Is tunnel lining the same thing as tunnel structural support? And then also there is always the initial and final lining? Are three all different things? And how do they relate to waterproofing? It seems that there are endless methods which are a combination of many materials and applications and soil and water conditions. I need some general thoughts to direct me in the right direction.
Tunnel linings come in a wide variety of materials and functions.
Some are just finishing precast panels covering the tunnel structure which could be an elaborate system of tie-back wires, steel frames, shotcrete.
Some are actually part of the structure, but generally not the waterproofing.
Here is a link to the design concern guide.