الفهرس 
Chapter (1): IntroductionOnly 14 pages are availabe for public view
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Abstract
The current research investigates two of the alternative solutions of tunnel development. The first trend is adding two tunnels to an existing twin roadway tunnels vertically and horizontally. The influence of variation of relative position and spacing distance is investigated in a parametric study. Several numerical two and three-dimensional models are employed. The results helped to find out the minimum practical and safe spacing distance between the driven new tunnels and the existing ones without the need to the relatively costly soil strengthening techniques.
The second trend is widening tunnels. Three different techniques are presented for widening roadway tunnel. Horse-shape and PSS-Arch techniques widening techniques could be used with active traffic flow. Only with banned traffic flow, the third widening NATM technique can be implemented. Both surface and tunnels deformations are checked. Also, internal stresses for the existing and widen tunnel are investigated during different widening stages.