الفهرس | Only 14 pages are availabe for public view |
Abstract Accurate reviewing the results we concluded that; [1] All the programs yielded the same dimensions for the optimal model of the tunnel. Comparison between single and twin tunnel system, a higher stress was obtained in the lining of bottom twin tunnel compared with the stress in single tunnel lining. It was found that, stresses in bottom twin tunnel increased about 100% than stresses in a single tunnel. Moreover, when trains pass through a tunnel, stresses decrease about 10% for single tunnel and about 5% for twin tunnels.Also, in case of the twin tunnel, construction of the bottom tunnel before the top tunnel is preferable to decrease the stresses in the top tunnel lining. [2] For twin tunnel configuration, it was found that : Maximum surface settlement decreases with increasing the distance between tunnels for different tunnel alignment. The distance between tunnels has a major effect on soil movement and internal forces in tunnel lining when this distance less than 2.20D for horizontal alignment, 1.80D for diagonal alignment and 1.25D for vertical alignment. A slight difference in lining internal forces for the construction procedure of twin tunnels, when distance between tunnels more than previous values . These findings are consistent with previous studies those given in the literature, for example (Chehade and Shahrour, 2007) found that the proper clear distance between tunnels equal to 2.0D for horizontal alignment and take the clear distance between tunnels equal to 1.0D for vertical alignment . Although the results of this research agree with previous results, but the results on the distance between two tunnels and the tunnel diameter is only applicable to the given ground conditions, which may be not applicable to other regions with different conditions, which is a limitation. [3] For railway alignment, it was found that : The development of rail levels is affected to a great extent by the change in vertical distance between tunnels (S3). The vertical and horizontal grades developed in the metro line depend on twin tunnels distance (vertical and horizontal) and lengths between stations, especially for twin tunnels which change from vertical to horizontal alignment. This means twin tunnel configuration with railway alignment leads to an increase in metro line safety. According to the results that have been obtained, the proposed twin tunnels by contractor have some problems, i) The proposed distances between tunnels are not appropriate distances comparing with the calculated . ii) Higher gradients up to 3.5% . Higher stresses were generated in the rail head due to increasing of lateral forces on the rails which placed at horizontal curves. This stresses occur at head side 1 (inner Side) and head side 2 (outer side) in the rail head. Increasing of these stresses than the allowable stresses causes side wear of the rails. According to obtained results, increasing the lateral force from 4.77t to 9.06t leads to the following: (I) Increase the normal stresses in the rail head to 260%. II) Increase the normal stresses in the rail web to 207%. III) Increase the shear stresses in the rail head to 309%. IV) Increase the shear stresses in the rail web to 135%. [4] For both tunnel systems, higher displacement occurs in tunnel lining during the earthquake, the total displacement changes randomly during seismic waves. the maximum change in line with internal forces (bending moment, shear force and normal force) occurs at third time of earthquake duration . Horizontal twin tunnels are the most affected by seismic action, then diagonal twin tunnels and single tunnel. In addition, vertical twin tunnels are less affected by the seismic action compared to the other systems. The maximum change of internal forces during an earthquake occurs in shear force, then bending moment. Moreover, the normal force is less affected by seismic actions [5] The economic evaluation of tunnel systems has been carried. Empirical formulas were obtained to estimate an approximate cost of single and twin tunnel projects. Twin tunnel configuration is widely used in many countries in spite of the higher cost of the twin tunnel project compared to the cost of single tunnel projects. Total cost of the twin tunnels increases (30-80%) more the total cost of single tunnel. The total cost of tunnels varies from project to another according to tunnel diameter, overburden height, tunnel configuration, length of tunnel between stations, construction quality, type of rolling stock, type of TBM,… etc. |