Q. Number of segments for segmental linings in tunnelling?

For the construction of tunnels by segmental linings, choice of the number of segments affects the durability and cost of tunnels. With an increase in the number of segments, number of joints also increases accordingly. This increases the potential for water ingress into the tunnels.  

Though if the number of segments is kept to a minimum, speed of the erection of segments can be increased. Though, it is expected that higher bending moment would be persuaded in the tunnel rings forsmaller number of segments and extra cost is incurred in the provision of additional reinforcement.