When a tunnel is excavated in all but the most competent of ground conditions it is an inevitable consequence that some form of support will be required if the tunnel is to retain adequate stability and/or maintain sufficient dimensions to facilitate its use in the intended manner.
The form and function of the support will vary according to a wide range of factors apart from just geotechnical considerations and it would seem that for every different tunnel there is a different lining solution
Civil engineering tunnels
Tunnels in the civil engineering category are generally driven at relatively shallow depths by comparison to those situations involving mining tunnels.
Civil engineering tunnels require higher tolerances in terms of the final tunnel profile and its ensuing stability.
Many civil engineering tunnels relate to public usage and high density traffic with projected working lives in excess of 100 years.
As a result, long term stability is desired coupled with an appropriately high factor of safety (>2.0).
Other factors which are critical to the design and use of civil engineering tunnels include line, grade, special surface finishes and prevention of water inflow or outflow in respect of the tunnel structure.