It has now become very important to increase means of transportation in urban areas due to    the large population, especially underground metro lines. In the present research a parametric study on two circular adjacent tunnels was carried out based on numerical analysis using PLAXIS 3D finite element package. The proposed model was verified based on the results of case study by Hamid et al. (2014). The verified model was modified for the parametric study based on characteristics soil profile from Greater Cairo Metro Line 4. The parametric study included the spacing between the tunnels, and lining thickness. The effect of distance between the twin tunnels was investigated for range of 1.50 to 5.5 times the diameter of tunnel, and thickness of lining thickness for the range of 0.025 to 0.105 of tunnel diameter, for tunnel with diameter of 6.00 m. The effect of these parameters on ground surface settlements, the tunnel deformed shape and induced stresses at the tunnels top were analyzed and discussed. It was found that increasing the tunnel spacing from 1.5D to 5.5 had decreased settlement of ground surface by an average value of 11%. On the other hand, increasing lining thickness of tunnel from 0.025D to 0.105D decreased maximum vertical displacement at crown of tunnel by average value of 23%. On the other hand, the maximum horizontal induced stress decreased by about 67%.  Maximum soil lateral stress decreases with the increases of distance between the twin tunnels up to 4.5D, after which the stress around tunnel increased as each tunnel behaves as a single tunnel.
 
 
Special Issue of AEIC 2024 (Civil Engineering  Session)