Influence of effective parameters in optimum distance of two parallel tunnels

Construction a new tunnel parallel to pre existing tunnel is one of the most complex problems in tunneling. In most engineering projects such as highway and water supply networks, it is essential to construct a new tunnel parallel to existing tunnel. New tunnel causes increasing bending moment in tunnel lining. Increasing the distance of two tunnels, decreases the increasing bending moment. Optimum distance of the tunnels is the distance that new tunnel has no effect in old tunnel.
This research studies the influence of parameters that affect optimum distance. Finite difference method is used for analysis of problem.
Results Show that at rest earth pressure has maximum effect and tunnel diameter, lining elasticity, cohesion and friction of media and elasticity of media affect the optimum distance.