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Abstract In this thesis, two study cases were performed to study the tunnel-soil system under static and seismic loads and also to verify the constructed model by Plaxis. The first case study was performed on the tunnel soil system considering continuous tunnel lining. In the verification study, soil was modeled using Mohr-Coulomb equivalent linear elastoplastic model to compare results with the nonlinear soil model used by Abdel-Motaal et al. (2014). Results are also compared with results calculated by analytical expressions using Penzien & Wu equations (1998). Construction stages were taken into consideration in this case. The second case study was performed on a Contract BC-24 Phase II Delhi Metro Line, which consists of a segmental tunnel with five segments and a keystone to study the effect of seismic load on the tunnel. Joints were modeled using hinges with free rotations. Construction stages were ignored in this case. Results were compared to results by Chow et al. (2008). In the two cases, the tunnel soil system was modeled using a 2D Plane strain model using Plaxis 2D program. Mohr-Coulomb’s model was used to simulate soil behavior. Soil elements modeled using 15 nodes triangle 161 elements. Tunnel lining was modeled with plate elements using a linear elastic model to simulate concrete properties. The earthquake was applied at the bedrock surface. Initial parametric study using seven different earthquakes was carried out on continuous tunnel lining. Study focused on the difference in internal forces in tunnel lining and displacement in tunnel lining under the effect of these earthquakes. As a main stage, a parametric study on segmental tunnel lining using a selected earthquake ground motion was performed by changing earthquake intensity, lining thickness, tunnel diameter, tunnel depth and the number of tunnel lining joints. The main aim of this study is to investigate the effect of these factors on the internal forces and settlement trough. 6.2 Conclusions The research findings are summarized as follows: 1) Two-dimensional finite element modeling (2D FEM) using the Plaxis program can accurately describe the behavior of the tunnel soil system under static and seismic loads. 2) Applying the equivalent soil method using the Mohr-Coulomb model provides acceptable results compared to the results of the nonlinear model. 3) Construction stages for constructing tunnels using TBM must be taken into consideration to get true values for straining actions in tunnel lining under static loads. 162 4) Changing the absolute peak acceleration at the base affects the shape of the acceleration time histories. 5) Peak values of acceleration at the ground surface increase with increasing peak values at the bedrock surface. 6) The peak values of acceleration are magnified at shallower depths above the bedrock towards the ground surface. 7) Increasing intensity of earthquake causes an increase in bending moment, normal force and displacement of tunnel, for the same earthquake. 8) For the same base acceleration, there is a variation in values of bending moment and normal force for the different earthquakes. Consequently, for tunnel design, it is recommended to consider different earthquakes. 9) Increasing the lining thickness is associated with a considerable increase in the maximum bending moment. It can be clarified as increasing lining thickness leads to an increase in its rigidity and hence the developed bending moment. 10) The max. normal force in the tunnel increases with increasing earthquake intensity. 11) For small earthquake intensity (0.05g) increasing tunnel rigidity by increasing the t/D ratio does not affect max normal force value. However, for higher intensity, increasing rigidity ratio from 0.0375 to 0.0625 leads to a decrease in normal force with an average percent 163 equal to 16%, however, changing rigidity from 0.0625 to 0.1125 has a limited decrease in values of normal force with an average equal to 5%. 12) In general, increasing tunnel diameter leads to a great increase in the max bending moment in tunnel lining. The average percent of the increase in bending moment by increasing diameter from 6m to 12 m is 260%. 13) For the different lining thicknesses, increasing tunnel diameter leads to an increase in the maximum normal force. from diameter 6m to 12m, the average increase in normal force is 400% for the different thicknesses. 14) As a result of increasing the number of tunnel lining joints, the max bending moment in the tunnel lining decreases with great values. For example, the average percentage of decrease in bending moment, by using six tunnel joints is 44% compared to the continuous tunnel. 15) For low rigidity tunnel, the existence of joints has a low effect on bending moment values compared to high rigidity tunnel. 16) The number of tunnel lining joints has a considerable effect on the developed bending moment for a low number of joints (less than 6 joints). After that, increasing the joints number have a relatively less effect on reducing the developed bending moment. 17) Increasing the number of lining joints is associated with a considerable decrease in the values of the developed normal force. 164 18) For small lining thickness (t=0.3m, t/D=0.0375), the reduction percentage in normal force is limited as the tunnel is flexible enough to be affected by the number of joints. Contrary, in rigid tunnels such as the case of (t=0.9, t/D= 0.0875) the reduction percentage in normal force is 54% in the case of using 12 joints. 19) Changing tunnel depth has a low effect on max. bending moment values thus for high earthquake intensity, average percentage of the increase in bending moment is about 25%. However, for low earthquake intensity, average percentage of the increase in bending moment is about 85%. 20) Increasing tunnel depth is associated with a considerable increase in values of normal forces as a direct effect of increasing the overburden pressure. 21) In general, seismic excitation is associated with high considerable values of surface settlement, relative to the static loading condition. 22) Increasing the number of joints is associated with a considerable increase in the surface settlement (more than 30 % increase). These predicted changes are due to increasing the tunnel lining flexibility by increasing the total number of joints. 23) Increasing tunnel diameter leads to increase values of settlement under seismic load. The increase extends for long distances from the centerline. Similar to the previous, this observation is due to 165 increasing tunnel flexibility by increasing tunnel diameter or the total number of joints. 24) The effect of decreasing the ratio of lining thickness to tunnel diameter makes the tunnel more flexible and as a result settlement values increase. This notice is observed locally just above the tunnel location (about 10%) and vanishes gradually in the lateral direction. 6.3 Recommendations for future studies 1) Increasing the range of the studied parameters such as the distribution of joints, and height of the surrounding soil layer. 2) Study segmental tunnel soil system for different types of soil. 3) Study the effect of the existing groundwater table at a certain depth. 4) Studying the axial forces and moments in the longitudinal direction of the tunnel and their variation during the earthquake, also study the effect of longitudinal joints. |