Introduction

Tunnels are artificial passages built underground to facilitate transportation or conveyance of people, materials, water, sewage, other fluids and gas in pipes, electric power etc., across obstructions like hills, rivers and other obstructions like buildings, industrial structures and other communication lines like major roads and rail tracks. An alternative definition of tunnels refers to underground structures which apart from serving the above noted purposes are built using special underground excavation methods without disturbing the surface. Even underground garages and power houses are treated as tunnels.