steps that must be done to create the tunnel project and visualize the design during construction phases are mentioned. Classification methods used in the process up to the sun are examined and classification tables of these methods are given. The parameters obtained from the classification tables and studies on the determination of support structure are given. This section describes the finite element method. Model studies and model studies with finite element method have been investigated. The load distributions of the results of calculations of supported and unsupported tunnel opening stages in these models are presented. In the fourth chapter, damage of supporting structure caused by truss caused by machine excavation is investigated. Damage that occurred during the construction phase is mentioned. The calculations mention the construction steps that should be considered except for the tunnel floor model and which cause damage to occur. Damage caused by Wenchang earthquake, an example of an earthquake, has been investigated. Possible damages to be found in the tunnels and repair methods which can be applied for these damages are given. Damage that may occur in tunnel walls may be caused by various defects such as concrete damage, damage affecting the use, damage to the floor surface. Because of observations, it has been found that various cracks occur in support structures. In the Turkish Reinforced Concrete Code [TS500] these cracks are limited to 0.3mm. However, to be able to obtain the specified order at the tunnel support structure, it is necessary to distribute the external pressure to the entire tunnel structure and to provide the equilibrium state. The effect of the variable structure of the ground and the construction methods, which this condition cannot be achieved for various reasons, has been observed. It has been observed that cracks can occur in the linings even during production, transportation, installation and other construction stages. Nowadays chemical products and solutions are being produced to eliminate the damages. Suggestions on how to apply these products and where to apply them are presented. Injection and repairs were made in a tunnel in construction phase. The ground an injection body is built up in front of the tunnel face using injection drills through the cutter head and the shield method which can support the tunnel construction. This method will allow the tunnels to be opened in more favorable conditions by improving the ground conditions. In the fifth section, using the Plaxis program, in case of existing tunnel inside the soil, the change of the base deformation due to the construction of the tunnel based on the position of the tunnel and in the tunnel under different soil conditions is examined. Tunnel cover thickness of 5, 10 and 15 meters was completed in the greywacke clay and lowly dispersed greywacke soils belonging to the Trakya formation. Tunnels of 5, 10 and 15 stories made on the tunnel opened by the A1 section of Kartal-Kadıköy metro project. The effects that will occur in the lining are calculated. In the calculations, the values obtained by obtaining the vertical deformation on the rail and the sectioning effects of the tunnel lining were examined. According to the tunnel cover thickness, the correlations of the vertical deformations that would occur in case of construction in two different soil types were obtained. The results of the vertical deformation on the rafts obtained at the rail points for these relational accounts are curved in relation to the construction time. The calculations were carried out in 7 stages. Phase 5, Phase 6 and Phase 7 address the tunnel-structure interaction. At these stages, a total of 6 points were determined for the two accounts, including three points. The relationship of these three points to each other is suggested, and two correlations between 5 meters and 15 meters are proposed in the greywacke clay soil and the slightly separated greywacke soil. However, a precise calculation is required to xxix determine vertical deformations. In the conclusion, preliminary conditions such as additional excavation loads during loading of the elements, loads during the movement of the elements should be evaluated well in the tunnel design. In these cases, it is stated that the original equipment, the equipment systems aiming to protect the seats and additional details should be considered. The effects of the machinery, equipment and other factors to be used at each stage on the tunnel lining should be evaluated, considering the construction steps in detail. It has been demonstrated that the design phase should continue throughout the tunnel construction. Prevention of damage that may occur is possible by reducing the tunneling effect of different loads and deformations, which will occur especially on the tunnel lining of different loads of the soil. For this purpose, it has been determined that it is beneficial for the injection mortar to be made of a compressible type behind the tunnel lining. In addition, by injecting between the tunnel support structure and the soil, the soil can be clamped and different load distributions can be prevented, which can significantly reduce damages on the inner surface of the tunnel. It has been proposed to use injection mortar and then chemical compounding to prevent excessive water behind the tunnel lining, respectively. When the tunnel-structure interaction is examined, it is seen that in clay soils with greywacke fragments, higher cross-sectional effects and over-rail deformations occur compared to less-diffused greywacke floors. If the tunnel cover is less than 10 meters, the on-rail deformations exceed 1 cm. As the tunnel cover increases, the vertical deformation decreases. When the slopes obtained from the curves are examined, it has a cover thickness of 5 meters, whereas the clay layer with greywacke clay has increased in the negative direction in proportion to the number of floors. It has been found that the vertical slope of 10 m and 15 m of cover thickness decreases in the negative direction due to the number of coats of the same slope. It was observed that the vertical slope of the 5-meter cover thickness of the greywacke soil was slightly increased, while the increase in the 10-meter and 15-meter cover thicknesses occurred at much lower values.